Renewable Hydrogen for Sustainable Energy: Production Mechanisms, Catalytic Advances, Challenges, and Future Perspectives

The global transition toward sustainable energy systems has intensified interest in renewable hydrogen as a key pathway for reducing greenhouse gas emissions and decarbonizing hard-to-abate sectors. This review critically examines major renewable hydrogen production routes, including alkaline water electrolysis (AWE), proton exchange membrane (PEM) electrolysis, solid oxide electrolysis cells (SOEC), biomass-based conversion, photoelectrochemical water splitting, and biological processes. Particular emphasis is placed on recent advances in catalytic and electrocatalytic materials and their influence on hydrogen-production efficiency, durability, operating flexibility, cost, and scalability. Noble-metal and non-noble-metal catalyst systems, electrode materials, and emerging catalytic strategies are discussed in relation to their suitability for different hydrogen-production technologies and renewable-energy operating conditions. The review further compares the major production pathways in terms of technological maturity, system efficiency, scalability, and compatibility with intermittent renewable energy. Key limitations associated with catalyst degradation, critical-material dependence, hydrogen storage, infrastructure development, and system integration are critically assessed. Current research gaps include the need for more durable and earth-abundant catalysts, improved long-term performance under realistic operating conditions, and stronger integration between materials development and system-level techno-economic requirements. Overall, this review highlights the importance of linking catalytic innovation with electrolyzer design, renewable-energy integration, infrastructure readiness, and sustainability considerations to enable economically viable and scalable renewable hydrogen production.