Journal Of Physical Chemistry Research Articles

(Invited, Digital Presentation) Electrocatalyst and Electrolyte Engineering for Oxygen Evolution in Acidic Media

The slow kinetics of the oxygen evolution reaction (OER) limits the performance of proton exchange membrane (PEM) electrolysers. Only iridium-based oxides are both reasonably active and stable for the OER in acidic electrolytes [1], and high amounts of Ir are needed at the anode of PEM electrolysers. In addition, the lack of stable support materials limits the utilisation of Ir. Designing novel electrocatalysts with enhanced OER activity and stability in acidic media remains a great challenge. In this talk, I will present some recent strategies aiming to understand and engineer the interfacial structure and properties for oxygen evolution electrocatalysis. We have developed self-supported high surface area nanostructured Ir-based networks as highly active electrocatalysts for OER [2]. These networks, prepared by alternating sputtering of Ir and Co, followed by selective Co leaching, show a unique morphology and combine excellent mass activity with promising stability [2]. In addition, our group is working in the development of an easy and affordable method to prepare IrOx catalysts by controlled electrodeposition of Co and Ni in a deep eutectic solvent followed by galvanic displacement [3]. By controlling the conditions during the galvanic displacement, we tune the morphology and thus the electrocatalytic properties for OER. Finally, we have investigated the role of both composition and concentration of the acidic electrolyte (perchloric and sulphuric acid) on the OER electrocatalytic performance of Ir nanoparticles [4]. Our work highlights the key role the electrolyte plays in the performance of Ir-based electrocatalysts during rotating disc electrode measurements.REFERENCES[1] M. Escudero-Escribano et al., Journal of Physical Chemistry B 2018, 122, 947.[2] A.W. Jensen, G.W. Sievers, K.D. Jensen, J. Quinson, J.A. Arminio-Ravelo, V. Brüser, M. Arenz, M. Escudero-Escribano, Journal of Materials Chemistry A 2020, 8, 1066.[3] F.B. Holde, K.N. Dalby, H. Falsig, P. Sebastián-Pascual, M. Escudero-Escribano, in prep., 2022.[4] J.A. Arminio-Ravelo, A.W. Jensen, K.D. Jensen, J. Quinson, M. Escudero-Escribano, ChemPhysChem 2019, 20, 2956.

(Digital Presentation) Conceptual Design of Oxide-Based Solid-State Li-Battery for Urban Air Mobility

In metropolitan areas, traffic congestion and pollution are serious challenges due to the continuous rapid growth in the number of vehicles and population. These concerns have prompted a global trend toward the electrification of transportation powertrains. Electric vertical take-off and landing (eVTOL) aircraft is an efficient and safe alternative mode of transportation with a significant impact on urban mobility, which attracts considerable attention [1]. It could avoid traffic on the ground and allow people to commute between two locations in less time while requiring no additional run-up space. Nevertheless, one of the main challenges with such aircraft is to provide electrical storage systems, such as batteries, which are safe, efficient, reliable, and capable of producing the energy and power demand to meet mission requirements [2].High flammability and risk of thermal runaway in current Li-ion batteries motivate to develop next-generation chemistries such as all-solid-state batteries (ASSB) as alternative electrical storage systems for eVTOL. However, ASSB currently suffer from low solid electrolyte conductivity, as well as non-utilised active material, and significant reaction overpotentials due to a small effective active area [3]. Electrode composition and structure have a crucial impact on three performance-relevant microstructure parameters, i.e. effective active area, effective ionic conductivity, and effective electronic conductivity. However, considering these restrictions experimentally by producing and evaluating a wide range of design parameters to achieve a well-performing design for ASSB is both time- and resource-intensive. To address these issues, we conduct model-based structure evaluation. Here, we extend the P2D model with a microstructure surrogate model based on Laue's work [4] for Li-ASSB (see Fig. 1-a), because electrode microstructure is important for the effective parameters. Further, this link between the P2D model and microstructure modelling could provide a better understanding of the electrode structure and especially the effects of percolation, which cannot be properly covered by classical Bruggeman approaches. This model is then incorporated into a global optimisation algorithm to determine the optimal design of solid-state cathode with respect to eVTOL power demand. Finally, we compare the performance of the battery at the identified optimal electrode design, electrode reference design, and electrode design with that of the Bruggeman approach. Based on our prior research, we identified that hybrid electrolytes with 12.7 vol% LLZTO had the best performance among other types of hybrid electrolytes at a relatively high C-rate, i.e. 1C. Therefore, we employed this electrolyte for the modelling of Li-ASSB for eVTOL application [5].Fig. 1-b shows an exemplary result from a simpler model without percolation, i.e. Bruggemann approach, and a microstructure surrogate model. As can be observed, taking into account a more realistic structure in the electrode, the ASSB could only meet 32% of the mission requirements. However, optimisation of solid-state cathode structure significantly increases flight time in comparison to the reference electrode.In summary, we could show that future electrification of transportation powertrains will necessitate optimisation of the solid-state electrode structure and composition in order to meet the high demands for energy and power density. Also, our work highlights the urgent need to consider microstructure physical effects at an early stage of design for a realistic sizing of batteries. References Jain et.al., Proc. 4th Int. Conf. Electron. Commun. Aerosp. Technol. (2020) 1173–1178Donateo et.al., Aerospace 7, no. 5 (2020): 56Bielefeld et.al., The Journal of Physical Chemistry C 123, no. 3 (2018): 1626-1634Laue et.al., Energy Technology, 8(2) (2020): 1801049Toghyani, et.al., J. Electrochem. Soc (2022). Figure 1

X-Ray Crystal Truncation Rod Studies of Electrochemical Double Layers

Electrochemical double layers (EDL) is traditionally described as diffuse distributions of cations and anions, proposed in Gouy and Chapman (GC) model[1] and further developed extensively over decades largely based on voltammetry measurements. However, the GC model is suspected to break down at large potentials, because it predicts the unlimited rise in differential capacitance. Stern suggested long ago that there should be a layer with a finite ion density, known as ‘Stern layer’[2]. While it is generally accepted that Gouy-Chapman model or its modified versions describe well electrochemical interphase structures, recent studies of Pt(111) surface in CsF solution using a model-independent direct inversion method[3] have shown that Stern layer forms over the large double-layer potential range on Pt(111) surface.[4]In this talk, we present synchrotron x-ray observation of Electrochemical Stern layers on the surfaces of RuO2 single crystals in 0.1 M CsF electrolyte. It is of fundamental importance to study if Stern layer forms on electrode surfaces other than Pt(111). In this case, we will examine RuO2 surfaces and compare the results to that of Pt(111) surface. RuO2 is chosen for several reasons. First, it is a well-studied system because of its oxygen evolution reactions and we are familiar with the structure because of our previous studies.[5,6] Second, it is an oxide with oxygen terminated while Pt is a pure metal. Third, the surfaces of RuO2 are squares or rectangles while that Pt(111) surface is triangles. The Stern layers formed at the interfaces of RuO2 (110) and (100) are compared to the previously reported Stern layer on Pt(111). [4] While the Cs+ density profiles at the potentials close to hydrogen evolution reactions are similar, the hydration layers intervening the surface and the Cs+ layer are significantly denser on RuO2 surfaces than that on Pt(111) surface, reflecting the oxygen termination of RuO2 surfaces. The overall similarities between Stern layers on ruthenium surfaces and platinum surface suggest the universal presence of Stern layers in all well-defined solid-electrolyte interfaces.[1] Bard, A. J.; Faulkner, L. R., Electrochemical methods: fundamentals and applications. 2nd ed.; John Wiley: New York, 2001.[2] Stern, O., The theory of the electrolytic double layer. Zeitschrift Für Elektrochemie 1924, 30, 508.[3] Kawaguchi, T. et al., J. Appl. Cryst., 2018 51, 679.[4] Liu, Y.; Kawaguchi, T.; Pierce, M.S.; Komanicky, V.; You, H., Layering and Ordering in Electrochemical Double Layers, J Phys Chem Lett, 2018, 9, 1265.[5] Y.S. Chu, T.E. Lister, W.G. Cullen, H. You, Z. Nagy, Physical Review Letters 2001, 86, 3364.[6] Rao, R.R. et al., Journal of Physical Chemistry C, 2018, 122, 17802

