Hydrogen generation promoted by single-atom-based thermochemical catalysts

Supplying energy in a clean and affordable manner, without damaging the environment, is one of the most pressing problems society now faces. Hydrogen can facilitate a low-carbon or net-zero emissions future; however, producing it on demand and in large quantities from thermodynamically stable gaseous-state, liquid-state and solid-state sources presents challenges, both environmentally and economically. Numerous catalytic routes have been proposed to promote H₂ production efficiently, and considerable improvements have been achieved by harnessing atomic-level catalysts. This Review presents an account of the advancements achieved for current and potential future H₂-generation technologies by incorporating single-atom-based catalyst materials. The reactions considered herein include a wide range of established and advanced reforming, partial-oxidation and direct dehydrogenation of various forms of hydrogen-containing substances. The relevant fundamental catalytic reaction mechanisms along with maximum-achievable H₂ capacities, high-performing catalyst materials and structure-activity insights are discussed. Further perspectives on the different processes are provided to include CO₂ emissions, techno-economics, environmental impact, low-carbon and waste-based production, concomitant CO₂ capture, and CO_x elimination and H₂ purification, along with cost and scalability factors of the catalysts.