Dissecting Structural Modi fi cation Effects on the Electrocatalytic Hydrogen Evolution Reaction Activity of Atomically Precise

It is important but still challenging to reveal the effect of precise structural modification of polyoxometalates (POMs) on electrocatalytic hydrogen evolution reaction (HER). Here, we present the syntheses of five polyoxoniobate (PONb) analogs with well-defined structures, including Na-GeNb 12 , Cu-GeNb 12 , GeV 2 Nb 12 , V 3 Nb 12 , and SiV 2 Nb 12 , as model systems, enabling us to unravel the effects of structural modification of POMs on the electrocatalytic HER at the atomic level. Our results revealed that the bridging O atoms of PONbs were the primary active sites for HER, whose catalytic performance was mostly affected by the central atom of PONb, followed by surface composition and then by counterion. Comprehensive characterizations and theoretical calculations were performed to confirm and interpret the above findings, which provide a rational atomic-level design of efficient POM-based HER electrocatalysts.