Harnessing the Structural Dynamics of Polyoxometalates: Role of Active Phase Segregation for Water Oxidation

ABSTRACT In situ surface reconstruction of Co‐polyoxometalates (Co‐POMs) has a significant influence on its electronic and structural properties during oxygen evolution reaction (OER). Therefore, depicting the role of POMs via tracking its electronic and structural framework evolution is crucial for resolving the true catalytic process. In this concern, a novel Keggin‐type POM [{CoW 12 O 40 (C 4 H 6 N 2 ) 2 (C 4 H 12 N) 3 (C 3 H 9 N)}.2H 2 O] (POM 1), (C 4 H 6 N 2 = 2‐methylimidazole, C 4 H 12 N = tetramethyl ammonium ion, and C 3 H 9 N = trimethylamine) is synthesized. Operando studies revealed the transformation of POM 1 (precatalyst) into r‐POM 1 during OER. As expected, r‐POM 1 exhibits outstanding activity in wide pH range. In addition, the reduced work function of in situ formed heterogeneous surface of r‐POM 1 indicates the formation of a built‐in electric field, beneficial for OER. Evolution of the active Co 3 O 4 phase in r‐POM 1 during OER owns to microstrain, resulting in improved electrochemical performance, whereas controlled Co 3 O 4 (pristine) has no strain in its crystal structure. To correlate the experimental findings, the computational calculations revealed lower hydroxylation energy in case of r‐POM 1 (−0.64 eV) as compared to POM 1 (4.5 eV). These combined findings offer compelling operando evidence of in situ active phase segregation during OER, resolving the mystery of POM being a precatalyst or heterogeneous catalyst.