Octamolybdate‐Type Polyoxometalate as Pre‐Catalyst for Electrocatalytic Acidic Water Oxidation

One of the major challenges for advancing sustainable energy sources is developing a molecularly defined and acid‐stable catalyst for water oxidation. In this study, we investigate an octamolybdate‐type polyoxometalate [{Cu(pzc) 2 }Mo 8 O 26 ]·8H 2 O (Cu POM) (pzc‐pyrazine carboxylic acid), as a potential precatalyst that exhibits remarkable catalytic activity and durability for OER in acidic media on undergoing in situ transformation to r‐POM (CuO and residual Mo─O). r‐POM delivers a low overpotential of 234 mV to achieve a current density of 10 mA cm − 2 , surpassing most reported OER catalysts under comparable conditions. Moreover, it exhibits an exceptional long‐term durability of 23 h at a high current density of 50 mA cm − 2 . Mechanistic investigations, supported by post‐catalytic structural characterization, reveal that Cu POM underwent transformation into r‐POM, which acts as the true catalytic species. The catalyst (r‐POM) provides both robust stability in harsh pH environments that synergistically contribute to its catalytic performance. This work highlights the promise of rationally designed polyoxometalates as next‐generation, acid‐resilient OER electrocatalysts for proton‐exchange membrane water electrolysers.