Journal Of Physical Chemistry Research Articles

Characteristics of Impactful Computational Contributions to The Journal of Physical Chemistry C

Characteristics of Impactful Computational Contributions to <i>The Journal of Physical Chemistry C</i>

(Invited) Photoluminescence Diagnostics of Nanoscale Dissolution of III-V Semiconductor Nanoheterostructures

Etching of semiconducting materials with atomic level resolution is of high interest to technologies addressing the fabrication of low-dimensional devices and the tunability of their optoelectronic properties. Atomic layer etching (ALE) based on cycling between a self-limited surface reaction and selective removal of the reaction products is a promising technique addressing the challenges of controlling the variability necessary in the atomic-scale material removal [1]. However, the requirement to alter the processing hardware while completing two cycles of ALE, as well as the lack of a simple diagnostic technique for monitoring in situ material etching with a sub-monolayer resolution, have restricted the application of this technique to laboratories equipped with relatively expensive hardware infrastructures. To alleviate some of the problems of the ALE technique, we have investigated digital photo-assisted etching of GaAs/AlGaAs nanoheterostructures, which has the potential to offer a simple approach for fabrication of low-dimensional devices. The premise of this approach is based on the expectation that dark corrosion of a semiconductor is negligible in a processed solution. This is the case, for instance, for some of the III-V semiconductors immersed in deionized water or weak aqueous solutions of ammonia. The photo-ALE is an innovative method of a cycled digital photocorrosion (DIP) of semiconductors that we have explored for shallow etching of three-dimensional GaAs/AlGaAs nanoheterostructures [2, 3]. The rate and stability of DIP depends on the energy and intensity of photons employed for optical excitation of the samples, as well as on the chemistry of a liquid environment employed for processing [4]. The excitation of electron-hole pairs allows the convenient application of the photoluminescence (PL) effect for monitoring in situ of the DIP process. The DIP process can also be monitored by measuring the open circuit potential of revealed surfaces [5], which is of a particular interest to materials with negligible PL emission.In the frame of this presentation, I will discuss some fundamental aspects of the DIP process and application of the PL effect for monitoring sub-monolayer removal of GaAs and AlGaAs. The compatibility of the photo-ALE technology with the chemistry of liquids employed for passivation of surfaces and coating with self-assembled monolayers offers the potential for in situ passivation of atomically clean surfaces. Furthermore, the sensitivity of a low-excitation intensity generated PL signal to surface defects allows spatially-resolvable recording of the perturbation of the DIP process. I will also discuss the perspective of an application of the photo-ALE to other III-V materials, as well as to Si and SiGe.______________________[1] K. J. Kanarik et al., "Overview of atomic layer etching in the semiconductor industry," Journal of Vacuum Science& Technology A: Vacuum, Surfaces, and Films, vol. 33, no. 2, p. 020802, 2015, doi: 10.1116/1.4913379.[2] S. Aithal, N. Liu, and J. J. Dubowski, "Photocorrosion metrology of photoluminescence emitting GaAs/AlGaAs heterostructures," Journal of Physics D: Applied Physics, vol. 50, no. 3, p. 035106, 2017.[3] M. R. Aziziyan, H. Sharma, and J. J. Dubowski, "Photo-Atomic Layer Etching of GaAs/AlGaAs Nanoheterostructures," Acs Appl Mater Inter, vol. 11, no. 19, pp. 17968-17978, 2019/05/15 2019, doi: 10.1021/acsami.9b02079.[4] H. Sharma, K. Moumanis, and J. J. Dubowski, "pH-Dependent Photocorrosion of GaAs/AlGaAs Quantum Well Microstructures," The Journal of Physical Chemistry C, vol. 120, no. 45, pp. 26129-26137, 2016/11/17 2016, doi: 10.1021/acs.jpcc.6b08844.[5]. S. Aithal and J. J. Dubowski, "Open circuit potential monitored digital photocorrosion of GaAs/AlGaAs quantum well microstructures," Appl Phys Lett, vol. 112, no. 15, p. 153102, 2018, doi: 10.1063/1.5023134.

Dissolution Stability of Photoanodes and Co-Catalysts in Photoelectrochemical Water Splitting

In the future energy scenario, production of hydrogen is a promising solution for the storage of renewables. Photoelectrochemical water splitting with integrated devices can be engaged for the production of hydrogen with the advantage of less space consumption and saving power lines to the production site. Current devices have already come close to the efficiency of an electrolyzer coupled to a solar cell [1]. However, to be profitable in commercial use several challenges have to be resolved. One of the most pressing issues is photostability of materials during operation. Even though photoelectrodes are able to reach lifetimes of several days in lab conditions, it is still a long way until real device lifespans of several years are possible.While efforts in the field of photoelectrochemical water splitting are mainly focused on achieving higher activity, research on stability is still at the very beginning. Evaluation of photostability is typically done by rather short (only few hours) chronoamperometry measurements and post mortem analysis. One option to study degradation processes in-situ is to use on-line inductively coupled plasma mass spectrometry (on-line ICP-MS) which became available recently and revealed photocorrosion of WO3 [2] and BiVO4 [3].In this study, we aim to achieve a better understanding of the key factors driving photocorrosion. It has already been shown, that WO3 exhibits significant differences in faradaic efficiency towards the oxygen evolution reaction (OER) in various electrolytes [4]. One reason behind this behavior might be degradation processes driven by the electrolyte. To study the effect of electrolytes on stability, dissolution of spray-coated WO3 films was investigated in four electrolytes (HClO4, H2SO4, HNO3 and CH3SO3H). Additionally, the influence of protective iridium co-catalyst layers on stability, synthesized in various thicknesses by atomic layer deposition (ALD) was explored. 1. Cheng, W.-H., et al., Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. ACS Energy Letters, 2018. 3(8): p. 1795-1800.2. Knöppel, J., et al., Time-resolved analysis of dissolution phenomena in photoelectrochemistry – A case study of WO3 photocorrosion. Electrochemistry Communications, 2018. 96: p. 53-56.3. Zhang, S., et al., Dissolution of BiVO4 Photoanodes Revealed by Time-Resolved Measurements Under Photoelectrochemical Conditions. The Journal of Physical Chemistry C, 2019.4. Reinhard, S., F. Rechberger, and M. Niederberger, Commercially Available WO 3 Nanopowders for Photoelectrochemical Water Splitting: Photocurrent versus Oxygen Evolution. ChemPlusChem, 2016. 81: p. 935-940.

