This comprehensive review provides a deep exploration of the unique roles of single atom catalysts (SACs) in photocatalytic hydrogen peroxide (H₂O₂) production. SACs offer multiple benefits over traditional catalysts such as improved efficiency, selectivity, and flexibility due to their distinct electronic structure and unique properties. The review discusses the critical elements in the design of SACs, including the choice of metal atom, host material, and coordination environment, and how these elements impact the catalytic activity. The role of single atoms in photocatalytic H₂O₂ production is also analysed, focusing on enhancing light absorption and charge generation, improving the migration and separation of charge carriers, and lowering the energy barrier of adsorption and activation of reactants. Despite these advantages, several challenges, including H₂O₂ decomposition, stability of SACs, unclear mechanism, and low selectivity, need to be overcome. Looking towards the future, the review suggests promising research directions such as direct utilization of H₂O₂, high-throughput synthesis and screening, the creation of dual active sites, and employing density functional theory for investigating the mechanisms of SACs in H₂O₂ photosynthesis. This review provides valuable insights into the potential of single atom catalysts for advancing the field of photocatalytic H₂O₂ production.

The development of cost-effective and high-performance catalysts for the production of hydrogen via electrocatalytic water splitting is crucial for meeting the increasing energy demand and expanding the hydrogen economy. In this study, a series of metal-free carbon nanotube (CNT) catalysts were designed and in situ functionalized by imidazolium ionic liquids (ILs) for enhanced electrocatalytic hydrogen evolution reaction (HER). The theoretical calculations and experimental results reveal that the functionalization of CNTs with imidazolium ILs facilitated the electron transfer process and exhibited superior hydrogen adsorption, thereby enhancing the performance of the HER. In particular, CNT-IM-Cl displays excellent electrocatalytic activity and shows a low onset overpotential and Tafel slope of 80 mV and 38 mV dec⁻¹, respectively. This study highlights the significant potential of IL in situ functionalized metal-free CNTs for the electrocatalytic HER and provides insight into the structure design of highly efficient electrocatalysts.