Modeling the Environment-Dependent Kinetics of Oxygen Reduction Reaction – Effect of Relative Humidity

For proton exchange membrane fuel cells (PEMFCs) to achieve broad commercialization, the kinetics of oxygen reduction reaction (ORR) need to be better understood to improve the efficiency with minimized use of expensive Pt-based electrocatalyst(1). The increasing demands of PEMFC-powered heavy-duty vehicles make this issue critical, especially to meet the efficiency target (ultimately 72%)(2). Previous first principle-based theoretical analyses reasonably explained catalyst-dependent activity in ideal conditions (on single crystal catalysts in HClO4 solution under room temperature)(3). To design a practical catalyst, further analysis is required to bridge the gap between the ideal and actual PEMFC conditions (typically, covered with perfluorosulfonic acids under 60 to 90 °C, and 30 to 100% RH). In this talk, we examine the effect of relative humidity (RH) on ORR activity on a platinum surface. The effect of RH on ORR activity has been a controversial topic: an experimental study suggested lower RH increases the ORR activity(4), while another study showed the opposite trend(5). By using a multiscale continuum model, we validate our hypothesis that the controversial experimental results stem from the difference in the properties of the electrode/electrolyte interface. In the mathematical calculation, we assume that the polycrystalline platinum catalysts consist of multiple single crystalline surfaces(6) and that their activity is described by the summation of the activities on the single crystalline surfaces. Based on transition state theory, the reaction rate of each elementary step is calculated from the reaction free energy, reactant concentration, and activation energy with explicit accounting of the double-layer structure and interactions. In the presentation, the calculation results will be compared with experimental solid-state data using microelectrodes, and the mechanism of RH-dependent ORR activity will be discussed. Reference I. E. L. Stephens, A. S. Bondarenko, U. Grønbjerg, J. Rossmeisl and I. Chorkendorff, Energy & Environmental Science, 5 (2012).D. A. Cullen, K. C. Neyerlin, R. K. Ahluwalia, R. Mukundan, K. L. More, R. L. Borup, A. Z. Weber, D. J. Myers and A. Kusoglu, Nature Energy, 6, 462 (2021).H. A. Hansen, V. Viswanathan and J. K. Nørskov, The Journal of Physical Chemistry C, 118, 6706 (2014).M. Shibata, M. Inaba, K. Shinozaki, K. Kodama and R. Jinnouchi, Journal of The Electrochemical Society, 169, 044507 (2022).H. Xu, Y. Song, H. R. Kunz and J. M. Fenton, Journal of The Electrochemical Society, 152 (2005).G. A. Tritsaris, J. Greeley, J. Rossmeisl and J. K. Nørskov, Catalysis Letters, 141, 909 (2011).

(Invited) In Situ spectroscopy of Electrochemical and Photoelectrochemical Interfaces

We explore various aspects of electrochemistry and photoelectrochemistry using in situ spectroscopy of electrode (metal) and photoelectrode (semiconductor) interfaces under electrochemical working conditions. Using sum frequency generation (SFG) spectroscopy, we measure the voltage dependence of the orientation of D2O molecules at a graphene electrode surface, which enables us to extract the free energy orienting potential of interfacial water.1 In particular, we measure the “free OD” feature in the spectra, which corresponds to the topmost water molecule that is rotated up out of the bulk water solution and is, therefore, not hydrogen bonded. Using transient absorption spectroscopy (TAS), we measure the lifetime of hot electrons photoexcited in plasmon resonant nanostructures.5 In a similar study, we use transient reflectance spectroscopy (TRS) to measure the photoexcited carrier dynamics in a GaP/TiO2 photoelectrode, as well as the electrostatic field dynamics at this semiconductor-liquid interface in situ under various electrochemical potentials.2 Here, the electrostatic fields at the surface of the semiconductor are measured via Franz−Keldysh oscillations (FKO). These spectra reveal that the nanoscale TiO2 protection layer enhances the built-in field and charge separation performance of GaP photoelectrodes. Using surface enhanced Raman scattering (SERS) spectroscopy, we monitor local electric fields via Stark-shifts of nitrile-functionalized silicon photoelectrodes.6 By monitoring Stark shifts in graphene-enhanced Raman spectroscopy (GERS), we measure local electric fields and local charge densities at monolayer graphene electrode surfaces.3 Lastly, we measure the stacking dependence of monolayer WSe2/MoSe2 heterostructures and observe resonant excitation of interlayer excitons for photocatalytic energy conversion.4 Montenegro, A., C. Dutta, M. Mammetkuliev, H.T. Shi, B.Y. Hou, D. Bhattacharyya, B.F. Zhao, S.B. Cronin and A.V. Benderskii, Asymmetric response of interfacial water to applied electric fields. Nature, 594, 62 (2021).Xu, Z.H., B.Y. Hou, F.Y. Zhao, Z. Cai, H.T. Shi, Y.W. Liu, C.L. Hill, D.G. Musaev, M. Mecklenburg, S.B. Cronin and T.Q. Lian, Nanoscale TiO2 Protection Layer Enhances the Built-In Field and Charge Separation Performance of GaP Photoelectrodes. Nano Letters, 21, 8017-8024 (2021).Shi, H.T., B.F. Zhao, J. Ma, M.J. Bronson, Z. Cai, J.H. Chen, Y. Wang, M. Cronin, L. Jensen and S.B. Cronin, Measuring Local Electric Fields and Local Charge Densities at Electrode Surfaces Using Graphene-Enhanced Raman Spectroscopy (GERS)-Based Stark-Shifts. ACS Applied Materials & Interfaces, 11, 36252-36258 (2019).Chen, J., C.S. Bailey, D. Cui, Y. Wang, B. Wang, H. Shi, Z. Cai, E. Pop, C. Zhou and S.B. Cronin, Stacking Independence and Resonant Interlayer Excitation of Monolayer WSe2/MoSe2 Heterostructures for Photocatalytic Energy Conversion. ACS Applied Nano Materials, DOI:10.1021/acsanm.9b01898 (2020).Yu Wang, Yi Wang, Indu Aravind, Zhi Cai, Lang Shen, Boxin Zhang, Bo Wang, Jihan Chen, Bofan Zhao, Haotian Shi, Jahan M. Dawlaty, and Stephen B. Cronin. In Situ Investigation of Ultrafast Dynamics of Hot Electron-Driven Photocatalysis in Plasmon-Resonant Grating Structures. Journal of the American Chemical Society. DOI: 10.1021/jacs.1c12069 (2022).Haotian Shi, Ryan T. Pekarek, Ran Chen, Boxin Zhang, Yu Wang, Indu Aravind, Zhi Cai, Lasse Jensen, Nathan R. Neale, and Stephen B. Cronin. Monitoring Local Electric Fields using Stark Shifts on Napthyl Nitrile-Functionalized Silicon Photoelectrodes. The Journal of Physical Chemistry C, 124, 17000-17005 (2020).