(Invited) Mechanism of Formic Acid synthesis in low pH during CO2 Reduction via electrified plasma/liquid interface

Electrochemical discharger over liquid water enriched with dissolved carbon dioxide (CO2) is capable of synthesizes formate (HCO2 -) and oxalate (C2O4 2 -), although in very low faradaic selectivity toward organic molecules ca. 9% [1]. The efficient CO2 reduction (CO2-R) toward these organic molecules via electrochemical discharge remains a challenge. This contribution devotes to find possible ways to produce these products efficiently. In this context, the mechanism of electrosynthesis for both formate and oxalate is postulated and used from a theoretical perspective [2] to figure out which parameters are key to reach as maximum selectivity as possible.Figure 1a shows the chemical reaction network (CRN) postulated for CO2-R via electrochemical discharge over water. The discharge promotes a periodic perturbation on the local concentration of the solvated electron within the nanoreactor (volume of less than one nanoliter beneath the plasma liquid interface), firing the set of reaction displayed in this CRN. Three final products are formed, one volatile and two dissolved in the liquid phase. Gaseous hydrogen is a volatile product synthetized majorly via recombination of two solvated electrons, reaction (1); other two routes for hydrogen synthesis described in reference 2 are negligible over uninterrupted long lasting discharge. On the other hand, organic molecules requires the carboxyl radical anion {CO2 -∙ (aq)} as precursor. In view of this CRN, the generalist model in reference (2) were used for implement the algorithm related to the chemical dynamical system. The computational experiments employed Wolfram language, 10- 6 s step, a stationary current at level 9.5 mA (the same used by the researchers in ref 1) and the parameters displayed in table 1. The selectivity toward a given product is the ratio of its quantity of mole with respect to that of injected electrons. Figure 1b shows time evolution for the concentrations of the main reactants, the intermediate (carboxyl radical anion) and the final products. Figure 1c shows the selectivity toward each final product considering two span of continuous stationary discharge.The computational experiments demonstrated that the chemical dynamics driven by a stationary injection of electron (term qe in the model) in water is mostly governed by the formation reaction of CO2 -∙ (aq) within the early 43 ms span of time. Within this period, full content of CO2 in the nanoreactor depletes as result of the fastest reaction rate for the formation of CO2 -∙ (aq) . The large local concentration (“local” qualifies the concentration inside the nanoreactor) of CO2 -∙ (aq) favors the oxalate formation, being the oxalate the major final product. Formate is only synthetized at significant formation rate between 0.040 and 0.043 s, when the concentration of both solvated electrons and CO2 -∙ (aq) start to be less dissimilar as consequence of the depletions of the aqueous CO2 in the nanoreactor. Anytime thereafter, the solvated electrons has increased concentration, and the hydrogen passes to form majorly. Considering the 300,000 s (5 minutes used in reference 1), about 7.72% faradaic efficiency toward organic molecules is obtained, corroborating the low efficiency for experiments in real life.In conclusion, this work postulate the mechanism of CO2 reduction via electrochemical discharge, and it suggests the employment of short span of stationary discharge to obtain faradaic efficiency toward organic molecules of 98.46%, being 96.89% selective toward oxalate. Figure 1: (a) postulated chemical reaction network for CO2-R via electrochemical discharge over water, (b) time evolutions for the concentrations of either reactants or products , and (c) selectivity toward formate (yellow), oxalate (orange) and hydrogen (pink) at STP CO2 saturation. Table 1: parameters for solving the dynamical model [3] Parameter Value Unit Ref k1 6.0×109 L mol−1 s−1 3 k2 9.0×109 L mol−1 s−1 3 k3 1.0×1010 L mol−1 s−1 3 k4 1.26×109 L mol−1 s−1 3 qe (9.5 mA) 98.46×10-9 mol s- 1 1 V 2.36×10-9 L 2 [H+]0 1.00×10-7 mol L-1 [CO2]0 40.00×10-3 mol L-1 References [1]Rumbach, P., R. Xu, and D.B. Go, Electrochemical Production of Oxalate and Formate from CO2 by Solvated Electrons Produced Using an Atmospheric-Pressure Plasma. Journal of The Electrochemical Society, 2016. 163(10): p. F1157-F1161.[2] Mota-Lima, A., et al., Electrosynthesis via Plasma Electrochemistry: Generalist Dynamical Model To Explain Hydrogen Production Induced by a Discharge over Water. The Journal of Physical Chemistry C, 2019. 123(36): p. 21896-21912.[3] Neta, P., J. Grodkowski, and A.B. Ross, Rate Constants for Reactions of Aliphatic Carbon‐Centered Radicals in Aqueous Solution. Journal of Physical and Chemical Reference Data, 1996. 25(3): p. 709-1050. Figure 1

Electrochemical Growth and OER Catalytic Activityof Ultrathin Epitaxial Cobalt Oxide Films

