(217b) When Electrocatalysis Matters and When It Does Not: Unexpected Observations in Water Electrolysis and Flow Battery Energy Storage

This presentation will summarize ongoing projects in our lab on applications of electrocatalysis in hydrogen production and flow battery energy storage. We are working to advance these technologies through a balanced effort in scientific inquiry (e.g., synthetic methods, structure-function relationships) and engineering design (e.g., device specification, performance metrics). A persistent theme in our work thus far has been ambitious experimental targets underpinned by naïve assumptions, where the process of stepping back to re-evaluate our assumptions has nevertheless led to intriguing new conclusions.

In the area of water electrolysis, we set out to improve on the performance and stability of Ni–Mo alloy hydrogen evolving electrocatalysts with an eye toward their use in alkaline electrolyzers. Our work focused initially on understanding composition and reaction mechanisms in nanostructured Ni–Mo alloys while we also worked to develop catalyst ink formulations that would be compatible with fabrication of membrane electrode assemblies. Ironically, the latter studies led to unexpected fundamental insights, where observed reaction rates were not limited by kinetics or mass transfer, but rather by interfacial electronic conductivity even in this nominally metallic catalyst material. Incorporating carbon black mitigated the conductivity limitation, resulting in markedly improved mass-specific activity.

In the area of flow battery energy storage, our initial efforts to pursue engineering design specifications for integrated solar-driven battery systems were quickly hampered by the remarkable lack of consensus on intrinsic rates of interfacial electron transfer for known flow battery redox couples. Thus, we have now developed analytical protocols (adapted from the electrolysis and fuel cell literature) for benchmarking the kinetics of flow battery electrode-electrolyte combinations. Results to date suggest that electrocatalysis plays a vital role in dictating the overpotential performance of essentially all known flow battery active materials—even those based on apparently straightforward 1-electron transfer reactions. We are working to modify these electroanalytical protocols for direct deployment in operational flow battery devices.