Toward economically viable green hydrogen production: enhanced catalytic atom-efficiency, dual-functional systems, and non-traditional water sources.

The light-driven hydrogen evolution reaction (HER) represents a promising renewable energy conversion technology to combat the global energy crisis, particularly as the field shifts toward utilizing abundant water sources including wastewater and seawater rather than freshwater. However, achieving an economically viable levelized cost of hydrogen (LCOH) requires overcoming several fundamental challenges. First, the leading photocatalytic systems rely heavily on Pt cocatalysts to achieve sufficient surface reaction kinetics, the scarcity and high cost of which severely limit scalability. Second, conventional photocatalytic HER systems consume sacrificial agents (e.g., Na2S, Na2SO3, and TEOA) as hole scavengers, elevating the LCOH through continuous reagent consumption while forfeiting opportunities for value creation. Third, the extensive usage of freshwater in the HER process competes with the freshwater usage for humans and agricultural purposes. In this review, we briefly introduce the fundamentals of the light-driven HER process and establish a set of standardized parameters for evaluating both photocatalytic performance and techno-economic feasibility. Subsequently, we systematically review the recent advances in three key areas: (1) strategies for enhancing the catalytic atom-efficiency, (2) innovative dual-functional photocatalytic systems that productively harness photogenerated holes to synthesize value-added products, including through the utilization of wastewater, and (3) seawater-based feedstocks. By integrating LCOH analysis with technical performance evaluation across diverse strategies and water sources, this review aims to accelerate the transition toward sustainable, green and cost-competitive photocatalytic hydrogen production.