Iron-group oxides are among the best earth abundant catalysts for the oxygen evolution reaction (OER) in alkaline and neutral electrolytes [1],[2]. Such oxides have been prepared with an amorphous or a crystalline structure, using thermal salt decomposition [3], autoclave synthesis [4], photochemical reactions [5], sol-gel synthesis [6], metal electrodeposition and subsequent oxidation, [7] and direct oxide electrodeposition [1], [8].This work focuses on well-defined epitaxial CoOx [9] electrocatalysts grown by direct electrodeposition on Au(111) according to an approach similar to that introduced by Switzer [8]. The growth modes of catalysts and the mechanisms of deposition will be discussed based on electrochemical characterizations, XRD characterizations and microscopic observations. In particular to explain that CoOOH may be obtained at a potential of +1V/RHE by oxidation of a Co(II) complex diluted in an alkaline solution while thermodynamics predicts that Co3O4 should be formed. The electrochemical properties in pre-OER and within OER will be discussed as a function of the surface structure and morphology of layers. In particular to show that the large pseudocapacitance measured at the electrode is not related to its ECSA but to electrical charging within the bulk of the electrode.[1] M. W. Kanan and D. G. Nocera, Science 321, 1072 (2008).[2] C. C. L. McCrory, S. Jung, I. M. Ferrer et al., Journal of the American Chemical Society 137, 4347 (2015).[3] C. Pirovano and S. Trasatti, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 180, 171 (1984).[4] D. Yuming, H. Kun, Y. Lin et al., Nanotechnology 18, 435602 (2007).[5] S. R. Alvarado, Y. Guo, T. P. A. Ruberu et al., The Journal of Physical Chemistry C 116, 10382 (2012).[6] A. Bergmann, E. Martinez-Moreno, D. Teschner et al., Nature Communications 6, 8625 (2015).[7] M. W. Louie and A. T. Bell, Journal of the American Chemical Society 135, 12329 (2013).[8] J. A. Koza, Z. He, A. S. Miller et al., Chem. Mat. 24, 3567 (2012).[9] F. Reikowski, F. Maroun, I. Pacheco et al., ACS Catalysis 9, 3811 (2019).

Solar Materials Find Their Band Gap

Finding new solar cell materials among the vast elemental combinatorial space is an onerous task—one that should not be left to serendipity. Two recent papers, one published in npj Computational Materials and another in Journal of Physical Chemistry C, report advanced machine learning approaches to predict the band gap of new ABX3 perovskite materials. These methods represent continued progress toward accelerated materials discovery for photovoltaics.

PQQ-Glucose Dehydrogenase-Calmodulin Chimera Enzyme: Different Triggered Activation for Multipurpose Biosensors

In the last decade, the rise of synthetic biology has driven the efforts to construct artificial allosteric protein switches in order to detected and quantify natural and artificial chemistries in vitro and in vivo. Typically, this involves construction of chimeric enzymes via insertion of a regulatory receptor domain into the biocatalytic reporter domain. Construction of such chimeric enzymes utilizes the recombinant DNA technology that is a core technology of protein engineering [1].Herein, we report on the bioelectrocatalytic properties of pyrroloquinoline quinone-dependent glucose dehydrogenase fusion with calmodulin (PQQ-GDH-CaM). This protein is catalytically inactive in its ground form but can be activated by the addition of calmodulin binding peptide that induces its conformational transition and activation. The PQQ-GDH-CaM was immobilized onto highly porous gold (hPG) produced electrochemically [2] by using a bifunctional linker, namely 4-mercaptobenzoic acid further activated through 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide (EDC/NHS) coupling to covalent bind the PQQ-GDH-CaM chimeric enzyme [3].At first, we characterized the switchable features of PQQ-GDH-CaM by simply exposing it to the activating peptide. Subsequently we devised an approach to use proteolytic activation of a caged-peptide to generate activating peptide for PQQ-GDH-CaM. Furthermore, the system was utilized to study different pathways for PQQ-GDH-CaM triggered activation according to different logic gates in order to realize multipurpose biosensors (e.g., glucose detection, peptide detection etc.) [4]. References Gamella, M., Guo, Z., Alexandrov, K., Katz, E. (2019). ChemElectroChem, 6(3), 638-645.Bollella, P., Hibino, Y., Kano, K., Gorton, L., Antiochia, R. (2018). Analytical chemistry, 90(20), 12131-12136.Koushanpour, A., Gamella, M., Guo, Z., Honarvarfard, E., Poghossian, A., Schöning, M. J., Alexandrov, K., Katz, E. (2017). The Journal of Physical Chemistry B, 121(51), 11465-11471.Bollella, P., Katz, E. (2019). International Journal of Unconventional Computing, 14(3-4), 181-198.

Formation of Ion Pairs and Charge-Transfer Complexes in the p-Doping of Organic Semiconductors

The formation of ion pairs (IPA) through integer charge transfer and ground-state charge-transfer complexes (CPXs) with only fractional charge transfer are the two known mechanisms in the molecular doping of conjugated polymers and molecules, which form the material class of organic semiconductors (OSCs). As it entails no immediate ionization of the OSC, CPX formation is regarded as detrimental to the doping efficiency. For IPA formation to occur, a match between the electron affinity (EA) of the p-dopant and the ionization energy (IE) of the OSC is expected as crucial, while their pronounced frontier molecular orbital overlap should promote CPX formation instead [1].To explore these complementary scenarios, we first studied the thermal de-doping of the prototypical conjugated polymer poly(3-hexylthiophene) (P3HT), p-doped with the common strong electron acceptor tetrafluoro-tetracyanoquinodimethane (F4TCNQ) [2]. We combined grazing incidence X-ray diffraction (GIXRD) with Fourier-transform infrared spectroscopy (FTIR) to determine the microstructure, and absorbance spectroscopy (UV/vis/NIR) to observe the spectral fingerprint of the two doping scenarios. We found two microstructural environments through their distinguished thermal stabilities, where, the dopants were observed (i) alternatingly stacked with the polymer backbone as well as (ii) dispersed in its sidechain region. From FTIR and UV/vis/NIR we deduce that all dopants are fully ionized, although packing between dopant and polymer backbone would be expected to favor CPX formation instead. Notably, while characteristic shifts of the mid-infrared cyano-stretch modes of TCNQ derivatives are known to well indicate the degree of charge transfer, we show here that they allow further to assess the dopant site in the polymer environment.We further investigated the influence of EA with respect to IE by contrasting F4TCNQ with its derivatives of lower degree of fluorination, which translates into reduced EA while leaving the spatial aspects of the dopant largely intact. We find that using F2TCNQ and FTCNQ still results in IPA formation in spite of EA < IE, which we understand through the lower degree of spatial, and therefore energetic order in OSCs as compared to inorganic semiconductors, which therefore possess no sharp band edges. Surprisingly, at high doping concentrations (additional) CPX formation occurred for all the differently strong dopants, which highlights the complexity of these systems going beyond the sole impact of the energetics of the individual constituents.Finally, we juxtaposed the known tendency of small molecular OSCs to form CPXs and that of polymer OSCs to form IPAs. To maximize the comparability with P3HT, alkylated oligothiophenes of different length were synthesized in-house (from 4 to 10 thiophene repeat units) and doped with F4TCNQ. For the longest oligomer, we were able to observe the switch from the CPX regime into that of IPA, i.e., we approach the doping behavior polymer limit. Knowing this threshold is valuable for applications in organic electronics where vacuum processible small molecular OSCs are preferred over polymeric OSCs, which are only processible via solution-based methods.[1] I. Salzmann, G. Heimel, M. Oehzelt, S. Winkler, N. Koch, Acc. Chem. Res. 2016, 49, 370.[2] H. Hase, K. O’Neill, J. Frisch, A. Opitz, N. Koch, I. Salzmann, The Journal of Physical Chemistry C 2018, 122, 25893.

