Electrochemical Environment Research Articles

Integration of Fullerenes as Electron Acceptors in 3D Graphene Networks: Enhanced Charge Transfer and Stability through Molecular Design.

Here, we report a concept that allows the integration of the characteristic properties of [60]fullerene in 3D graphene networks. In these systems, graphene provides high electrical conductivity and surface area while fullerenes add high electron affinity. We use molecular design to optimize the interaction between 3D graphene networks and fullerenes, specifically in the context of stability and charge transfer in an electrochemical environment. We demonstrated that the capacity of the 3D graphene network is significantly improved upon the addition of C60 and C60 monoadducts by providing additional acceptor states in the form of low-lying lowest unoccupied molecular orbitals of C60 and its derivative. Guided by experimental results and first-principles calculations, we synthesized and tested a C60 monoadduct with increased stability by strengthening the 3D graphene-C60 van-der-Waals interactions. The synthesis method and stabilization strategy presented here is expected to benefit the integration of graphene-C60 hybrid materials in solar cell and charge storage applications.

Modeling Corrosion with First-Principles Electrochemical Phase Diagrams

Understanding and predicting materials corrosion under electrochemical environments are of increasing importance to both established and developing industries and technologies, including construction, marine materials, geology, and biomedicine, as well as to energy generation, storage, and conversion. Owing to recent progress in the accuracy and capability of density functional theory (DFT) calculations to describe the thermodynamic stability of materials, this powerful computational tool can be used both to describe materials corrosion and to design materials with the desired corrosion resistance by using first-principles electrochemical phase diagrams. We review the progress in simulating electrochemical phase diagrams of bulk solids, surface systems, and point defects in materials using DFT methods as well as the application of these ab initio phase diagrams in realistic environments. We conclude by summarizing the remaining challenges in the thermodynamic modeling of materials corrosion and promising future research directions.

Characterizing Carbon Felt Electrodes for Vanadium Redox Flow Batteries Using Differential Electrochemical Mass Spectrometry

Carbon felts are commonly used as electrode materials for vanadium redox flow batteries (VRFBs). Their physical and chemical properties strongly influence the overall cell performance. The degradation of these materials due to parasitic side reactions (carbon corrosion, oxygen and hydrogen evolution) is partially responsible for performance losses of the cell [1]. Differential electrochemical spectrometry (DEMS) has been proven to be suitable for characterizing carbon materials, mainly in the context of fuel cell research [2–4]. Recently, Taylor et al. used DEMS to calculate the Faradaic efficiency of the V3+ reduction reaction on the oxidized edge and basal surfaces of graphite discs in a model study on the activity and stability of the negative electrode in VRFBs [5]. For our experiments, we modified a thin layer flow cell DEMS setup to conduct simultaneous electrochemical and online mass spectrometric measurements on commercial carbon felt electrodes. With this setup, half-cell tests, such as cyclic voltammetry, and coulometry of the redox couples under stopped flow of the electrolyte were performed. We used different potential windows, and two types of electrolytes while monitoring potential dependent H2, O2 and CO2 formation. At oxidizing potentials, we did not observe oxygen evolution, only carbon corrosion. In the presence of vanadium, an increase in CO2 and H2 formation at high respectively low potentials was observed. The DEMS method is capable to monitor side reactions occurring in VRFBs. Therefore, it is a useful tool to develop electrode materials, which exhibit a higher corrosion resistivity. 1. Eifert L, Banerjee R, Jusys Z, Zeis R (2018) Characterization of Carbon Felt Electrodes for Vanadium Redox Flow Batteries: Impact of Treatment Methods. J Electrochem Soc 165:A2577–A2586. doi: 10.1149/2.0531811jes 2. Colmenares LC, Wurth A, Jusys Z, Behm RJ (2009) Model study on the stability of carbon support materials under polymer electrolyte fuel cell cathode operation conditions. J Power Sources 190:14–24. doi: 10.1016/j.jpowsour.2009.01.078 3. Ashton SJ, Arenz M (2012) Comparative DEMS study on the electrochemical oxidation of carbon blacks. J Power Sources 217:392–399. doi: 10.1016/j.jpowsour.2012.06.015 4. Pérez-Rodríguez S, Sebastián D, Lázaro MJ, Pastor E (2017) Stability and catalytic properties of nanostructured carbons in electrochemical environments. J Catal 355:156–166. doi: 10.1016/j.jcat.2017.09.019 5. Taylor SM, Pătru A, Perego D, et al. (2018) Influence of Carbon Material Properties on Activity and Stability of the Negative Electrode in Vanadium Redox Flow Batteries: A Model Electrode Study. ACS Appl Energy Mater 1:acsaem.7b00273. doi: 10.1021/acsaem.7b002736. Eifert L, Banerjee R, Jusys Z, Zeis R (2018) Differential Electrochemical Mass Spectrometry of Carbon Felt Electrodes for Vanadium Redox Flow Batteries. ACS Appl Energy Mater 1 (12), 6714-6718 doi: 10.1021/acsaem.8b01550 Figure 1

