Cobalt Hydroxide‐Organic Frameworks Powering Improved Charge Transfer and Oxygen Evolution Kinetics in Photoelectrochemical Water Splitting

Severe charge carrier recombination and sluggish water oxidation kinetics are two critical factors limiting the efficiency of photoanodes for photoelectrochemical (PEC) water splitting. Herein, to address these two issues, a thin layer of cobalt-based metal hydroxide-organic framework, namely cobalt hydroxide-cyanurate framework (Co-HCF), is successfully grown onto the surface of the promising BiVO₄ photoanode via a simple alcohol-mediated solvothermal route. When used for PEC water oxidation, the optimized Co-HCF/BiVO₄ achieved a remarkable photocurrent density of 6.55 mA cm^-2 at 1.23 V versus RHE under AM 1.5 G illumination. This performance not only sets a new record for cobalt-catalyzed undoped BiVO₄ photoanodes, but also surpasses that of all previously reported undoped BiVO₄ photoanodes modified with conventional transition metal (oxy)hydroxides or metal-organic frameworks. Further mechanistic studies reveal that the enhanced PEC water splitting performance arises from the unique microstructure and intriguing physicochemical properties of Co-HCF, which collectively facilitate interfacial charge transfer and lower the kinetic barrier for water oxidation. This work highlights an effective pathway for the design and fabrication of promising metal hydroxide-organic frameworks as oxygen evolution cocatalysts for efficient solar energy conversion.