Journal of Physical Chemistry names new editors

The American Chemical Society has named Joan-Emma Shea of the University of California, Santa Barbara, editor in chief of the Journal of Physical Chemistry (JPC) A, B, and C, and Gregory D. Scholes of Princeton University editor in chief of the Journal of Physical Chemistry Letters. They will succeed George C. Schatz of Northwestern University, who is retiring. “The shift to two editors will allow for greater efficiencies in the publishing process and a better author experience and help ensure JPC reaches a diverse and growing global audience,” says James Milne, acting president of the ACS Publications Division. Shea is professor of chemistry and biochemistry at UC Santa Barbara, where she is using statistical and computational physics to study biological problems. She has been deputy editor of JPC B since 2014 and will become the first female editor in chief of JPC in its 124-year history. “I hope to inject

A New Editor-in-Chief for The Journal of Physical Chemistry

A New Editor-in-Chief for <i>The Journal of Physical Chemistry</i>

Publications Output of the Indian Association for the Cultivation of Science during 2008 2017 a Scientometric Assessment

&#x0D; &#x0D; &#x0D; The present scientometric study assesses the publication output of the scientists of Indian Association for the Cultivation of Science (IACS) during 2008 to 2017 as reflected in the Web of Science database to figure out the research performance, scholarly communication behaviour and its citation impact. The scientists of IACS contribute total 4,304 research articles including 22.58 percent international collaborated articles. Further, the publications have been evaluated in terms of year, types of collaboration, authorship pattern, source journals, impact factor, collaborating institutions, collaborating countries and citations. It is found that majority of the published articles are produced by three authored and the international collaborated articles which receive wider citation impact. The developed countries like USA, Japan, Germany and England are found as the most favoured countries by the scientists of IACS for research collaboration and the Journal of Physical Chemistry C shares maximum research articles. Further, Pareto’s 80/20 principle has also been applied to examine the scattering of journals as well as articles and the VOS viewer software has been used for mapping the network of collaborating countries.&#x0D; &#x0D; &#x0D;

(Invited) Functional Defects By Design—a High-Throughput Approach to Energy Materials Discovery

Defects and impurities introduce localized heterogeneities in solids and decisively control the behavior of a wide range of energy technologies. Fuel cell materials, especially proton conducting fuel cells, are a quintessential example in this regard. Designing and developing solid oxide materials that can selectively transport protons will enable us to develop the next generation proton conducting solid oxide fuel cells. Protons require less activation energy compared to oxygen ions which results in a lower operating temperature, higher operating efficiency and better material reliability. In this work [1,2,3,4] we focus obtaining fundamental insights on how properties of host material structure along with dopants, disorder and strain influences proton transport properties in solid oxides by coupling high-throughput computations with functional imaging, neutron spectroscopy and transport measurements.We initially focus on the perovskite family of compounds (such as doped BaZrO3). We benchmark our calculations against a wide range of experimental measurements such as kelvin probe force microscopy (KPFM), inelastic neutron scattering (INS) and atom probe tomography (APT). To obtain better insights on why certain cubic perovskite/dopant combinations are better at conducting protons compared to others, we developed a high-throughput framework to perform ab initio calculations. The high-throughput framework can scale massively to tens of thousands of nodes to fully exploit the computational capability of the Oak Ridge Leadership Computing facility. We employ this approach to calculate proton transport properties in several cubic perovskite materials with different host atoms and dopants. The results obtained from these calculations enables us to obtain better insights on how material structure – such as atomic properties (electronegativity, ionic radius) and lattice properties (sub-lattice distortion) influences proton transport. The results obtained from this high-throughput analysis is being employed to develop a machine learning framework to predict structure-property correlations on a larger set of perovskites materials. Finally, we explore the role of disorder on proton transport by studying for example fluorite based lanthanum tungstate materials. [1] “Defect Genome of Cubic Perovskites for Fuel Cell Applications”, Journal of Physical Chemistry C, 121, 26637 (2017)[2] “The Influence of Local Distortions on Proton Mobility in Acceptor Doped Perovskites”, Chemistry of Materials, 2018, 30 (15), pp 4919–4925[3]“The Influence of the Local Structure on Proton Transport in a Solid Oxide Proton Conductor La0.8Ba1.2GaO3.9”, J. Mat. Chem. A, 5, 15507 (2017)[4] “Influence of Non-Stoichiometry on Proton Conductivity in Thin Film Yttrium-doped Barium Zirconate”, ACS Appl. Mater. Interfaces, 2018, 10 (5), pp 4816–4823

Rate and Voltage Dependence of the Electrode-Electrolyte Interface in Ni Containing Lithium-Ion Cathode Materials

