Manipulating the Morphology and Electronic State of a Two-Dimensional Coordination Polymer as a Hydrogen Evolution Cocatalyst Enhances Photocatalytic Overall Water Splitting

To achieve efficacious photocatalytic overall water splitting, surface modification of photocatalysts with proficient cocatalysts for hydrogen evolution reaction (HER) is imperative. NiBHT, a conductive two-dimensional coordination polymer (2D CP), or a 2D metal-organic framework (2D MOF), endowed with remarkable chemical stability and HER selectivity, emerged as a promising candidate for an HER cocatalyst. However, the bulky morphology of NiBHT hampered its performance. Here, we demonstrate a strategy to miniaturize NiBHT by incorporating the benzene-1,2-dithiol (BDT) ligand, yielding NiBHT nanoparticles (NiBHT-NP). Beyond morphology, empirical evidence unveiled alterations in the electronic state and catalytic activity of NiBHT-NP, and the ramifications of BDT modulation on intrinsic characteristics are elucidated through density functional theory (DFT) calculations. As a model system, CoO_x/SrTiO₃:Al photocatalyst with NiBHT-NP modification exhibited an apparent quantum efficiency (AQE) of 10.3% at 365 nm for overall water splitting. This pioneering work showcases that a modulator ligand may manipulate the morphology, electronic state, and catalytic behavior of 2D CPs, holding prodigious potential for developing more effective CP-based HER cocatalysts.