Hydrogen Isotope Separation via Ion Penetration through Group-IV Monolayer Materials in Electrochemical Environment.

Based on density functional theory calculations, the chemical penetration behaviors and separation properties of hydrogen isotope ions through pristine and fully hydrogenated group-IV monolayer materials are investigated. Both the penetration energy profiles and kinetic isotope effects are studied to evaluate the performance of four group-IV (C, Si, Ge, and Sn) monolayer materials for hydrogen isotope separation. To examine the thermodynamically stable morphologies of these monolayer materials in electrochemical aqueous environment, the Pourbaix diagrams varying with pH and external bias are constructed. The fully hydrogenated monolayer materials are found to be thermodynamically favorable in some conditions, and the proton penetration and hydrogen isotope separation behaviors are different from their pristine counterparts. The silicene is found to be a suitable candidate material for hydrogen isotope separation in an electrochemical environment.

Porous graphitic activated carbon sheets upcycled from starch-based packing peanuts for applications in ultracapacitors

Porous graphitic activated carbon made from biodegradable starch-based packing peanuts contain metallic impurities, such as sodium and potassium impurities. The metallic impurities are not only eliminated in the activation process and revelation. These carbon sheets appear to form an ultrathin graphitic layer on the surface of the disordered carbon framework of the packed peanut-derived activated carbon. The shell-like graphitic structure can be explained by potassium penetration into the carbon structure during chemical activation and subsequent catalytic graphitization by the metallic impurities. These graphitic structures produce high-power density properties. As sodium impurities are present in the depth of the PP-C, it is possible to synergize the effects of potassium. The combination of these structural properties enables the carbon sheets to provide a harmonious electrochemical environment for the full realization of fast ion transport and high capacitance.

Role of Dissolution Intermediates in Promoting Oxygen Evolution Reaction at RuO2(110) Surface

RuO2 is one of the most active electrocatalysts toward oxygen evolution reaction (OER), but it suffers from rapid dissolution in electrochemical environments. It is also established experimentally ...

Development and application of flexible integrated microsensor as real-time monitoring tool in proton exchange membrane water electrolyzer