Compressive Stress and Charge Redistribution during CO Adsorption Onto Pt

Electroorganic reactions, where energy is either stored or released from chemical bonds within carbon-based molecules, are essential to help achieve a circular carbon-based economy. Central to electrochemical conversion of organic molecules is carbon monoxide (CO), which serves as both an intermediate in electrochemical CO2 reduction to hydrocarbons and electrochemical oxidation in fuel cells that operate via oxygenated hydrocarbons (e.g., ethanol, methanol). For the latter, Pt has been the predominate catalyst of choice, and substantial effort has been spent to identify the mechanistic details for complete oxidation of alcohol-based fuels. With CO conversion serving as an important if not rate-limiting step of the oxidative process, it is critical to understand the state of a catalytic surface when CO is present.The change in surface stress associated with the adsorption and oxidative stripping of CO on (111)-textured Pt is examined using the wafer curvature method in 0.1 mol/L KHCO3 electrolyte.1 The curvature of the Pt cantilever electrode was monitored as a function of potential in both CO free and CO-saturated electrolyte. Although CO adsorbs as a neutral molecule, significant compressive stress, up to -1.3 N/m, is induced in the Pt. The magnitude of the stress change correlates directly with the CO coverage, and within the detection limits of the stress measurement, is elastically reversible. Density functional theory calculations of a CO bound Pt surface indicate that charge redistribution from the first atomic layer of Pt to subsurface layers account for the observed compressive stress induced by the charge neutral adsorption of CO. A better understanding of adsorbate-induced surface stress is critical for the development of materials platforms for sensing and catalysis. References D. Raciti, K.A. Schwarz, J. Vinson, and G.R. Stafford, The Journal of Physical Chemistry C , 126, 4446-4457 (2022).

Growth and Properties of Graphene and Graphene Nanoribbons on Ge

The synthesis of graphene directly on Ge and on Ge deposited on Si provides a scalable route toward integrating graphene onto conventional semiconductors. This presentation will first survey the growth modes of graphene on Ge(001), Ge(011), Ge(111), Ge(112), Ge(001)-6°, and Ge(001)-9° via chemical vapor deposition (CVD), reporting on the effect of Ge surface orientation on graphene island formation and shape, strain in large-area graphene films, and the nanofaceting of the Ge below graphene.[1] We will then focus on the anisotropic growth of semiconducting graphene nanoribbons on Ge(001) and Ge(001)-9° and of nominally single crystal graphene on Ge(110).On Ge(001), we have discovered how to drive graphene crystal growth with a large shape anisotropy through control of kinetics.[2-6] This discovery enables the direct synthesis of narrow, armchair, semiconducting nanoribbons. The ribbons are self-orienting, self-defining, and have smooth edges. The ribbons exhibit excellent transport properties (e.g., high on-state conductance and on/off ratio at room temperature) and provide a promising pathway towards the direct integration of high-performance nanocarbon electronics onto conventional semiconductor wafer platforms.On Ge(001), nominally single crystal graphene has been reported in limited cases; however, conflicting studies have evidenced polycrystallinity. Here, the factors affecting the mosaicity of graphene on Ge(110) will be elucidated using low energy electron diffraction and microscopy data.[7][1] R. M. Jacobberger, D. E. Savage, X. Zheng, P. Sookchoo, R. R. Delgado, M. G. Lagally, M. S. Arnold, SUBMITTED (2022).[2] R. M. Jacobberger, M. S. Arnold, et al., Direct Oriented Growth of Armchair Graphene Nanoribbons on Germanium, NATURE COMMUNICATIONS, 6, 8006 (2015).[3] B. Kiraly, M. S. Arnold, M. C. Hersam, N. P. Guisinger et al., Sub-5 nm, Globally Aligned Graphene Nanoribbons on Ge (001), APPLIED PHYSICS LETTERS, 108, 213101 (2016).[4] A. J. Way, R. M. Jacobberger, M. S. Arnold, Seed-Initiated Anisotropic Growth of Unidirectional Armchair Graphene Nanoribbon Arrays on Germanium, NANO LETTERS, 18, 898 (2018).[5] V. Saraswat, Y. Yamamoto, H.J. Kim, R.M. Jacobberger, K.R. Jinkins, A.J. Way, N.P. Guisinger, M.S. Arnold Synthesis of armchair graphene nanoribbons on germanium-on-silicon, THE JOURNAL OF PHYSICAL CHEMISTRY C 123 (30), 18445-18454 (2019).[6] A. J. Way, R. M. Jacobberger, N. P. Guisinger, V. Saraswat, X. Zheng, A. Suresh, J. H. Dwyer, P. Gopalan, Michael S. Arnold, SUBMITTED (2022).[7] R. M. Jacobberger, Z. Miao, T. Yu, V. Saraswat, M. G. Lagally, M. S. Altman, M. S. Arnold, SUBMITTED (2022).

Influence of the Molar Ratio of Co and V in Bimetallic Oxides on Their Pseudocapacitive Properties

Bimetallic oxides have attracted significant attention as supercapacitor electrode materials due to their highly reversible redox processes, which are commonly associated with their surface chemistry and morphological features. In this work, bimetallic oxides with different molar compositions of Co and V, denoted Co0.6V0.4, Co0.65V0.35, and Co0.7V0.3, were synthesized by a modified solvothermal method using glycerol as stabilizing agent. The electrochemical characterizations were measured in a three-electrode cell. The role of the composition of CoV oxides on the pseudocapacitive properties was studied through the analysis of the energy storage mechanism following the power - law and Dunn's methodology (Wang et al., 2007), to obtain the b values. The synthesized CoV oxides were observed to be small conglomerate particles with undefined morphology and crystal structure corresponding to Co3V2O8 with small shifts due to crystal lattice distortion as was evidenced by TEM and XRD characterizations (Fig.1). These results indicated that the bimetallic oxides with a molar composition of Co0.6V0.4, Co0.65V0.35 and Co0.7V0.3 showed values of b of 0.91, 0.73, and 0.82 and a capacitive current contribution of 68, 63, and 66% analyzed at a scan rate of 1 mVs-1, respectively. In addition, the Co0.7V0.3 oxide showed a specific capacitance of 299 F g-1 at a current density of 0.5 A g-1 using 1 mol L-1 of KOH, and a high-rate capability of 81% at current densities of 0.5 - 6 A g-1. The better electrochemical performance of this sample is attributed to the synergistic effect of the Co and V atoms, since a minimal amount of V atoms may distort the crystal lattice and improve the electrolyte diffusion. Keywords: Co-V oxides; capacitance; pseudocapacitive; supercapacitors; rate capability. References Wang, J., Polleux, J., Lim, J. & Dunn, B. (2007). Pseudocapacitive contributions to electrochemical energy storage in TiO2 (anatase) nanoparticles. The Journal of Physical Chemistry C, 111(40), 14925–14931. Figure 1

(Invited) Near-Surface pH during the Electrodeposition of Iron Group Metals

The all-iron flow battery initially proposed in 1981 by Hruska and Savinell represents a cost effective and environmentally benign system for large scale energy storage1. The all-iron chemistry consists of the Fe2+/Fe3+ redox reaction at the positive electrode, and iron plating and stripping at the negative electrode. Because the standard reduction potential for iron plating is more cathodic than that of hydrogen evolution, electrolyte pH heavily influences coulombic plating efficiency as well as deposit morphology and microstructure2-5. Increasing the electrolyte pH decreases the diffusion limited current for hydrogen evolution and shifts the equilibrium potential more negative6. However, iron is not stable at high pH as shown by the Pourbaix diagram, where it will precipitate as hydroxide species. Boric acid is a common component in iron group plating baths where it is believed to function as a buffering agent helping to stabilize pH near the electrode7-9. However, it is not understood how boric acid with a pKa value of 9.27 can buffer at low pH10. The aim of this work is to further understand the effects of pH near the electrode surface and the role of boric acid on the electrodeposition of iron group metals.Electrodeposition of selected iron group metals will be discussed with a focus on the effect of boric acid. We present an in-situ technique for monitoring near surface pH as a function of plating current density. This measurement is accomplished using a tungsten microelectrode which acts as an indicator for hydrogen ion activity11-13. Our results demonstrate that boric acid is not effective in buffering the near surface pH in the acidic baths tested. Even at high current densities in a pH 2.5 electrolyte, the near surface pH did not exceed 6. However, the addition of boric acid improved deposit morphology and current distribution; coupons plated from electrolytes containing boric acid, and those without, are compared and discussed. At high current density and high pH, boric acid incorporates into the deposits, which is studied by use of inductively coupled plasma optical emission spectrometry (ICPOES). Electrochemical impedance spectroscopy, cyclic voltammetry, and coulombic efficiency data aid in understanding additive adsorption as well as the influence of boric acid on the deposition mechanism. In addition to surface specific information, the effects of boric acid on exhaustive plating and long-term bath stability will be presented to account for buffering effects in the bulk electrolyte when pH exceeds 6.References W. Hruska and R. F. Savinell, Journal of The Electrochemical Society, 128, (1) 18-25 (1981)R. Gabe, Journal of Applied Electrochemistry, 27, 908 (1997)Nakahara and S. Mahajan, Journal of the Electrochemical Society, 127 (2) (1980)Cohen-Hyams, Wayne D. Kaplan, Joseph Yahalom, Electrochemical and Solid-State Letters, 5 (8) C75-C78 (2002)Hawthorne et al., Journal of The Electrochemical Society, 162 (1) A108-A113 (2015)Hilbert, Y.Miyoshi, G. Eichkorn, and W. J. Lorenz, Journal of the Electrochemical Society, 118, 1927 (1971)Zech and D. Landolt, Electrochimica Acta, 45 (21) 3461-3471 (2000)P. Hoare, Journal of The Electrochemical Society, 133 (12) 2491-2494 (1986).Santos, R. Matos, F. Trivinho-Strixino and E. C. Pereira, “Effect of temperature on Co electrodeposition in the presence of boric acid” Electrochimica Acta, vol. 53, pp. 644-649 (2007)R. Lide, CRC Handbook of Chemistry and Physics, p. 1274, CRC Press, Boca Raton, FL (2005)E. S. El Wakkad, H. A. Rizk and I. G. Ebaid, The Journal of Physical Chemistry, 59, (10) 1004-1008 (1955)O. Park, C.-H. Paik and H. C. Alkire, Journal of The Electrochemical Society, 8, (143) p. 174 (1996)Webb and R. Alkire, Journal of The Electrochemical Society, 146, (6) p. B280 (2002)

