Au-Coordinated Motifs with Optimization of Electronic Structure and Hydrogen Bond Network in Zr-Based Metal–Organic Frameworks for Enhanced Photocatalytic Hydrogen Evolution

Metal-organic frameworks (MOFs) have emerged as prospective candidates for photocatalytic hydrogen evolution, yet their efficiencies are still limited by insufficient charge carrier utilization and a high energy barrier for proton transfer and reduction. In this study, we molecularly engineered the Au-coordinated motifs within Zr-based MOFs (NU) by grafting different N-heterocycle ligands for high-efficiency photocatalytic hydrogen evolution. The introduced pyrazole unit enables the formation of atomically dispersed Au-N/O coordination motifs, which increase the oxidation state of Au sites, facilitating the capture of photogenerated electrons to boost charge separation and transfer as well as subsequent proton reduction. Besides, the formed pyrazole-water interaction strengthens the hydrogen bond network, promoting the Grotthuss proton transport with an activation energy of 0.17 eV. These superiorities endow the optimal Au/NU-2N with an exceptional photocatalytic hydrogen evolution rate of 10.64 mmol g_cat ^-1 h^-1 or 261.43 mmol g_Au ^-1 h^-1 when using ascorbic acid as an electron donor, representing a 158-fold enhancement over the Au/NU benchmark without ligand grafting. In addition, it exhibits a superior apparent quantum yield (AQY) of 1.41% at 400 nm and remarkable durability, maintaining its performance over 64 h of continuous operation. Thus, these performance advantages of Au/NU-2N surpass those of many reported MOF-based photocatalysts. This work demonstrates the great importance of simultaneously optimizing the electronic structure and hydrogen bond network for catalytic sites by ligand coordination, which may inspire more designs of high-efficiency photocatalysts.