Hydrogen evolution reaction (HER) for electrocatalytic water splitting to produce green hydrogen has recently emerged as a green process to solve energy and environmental issues. In this study, we have developed mononuclear Pt-polyoxometalates of [Pt₁Mo₆(OH)₆O₁₈](NH₄)₂ (PtMo₆) and [Pt₁Mo₆(OH)₃O₁₈)O₃C₅H₉]TBA₂ (PtMo₆-L, TBA: tetrabutylammonium), which are well characterized by various technologies. PtMo₆-L clusters coated onto glassy carbon show good performances in HER, achieving an overpotential of 37 mV@10 mA·cm^–2 with a Tafel slope of 42 mV·dec⁻¹, which outperforms the naked PtMo₆ cluster and is comparable to the commercial 20 wt% Pt/C. PtMo₆-L should obey Heyrovsky-Volmer mechanism that is similar with Pt/C. In contrast, PtMo₆ should adopt Tafel-Volmer mechanism. The experimental results combined with Density Functional Theory calculations corroborate that the Pt-O-H group of polyoxometalate clusters should be the active site and play an important role during the efficient HER. Moreover, mechanistic studies reveal that the more negative charge of the C₅H₉-bonded O1 in PtMo₆-L is prone to adsorb and activate the proton (H⁺), resulting in enhanced electrocatalytic HER activity. In all, these efforts push forward the HER research to study the relationships between polyoxometalate structures and electrocatalytic property at the precise atomic/molecular level.

Iridium-based materials are less studied in proton exchange membrane water electrolyzers (PEMWEs), which are crucial for the generation of green hydrogen, due to their rarity and high cost. Herein, doping Cr with cobalt oxide resulted in rich oxygen vacancies with the Co²⁺/Cr³⁺ redox couples and surface hydroxyl groups, which considerably enhance the capacity of the material to adsorb and activate oxygen intermediates. Due to its structural and electrical characteristics, CrCo₈O_x has proven to be a stable and effective catalyst for acidic oxygen evolution reaction (OER) and high-performance PEMWEs applications. A high current density of 100 mA·cm⁻² was attained by the CrCo₈O_x anode catalyst and maintained for 130 h, whereas a current density of 300 mA·cm⁻² was maintained for 20 h. In situ Fourier transform infrared (FT-IR) spectroscopy combined with density functional theory (DFT) calculations corroborate the oxide path mechanism (OPM) over pristine Co₃O₄ rather than the associative electron mechanism (AEM) over Cr-doped CrCo₈O_x composites. Such outstanding results indicate a bright future for industrial deployment and provide broad recommendations for developing PEMWEs with high efficiency.

Atomically precise metal nanoclusters, consisting of tens to hundreds of metal atoms, represent a unique class of catalytic materials with well-defined electronic structures and tunable surface chemistry. These features enable nanoclusters to act as versatile components in photocatalytic systems, where they regulate light absorption, charge separation, and interfacial reaction dynamics. Photocatalysis provides a sustainable pathway for converting solar energy into fuels and value-added chemicals; however, its practical application is limited by intrinsic thermodynamic and kinetic barriers, as well as catalyst stability and selectivity challenges. Recent advances have spotlighted the integration of nanoclusters with extended porous frameworks, including metal–organic frameworks (MOFs) and covalent organic frameworks (COFs), as a powerful strategy to overcome these limitations. These hybrid architectures allow precise control over active-site geometry, electronic environments, and substrate accessibility, while promoting synergistic effects such as enhanced charge transport and stabilization of reactive intermediates. This review highlights emerging synthetic methodologies, modification strategies, and recent photocatalytic applications (CO₂ reduction, H₂ evolution, H₂O₂ production, organic synthesis, pollutant removal, CH₄ conversion, etc) reported over the past three years. We discuss mechanistic insights, structure–function relationships, and critical challenges, including conductivity, robustness, and scalability. Finally, we propose integrated design principles for constructing hybrid nanocluster–framework photocatalysts with optimized efficiency, selectivity, and durability, offering a roadmap for the rational development of next-generation energy-conversion and chemical-synthesis platforms.