Synergistic Effects in the Activity of Nano-Transition-Metal Clusters Pt12 M (M=Ir, Ru or Rh) for NO Dissociation.

The dissociation of environmentally hazardous NO through dissociative adsorption on metallic clusters supported by oxides, is receiving growing attention. Building on previous research on monometallic M13 clusters [The Journal of Physical Chemistry C 2019, 123 (33), 20314-20318], this work considers bimetallic Pt12 M (M=Rh, Ru or Ir) clusters. The adsorption energy and activation energy of NO dissociation on the clusters have been calculated in vacuum using Kohn-Sham DFT, while their trends were rationalized using reactivity indices such as molecular electrostatic potential and global Fermi softness. The results show that doping of the Pt clusters lowered the adsorption energy as well as the activation energy for NO dissociation. Furthermore, reactivity indices were calculated as a first estimate of the performance of the clusters in realistic amorphous silica pores (MCM-41) through ab initio molecular dynamics simulations.

Towards Understanding the Impact of Electrochemical Double Layer on the Performance of Graphene Devices

The effect of electrochemical double layer (EDL) on the performance of graphene-based sensing platforms has been an area of controversy over the last two decades 1. The hydrophobic nature of bare graphene tends to repel the water and minimizes the solution/solid surface interactions 2. However, the presence of oxygen-based functional groups on graphene introduces negatively charged sites and causes a negative surface zeta potential. Hence, the instant formation of an EDL on a graphene surface in an aqueous solution is inevitable, affecting the graphene surface's chemical/physical interactions 3. Thus far, multiple theories and techniques have been developed to investigate the impact of EDL on graphene sensing performance; however, they either suffer from complexity in design or have ignored the co-existence of other solution parameters such as pH and oxidation-reduction potential 4.In this work, we propose the use of alkaline chloride salts to understand the impact of the ionic strength and EDL of the solution on the few-layer graphene (FLG) based chemiresistive sensors. Considering the full ionization of NaCl and the low redox potential of the generated ions, alkaline chlorides are considered good candidates to modulate the electronic band structure of FLG without altering its surface chemistry 5. By use of Helmholtz theory of EDL, it is postulated the Inner Helmholtz Layer (IHL) to be formed by Na+ ions due to the negative surface charge of FLG. Whereas the hydrated counter ions, Cl-, form the Outer Helmholtz Layer (OHL). Upon the formation of a positively charged immobile layer of Na+ ions on the surface (IHL), the electrostatic gating effect of EDL dopes the graphene with electrons. This charge separation can be modelled as two parallel plates of a capacitor with infinitely thin dielectric 6.Since the presence of oxygen-based functional groups on FLG is inevitable during the synthesis process, it is considered inherently p-doped. Accordingly, upon the addition of NaCl concentrations, the FLG surface current decreases. However, at higher concentrations (around 2000 ppm NaCl), the sensor response is inversed, and surface current increases by the addition of NaCl (Figure-left). In fact, high ionic strength increases the EDL compactness and decreases the charge screening length (Debye length). As a result of this sharper difference in solid/solution potentials (Figure-right), a more n-doped surface having electron as majority charge carriers is obtained, changing the nature of the response.We have also demonstrated that the formation of sodium-oxygen metal complexes on FLG is not likely in an aqueous environment. According to the Raman spectroscopy results of FLG, an increase in the intensity ratio of D (defect) to G bands is observed upon exposure to water and NaCl. Moreover, the noticeable right shift in the 2D band position demonstrates the p-doping of FLG 7. Furthermore, the reversible response of the sensor during multiple exposures to NaCl demonstrates the sensor response originates from EDL, not the formation of sodium-oxygen metal complexes. In fact, the full or half hydrated Na+ ions in IHL electrostatically interact with surrounding oxygen. However, since the oxygen atom in water is more negatively charged compared to the oxygen on the graphene surface, Na+ is unlikely to bound to the surface after hydration. Therefore, using NaCl could be a suitable medium to study the impact of EDL on the performance of graphene devices.Reference Jurado et al., Scientific Reports, 7(1), pp.1-12 (2017).Angizi, S et al., Langmuir, 37(41), pp.12163-12178 (2021).Jung et al., Nano Letters, 21(1), pp.34-42 (2020).Pak et al., The Journal of Physical Chemistry C, 118(38), pp.21770-21777 (2014).Lee et al., ACS Applied Materials & Interfaces, 11(45), pp.42520-42527 (2019).Kwon et al., The Journal of Physical Chemistry C, 116(50), pp.26586-26591 (2012).Bruna et al., ACS Nano, 8(7), pp.7432-7441 (2014). Figure 1

Kinetic and Product Composition Studies of 9,10-Anthraquinone-2,7-Disulfonic Acid: Correlating Transient/Steady-State Modeling with Experimental Analysis

