The chemical complexity of single-phase multicationic oxides, commonly termed high entropy oxides (HEOs), enables the integration of conventionally incompatible metal cations into a single-crystalline phase. However, few studies have effectively leveraged the multicationic nature of HEOs for optimization of disparate physical and chemical properties. Here, we apply the HEO concept to design robust oxidation catalysts in which multicationic oxide composition is tailored to simultaneously achieve catalytic activity, oxygen storage capacity, and thermal stability. Unlike conventional catalysts, HEOs maintain single-phase structure, even at high temperature, and do not rely on the addition of expensive platinum group metals (PGM) to be active. The HEOs are synthesized through a facile, relatively low temperature (500 °C) sol-gel method, which avoids excessive sintering and catalyst deactivation. Nanostructured high entropy oxides with surface areas as high as 138 m2/g are produced, marking a significant structural improvement over previously reported HEOs. Each HEO contained Ce in varying concentrations, as well as four other metals among Al, Fe, La, Mn, Nd, Pr, Sm, Y, and Zr. All samples adopted a fluorite structure. First row transition metal cations were most effective at improving CO oxidation activity, but their incorporation reduced thermal stability. Rare earth cations were necessary to prevent thermal deactivation while maintaining activity. In sum, our work demonstrates the utility of entropy in complex oxide design and a low-energy synthetic route to produce nanostructured HEOs with cations selected for a cooperative effect toward robust performance in chemically and physically demanding applications.

Anodic stripping voltammetry (ASV) is a well-known powerful, sensitive, and selective analysis technique used for the detection of metal ion species in solution. While ASV was initially developed with mercury (Hg) as the plating electrode more recent applications have used bismuth (Bi) as a less toxic and less oxygen sensitive electrode that has low background currents, better reproducibility, and little to no need for electrode conditioning, as compared to Hg electrodes. ASV is most commonly performed under neutral to acidic electrolyte conditions where metals, as metal cations are readily soluble; however, the extension of an ASV method into highly alkaline environments (pH > 14) could prove useful for the in situ electrolyte monitoring of alkaline batteries and fuel cells such that potential diagnostics of their performance vs. electrolyte composition could be realized. With this in mind, we recently extended the ASV method to highly alkaline electrolytes, in order to determine Zn diffusion across separator membranes.[1] Zinc (Zn) alkaline battery chemistries such as Zn/MnO 2 and Zn/Air are currently attracting a lot of attention due to their potential as safe, low cost, high energy density rechargeable batteries. A main failure mechanism for these cells is the poisoning of the cathode material during cycling due to Zn crossover from the anode to the cathode. Advanced separators that successfully stop or limit this crossover are crucial in order to increase the cycle lifetime of these batteries. ASV, utilizing a Bi film, along with cadmium (Cd) and lead (Pb) as the plating mediators, was utilized to determine Zn concentrations in highly alkaline environments (30% NaOH or 35% KOH). To evaluate the utility of this assay, zincate diffusion through commercial off-the-shelf (COTS) Celgard 3501 and Cellophane 350P00 membranes was monitored using both ASV and inductively coupled plasma – mass spectrometry (ICP-MS) methods. The obtained zincate diffusion coefficients for both techniques are shown to compare favorably. While the traditional complexometric or elemental analysis methods can take days to weeks to determine Zn membrane diffusion metrics, this ASV method provides a real-time measurement which significantly increases the throughput for the screening of these membranes. During our development of an ASV method for Zn, we realized that in general there was a lack of ASV methods in highly alkaline electrolyte and hence turned our attention to the development of an ASV method for the determination of Cu, as cuprate [Cu(OH) 4 2- ]. Cu has been notoriously difficult to measure by ASV, even under acidic conditions.[2] In fact, most studies using Bi film electrodes for the direct determination of Cu have deemed it impossible and thus studies for the determination of the Cu concentration in a matrix are normally still performed separately with Hg electrodes. After investigation of potential metal film electrodes and mediators including Cd, Ag, Sb, and Zn, it was found that lead (Pb) serves as a good mediator for the plating of Cu in highly alkaline solutions which permits the replacement of the interfering Bi film electrode. Various aspects of this work will also be presented. [1]. J. Duay, T. N. Lambert and R. Aidun “Stripping Voltammetry for the Real Time Determination of Zinc Membrane Diffusion Coefficients in High pH: Towards Rapid Screening of Alkaline Battery Separators” Electroanalysis 2017 , 29, 2261-2267 . [2]. J. Duay, J. E. Ortiz-Santiago and T. N. Lambert “Copper Sensing in Alkaline Electrolyte Using Anodic Stripping Voltammetry by means of a Lead Mediator” Electroanalysis 2017 , DOI: 10.1002/elan.201700526. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. Dr. Imre Gyuk, Energy Storage Program Manager, Office of Electricity Delivery and Energy Reliability is also thanked for financial support of this project.

Poly(3,4-ethylenedioxythiophene)/manganese oxide hybrid films with high surface Mn(III)concentration and strong electronic coupling are effective electrocatalysts for the oxygen reduction reaction.

An anodic stripping voltammetry (ASV) sensing platform which provides real time determination of zincate diffusion through membrane separators in alkaline electrolyte with total experimental times on the order of hours is presented. Advanced separators are essential for future rechargeable alkaline zinc batteries. In order to be screened, these membranes need to be evaluated for their zincate blocking performance. Current complexometric titration and elemental analysis methods for zincate membrane diffusion characterization can take days to weeks to obtain results as well as include large sample dilution factors and require additional sample processing. The anodic stripping voltammetry (ASV) sensing platform presented here provides real time determination of zincate diffusion in alkaline electrolyte with total experimental times on the order of hours. This method eliminates the need for sample dilution and post experiment sample processing. This technique significantly increases the throughput for the screening of advanced alkaline battery separators resulting in rapid turnaround times in the analysis of these vital membranes. To evaluate the utility of this method, zincate diffusion through commercial Celgard 3501 and Cellophane 350P00 was monitored using both ASV and inductively coupled plasma-mass spectrometry (ICP-MS) methods. The obtained zincate diffusion coefficients for both techniques were found to compare favorably.

Rechargeable alkaline Zn/MnO2 batteries are being developed for use as cost-effective grid-scale energy storage devices. Previous studies have shown that limiting the depth of discharge (DOD) of the MnO2 cathode extends cell lifetime while still providing a cost-effective battery system. Herein, a comprehensive study of triethanolamine (TEA) as an additive in Zn/MnO2 limited DOD batteries is provided by examining the effect of TEA in full cells as well as independently on the cathode, anode, separator, and electrolyte. Improvement in cycle-ability of the cathode (on average, 80% of cycled capacity remains after 191 cycles without TEA, 568 cycles with TEA) and a decrease in ionic zinc mobility across Celgard 3501 (7.91 x 10(-5) cm(2)/min without TEA, 3.56 x 10(-5) cm(2)/min with TEA) and Cellophane 350P00 (3.26 x 10(-5) cm(2)/min without TEA, 4.74 x 10(-6) cm(2)/min with TEA) separators upon the addition of TEA are demonstrated. However, TEA increased both the reduction potential of Zn (-0.68 V vs. Hg/HgO without TEA, -0.76 V with TEA) and the solubility of Zn2+ (0.813 M without TEA, 1.023 M with TEA). Overall, the addition of TEA extended the lifetime of limited DOD cells on average by 297%. (c) The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. All rights reserved.