Performance, safety, lifetime, and cost of lithium-ion batteries (LIB) are strongly influenced by the active materials used. As a result, cell chemistries are selected with the end goal in mind. For applications requiring superior power and safety, cells containing LiFePO4 cathodes and graphite anodes with an organic liquid electrolyte are frequently used. The major drawback of LIB cells designed for high-power is a relatively low energy density compared to high-energy cells, which conversely have poor rate capability. While graphite anodes remain a constant in most commercial LIB, recent research has identified cathode materials which would potentially mitigate the tradeoff between power, energy, and safety. In particular, spinel structured “LNMO” (LiNi0.5Mn1.5O4) and layered nickel-rich “NCM” compounds (LiNixMnyCozO2, X ≥ 0.5) have reportedly high energy densities relative to LiFePO4 while maintaining good power capability and thermal stability (1) (2). While LNMO and NCM compounds have similar composition and produce Ni4+ when fully charged, several reports have highlighted variations in surface chemistry resulting from electrolyte-electrode interactions as a function of cathode stoichiometry (3; 4; 5). One issue known to influence the surface chemistry and associated cycling stability of transition metal oxide cathode materials is the upper voltage cutoff needed to extract lithium during charge. Layered compounds can typically be reversibly delithiated within a voltage range of 4.2 to 4.6 V vs. Li/Li+ depending on the specific stoichiometry, while the spinel must be charged in excess of 4.8 V vs. Li/Li+, which historically has been a major hurdle to application. These upper voltage cutoff are already within the range of expected electrolyte oxidation, which is exacerbated by over potentials produced when charging at high current densities which further increase the upper voltage cutoff required to fully delithiate the cathode. This presentation will focus on analysis of the electrode-electrolyte interface, which is known to be a critical indicator of cell safety and lifetime, as a function of high-rate cycling and upper voltage cutoff. Composite cathodes containing spinel LNMO and layered NCM523 were cycled in a conventional lithium-ion electrolyte at various rates of charge and discharge, then disassembled in an inert atmosphere for analysis by X-ray Photoelectron Spectroscopy (XPS). Capacity and electrochemical impedance measurements were correlated with XPS analysis. Our results indicated that even when cycled in identical electrolytes spinel and layered compounds have notably different responses to an increased charge rate, specifically high rate charging (5C rate) is actually found to benefit LNMO, leading to lower impedance rise and associated formation of LiF, while the opposite is true for NCM523. One complicating factor in the XPS analysis of composite electrode is the presence of inactive components, specifically the binder and conductive additive. Both of these compounds dilute the overall signal detected from the active material, and some reports suggest may even contribute to the specific surface chemistry observed. To remove these effects, sol-gel films of identical composition to the composite electrode active materials were also synthesized and subjected to electrochemical cycling in the same electrolyte. [1] Review-Li-Rich Layered Oxide Cathodes for Next-Generation Li-Ion Batteries: Chances and Challenges. Rozier, P and Tarascon, JM. 14, 2015, Journal of the Electrochemical Society, Vol. 162, pp. A2490-A2499. [2] Spinel LiNi0.5Mn1.5O4 and its derivates as cathodes for high-voltage Li-ion batteries. Liu, G Q, Wen, L and Liu, Y M. 2010, Journal of Solid State Electrochemistry, Vol. 14, pp. 2191-2202. [3] Coupled LiPF6 Decomposition and Carbonate Dehydrogenation Enhanced by Highly Covalent Metal Oxides in High-Energy Li-Ion Batteries. Yu, Y, et al. 2018, Journal of Physical Chemistry C, Vol. 122, pp. 27368-27382. [4] XPS Studies of Surface Chemistry Changes of LiNi0.5Mn0.5O2 Electrodes during High-Voltage Cycling. Quinlan, RA, et al. 4, 2013, Journal of the Electrochemical Society, Vol. 160, pp. A669-A677. [5] Probing the Electrode-Electrolyte Interface in Cycled LiNi0.5Mn1.5O4 by XPS Using Mg and Synchrotron X-rays. Mansour, AN, et al. 14, 2016, Journal of the Electrochemical Society, Vol. 163, pp. A2911-A2918.

Adsorption Behavior of Perfluorosulfonic Acid Ionomers on a Pt(111) Surface Observed By Atomic Force Microscopy

Understanding of the adsorbed structure of ionomers on the Pt electrocatalyst and carbon support surfaces are very important to improve the cell performance of polymer electrolyte membrane fuel cells (PEMFCs). The effect of the solvent composition and temperature on the adsorbed structure of ionomers have been studied by using various techniques, such as 19F nuclear magnetic resonance (19F NMR) spectroscopy, cryogenic scanning electron microscopy (cryo-SEM), dynamic light scattering (DLS), small angle X-ray scattering (SAXS), small angle neutron scattering (SANS), and electron spin resonance (ESR) techniques. However, it has not been fully clarified yet, due to the complexity of the system composed of a variety of ingredients including the Pt electrocatalyst, carbon support, ionomers, solvent and other contaminants. Thus, we have investigated the adsorbed structure of ionomers on the Pt(111) surface as a model of an electrocatalyst by using atomic force microscopy (AFM) at various solvent compositions. A droplet of aqueous solutions of Nafion was placed on Pt (111) surfaces mounted on the AFM sample holder. AFM measurements were performed with Acoustic AC mode AFM using Agilent 5500 AFM microscope (Agilent Technologies, USA) with a silicon nitride cantilever. The images were recorded over a period of ~30 minutes with a scanning area of 1 µm × 1 µm. In a 2 wt% aqueous solution of Nafion, relatively small aggregates of Nafion ionomers with a height of ~2-3 nm were observed at the Pt(111) surface. Amount of adsorption increased with time and, eventually, the surface was entirely covered by randomly oriented aggregates with a thickness of ~4 nm. In a 0.2 wt% aqueous solution, aggregates larger than those observed in the 2 wt% aqueous solution were imaged, suggesting that larger aggregates were formed in the lower concentration solution. Such a concentration-dependent adsorption behavior is further discussed on the basis of solvent composition and conformation of Nafion ionomers in liquid phase. References Masuda, H. Naohara, S. Takakusagi, P. R. Singh, K. Uosaki: Chemistry Letters, 38, 884 (2009).Masuda, S. Faridah, P. Singh, H. Naohara, K. Uosaki, Journal of Physical Chemistry C, 117, 15704 (2013).Masuda, K. Ikeda, K. Uosaki, Langmuir, 29, 2420 (2013).