Organic-based quinones have been studied for use as an electrolyte for redox-based flow batteries due to their good chemical stability, high solubility, and low cost. In biological applications, quinones can be more advantageous than other charge carriers, such as viologens, due to all of the aforementioned reasons as well as their lower toxicity. One such quinone, 9,10-anthraquinone-2,7-disulfonic acid (AQDS), is reported to have lower redox potentials [1], but the reaction pathways to form desired AQDS products are more highly pH-dependent [2], which can be problematic in biological applications with restrictive pH ranges to maintain biocatalyst reactivity. Competition with dimerization has also been reported to be an issue, inhibiting the production of desired charged species for use in catalysts [3]. Consequently, there is a need to reliably predict the state of the charge carrier, requiring more robust theoretical models.The kinetics of AQDS are first studied here experimentally in a single-cell configuration with a buffer selected to maintain a neutral pH condition (pH = 7). Cyclic voltammetry (CV) studies revealed highly reversible kinetics for AQDS, indicating an advantage in its choice as a charge carrier over viologens, which tend to have certain additional irreversible redox reactions. Furthermore, a Randles-Sevcik analysis of the peak current vs. scan rate revealed strong equivalence in the reduction and oxidation reactions. Diffusion coefficients of 1-2 x 10-9 m2/s are consistent with previously reported values [4]. Additionally, kinetic constants were determined using the Kochi equation [5] and were found to be on the order of 10-3 to 10-5 cm/s, indicating more sluggish kinetics than would otherwise be anticipated.Chronoamperometry studies were conducted in an H-cell reactor with 10 mM AQDS in the cathode chamber with a pH buffer. One set of experiments was run using CO2 as the purge gas (used in biological applications to convert to usable organic products, decreasing pH to 6.3), and the other set was run using N2 (to serve as an inert gas and help maintain near neutral pH). Charging with -0.75 V vs. Ag/AgCl over a duration of 1.5 hours, the AQDS displayed high initial currents relative to a blank sample; however, longer steady-state times suggested slower reaction kinetics consistent with the CV study. Under the more pH neutral conditions, initial AQDS reduction was further delayed, indicating greater product favorability in more acidic environments. This knowledge is useful for battery applications where inert gases are typically used to purge but poses a challenge when catalysts such as enzymes are highly sensitive to pH.Finally, a transient-based equilibrium model is developed for AQDS in a batch reactor. The model is simulated using Butler-Volmer kinetics until steady-state is reached, using the same conditions studied for the experimental chronoamperometry. AQDS displays a lower charge input than other charge carriers, such as viologens, at -0.5 V vs. Ag/AgCl but is limited by slower kinetics. An extended transient study revealed AQDS kinetics taking nearly 10 hours to reach final equilibrium concentrations. The product composition of AQDS depends heavily on pH as well as voltage, with four unique product composition ranges. The use of a steady-state equilibrium model to connect with the transient model for the complete range of product compositions is reported here at various pH and voltage values. Designing charge carrier reduction experiments around such conditions predicted theoretically, rather than only -0.75 V, may enable more rapid and reliable charge carrier production to assist in applications such as fuel cells, batteries, and catalytic CO2 conversion to value-added products. Forster RJ, O'Kelly JP. Protonation reactions of anthraquinone-2, 7-disulphonic acid in solution and within monolayers. Journal of Electroanalytical Chemistry. 2001 Feb 16;498(1-2):127-35.Batchelor-McAuley C, Li Q, Dapin SM, Compton RG. Voltammetric characterization of DNA intercalators across the full pH range: Anthraquinone-2, 6-disulfonate and anthraquinone-2-sulfonate. The Journal of Physical Chemistry B. 2010 Mar 25;114(11):4094-100.Wiberg C, Carney TJ, Brushett F, Ahlberg E, Wang E. Dimerization of 9, 10-anthraquinone-2, 7-Disulfonic acid (AQDS). Electrochimica Acta. 2019 Sep 10;317:478-85.Huskinson B, Marshak MP, Suh C, Er S, Gerhardt MR, Galvin CJ, Chen X, Aspuru-Guzik A, Gordon RG, Aziz MJ. A metal-free organic–inorganic aqueous flow battery. Nature. 2014 Jan;505(7482):195-8.Klingler RJ, Kochi JK. Electron-transfer kinetics from cyclic voltammetry. Quantitative description of electrochemical reversibility. The Journal of Physical Chemistry. 1981 Jun;85(12):1731-41. Figure 1

Development of Double Perovskite Oxide Photocatalysts for Efficient Visible-Light Driven Photocatalytic Water Splitting and CO2 Reduction

Energy and environment are the key global challenges in the 21st century. Solar energy is considered the most promising clean and sustainable energy resource due to its university, inexhaustible and environmental friendliness. One of the most viable means of solar energy conversion and utilization is artificially converting solar energy into chemical energy as natural photosynthesis does. H2 produced from water splitting and CO2 reduction, are the major research topics of artificial photosynthesis. However, the effective conversion of solar energy into chemical energy by cost-effective artificial means on a large scale remains elusive. Metal oxide-based photocatalysts are the most studied materials for photocatalytic water splitting and CO2 reduction. Particularly, perovskite oxides with the chemical formula of ABO3 have been intensively studied as semiconductor photocatalysts. However, overwhelmingly of the perovskite oxides are only active under UV-light-irradiation, which limited their potential in solar energy application. Therefore, breakthrough technology and step-change materials, particularly, visible-light-responsive photocatalysts are highly desirable for the development of photocatalytic systems. In recent years, copious progress has been made in designing materials that function under visible-light-irradiation. So far, the most successful strategy is anion doping of oxide semiconductors, such as nitrogen or sulfur dope to form oxynitrides and oxysulfides, respectively. For example, nitrogen-doped oxynitrides such as (Ga1-xZnx)(N1-xOx) and ANbO2N (A=Sr, Ba, and La)1, and sulfur-doped oxysulfides such as Sm2Ti2S2O5 2 showed efficient photocatalytic overall water splitting activities under visible-light-irradiation. Particularly, oxynitrides (Ga1-xZnx)(N1-xOx) based photocatalyst sheet, showed remarkable photocatalytic overall water splitting activity with AQE of more than 30% at l»420 nm3. However, these oxynitrides and oxysulfides suffer stability problems due to photocorrosion, hindering their potential practical application in photocatalytic applications. Recently, it has been theorized that double perovskite oxides (DPOs) with the chemical formula of A2BʹB"O6 can function as efficient and stable visible-light-responsive photocatalysts for photocatalytic water splitting and CO2 reduction. However, DPOs have been rarely studied for photocatalytic water splitting and CO2 reduction due to the difficulty of obtaining pure phase materials and the paucity of exposed active sites. Thus, developing efficient and stable visible-light-responsive DPOs photocatalysts for photocatalytic water splitting and CO2 reduction becomes important. In this regard, recently, we have demonstrated a series of efficient and stable visible-light-responsive DPOs photocatalysts for photocatalytic water splitting. For instance, Sr2CoWO6 and Sr2CoTaO6 can serve as an efficient and stable bifunctional photocatalyst for both photocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction(HER)4, 5, and Sr2NiWO6 can efficiently drive the photocatalytic OER6. Even though these DPOs have been demonstrated as visible-light-responsive photocatalysts with suitable CB and VB positions that straddle the theoretical potentials for overall water splitting, however, one-step overall water splitting has not been achieved so far, and their potential for photocatalytic CO2 reduction has not been studied yet. Overall water splitting under visible-light-irradiation based on particulate photocatalysts is a challenging reaction, which is regarded as one of the “Holy Grail” of sciences. And oxide semiconductors showing both photocatalytic OER and HER activities are rare. Nevertheless, bifunctional photocatalytic OER and HER were successfully demonstrated based on Sr2CoWO6 and Sr2CoTaO6. Further improvement of the material designs and developing appropriate cocatalysts may play a key role in achieving one-step overall water splitting under visible-light-irradiation based on DPOs photocatalysts. This work is mainly to explore the possibility of utilizing DPOs materials as visible-light-responsive photocatalysts for photocatalytic water splitting and CO2 reduction reaction, which is challenging work but has great potential value in advancing science and technology in photocatalysis. We anticipated that this work will provide a novel and rational strategy for improving the light absorption, charge separation and charge utilization in DPOs photocatalysts. References Maeda, K.; Teramura, K.; Masuda, H.; Takata, T.; Saito, N.; Inoue, Y.; Domen, K. The Journal of Physical Chemistry B 2006, 110 (26), 13107-13112.Ma, G.; Kuang, Y.; Murthy, D. H.; Hisatomi, T.; Seo, J.; Chen, S.; Matsuzaki, H.; Suzuki, Y.; Katayama, M.; Minegishi, T. The Journal of Physical Chemistry C 2018, 122 (25), 13492-13499.Kato, H.; Asakura, K.; Kudo, A. Journal of the American Chemical Society 2003, 125 (10), 3082-3089.Idris, A. M.; Liu, T.; Shah, J. H.; Zhang, X.; Ma, C.; Malik, A. S.; Jin, A. Solar RRL 2020, 4 (3), 1900456.Idris, A. M.; Liu, T.; Hussain Shah, J.; Han, H.; Li, C. ACS Sustainable Chemistry&Engineering 2020, 8 (37), 14190-14197.Idris, A. M.; Liu, T.; Hussain Shah, J.; Malik, A. S.; Zhao, D.; Han, H.; Li, C. ACS Applied Materials&Interfaces 2020, 12 (23), 25938-25948.