The proton exchange membrane (PEM) water electrolyzer has such advantages as simple system, low operating temperature and small-scale hydrogen production according to real time requirement, and the hydrogen production process is clean, meeting the environmental requirements. The PEM water electrolysis hydrogen production is the reverse reaction of fuel cell, but the water electrolysis requires high operating voltage, the resistance is likely to generate a lot of waste heat, and the nonuniform current density results in hot spots, the internal temperature rises, accelerating the decomposition of hydrogen molecules, the water electrolyzer is likely to age and fail. In addition, four important physical parameters (temperature, flow, voltage and current) in the running water electrolyzer can influence its performance and life, but the present bottleneck is external, theoretical, simulated or single measurement, the authentic information in the water electrolyzer cannot be obtained accurately and instantly. This study uses micro-electro-mechanical systems (MEMS) technology to develop a flexible integrated (temperature, flow, voltage and current) microsensor applicable to the high voltage and electrochemical environment in water electrolyzer, which is integrated with a 20 μm thick polyimide (PI) film material. The real-time microscopic diagnosis and measurement in the PEM water electrolyzer can measure the internal local temperature, voltage, current and flow distribution uniformity instantly and accurately, so as to optimize the operating conditions and analysis.

Electrochemical Environments for Operando Three-Dimensional Studies of Rechargeable Batteries

In the quest for sustainable alternatives to fossil fuel consumption and accompanying greenhouse gas emissions, rechargeable batteries have an integral role to play within the renewable energy ecosystem. Due to their high energy density and extensive commercial availability, Li-ion batteries have recently been favored in the electrification of transportation amongst other applications. Whilst great strides have been made in improving the safety and performance of Li-ion batteries since their commercialization in the 1980’s, scarcity and geopolitical risk surround metals that are critical to Li-ion positive electrodes, such as cobalt, copper, and nickel. More nascent in the developmental pipeline are Li-S and Li-air technology and chemistries with Na, Mg, Zn, etc. as the working ion, promising capacity gains of an order of magnitude, lower cost or improved safety. Regardless of the working ion, most rechargeable batteries are bound by one common feature – the electrochemical reactions within each cell typically occur on heterogenous porous electrodes. Microstructure variations and broader interactions with other cell components lead to a confluence of factors, emerging across several time- and length-scales, that affect the rate of degradation within batteries, the complexities of which have yet to be fully understood. With the advent of electron, X-ray and neutron scattering techniques, great progress has been made in capturing the physicochemical states within batteries. Through X-ray based techniques alone, detailed information can be obtained about the electronic states (X-ray absorption spectroscopy), crystalline states (X-ray diffraction) and mass densities (transmission X-ray microscopy) of materials (1), revealing the influence of intricate electrode microstructures on performance bottlenecks and degradation pathways. The insights offered by these techniques are vastly expanded by the development of suitable in-situ and operando electrochemical cells, which enable the same spatial volume to be tracked within controlled electrochemical environments (2), although many studies in the literature often cite poorer electrochemical performance compared to other large format cell geometries. This talk will focus on recent developments in in-situ and operando electrochemical cells, highlight examples of in-situ studies performed on lithium-based batteries, and discuss some of the challenges faced in constructing appropriate cell designs. In combination with lab-based instrumentation, longitudinal studies of battery degradation can be conducted at various length-scales, whilst the high temporal resolution achievable at synchrotron facilities enable highly dynamic processes to be captured. The overarching goals of these investigations range from accelerating the development of next generation battery chemistries by elucidating complex reaction mechanisms, to informing better design and engineering that will improve the safety and longevity of Li-ion batteries.

CO Site Preference on Copper Surfaces in Electrochemical Environments: Deciphering Voltage and Electrolyte Composition Effects

The development of effective electrocatalysts to convert carbon dioxide into value-added products such as methane and ethylene requires a detailed atomistic understanding of the reaction pathway. While it is well known that copper (100) surfaces exhibit a higher selectivity towards ethylene production, both electrochemical and non-electrochemical pathways have been proposed to describe this process. In both cases, the presence of adsorbed CO plays a crucial role and the pathways are observed to be active under different conditions. In this work, we study the role of the electrochemical environment in stabilizing CO across different copper surface sites and evaluate the energy barriers of key steps in the carbon dioxide electroreduction pathway. Using the recently developed Effective Screening Medium – Reference Interaction Site Method (ESM-RISM), we provide a detailed assessment of the roles of both applied voltages and electrolyte composition effects. Our results demonstrate that these two factors are synergistic, leading to behavior that qualitatively deviates from conventional models. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