The Thermodynamic and Kinetic Influence of Solvent, Counter Anion and Salt Concentration on ORR in Li-O2 Batteries

Aprotic Li-O2 batteries have been extensively studied due to their very high theoretical gravimetric energy density; potentially 2-3 times that of commercial Li-ion batteries1. Despite this significant research effort, practical rechargeable Li-O2 batteries remain elusive due to significant issues relating to high overpotential and parasitic side reactions that limit the cycling performance of the battery chemistry. In order to address these issues, a stronger fundamental understanding of the underlying oxygen redox reactions is needed. In this work, the complex influence of the solvent2, counter anion3 and salt concentration4 during the oxygen reduction reaction are unified within a single framework. Ionic coupling between Li+ ions and the superoxide (O2 -) anion formed following the first electron transfer is highlighted as the critical parameter for determining the selectivity between the two competitive discharges pathways. By weakening the Li+-O2 - coupling through interactions with solvent/counter anions with high donor number, or by lowering the Li+ activity, we observe a significant enhancement in the proportion of observed soluble discharge products. Additionally, electrolyte design strategies for suppressing the direct two electron transfer reaction to form an insulating film of Li2O2 will be discussed in their relation to enabling redox mediators during the reduction process, such as DBBQ5 and EV. References D. Aurbach, B. D. McCloskey, L. F. Nazar, and P. G. Bruce, Nature Energy, 1, 16128 (2016).D. G. Kwabi et al., Angewandte Chemie International Edition, 55, 3129–3134 (2016).C. M. Burke, V. Pande, A. Khetan, V. Viswanathan, and B. D. McCloskey, Proceedings of the National Academy of Sciences, 112, 9293–9298 (2015).R. Tatara et al., The Journal of Physical Chemistry C, 121, 9162–9172 (2017).X. Gao, Y. Chen, L. Johnson, and P. G. Bruce, Nature Materials, 15, 882–888 (2016).

Local Structure and Its Impact on Ionic Conductivity in Cubic Perovskite Protonic Conductor, an Ab-Initio Based cluster Expansion Study

Cubic perovskite of ceramics are typical parent structures for proton conducting electrolyte in intermediate-temperature solid oxide fuel cells, e.g. BZCYYb1. Proton conductivity within this type of materials is well known to be affected by hydration capability, as well as proton mobility. Although a few previous experimental characterizations2-5have unveiled a few pieces of information regarding local structures of proton, dopant and vacancy, a systematic and comprehensive understanding of the underline driving-force for local structure evolution is lacking. Similarly, typical ab-initioDFT calculations assume a fixed dopant concentration with very limited configurations in consideration6-12. Atomically, local structure is the fundamental building-block that constitutively determines macroscopic hydration and mobility of ions. By carrying out ab-initiocalculations, with cluster expansion and Monte-Carlo simulations, competition between entropic-driven defect randomization and enthalpic-driven defect agglomeration is discovered. A temperature vs. dopant-concentration phase diagram is generated. Conductivity is a consequence of dopant, vacancy and proton interactions. Although trapping effects acting on vacancy and proton vary among dopants, a statistical average of ionic mobility is generated through the above approach. By using BaHfO3 as the prototype, representative dopants such as In, K, Sc, Y, Gd, Lu are taken as examples. REFERENCES Yang, L.; Wang, S. Z.; Blinn, K.; Liu, M. F.; Liu, Z.; Cheng, Z.; Liu, M. L., Enhanced Sulfur and Coking Tolerance of a Mixed Ion Conductor for SOFCs: BaZr0.1Ce0.7Y0.2-xYbxO3-delta. Science 2009, 326(5949), 126-129. Mburu, C. W.; Gaita, S. M.; Knee, C. S.; Gatari, M. J.; Karlsson, M., Influence of Yttrium Concentration on Local Structure in BaZr1–xYxO3−δ Based Proton Conductors. The Journal of Physical Chemistry C 2017, 121(30), 16174-16181. Noferini, D.; Koza, M. M.; Rahman, S. M. H.; Evenson, Z.; Nilsen, G. J.; Eriksson, S.; Wildes, A. R.; Karlsson, M., Role of the doping level in localized proton motions in acceptor-doped barium zirconate proton conductors. Phys Chem Chem Phys 2018, 20(20), 13697-13704. Blanc, F.; Sperrin, L.; Lee, D.; Dervisoglu, R.; Yamazaki, Y.; Haile, S. M.; De Paepe, G.; Grey, C. P., Dynamic Nuclear Polarization NMR of Low-gamma Nuclei: Structural Insights into Hydrated Yttrium-Doped BaZrO3. J Phys Chem Lett 2014, 5(14), 2431-6. Giannici, F.; Shirpour, M.; Longo, A.; Martorana, A.; Merkle, R.; Maier, J., Long-Range and Short-Range Structure of Proton-Conducting Y:BaZrO3. Chemistry of Materials 2011, 23(11), 2994-3002. Hermet, J.; Bottin, F.; Dezanneau, G.; Geneste, G., Thermodynamics of hydration and oxidation in the proton conductor Gd-doped barium cerate from density functional theory calculations. Physical Review B 2012, 85(20). Hermet, J.; Torrent, M.; Bottin, F.; Dezanneau, G.; Geneste, G., Hydrogen diffusion in the protonic conductor BaCe1−xGdxO3−x2from density functional theory. Physical Review B 2013, 87(10). Bévillon, É.; Geneste, G., Hydration properties of BaSn0.875M0.125O3−δ substituted by large dopants (M=In, Y, Gd, and Sm) from first principles. Physical Review B 2008, 77(18). Bévillon, É.; Hermet, J.; Dezanneau, G.; Geneste, G., How dopant size influences the protonic energy landscape in BaSn1−xMxO3−x/2(M = Ga, Sc, In, Y, Gd, La). J. Mater. Chem. A 2014, 2(2), 460-471. Geneste, G.; Amadon, B.; Torrent, M.; Dezanneau, G., DFT+U study of self-trapping, trapping, and mobility of oxygen-type hole polarons in barium stannate. Physical Review B 2017, 96(13). Geneste, G.; Dezanneau, G., Competition between elastic and chemical effects in the doping, defect association, and hydration of barium stannate. Solid State Ionics 2017, 308, 121-132. Geneste, G.; Ottochian, A.; Hermet, J.; Dezanneau, G., Proton transport in barium stannate: classical, semi-classical and quantum regimes. Phys Chem Chem Phys 2015, 17(29), 19104-18.