Physicochemical Interplay in Solid Polymer Electrolytes: Benchmarking, Prospects and Limits in High Voltage Batteries

A systematic R&D of solid electrolytes (SEs) requires reasonable benchmark systems for the intra- and interlaboratory comparison and evaluation. Given its abundance, costs, compatibility with Li and a relative simplicity in processing, the poly(ethylene oxide)-based solid electrolyte (PEO-based SE) is a reasonable benchmark SE system for solid-state lithium batteries.(1)On the basis of recent progress in cell design and methodology,(2-5) the physicochemical properties of PEO-based SE are elaborated as a function of Li salt concentration and related with the performance in LiNi0.6Mn0.2Co0.2O2 (NMC622)||lithium cells. The overall aim is to unravel the apparently complex interplay of relevant parameter and finally to demonstrate the prospects and limits of the SPE benchmark in practical lithium-based batteries.(6)For instance, despite the decrease of the crystalline phases with a Li salt in a plasticizing manner leading to SE membrane softening, the accompanied increase in amorphous phases enhances the Li+ diffusion coefficient, which can be easily obtained from the analysis of Li||Li cells with the Sand equation. Both, the increased diffusivity of Li+ and the overall amount of charge carriers leads to improved ionic conductivities with higher Li salt concentration, particularly below the melting point (Tm < 60 °C). In terms of anodic behavior, neither SE decomposition nor Al current collector dissolution is visibly affected by the Li salt concentration, revealing a surprisingly high bulk electrolyte stability of 4.6 V vs. Li|Li+ on practical, i.e. composite electrodes; and an Al dissolution tendency as low as in conventional LiPF6/carbonate-based liquid electrolytes. Finally, at an operation temperature below Tm, Li salt concentration is demonstrated to have a direct link with characteristic performance aspects of e.g. NMC622||Li cells. J. Mindemark, M. J. Lacey, T. Bowden and D. Brandell, Prog. Polym. Sci., 81, 114 (2018).L. Stolz, G. Homann, M. Winter and J. Kasnatscheew, Materials Advances, 2, 3251 (2021).G. Homann, L. Stolz, M. Winter and J. Kasnatscheew, iScience, 23, 101225 (2020).L. Stolz, G. Homann, M. Winter and J. Kasnatscheew, Materials Today, 44, 9 (2021).G. Homann, L. Stolz, J. Nair, I. C. Laskovic, M. Winter and J. Kasnatscheew, Sci Rep, 10, 4390 (2020).L. Stolz, S. Röser, G. Homann, M. Winter and J. Kasnatscheew, The Journal of Physical Chemistry C, 125, 18089 (2021). Figure 1

ORR Activity and Surface Strain Relations of Commercial Pt Alloy Catalysts

Understanding and improving the catalysts for the ORR (Oxygen Reduction Reaction) is of great importance for the development of low temperature fuel cells. Within the past two decades great effort has been taken into the development of platinum alloy nano-catalysts and brought to commercialization. While thorough studies on the activity and stability of the individual catalysts have received great attention in the scientific literature, consistent comparisons of different platinum alloy nano-catalysts are scare: Due to different preparation methods and experimental conditions, the reported specific activities of, e.g. Pt3Co/C, vary by one order of magnitude [1][2]. In the first part of this talk we will present consistent electrochemical measurements on 7 different commercially available platinum alloy nano-catalysts (20% Pt loading on Vulcan XC-72R). In the second part we will present our results in context of the scientific understanding the ORR on platinum-based catalysts. Therefore, we conducted an extensive TEM survey on the measured nano-catalysts and gained further insights into the platinum surface strain. We find that the platinum surface strain of nano-catalysts is not only a phenomenon of an over-layer formation on platinum alloys, but also an inherent property of its nano-particular form. Wang, C. et al. “Monodisperse Pt3Co nanoparticles as a catalyst for the oxygen reduction reaction: Size-dependent activity.” Journal of Physical Chemistry C, 113(45), 19365–19368. https://doi.org/10.1021/jp908203p Koh, S. et al. “Activity-stability relationships of ordered and disordered alloy phases of Pt3Co electrocatalysts for the oxygen reduction reaction (ORR).” Electrochimica Acta, 52(8 SPEC. ISS.), 2765–2774. https://doi.org/10.1016/j.electacta.2006.08.039 Figure 1

(Digital Presentation) Electrochemical Glutamate Sensor Using Copper Oxide Nanomaterials Functionalized with Multiwall Carbon Nanotubes

Glutamate is the most abundant neurotransmitter in the central nervous system (CNS) and plays an important role in different physiological processes. Excess amounts of glutamate cause excitotoxicity resulting in different diseases such as Alzheimer’s and glioma, pain disorders, spinal cord injuries, and cancer1-4. The concentration of glutamate in body fluids such as saliva is associated with those diseases. Therefore, glutamate is a potential biomarker for pathologies. By measuring glutamate levels in biofluids these pathologies can be monitored.Lab-based techniques such as liquid chromatography and gas chromatography offer a low limit of detection, high sensitivity, and precise detection of biomarkers4-7. These techniques are expensive, bulky, time-consuming, and require skilled personnel to operate them and therefore are not suitable for wearable and personalized healthcare applications. In contrast, electrochemical sensors are simple, low-cost, handy, and offer rapid and high sensing performance of biomarkers/analytes8,9.In this work, we fabricated a very simple, low-cost, and reusable enzyme-free electrochemical sensor using copper oxide (CuO) nanomaterials for label-free detection of glutamate. CuO nanomaterials were synthesized by a low-cost wet chemical process. The CuO nanomaterials were dispersed in DI water and the working electrode was prepared by drop casting of CuO dispersion on a screen-printed carbon electrode (SPCE). Multiwall carbon nanotubes (MWCNTs) were used with CuO to enhance the electron transfer from CuO to SPCE (Figure a). Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used to perform glutamate sensing in deionized (DI) water at pH 7.4. The peak oxidation current (I pa) is proportional to glutamate (G) presence in DI water (Figure b). The sensor showed good oxidation current event at a low concentration of glutamate (20 µM) in DI water. The normal concentrations of glutamate in body fluids such as plasma and saliva are about 5-100 µM, and 1-30 µM respectively 3. Therefore, CuO nanostructure-based nonenzymatic electrochemical sensor is very potential for low cost, portable, rapid detection of glutamate in those body fluids. We will further discuss details of CuO synthesis, electrode fabrication process, sensing mechanism, and challenges of the glutamate sensor.References Lewerenz and P. Maher, Frontiers in neuroscience. 9 (2015) 469.Takano et al., Nature medicine. 7 (2001) 1010-1015.H Jasim et al., Scientific reports 8.1 (2018): 1-9.Schultz, Z. Uddin, G. Singh, and M. M. Howlader, Analyst. 145 (2020) 321-347.Klimuntowski, M. M. Alam, G. Singh, and M. M. Howlader, ACS Sensor. 5(3) (2020) 620–636.Budczies et al., International journal of cancer. 136 (2015) 1619-1628.Xin et al, Chinese Journal of Analytical Chemistry. 35 (2007), 1151-1154.Hughes et al., Sensors and Actuators B: Chemical. 216 (2015) 614-621.Rocchitta et al., Sensors, 16 (2016) 780.X Zhang et al., The Journal of Physical Chemistry C 112.43 (2008): 16845-16849.Y Li et al., Materials Research Bulletin 43.8-9 (2008): 2380-2385.RP Allaker, and Z Yuan, Nanobiomaterials in clinical dentistry. Elsevier, 2019. 243-275. Figure 1

