Identifying and Interpreting Geometric Configuration-Dependent Activity of Spinel Catalysts for Water Reduction

The catalytic activity of transition metal-based catalysts is overwhelmingly dependent on the geometric configuration. Identification and interpretation of different geometric configurations' contributions to catalytic activity plays a pivotal role in catalytic performance elevation. Spinel structured AB₂X₄, consisting of tetrahedral (A²⁺-X) and octahedral (B³⁺-X) geometric configurations, is a prototypical category of multi-geometric-configuration featured catalysts. However, it is still under debate about the predominant geometric configuration responsible for spinel catalyst activity, and the mechanistic origin of specific activity discrepancy among varied geometric configurations also remains ambiguous. Herein, Co²⁺ and Co³⁺ in Co₃O₄ are replaced by catalytically inert Zn²⁺ and Al³⁺ to yield ZnCo₂O₄ and CoAl₂O₄, respectively, thus ensuring the manipulable exposure of monotypic active configurations. By means of pulse voltammetry and in situ extended X-ray absorption fine structure, (Co³⁺-O) is identified to be dominant for alkaline HER. In-depth theoretical investigation in combination with X-ray absorption spectroscopy further interprets the synergistic effect between Co and O sites in (Co³⁺-O) configuration on water reduction kinetics upon both water dissociation and hydrogen desorption steps. Furthermore, specific facet dependence of catalytic activity is also deciphered based on precise facet exposure identification and serial theoretical analysis. This work unambiguously figures out the subtle geometric configuration dependence of spinel catalyst activity for water reduction and highlights the synergistic relationship among different components confined in geometric configuration, thereby shedding new light on the rational design of advanced catalysts from the atomic level of geometric configuration optimization.