A Cobalt-Based Metal-Organic Framework as Cocatalyst on BiVO₄ Photoanode for Enhanced Photoelectrochemical Water Oxidation

A metal-organic framework (MOF)-modified bismuth vanadate (BiVO₄ ) photoanode is fabricated by an ultrathin sheet-induced growth strategy, where ultrathin cobalt oxide sheets act as a metal source for the in situ synthesis of Co-based MOF poly[Co₂ (benzimidazole)₄ ] (denoted [Co₂ (bim)₄ ]) nanoparticles on the surface of BiVO₄ . [Co₂ (bim)₄ ] with small particle size and high dispersion can serve as a promising cocatalyst to accept holes transferred from BiVO₄ and boost surface reaction kinetics for photoelectrochemical (PEC) water oxidation. The photocurrent density of a [Co₂ (bim)₄ ]-modified BiVO₄ photoanode can achieve 3.1 mA cm^-2 under AM 1.5G illumination at 1.23 V versus the reversible hydrogen electrode (RHE), which is better than those of pristine and cobalt-based inorganic materials-modified BiVO₄ photoanodes. [Co₂ (bim)₄ ], with porosity and abundant metal sites, exhibits a high surface charge-separation efficiency (83 % at 1.2 V versus RHE), leading to the enhanced PEC activity. This work will bring new insight into the development of MOF materials as competent cocatalysts for PEC water splitting applications.