(Invited) On-Line Inductively-Coupled Plasma Mass Spectrometry Characterization of Transition Metal Dissolution in Electrochemical Environments

While in-cell studies are the best way to characterize the performance and stability of electrochemical materials, the device environment often presents challenges to the real-time measurement of degradation processes. Several techniques have been developed to mimic the device environment, but to enable the real-time characterization of degradation processes. For example, low temperature fuel cell catalysts are often characterized using an aqueous electrolyte tuned to have pH and adsorption characteristics comparable to those of the solid ionomers used in fuel cells’ membrane-electrode assemblies. The material can then be subjected to various potential waveforms typical of those encountered in the device or intended to accelerate the materials degradation and the electrolyte analyzed, ex situ, for degradation products using a number of techniques. One such technique which is particularly useful is inductively-coupled mass spectrometry (ICP-MS), as it is able to detect transition metals in solution at concentrations as low at parts-per-trillion (ppt). This method, while valuable, provides limited information regarding the mechanisms of materials degradation (e.g., potential and time-dependence of dissolution processes). Recently, techniques have been developed which couple electrochemical flow or rotating disk electrode (RDE) cells directly to an ICP-MS allowing for precise time- and potential-resolved detection of dissolved species. One iteration of this technique is that pioneered by Mayrhofer et al. 1 in which a cell is sealed to a planar substrate on which the electrode material of interest is deposited. A stream of electrolyte is pumped over the material and the effluent electrolyte analyzed by ICP-MS. This cell can be rastered over the substrate/electrode material and thus has been dubbed a “scanning flow cell”. Lopes et al. 2 developed a stationary ICP-MS probe coupled with an RDE which allows measurement of the kinetics of a reaction simultaneously with detection of dissolution products. Another version of the technique uses a commercial flow cell from BASi with the electroactive material deposited on a glassy carbon working electrode and electrolyte drawn through the cell using the peristaltic pump of the ICP-MS.3,4 An overview of the application and utility of this technique in determining the potential-dependent degradation mechanisms of platinum and platinum alloy fuel cell catalysts will be presented. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Fuel Cell Performance and Durability Consortium (FC-PAD). Argonne National Laboratory is managed for the U.S. Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357. References O. Klemm, A. A. Topalov, C. A. Laska, K. J. J. Mayrhofer, Electrochem. Commun., 13, 1533 (2011).P. Lopes, D. Strmcnik, D. Tripkovic, J. G. Connell, V. Stamenkovic, and N.M. Markovic, Acs Catal, 6, 2536 (2016).P. Jovanovic, A. Pavlisic, V.S. Selih, M. Sala, N. Hodnik, M. Bele, S. Hocevar, and M. Gaberscek, Chemcatchem, 6, 449 (2014).R.K. Ahluwalia, D.D. Papadias, N.N. Kariuki, J.-K. Peng, X. Wang, Y. Tsai, D.G. Graczyk, and D.J. Myers, J. Electrochem. Soc., 165(6), F3024 (2018).

