Facile, Room Temperature, Electroless Deposited (Fe_1-x, Mn_x )OOH Nanosheets as Advanced Catalysts: The Role of Mn Incorporation

Herein, bimetallic iron (Fe)-manganese (Mn) oxyhydroxide ((Fe_1-x, Mn_x )OOH, FeMnOOH) nanosheets on fluorine-doped tin oxide conducting substrates and on semiconductor photoanodes are synthesized by a facile, room temperature, electroless deposition method as catalysts for both electrochemical and photo-electrochemical (PEC) water splitting, respectively. Surprisingly, Mn-doped FeOOH can significantly modulate the nanosheet morphology to increase the active surface area, boost more active sites, and augment the intrinsic activity by tuning the electronic structure of FeOOH. Due to the 2D nanosheet architecture, the optimized FeMnOOH exhibits superior electrochemical activity and outstanding durability for the oxygen evolution reaction with a low overpotential of 246 mV at 10 mA cm^-2 and 414 mV at 100 mA cm^-2 , and long-term stability for 40 h without decay, which is comparable to the best electrocatalysts for water oxidation reported in the literature. By integrating with semiconductor photoanodes (such as α-Fe₂ O₃ nanorod (NR) arrays), bimetallic FeMnOOH catalysts achieve solar-driven water splitting with a significantly enhanced PEC performance (3.36 mA cm^-2 at 1.23 V vs reversible hydrogen electrode (RHE)) with outstanding long-term stability (≈8 h) compared to that of the bare Fe₂ O₃ NR (0.92 mA cm^-2 at 1.23 V vs RHE).