Decoding the Oxygen Evolution Reaction Mechanism in a Novel Octanuclear Nickel(II) Double Cubane Cluster: Unleashing the Electrocatalytic Performance

ABSTRACT The synthesis of efficient electrocatalysts for the oxygen evolution reaction (OER) in water splitting remains challenging due to slow reaction kinetics. In the present investigations, a novel octanuclear nickel(II) double cubane molecular cluster, [Ni ^II ₄ (LH ₃ ) ₃ ( µ ₃ ‐OH)( η ¹ ‐H ₂ O) ₂ ] ₂ ·2NO ₃ ·2H ₂ O·CH ₃ OH ( 3 ), has been synthesized using a Schiff‐base ligand LH ₄ (2‐[2‐hydroxy‐3‐(hydroxymethyl)‐5‐methylbenzylideneamino]‐2‐methylpropane1,3‐diol). Complex 3 was immobilized on activated carbon cloth (CC), referred to as CC‐3 , and investigated as an electrocatalyst for the OER in an alkaline medium. Single‐crystal X‐ray diffraction revealed that complex 3 comprised two distorted cubane‐like [Ni ₄ ( µ ₃ ‐OR) ₃ ( µ ₃ ‐OH)] ⁺ cores interconnected by flexible pendant ─CH ₂ OH groups from the ligand. Electrochemical analysis showed that CC‐3 exhibited excellent OER activity in 1.0 m KOH, which was reflected in a low overpotential of 290 mV at 10 mA cm ^{− 2} with a Tafel slope of 48 mV dec ⁻¹ . The catalyst showed remarkable stability, undergoing negligible degradation after 2000 CV cycles and 20 h of chronoamperometric measurement. Mechanistic studies suggest the formation of catalytically active high‐valent Ni ³⁺ ─OH intermediates during the OER. Fe ³ ⁺ addition to the electrolyte enhanced OER activity, attributed to high‐valent reactive species stabilization. This work demonstrates polynuclear nickel complexes as effective molecular electrocatalysts for OER, providing insights into their catalytic mechanisms.