Coherent-x-Ray Imaging of Nanoparticle Alloy Electrodes and Catalysts

Bragg coherent diffraction imaging (BCDI) studies of silver nanoparticles revealed a new dissolution mechanism that has not previously been observed.1 We find that a long incubation time, ~30 sec, before start dissolution reaction when the particle starts from the pristine state. During the incubation period, however, electrochemical potential-induced pressure nucleates a dislocation loop within the nanoparticle that eventually exposes to the surface. Only then, rapid dissolution is activated at the surface sites. This result points to an important connection between structure and stability of silver in an electrochemical environment and demonstrates the potential of BCDI to elucidate this relationship. Understanding silver dissolution process is important in studying dealloying process of binary alloys. Dealloying is a selective dissolution of one element in an alloy resulting in a porous, strained structure often with new properties, such as highly active electrocatalysts.2 In the past, the pore formation during dealloying has been visualized using electron microscopy and the dealloying-induced strain has been studied at the ensemble level using x-ray diffraction.3 However, the information on lattice strain, which has been unavailable, could play an integral role in understanding and controlling properties and activities for a variety of applications. In our BCDI studies, 3D strain distributions of individual nanoparticles and thin film grains of silver-gold alloys were investigated during dealloying in nitric acid.4 Isolated particles exhibit dramatic changes in their shapes as expected (See the graphical abstract). Our results (not shown) also demonstrate that significant local strains occur as a result of dealloying. The same dealloying process was used for nanoscale grains of a thin film instead of the isolated nanoparticles. The results show that isolated nanoparticles are significantly more strained than the grain embedded in the film texture,4 primarily because strain can be relieved via grain boundaries in the case of the single grain. These observations demonstrate that the unique capabilities of BCDI techniques. We also have begun working on alloys under catalytic environment where the compositions and shapes of alloy nanoparticles are highly sensitive to gas and temperature environment. We will present some preliminary results as time permits in my presentation. Liu, Y., et al., Nano Letters (2017) 17 (3), 1595Erlebacher, J., et al., Nature (2001) 410 (6827), 450Yang, R. Z., et al., Journal of Physical Chemistry C (2011) 115 (18), 9074Cha, W., et al., Advanced Functional Materials (2017) 27 (25) Figure 1

In Situ Mössbauer and X-Ray Absorption Spectroscopy Studies of Atomically-Dispersed Fe-N-C Oxygen Reduction Reaction Catalysts

The identity of the active site in iron-nitrogen-carbon polymer electrolyte fuel cell (PEFC) oxygen reduction reaction (ORR) electrocatalysts has been the subject of debate for decades. This is primarily because these catalysts are typically formed through high temperature treatment of iron-nitrogen-carbon-containing precursors, with the resulting material containing multiple iron species, and because common characterization techniques are not surface specific. For example, X-ray absorption and Mössbauer spectroscopies, two of the most widely used techniques for characterizing this class of catalysts, are bulk techniques. They, however, can be rendered surface specific by using probe molecules that adsorb/coordinate with the active site and perturb the spectral signatures of the absorbing atom. They can also be rendered surface specific by altering the oxidation state and coordination of the absorbing atom by changing the catalyst potential in an electrochemical environment. In this study we used both of these methods to probe the surface iron species in an Fe-N-C ORR catalyst. These studies were enabled by the recent development, at Los Alamos National Laboratory, of a highly active iron-zinc zeolitic imidazolate framework-derived catalyst with the vast majority of iron in atomically-dispersed sites, as determined by ex situ scanning transmission electron microscopy, Mössbauer spectroscopy, and X-ray absorption spectroscopy.1 These same techniques showed that the use of an 57Fe salt in the precursor, necessary for the in situ Mössbauer experiments, did not affect the catalyst’s morphology or Fe speciation. The results from the in situ X-ray and Mössbauer spectroscopy studies will be correlated to determine the change in the oxidation state and coordination of surface Fe sites as a function of catalyst potential. Results will be presented showing that the Fe sites are predominantly located on the surface of the catalyst and able to adsorb the probe molecule.1 Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under the auspices of the Electrocatalysis Consortium (ElectroCat). This research used the resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Electron microscopy was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357. References D.J. Myers, P. Zelenay, K.C. Neyerlin, and K.L. More, “ElectroCat (Electrocatalysis Consortium)”, 2018 Department of Energy Hydrogen and Fuel Cells Program Annual Merit Review and Peer Evaluation Meeting, Washington DC, June, 2018. (https://www.hydrogen.energy.gov/pdfs/review18/fc160_myers_2018_o.pdf)

Justifying the ECSA of the Pt Surface in Alkaline Solutions by Elucidating its Lower HUPD Area in Alkaline than in Acid

