Discovering improved electrocatalysts for the oxygen evolution reaction (OER) is of great importance for efficient solar fuels generation, electrowinning of metals, regenerative fuel cells, and recharging metal air batteries. The slow kinetics of the 4-electron OER requires large overpotentials to drive water oxidation at appreciable current densities. Among the numerous compositions investigated, mixed metal oxides in the (Ni-Fe)Ox and (Ni-Co)Ox composition spaces are among the most active and most studied OER catalysts. Although this technologically important reaction has been studied for more than 50 years, many of themechanistic details remain under investigation. Lacking a robust fundamental understandingof the basic science and mechanistic details of multi-electron heterogeneous electrocatalysis, an efficient high-throughput synthesis and property screening methodology is well-suited to discovering the requisite new catalytic materials.  We have established high throughput methods to systematically investigate the performance of pseudo-quaternary materiallibraries as OER electrocatalysts.  We report a new Ce-rich family of active catalysts composed of earth abundant elements, which was discovered using high-throughput methods to produce 5456 discrete compositions in the (Ni-Fe-Co-Ce)Ox composition space. The activity and stability of this new OER catalyst was verified by re-synthesis and extensive electrochemical testing ofsamples in a standard format in 1.0 M NaOH, as well as by operation in a photovoltaic-powered electrolyzer for more than 100 hours.  The most interesting variations in activity lie in a pseudoternary cross-sectional plane containing 665 compositions. Our detailed investigation of this psuedoternary cross-section has revealed systematic trends in Tafel slopes and electrochemical signals with composition, which provide a connection between the previously known Ni-Fe and newly discovered Ni-Co-Ce catalysts.  Characterization of selected compositions by XRD, XPS, SEM, TEM, EDS, XRF mapping, and EXAFS, both as-synthesized and after electrochemical testing, reveal important differences in nanostructure and stability along with the observed differences in electrochemical performance under OER conditions.

Discovering Ce-rich oxygen evolution catalysts, from high throughput screening to water electrolysis

247th National Meeting (2014)

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