Targeted Re-Speciation of Ca2+ in Borohydride-Based Electrolytes

Given concerns about the low earth abundance of Li in Li-ion batteries, there is growing interest in developing a beyond-Li materials basis for rechargeable batteries. Divalent batteries based on calcium (Ca) have received attention due to their ~2000-fold higher concentration in the earth’s crust along with attractive theoretical metrics if Ca is used as the metallic anode. At present, only a small number of nonaqueous electrolytes have been identified that allow for Ca electrodeposition,1-5 limiting the design space for Ca battery development; thus, learning how to tailor Ca2+ speciation and electroactivity is of central importance to engineer next-generation battery electrolytes. Unlike many Li+ analogues in common battery electrolytes, Ca2+ cations are prone to coordinate with one or both anions in solution even at low concentrations (< 1 M), which can substantially impair their ability to participate in electrochemical processes. Recent studies have shown that in an electrolyte system of growing interest, Ca(BH4)2 in tetrahydrofuran (THF), unexpected promotion of active CaBH4 + clusters from neutral Ca(BH4)2 ion pairs occurs at salt concentrations greater than 1 M, such that higher salt concentrations are necessary to provide charge mobility and high current densities.6 Learning how to break ion-pairing constraints and more flexibly modulate Ca2+ speciation over broader ranges of salt concentrations is therefore important to identify handles for next-generation electrolyte design.This study investigates an alternative means to tailor the Ca2+-to-BH4 - ratio, and thus the generation of electroactive Ca ionic species, by using an exemplar dual-salt electrolyte, Ca(BH4)2 + Ca(TFSI)2 in THF, at varying anion ratios for a constant total salt concentration of 1 M Ca2+. Introduction of a more highly-dissociating source of Ca2+ in Ca(TFSI)2 effectively drives re-speciation of the more strongly ion-pairing Ca(BH4)2 as indicated by a 4x increase in ionic conductivity (Fig. 1a) and Raman spectroscopy measurements (Fig. 1b),7 generating larger populations of charged species and supporting a ~2x increase in plating current density. We further find that TFSI- enables Ca plating at high current densities when its concentration is less than that of Ca(BH4)2, but leads to a dramatic shut-down of plating activity when concentrations exceed that of Ca(BH4)2 (Fig. 1c),7 providing direct evidence of the role of coordination-shell chemistry on modulating Ca2+ plating activity. On the other hand, Ca stripping activity is suppressed by the presence of TFSI- at all salt concentrations (Fig. 1d),7 which decomposes onto the Ca surface, passivating the deposits with compounds comprising ~30% C, 35% O, and 10% F. Results are compared to that of a second dual-salt electrolyte system, Ca(BH4)2 + TBABH4 in THF, which enables enrichment of BH4 - concentrations to be higher than 2x that of Ca2+ and similarly experiences a 4x increase in ionic conductivity and ~2x increase in plating current density. This work reveals factors that modulate Ca2+ coordination and activity and highlights future directions to attain both high plating currents and reversibility for Ca-based electrolyte design.1 Ponrouch, A., Frontera, C., Bardé, F. & Palacín, M. R. Towards a calcium-based rechargeable battery. Nature Materials 15, 169 (2015).2 Wang, D. et al. Plating and stripping calcium in an organic electrolyte. Nature Materials 17, 16 (2017).3 Shyamsunder, A., Blanc, L. E., Assoud, A. & Nazar, L. F. Reversible Calcium Plating and Stripping at Room Temperature Using a Borate Salt. ACS Energy Letters 4, 2271-2276 (2019).4 Li, Z., Fuhr, O., Fichtner, M. & Zhao-Karger, Z. Towards stable and efficient electrolytes for room-temperature rechargeable calcium batteries. Energy & Environmental Science (2019).5 Kisu, K. et al. Monocarborane cluster as a stable fluorine-free calcium battery electrolyte. Scientific Reports 11, 7563 (2021).6 Hahn, N. T. et al. The critical role of configurational flexibility in facilitating reversible reactive metal deposition from borohydride solutions. Journal of Materials Chemistry A 8, 7235-7244 (2020).7 Melemed, A. M., Skiba, D. A., Gallant, B. M. Toggling Calcium Plating Activity and Reversibility through Modulation of Ca2+ Speciation in Borohydride-based Electrolytes. Manuscript in revision. 8 Rey, I. et al. Spectroscopic and Theoretical Study of (CF3SO2)2N- (TFSI-) and (CF3SO2)2NH (HTFSI). The Journal of Physical Chemistry A (1998).9 Tchitchekova, D. S. et al. On the Reliability of Half-Cell Tests for Monovalent (Li+, Na+) and Divalent (Mg2+, Ca2+) Cation Based Batteries. Journal of The Electrochemical Society 164, A1384-A1392 (2017). Figure 1

Reactive Molecular Dynamics Study for CO2 Electrocatalytic Conversion on Lmfcr (M= Sr, Ca) Perovskite-Based Solid Oxides

Due to their mixed conducting properties as well as their electronic, crystallographic, and chemical versatility, perovskite-based oxides have been shown to be very promising electrocatalysts for CO2 conversion to syngas in high temperature (600 – 1000 °C) solid oxide electrolysis cells (SOECs) integrated with renewable energy resources. In addition to generating fuels and value-added chemicals, CO2 reduction (CO2RR) in SOECs serves to lower atmospheric CO2 emissions. La-based (1) perovskite oxides have been intensively used instead of precious metals and metal-cermet materials (e.g., Ni-YSZ, Ni-GDC) for CO2 electrolysis in high temperature SOECs. The effect of the dopant cations on the electrocatalytic performance and degradation have also been investigated since the segregation of dopants can reconstruct the surface (2). Our team has been actively developing the family of La0.3a0.7Fe0.7Cr0.3O3−δ (LMFCr, where M = Ca or Sr) for CO2 reduction (3,4) showing that CO2RR is more active than CO oxidation, and that the catalyst is also highly active on the air side. More recently, we have shown that Fe-Ni exsolved LCFCr significantly improves the rate of CO oxidation (5), while hardly changed CO2RR. However, a full atomistic scale understanding of the CO2 reduction mechanism and related degradation issues, such as dynamic changes of the surface composition as a function of operating conditions, does not yet exist. The oxygen vacancy concentration (V0) and surface termination of the perovskite material are important factors that affect the CO2RR, as shown recently (6) utilizing DFT methods.In this study, we used Density Functional Theory (DFT) to explore the energetics of the catalytic conversion of CO2 to CO on LMFCr (M = Sr, Ca) perovskite surfaces. The DFT calculations were then used to generate datasets of optimized lattice structures, including point defects, equations of state, surface energies, and surface CO2/CO interactions in order to develop reactive force fields (ReaxFF). The datasets were optimized by using an evolutionary algorithm, CMA-ES, and validated in order to explore the dynamics of the catalytic conversion process under varying conditions, such as temperature, inlet CO2/CO gas ratio, the perovskite surface composition and applied electrical field.Our results have shed light on reaction steps involving adsorption of CO2 at high temperatures, C=O bond activation, and the dominant intermediates as transition states during the conversion process and their role in generating CO. These observations will serve as a foundation to determine the elementary reaction steps involved in the CO2 splitting mechanism on LMFCr at high temperatures. Furthermore, this study will enable us to determine the optimal conditions for the reaction to occur and shed light on possible surface degradation mechanisms, allowing future optimization of the stability and catalytic activity of these promising perovskites.ACKNOWLEDGMENTSThis computational research was supported by the Canada First Research Excellence Fund (CFREF), while the platforms for this computational work were provided by Westgrid (https://www.westgrid.ca) and Compute Canada (https://www.computecanada.ca). Thanks are also extended to Oliver Calderon and Misha Pidburtnyi for helpful discussions.References Cao, Z., Wei, B., Miao, J., Wang, Z., Lü, Z., Li, W., Zhang, Y., Huang, X., Zhu, X., Feng, Q. and Sui, Y., (2016). Efficient electrolysis in symmetrical solid oxide electrolysis cell with highly active 3Sr0.7Fe0.7Ti0.3O3 electrode material. Electrochemistry Communications, 69, 80-83.Zhang, Y. Q., Li, J. H., Sun, Y. F., Hua, B., & Luo, J. L. (2016). Highly active and redox-stable Ce-doped LaSrCrFeO-based cathode catalyst for CO2 SOECs. ACS Applied Materials & Interfaces,, 8(10), 6457-6463.Addo, P. K., Molero‐Sanchez, B., Chen, M., Paulson, S., & Birss, V. (2015). CO/CO2 study of high performance La0. 3Sr0. 7Fe0. 7Cr0. 3O3–δ reversible SOFC electrodes. Fuel Cells, 15(5), 689-696.Molero-Sánchez, B., Morán, E., & Birss, V. (2017). Rapid and Low-Energy Fabrication of Symmetrical Solid Oxide Cells by Microwave Methods. ACS Omega, 2(7), 3716-3723.Ansari, H. M., Bass, A. S., Ahmad, N., & Birss, V. I. (2022). Unraveling the evolution of exsolved Fe–Ni alloy nanoparticles in Ni-doped La 0.3 Ca 0.7 Fe 0.7 Cr 0.3 O 3− δ and their role in enhancing CO 2–CO electrocatalysis. Journal of Materials Chemistry A.Kozokaro, V. F., Addo, P. K., Ansari, H. M., Birss, V. I., & Toroker, M. C. (2020). Optimal Oxygen Vacancy Concentration for CO2 Reduction in LSFCr Perovskite: A Combined Density Functional Theory and Thermogravimetric Analysis Measurement Study. The Journal of Physical Chemistry C, 124(50), 27453-27466.