The ideal way to compare electrocatalysts’ inherent activity, is to compare the turnover frequency per active site (TOF), while eliminating the contribution from the electrochemical surface area (ECSA) of electrocatalysts.(1) However, It is difficult to directly evaluate the TOF, especially for complex nano-scale electrocatalysts in complex electrochemical environments. A more common way to evaluate TOF is via normalization of the current density by the ECSA under relevant electrochemical environments. Accurate estimation of ECSA is thus essential for estimating the activity and understanding the electrocatalyst kinetics. Taking the fundamental hydrogen reduction and oxidation reactions (HER/HOR) as an example, the exchange current normalized by the ECSA is used to estimate the intrinsic kinetics of electrocatalysts. The ECSA of Pt surfaces is conventionally characterized by conducting underpotential deposition/adsorption of hydrogen (HUPD).(2) However, the HUPD integrated area of the carbon supported Pt (Pt/C) nanoparticles and Pt polycrystalline (Pt(pc)) obtained in alkaline is smaller than in acid.(3) In spite of the apparent discrepancy, both the HUPD area in acid and alkaline were used as the ECSA of Pt surfaces when evaluating the inherent HER/HOR activity.(4-6) It is therefore fundamentally important to understand the cause of the lower HUPD area in alkaline than in acid, so as to justify the ECSA evaluation method. Herein, we show with experimental evidence (Figure 1) that the difference of the HUPD area between in acid and alkaline may be explained by the non-specific adsorption of the alkali metal cations (AM+) selectively onto the stepped Pt surfaces.(7) The cation effect is absent for the Pt (111) surface free of defects, and thus its HUPD area remains constant in the wide pH range of 1~13. Since the adsorbed AM+ participate in the HER/HOR, it is reasonable to adopt the HUPD area in alkaline representing the ECSA for the alkaline HER/HOR. We further show that this argument also applies for bimetallic Pt-alloys. Acknowledgement: This work was supported by the Office of Naval Research (ONR) under award number N000141712608. The authors declare no competing financial interests. References D. Voiry, M. Chhowalla, Y. Gogotsi, N. A. Kotov, Y. Li, R. M. Penner, R. E. Schaak and P. S. Weiss, ACS Nano, 12, 9635 (2018).M. J. J. Ian T. McCrum, J. Phys. Chem. C, 121, 6237 (2017).P. J. Rheinlander, J. Herranz, J. Durst and H. A. Gasteiger, Journal of the Electrochemical Society, 161, F1448 (2014).J. Durst, A. Siebel, C. Simon, F. Hasché, J. Herranz and H. A. Gasteiger, Energy Environ. Sci., 7, 2255 (2014).J. Ohyama, T. Sato, Y. Yamamoto, S. Arai and A. Satsuma, Journal of the American Chemical Society, 135, 8016 (2013).W. Sheng, H. A. Gasteiger and Y. Shao-Horn, Journal of The Electrochemical Society, 157, B1529 (2010).X. Chen, I. T. McCrum, K. A. Schwarz, M. J. Janik and M. T. M. Koper, Angew Chem Int Ed Engl, 56, 15025 (2017). Figure 1

Atmospheric Electricity Influencing Biogeochemical Processes in Soils and Sediments.

The Earth’s subsurface represents a complex electrochemical environment that contains many electro-active chemical compounds that are relevant for a wide array of biologically driven ecosystem processes. Concentrations of many of these electro-active compounds within Earth’s subsurface environments fluctuate during the day and over seasons. This has been observed for surface waters, sediments and continental soils. This variability can affect particularly small, relatively immobile organisms living in these environments. While various drivers have been identified, a comprehensive understanding of the causes and consequences of spatio-temporal variability in subsurface electrochemistry is still lacking. Here we propose that variations in atmospheric electricity (AE) can influence the electrochemical environments of soils, water bodies and their sediments, with implications that are likely relevant for a wide range of organisms and ecosystem processes. We tested this hypothesis in field and laboratory case studies. Based on measurements of subsurface redox conditions in soils and sediment, we found evidence for both local and global variation in AE with corresponding patterns in subsurface redox conditions. In the laboratory, bacterial respiratory responses, electron transport activity and H2S production were observed to be causally linked to changes in atmospheric cation concentrations. We argue that such patterns are part of an overlooked phenomenon. This recognition widens our conceptual understanding of chemical and biological processes in the Earth’s subsurface and their interactions with the atmosphere and the physical environment.

