Operando PEC-XAS characterization of Ni-based co-catalysts on hematite photoanodes: shedding light into substrate/catalyst electronic coupli

Water oxidation photoanodes made from earth-abundant metal oxides offer promising opportunities for sustainable solar energy conversion due to their stability, environmental compatibility, and tunable properties. Hematite (α-Fe2O3) is a leading candidate because of its favorable band gap and abundance but faces challenges like high surface recombination and slow charge transfer kinetics. Nickel-based co-catalysts, have shown potential in addressing these limitations by enhancing charge separation and reducing recombination losses. Additionally, these catalysts exhibit high selectivity for organic oxidation reactions, such as 5-hydroxymethyl furfural (HMF), demonstrating their versatility. Despite progress, the exact enhancement mechanisms of Ni-based co-catalysts remain unclear. Preliminary operando XAFS and Fixed Energy X-ray Absorption Voltammetry (FEXRAV) studies performed at ESRF facilities (CH-7070) have shown that nickel oxidation states are sensitive to applied bias, light condi