Instrument for Measuring Local Ionic Conductivity of Porous Electrodes

Due to the nature of how porous battery electrodes are fabricated, their microstructure is not uniform. For instance, there are variations in composition, effective electronic transport, and effective ionic transport. Such heterogeneity has been associated with several battery application issues. For example, variability in transport of ions can lead to a tendency for localized plating of lithium on anodes during fast charging [1-2]. Studying the heterogeneity of electrodes is a growing research topic. Our research group has previously developed a micro-four-line probe that successfully measured the variation of electronic conductivity of electrodes [3]. Another method to study the microstructure of electrodes is by means of SEM and X-ray tomography, and the variation of tortuosity (effective ionic resistance) in electrodes was computed by analyzing the tomographic data of microstructure [4]. We report here on a new technique to measure the local ionic resistance on a sub-mm length scale. A probe was made to detect the local transport of ions through a small aperture. The probe is scanned across the surface of a porous thin-film electrode in order to create maps of tortuosity or MacMullin number. The measurement was performed using electrochemical impedance spectroscopy, and an associated model is needed to invert the experimental results. [1] Harris et al., The Journal of Physical Chemistry C 117, 6481 (2013). [2] Vogel et al., Electrochimica Acta 297, 820 (2019). [3] Lanterman et al., Journal of the Electrochemical Society 162, A2145 (2015). [4] Kehrwald et al. Journal of The Electrochemical Society 158, A1393 (2011). Figure 1

Programming the Knowledge: A Trial QSAR Study Towards the Stability of Dialkoxy Benzene Based Catholyte Molecules for Nonaqueous Redox Flow Batteries

Programming the knowledge: A trial QSAR study towards the stability of dialkoxy benzene based catholyte molecules for nonaqueous redox flow batteries Lu Zhang1, Jingjing Zhang1, Benjamin Silcox3, Illya A. Shkrob1, Rajeev S. Assary2, Lei Cheng2, Levi Thompson4 1Chemical Sciences and Engineering Division, 2Material Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, United States 3Chemical Engineering, University of Michigan, 500 S State St, Ann Arbor, MI 48109, United States 4Department of Chemical and Biomolecular Engineering, University of Delaware,Newark, DE 19716, Unite States The stability of redox active molecules is a paramount property that dramatically affects the cycling performance in redox flow batteries. Computationally, it requires huge amount of resource to exhaustively iterate all the possible degradation pathways in order to estimate the stability of active species, such as radical cations.1 QSAR, or quantitative structure–activity relationship, provides an interesting approach to correlate chemical structures and properties based on the idea of property changes are all coming from structure modifications. While this approach simplified the insightful analysis of the detailed mechanism, it becomes particular useful to simulate or even predict complex properties, such as the stability of redox molecules. In this talk, we developed a series of dialkoxy benzene based catholyte molecules that are of potential use to nonaqueous redox flow batteries and systematically changed their substitutions on the alkoxy moieties. Then their electrochemical/chemical properties, including redox potential, charged state stability (reflected by EPR life time), and even cycling numbers, have been characterized and analyzed. Importantly, a number of descriptors have been identified based on our long accumulated knowledge regarding stability of the charged radical cations. Finally, a linear regression model was established using those descriptors to simulate the EPR life time, and even cycling numbers and the resulted fittings delivered quite satisfactory correlation between the selected descriptors and properties. While this is only a trial study based on a small set of molecules, the QSAR approach proves to be useful in understanding complex properties for redox active molecules, which could stimulate further understanding and development of such promising materials. Assary, R. S.; Zhang, L.; Huang, J.; Curtiss, L. A., Molecular Level Understanding of the Factors Affecting the Stability of Dimethoxy Benzene Catholyte Candidates from First-Principles Investigations. The Journal of Physical Chemistry C 2016, 120 (27), 14531-14538.

A Mechanism Study of Structural Transition of Lithium Vanadium Phosphate during the 1st Charge/Discharge in Comparison to Ti-Doped One

Battery is one of the most attractive energy storage systems for its usefulness in energy conversion in these days. A great attention has been paid to the Li-ion batteries, and a lot of attempts to develop the system exhibiting higher energy density and higher safety have been tried for many years. However, the safety of Li-ion battery has been problems continuously while the energy density has developed largely. The safety issues of Li-ion battery generally come from thermal runaway, mainly derived from oxygen evolution from cathode materials. Phosphate materials including frames of PO4 polyanions such as LiFePO4 are regarded as a suitable cathode material in Li-ion battery in terms of the point of view. Lithium vanadium phosphate (LVP) has high expectations as a cathode material because of its higher operating voltage (~3.6V) and theoretical capacity(197mAh/g) compared to LiFePO4. While monoclinic LVP has a higher energy density, large hysteresis comes from asymmetric charge/discharge profile, and capacity fading are the main problems when three lithium ions are extracted by raising the voltage up to 4.8V. To overcome these limitations, fine studies about the mechanism have been carried out by a few groups. Although the mechanism studies were carried out by L. Nazar group about structural transition [1] and by Lee and Park about the possible pathway of lithium ion in the structure [2], representatively, the reasons for capacity fading on LVP should be studied more. In this work, we investigated the structural changes of LVP during the first charge and discharge process of voltage window of 3.0V to 4.8V by using Galvanostatic Intermittent Titration Technique (GITT), synchrotron radiation-based X-ray Absorption Spectroscopy (XAS) and in situ X-ray diffraction (XRD). The irreversible structural transitions between charge and discharge process are one of the possible reason for the capacity fading. Also, we conducted comparison study on the electrochemical and structural properties between LVP and Li3Ti0.03V1.97(PO4)3/graphene (LVP-Ti) to overcome limitations of LVP. In situ XRD patterns show four consecutive two-phase transitions on LVP during the charge process. During the reinsertion of lithium ion, the patterns of LVP look like a combined process of single solid solution and two-phase transitions between full charged LVP (FC-LVP) and Li2V2(PO4)3 (Li2 phase) without forming Li1V2(PO4)3. In GITT data, a two phase transition behavior which was previously reported as a solid solution behavior during the Li-ion insertion from full charged LVP to Li2 phase in the discharge process is observed. From these data, it can be said that transforming behavior from FC-LVP to Li2 phase is closer to two-phase reaction. In LVP-Ti case, the charge capacity was 185.84 mAh/g and the discharge capacity was 171.20 mAh/g in the first cycle, which were higher than those of LVP, 178.84 mAh/g and 162.99 mAh/g. And in situ XRD patterns show four consecutive two-phase transitions as in LVP. During the phase transition in charge/discharge, LVP-Ti faces less lattice mismatch than LVP, resulting in better electrochemical performance, and this phenomenon is originated from smaller particle size and enduring strain. The XAS result shows that the XANES peaks of LVP-Ti change gradually which is in line with the XRD result as same as in LVP case. However, the larger peak area of the pre-edge for LVP-Ti suggesting that more electrons were released upon charging. This means that the higher capacities of LVP-Ti is contributed by further utilization of the V redox reaction. [1] Yin, S-C., Hiltrud Grondey, Pierre Strobel, M. Anne, and Linda F. Nazar. "Electrochemical property: structure relationships in monoclinic Li3-yV2(PO4)3." Journal of the American Chemical Society 125, no. 34 (2003): 10402-10411. [2] Lee, S., & Park, S. S. (2012). Atomistic simulation study of monoclinic Li3V2(PO4)3 as a cathode material for lithium ion battery: structure, defect chemistry, lithium ion transport pathway, and dynamics. The Journal of Physical Chemistry C, 116(48), 25190-25197.