Vanadium disulfide flakes with nanolayered titanium disulfide coating as cathode materials in lithium-ion batteries

Unlike the vast majority of transition metal dichalcogenides which are semiconductors, vanadium disulfide is metallic and conductive. This makes it particularly promising as an electrode material in lithium-ion batteries. However, vanadium disulfide exhibits poor stability due to large Peierls distortion during cycling. Here we report that vanadium disulfide flakes can be rendered stable in the electrochemical environment of a lithium-ion battery by conformally coating them with a ~2.5 nm thick titanium disulfide layer. Density functional theory calculations indicate that the titanium disulfide coating is far less susceptible to Peierls distortion during the lithiation-delithiation process, enabling it to stabilize the underlying vanadium disulfide material. The titanium disulfide coated vanadium disulfide cathode exhibits an operating voltage of ~2 V, high specific capacity (~180 mAh g−1 @200 mA g−1 current density) and rate capability (~70 mAh g−1 @1000 mA g−1), while achieving capacity retention close to 100% after 400 charge−discharge steps.

A Facile Method to Synthesize Pt–Ni Octahedral Nanoparticles with Porous and Open Structure Features for Enhanced Oxygen Reduction Catalysis

In recent years, nanocatalysts with an open structure have been fascinating to use for electrocatalytic reactions due to their high specific area, large void space, and potentially highly active sites. Meanwhile, a porous structure is more beneficial to create a confined environment which would enhance catalytic activity. Herein, we show the porous Pt–Ni octahedral nanoparticles which exhibit abundant Pt–Ni alloy structures with transparent features and tiny Pt–Ni octahedral nanoparticles. By controlling the anisotropy of Pt with surfactant in solvothermal synthesis, we have synthsised composition-segregated octahedral Pt–Ni nanoparticles and tiny Pt–Ni octahedral nanoparticles at different precursor ratios. After subsequent chemical etching, the structure of composition-segregated octahedral Pt–Ni nanoparticles evolved into a porous and open structure. The porous octahedral Pt–Ni nanoparticles show ∼7.1 times higher specific activity and ∼5.7 times higher mass activity for the oxygen reduction reaction than that of TKK-Pt/C catalyst and 1.6 times mass activity of tiny Pt–Ni octahedral nanoparticles. The activity enhancement is attributed to the idea that some of the Pt atoms deposited on the faces of octahedron and formed a Pt–Ni alloy with Ni atoms. After chemical etching, many active sites and alloy phases are exposed to the electrochemical environment, which leads to enhanced electrochemical activity.

Synthesis and Electrochemical Stability of Ultrahigh Aspect Ratio Nanoporous Gold after Calixarene-Phosphine Ligand Removal.

Leveraging our previous report on the synthesis of calixarene-capped ultrahigh aspect-ratio nanoporous gold, we now report a new class of nanoporous gold comprising removed calixarene-phosphine ligands using UV/ozone treatment. The removal of the calixarene ligands by this treatment is supported by XPS measurements. TEM further shows the extraordinary stability of the ∼1 nm building blocks comprising the nanoporous gold wall after UV/ozone treatment and subsequent strongly reducing electrochemical environments. Sensing of nitrobenzene is used as a method of characterization to show that the surface chemistry of the nanoporous gold assemblies has radically changed after the UV/ozone treatment.