(Digital Presentation) Chiroptical Effect in Aligned Carbon Nanotube Films

The dissymmetric interaction between circularly polarized light and solid-state materials is central to developing next-generation chiral photonic devices for applications such as spectroscopy and imaging. The strong quantum confinement in 1D single-wall carbon nanotubes (SWCNTs) features extraordinary electrical and optical properties and enables high-performance optoelectronic devices for the generation, modulation, and detection of light. The recent success of separating chirality-enriched [1], especially enantiomer-enriched, SWCNT suspensions and their macroscopic alignment assembly [2] further pushes the frontier of improving the performance and bringing new chiral functionalities of SWCNT-based optoelectronic devices. However, the chiroptical spectroscopy characterization mainly focuses on solution samples or individual SWCNTs. There has been no report of such studies in macroscopic solid-state films of SWCNTs. In this work, we investigate the circular dichroism (CD) spectroscopy of the solution and large-area films of non-racemic, chirality-mixture SWCNTs synthesized using the arc-discharge method. We prepared multiple films with various degrees of alignment using the controlled vacuum filtration method [2]. By carefully designing a cuvette that is manufactured through a stereolithography-type 3D printer (Fig. 1a) and performing a 4-configuration measurement by flipping and rotating samples (Fig. 1b), the effects from linear dichroism and birefringence can be minimized [3]. As expected, both solution and random film samples displayed zero CD; see Fig. 1c. In stark contrast, the aligned films displayed strong CD signals (~ 480 mdeg at the peak position). More surprisingly, the signs of obtained CD signals from different aligned films can be completely opposite even though their degrees of alignment, in terms of reduced linear dichroism (LDr) at the wavelength of 1035 nm, and thicknesses are nearly the same; see Fig. 1c. We will discuss possible origins of these surprising chiroptical responses in terms of slight and gradual twisted rotations of alignment directors, which can happen during spontaneous alignment in the vacuum filtration process.[1] Ichinose, Y., Eda, J., Yomogida, Y. et al. Extraction of High-Purity Single-Chirality Single-Walled Carbon Nanotubes through Precise pH Control Using Carbon Dioxide Bubbling. The Journal of Physical Chemistry C 121, 13391-13395 (2017).[2] He, X., Gao, W., Xie, L. et al. Wafer-scale monodomain films of spontaneously aligned single-walled carbon nanotubes. Nature Nanotech 11, 633–638 (2016).[3] Albano, G., Pescitelli, G. et al. Chiroptical Properties in Thin Films of π-Conjugated Systems. Chemical Reviews 120 , 10145-10243 (2020). Figure 1

Accessing in Situ Photocorrosion Under Realistic Light Conditions

High-impact photoelectrode materials for photoelectrochemical (PEC) water splitting are distinguished by synergistically attaining high photoactivity and stability at the same time. With numerous efforts toward optimizing the activity, the bigger challenge of tailoring the durability of photoelectrodes to meet industrially relevant levels remains. In situ photostability measurements using flow cells hold great promise in understanding stability-related properties1-3 compared to traditional procedures, such as measuring the drop in photocurrent over time at 1.23 VRHE.In this work, a photoelectrochemical scanning flow cell connected to an inductively coupled plasma mass spectrometer (PEC-ICP-MS) and equipped with a solar simulator, Air Mass 1.5 G filter, and monochromator was developed (Figure 1A). The established system is capable of independently assessing basic PEC metrics, such as photopotential, photocurrent, incident photon to current efficiency (IPCE), and band gap in a high-throughput manner, as well as the in situ photocorrosion behavior of photoelectrodes under standardized and realistic light conditions by coupling it to an ICP-MS.4 In situ photocorrosion measurements conducted on spray-coated WO3 revealed that dissolution starts at 0.8 VRHE with the dissolution rate rapidly increasing past 1.2 VRHE, coinciding with the onset of the saturation photocurrent (Figure 1B). Wavelength-dependent photodegradation measurements show that WO3 only dissolved when irradiated with wavelengths lower than its band gap (Figure 1C). By using standardized illumination conditions such as AM 1.5 G under 1 Sun, the obtained dissolution characteristics are translatable to actual devices under realistic light conditions. The gained insights can then be utilized to advance synthesis and design approaches of novel PEC materials with improved photostability.Another aspect of flow cell systems is that they are well suited for operation in a high-throughput manner. In fact, scanning droplet cells have been successfully employed for rapid (photo)electrochemical screening of (photo)electrocatalyst libraries.5, 6 In here, we demonstrate proof-of-concept approaches for a full automation of the presented system to establish a platform that is capable of not only performing complete sets of PEC measurements but at the same time assess the in situ photostability of a photoelectrode material library. Such a platform would enable material discovery, which is tailored to search not only for the most active but also for the most stable PEC material. References Knöppel, J.; Zhang, S.; Speck, F. D.; Mayrhofer, K. J. J.; Scheu, C.; Cherevko, S., Time-resolved analysis of dissolution phenomena in photoelectrochemistry – A case study of WO3 photocorrosion. Electrochem. Commun. 2018, 96, 53-56.Dworschak, D.; Brunnhofer, C.; Valtiner, M., Photocorrosion of ZnO Single Crystals during Electrochemical Water Splitting. ACS Appl Mater Interfaces 2020, 12 (46), 51530-51536.Zhang, S.; Rohloff, M.; Kasian, O.; Mingers, A. M.; Mayrhofer, K. J. J.; Fischer, A.; Scheu, C.; Cherevko, S., Dissolution of BiVO4 Photoanodes Revealed by Time-Resolved Measurements under Photoelectrochemical Conditions. The Journal of Physical Chemistry C 2019, 123 (38), 23410-23418.Jenewein, K. J.; Kormányos, A.; Knöppel, J.; Mayrhofer, K. J. J.; Cherevko, S., Accessing In Situ Photocorrosion under Realistic Light Conditions: Photoelectrochemical Scanning Flow Cell Coupled to Online ICP-MS. ACS Measurement Science Au 2021, 1 (2), 74-81.Gregoire, J. M.; Xiang, C.; Liu, X.; Marcin, M.; Jin, J., Scanning droplet cell for high throughput electrochemical and photoelectrochemical measurements. Rev. Sci. Instrum. 2013, 84 (2), 024102.Sliozberg, K.; Schafer, D.; Erichsen, T.; Meyer, R.; Khare, C.; Ludwig, A.; Schuhmann, W., High-throughput screening of thin-film semiconductor material libraries I: system development and case study for Ti-W-O. ChemSusChem 2015, 8 (7), 1270-8. Figure 1