Solubility and Stability of NaO2 in Diglyme-Based Na-O2 Batteries

Aprotic Na-O2 batteries have attracted extensive attention because of their relatively large theoretical energy density and low charge overpotential. Several discharge products have been reported, including NaO2,[1] Na2O2,[2] Na2O2·2H2O,[3] Na2CO3,[4] which adds in complexity to specify the chemistry and reaction mechanism of Na-O2 battery.[5] In ether-based electrolyte, NaO2 is recognized as the major discharge products and often appeared as NaO2 cubes with size of 1-50 μm. These NaO2 cubes is believed to form through a dissolution-precipitation process as previously reported by operando transmission electron microscope (operando TEM),[6] rotating ring-disk electrode (RRDE),[7] atomic force microscopy (AFM)[8] and two-working electrode electrochemical technique.[9] The solubility and stability of NaO2 in electrolyte are important factors which influence the dissolution-precipitation path and cycling performance respectively. However, direct measurement of NaO2 solubility in ether-based Na-O2 batteries is still not available[9] and the lack of investigation on NaO2 stability makes such system even more mysterious. The two-working electrode electrochemical technique shows great promise in measuring the solubility of NaO2 in cell conditions, because it can quantitatively detect dissolved NaO2. Herein, modified two-working electrode Na-O2 batteries (Figure a) are fabricated and galvanostatic method is applied to investigate the solubility of NaO2.[9] NaO2 is generated on one air electrode (WE1), dissolved in electrolyte and oxidized on the other air electrode (WE2). Based on the assumptions that all dissolved NaO2 can be oxidized and the oxidation rate of NaO2 is significantly larger than dissolution rate, the solubility of NaO2 in electrolyte can be estimated. As discharge time of WE1 increases, the length of charge plateau of dissolved NaO2 at ~2.3 V vs. Na/Na+ on WE2 firstly increases and gradually approach a maximum value (Figure b), implying saturation of NaO2 in electrolyte is reached. Substantial solubility of NaO2 (~1.4 mM) in diglyme-based electrolyte is obtained. Conventional two-electrode Na-O2 batteries consisting of a Na anode and a carbon cathode are also fabricated to investigate NaO2 stability. These Na-O2 batteries are discharge-(rest)-charge tested at 25 μA/cm2 for varied time (Figure c-e). The percentage of recovered NaO2 (ratio of charge capacity due to NaO2 to total discharge capacity) against discharge time is ploted in Figure f, the longest discharge time shows the highest recovery percentage of NaO2. The recovery results depend on the concentration of NaO2 in electrolyte, which is in turn governed by supersaturation and precipitation processes. The average degradation rate of NaO2 during rest for varied discharge time can also be calculated to evaluate cycling performance. Our research therefore provides additional insights to dissolution-precipitation mechanism and NaO2 stability. The authors acknowledge the financial support from National Natural Science Foundation of China (NSFC)/Research Grant council (RGC) of Hong Kong Joint Research Scheme N_HKU728/17. [1] P. Hartmann, C. L. Bender, M. Vračar, A. K. Dürr, A. Garsuch, J. Janek, P. Adelhelm, Nat. Mater. 2013, 12, 228. [2] Y. Hu, X. Han, Q. Zhao, J. Du, F. Cheng, J. Chen, J. Mater. Chem. A 2015, 3, 3320. [3] X. Bi, R. Wang, L. Ma, D. Zhang, K. Amine, J. Lu, Small Methods 2017, 1, 1700102. [4] J. Kim, H. D. Lim, H. Gwon, K. Kang, Phys. Chem. Chem. Phys. 2013, 15, 3623. [5] S. Zhao, B. Qin, K. Y. Chan, C. Y. V. Li, F. Li, Recent development of aprotic Na-O2 batteries, Batteries & Supercaps 2019, Under review. [6] L. Lutz, W. Dachraoui, A. Demortière, L. R. Johnson, P. G. Bruce, A. Grimaud, J. M. Tarascon, Nano Lett. 2018, 18, 1280. [7] C. Xia, R. Black, R. Fernandes, B. Adams, L. F. Nazar, Nature Chemistry 2015, 7, 496. [8] I. M. Aldous, L. J. Hardwick, Chem. Commun. 2018, 54, 3444. [9] P. Hartmann, M. Heinemann, C. L. Bender, K. Graf, R.-P. Baumann, P. Adelhelm, C. Heiliger, J. Janek, The Journal of Physical Chemistry C 2015, 119, 22778. Figure 1