Capacity degradation of Laves phase-related body-centered-cubic solid solution metal hydride alloys in battery

The nickel/metal hydride (Ni/MH) is a good example of using metal hydride alloy which is cable of reversely storing the hydrogen energy in an electrochemical environment. The failure mode of two Laves phase-related body-centered-cubic metal hydride alloys doped with Y, and Ce separately in sealed Ni/MH batteries is studied by scanning electron microscopy with x-ray energy dispersive spectroscopy and x-ray diffraction analysis. These two alloys come from a series of studies targeting toward using Ni/MH battery as a low-cost and high-durability alternative to rival Li-ion battery in the electric vehicle application. This group of alloys demonstrates a discharge capacity up to 400 mAh g−1 under a C/4 discharge rate. The main failure mode of these two alloys is found to be selective dissolution of C14 phase which contributes to a fast increase in internal resistance. Due to the deprival of Cr from the first solidified BCC phase, the next solidified C14 phase does not have enough Cr to protect it from the KOH corrosion. Rapid quench fabrication method and addition of other corrosion-resistant non-BCC former, such as Cu, Pd, and Hf, in the alloy composition are suggested.

One-Step Integrated Surface Modification To Build a Stable Interface on High-Voltage Cathode for Lithium-Ion Batteries.

As one of the most promising cathode materials for next-generation energy storage applications, spinel LiNi0.5Mn1.5O4 (LNMO) has been highlighted due to many advantages. However, it is still hindered by poor electrochemical stability derived from the bulk/interface structure degradation and side reactions under high working voltage. In this work, fast ion conductor Li3V2(PO4)3 (LVPO) is adopted to modify the surface of spinel LNMO by a one-step facile method to harvest the maximum benefit of interface properties. It is found that 1 wt % LVPO-LNMO exhibits the most excellent cycling performances, retaining great capacity retention of 87.8% after 500 cycles at room temperature and 82.4% for 150 cycles at 55 °C. Moreover, the rate performance is also significantly improved (90.4 mAh g-1 under 20C). It is revealed that the LVPO-involved layer could effectively suppress the surface side reactions under high working voltage, which mainly contributes to an improved interface with desirable structural stability and excellent kinetics behavior without sacrificing the surface electrochemical activity in an electrochemical environment. Thus, the dissolution of transition-metal ions is effectively mitigated, avoiding further structure degradation of the bulk material. Especially, it is also established that the vanadium (V) ions in LVPO could be to a certain extent migrated into the surface lattice of LNMO to generate a V-involved transition layer (Li-Ni-Mn-V-O surface solid solution), which greatly co-contributes to the enhanced electrochemical performances owing to the prominently depressed charge-transfer resistance.

Biodegradable batteries with immobilized electrolyte for transient MEMS.

Biodegradable batteries play an important role in fully degradable biomedical or environmental systems. The development of biodegradable batteries faces many challenges including power content, device compactness, performance stability, shelf and functional lifetime. In particular, a key driver in the lifetime and overall size of microfabricated biodegradable batteries is the liquid electrolyte volume. Harnessing liquid from the environment to serve as the battery electrolyte may, therefore, be desirable; however, for stable operation, maintaining a constant electrochemical environment inside the cell is required even in the presence of changing body or environmental conditions. We report a biodegradable battery featuring a solid electrolyte of sodium chloride and polycaprolactone. This approach harnesses the body fluid that diffuses into the cell as an element of the electrolyte; however, the large excess of sodium chloride suspended in the polycaprolactone holds intracell ionic conditions constant. A constant discharge profile can then be achieved even in the presence of varying external aqueous conditions, enabling compact, stable-performing cells. This design also features easy integration and automatic activation, providing a simplified strategy to fabricate batteries with long shelf life and desirable functional life span. In addition, the polymeric skeleton of the solid electrolyte system acts as an insulating layer between electrodes, preventing the metallic structure from short-circuit during discharge.