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Due to its clean and sustainable nature, solar energy has been widely recognized as a green energy source in driving a variety of reactions, ranging from small molecule activation and organic transformation to biomass valorization. Within this context, organic reactions coupled with H 2 evolution via semiconductor-based photocatalytic systems under visible light irradiation have gained increasing attention in recent years, which utilize both excited electrons and holes generated on semiconductors and produce two types of value-added products, organics and H 2 , simultaneously. Based on the nature of the organic reactions, in this review article we classify semiconductor-based photocatalytic organic transformations and H 2 evolution into three categories: (i) photocatalytic organic oxidation reactions coupled with H 2 production, including oxidative upgrading of alcohols and biomass-derived intermediate compounds; (ii) photocatalytic oxidative coupling reactions integrated with H 2 generation, such as C–C, C–N, and S–S coupling reactions; and (iii) photo-reforming reactions together with H 2 formation using organic plastics, pollutants, and biomass as the substrates. Representative heterogeneous photocatalytic systems will be highlighted. Specific emphasis will be placed on their synthesis, characterization, and photocatalytic mechanism, as well as the organic reaction scope and practical application. 

Hydrogen production from water electrolysis with renewable energy input has been the focus of tremendous attention, as hydrogen is widely advocated as a clean energy carrier. In order to realize large-scale hydrogen generation from water splitting, it is essential to develop competent and robust electrocatalysts that will substantially decrease the overpotential requirement and improve energy efficiency. Recent advances in electrocatalyst design reveal that interfacial engineering is an effective approach in tuning the adsorption–desorption abilities of key catalytic intermediates on active sites, accelerating electron transfer, and stabilizing the active sites for long-term operation. Consequently, a large number of hybrid electrocatalysts consisting of metal/compound interfaces have been demonstrated to exhibit superior performance for electrocatalytic hydrogen evolution from water. This article highlights examples of these hybrid electrocatalysts, including noble metal and non-noble metal candidates interfaced with a variety of compounds. Specific emphasis is placed on the synthetic methods, reaction mechanisms, and electrocatalytic activities, which are envisioned to inspire the design and development of further improved electrocatalysts for hydrogen evolution from water splitting on an industrial scale. 

Electrocatalytic water splitting to produce clean hydrogen is a promising technique for renewable energy conversion and storage in the future energy portfolio. Aiming at industrial hydrogen production, cost-effective electrocatalysts are expected to be competent in both hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs) to accomplish the overall water splitting. Limited by the low tolerance and/or poor activity of most 1st-row transition metal-based electrocatalysts in strongly acidic media, bifunctional electrocatalysts are currently advocated to work at high pH values. Herein, this review summarizes the recent progress of nonprecious bifunctional electrocatalysts for overall water splitting in alkaline media, including transition metal-based phosphides, chalcogenides, oxides, nitrides, carbides, borides, alloys, and metal-free materials. Besides, some prevalent modification strategies to optimize the activities of catalysts are briefly listed. Finally, the perspective on current challenges and future prospects for overall water splitting driven by advanced nonprecious electrocatalysts are briefly discussed.