Design of Materials for Energy Storage and Conversion in High Temperature Environment

Abstract

The kinetics and thermodynamics of electrochemical energy storage and conversion technologies such as fuel cells and electrolyzers often times benefit from high temperature operation. For example, the thermodynamic electrical energy requirements for water electrolysis decrease substantially from 1.23 to below 1 volt by increasing the process temperature from ambient conditions to 850 °C. Unfortunately, materials degradation via sintering, crystal structure disproportion to thermodynamically more stable phases, and interfacial reactions also increases exponentially with increasing temperature. Lifetime requirements for energy conversion technologies often times exceed 10 years of usage with no more than 20% degradation.[1] The requirement of high gas/electrode/solid electrolyte interfacial area for large areal current densities repeatedly necessitates the usage of nano to micro structured materials, further acerbating materials degradation. Oftentimes it is much easier to synthesize a promising new electrode or electrolyte material than it is to characterize the long-term stability of a material in the extremely reducing or oxidizing high temperature environments.[2] We have developed experimental methods in conjunction with thermochemical modeling to evaluate the stability of important classes of perovskite and fluorite oxide materials.[3] We have performed thermogravimetric, FT-IR and electrochemical linear sweep voltammetry methods to rapidly determine oxide materials stability under operationally relevant conditions and these results are compared to stability calculations. Generalizations can be made to predict expected materials redox stability based on relatively straightforward chemical bonding principles, known cation coordination environments and more sophisticated computational chemistry methods. Stability determinations of perovskite oxide electrocatalysts for electrochemical oxidative coupling of methane offer an excellent examples of our approach towards evaluation of materials durability under challenging temperature and reducing conditions.[1] A. Hauch, S. D. Ebbesen, S. H. Jensen, and M. Mogensen, “Highly efficient high temperature electrolysis,” J. Mater. Chem., vol. 18, no. 20, pp. 2331–2340, 2008, doi: 10.1039/B718822F.[2] C. Zhu, S. Hou, X. Hu, J. Lu, F. Chen, and K. Xie, “Electrochemical conversion of methane to ethylene in a solid oxide electrolyzer,” Nat. Commun., vol. 10, no. 1, p. 1173, 2019, doi: 10.1038/s41467-019-09083-3.[3] F. H. G. Kannan P. Ramaiyan, Luke H. Denoyer, Angelica Benavidez, “Electrochemical oxidative coupling of methane to produce higher hydrocarbons using Sr2Fe1.5Mo0.5O6-d electrocatalysts,” Submitt. Commun. Chem., 2021.