The efficiency of photocatalytic ammonia (NH₃) synthesis is severely limited by the extremely difficult activation of N₂ owing to its high N≡N triple bond energy. To address this challenge, we propose an N-doping strategy to facilitate the N₂ activation. Our strategy involves optimizing the electronic structure of the metal active sites by modulating the coordination element. First, we introduce five different N-coordination ligands with distinct steric hindrances and N electron densities (2-methylimidazole (MI), isoindolin-1-one (II), 1,2-benzisothiazolin-3-one (BIT), benzo[d]isoxazol-3-ol (BIX), and terephthalamide (TA)) into an amino-functionalized metal–organic framework (MOF), NH₂-MIL-68 (NM), to construct the N-coordination via the partial replacement of the O-coordination in the metal clusters. Electrochemical impedance spectroscopy and photocurrent analysis demonstrate that N-doping enhances electron transfer and carrier separation. Moreover, incorporating ligands with moderate sizes and steric hindrances (II, BIT, and BIX) more effectively boosts the carrier separation efficiency than incorporating small (MI) or large (TA) ligands. Furthermore, the N-doped MOF modified with BIT (in which N exhibits a moderate electron density) exhibits the strongest carrier separation capability. Concurrently, the X-ray photoelectron spectroscopy, density functional theory, and N₂ temperature-programmed desorption results confirm that the established low-electronegativity N-coordination elevates the electron density of the metal active sites, which consequently enhances the N₂ activation process. The systematic optimization of the N-coordinating ligand species and doping concentrations allows the optimal NM-0.5BIT to achieve a NH₃ production rate of 175.5 μmol/(g·h). The proposed N-doping strategy offers several insights into the activation of inert molecules and the development of organic framework photocatalysts.

The rising global energy demand and climate crisis have intensified the need for sustainable technologies to mitigate carbon emissions while enabling renewable energy conversion. Photocatalysis, particularly using solar energy, has emerged as a promising green solution for hydrogen production and CO₂ reduction. Among various semiconductor photocatalysts, cerium oxide (CeO₂) has garnered considerable interest due to its favourable properties, including strong redox capability, high oxygen storage capacity, chemical stability, and earth abundance. However, intrinsic drawbacks such as a wide band gap, limited visible-light absorption, and rapid charge recombination restrict its standalone performance. This review comprehensively examines recent advancements in CeO₂-based photocatalysts, focusing on structural modifications and the formation of heterojunctions, including S-scheme, Type II, and Z-scheme architectures, that enhance charge separation and retain redox potential. Fabrication strategies are broadly classified into bottom-up and top-down methodologies, with particular emphasis on techniques such as sol–gel, hydrothermal, and co-precipitation methods, which are comprehensively discussed for their effectiveness in optimizing morphology and surface activity. Furthermore, the integration of CeO₂ with advanced materials (e.g. g-C₃N₄, Ti₃C₂, Metal–organic frameworks (MOFs)) and defect engineering approaches is highlighted for improving photocatalytic efficiency under solar irradiation. Promising applications in photocatalytic reduction of CO₂ to value-added chemicals and solar-driven catalytic hydrogen evolution are explored. The review also outlines current challenges, such as poor selectivity, low photostability, and scalability, and provides future perspectives on rational design, real-world testing, and eco-friendly fabrication routes to accelerate the deployment of CeO₂-based photocatalytic systems.

The intermittent nature of solar irradiance is a critical constraint for the realization of continuous photocatalytic hydrogen evolution, thus urging the development of more powerful systems persistently active after illumination. This limitation is bypassed in round-the-clock photocatalytic architectures, which incorporate advanced charge storage to de-correlate photon absorption and catalytic turnover time scales. The strategies involve defect-mediated trap states, multi-electron redox processes, radical-dependent stabilization, and an interfacial charge pool in Faradaic junctions to work together, leading to extended hydrogen evolution reaction (HER) in the dark. Long afterglow phosphorescent materials (e.g., Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺) incorporated in heterojunction architectures with type II or Z-scheme band alignments can also promote fast charge separation for energy storage and subsequently enable controlled release after light quenching by the phosphorescent emission. Advances in band-structure engineering, plasmonic coupling, and redox-active interfacial design result in systems with extraordinary stability and catalytic activity under natural day–night cycles. These stable photocatalytic systems offer a fundamentally new strategy for efficient and environmentally benign sunlight-driven fuel production, meeting both performance and sustainability challenges to renewable energy technologies.

This work presents an emerging strategy for round-the-clock hydrogen evolution by integrating long afterglow phosphorescent materials into heterojunction photocatalysts. The system enables sustained HER even in darkness by utilizing defect engineering, Faradaic charge storage, and phosphorescence-driven delayed charge release. This approach offers a breakthrough in decoupling light absorption from catalytic activity, addressing solar intermittency, and paving the way for stable, efficient, and sustainable solar-to-hydrogen energy conversion.