Shaping the Future of Green Hydrogen Production: Overcoming Conventional Challenges with Molecular Catalysts, Immobilization, and Scalable Electrolyzers

The energy crisis is a daunting global problem that calls for innovative and supportable solutions to ensure future energy security and environmental stability. To counter this energy uncertainty, accelerating renewable-driven hydrogen production stands as a vital option to foster carbon-neutral energy infrastructure. This review conveys an overview of worldwide hydrogen generation techniques (steam methane reformation, thermochemical, biological, and electrolytic), highlighting the key features, indicating the pros and cons, and unraveling the potential environmental consequences. Herein, the conventional gray and cutting-edge green hydrogen production technologies are compared, with a focus on sustainable water electrolysis utilizing renewable energy sources. The existing difficulties with conventional electrolysis, including the usage of expensive catalysts in both cathode and anode, are discussed along with the possible gateway with cost-effective and sustainable electrocatalysts. This review focuses on the potential of three types of 3d transition metal-based molecular catalysts─cobaloximes, iron porphyrins, and nickel bis-phosphines─for hydrogen evolution reactions (HER), stressing their strategic synthetic designs, mechanistic routes, and catalytic parameters. Despite their high activity and selectivity, these molecular systems confront stability and scalability issues, limiting their practical applicability. To address this, the immobilization of these catalysts into solid matrices is studied, simplifying their integration into membrane electrode assembly (MEA) water electrolyzers for industrial-scale renewable-driven hydrogen production. To bridge the gap between lab-scale investigations and commercial implementation, several design components of the MEA stack are examined, such as flow patterns and scaling methodologies. A comprehensive approach to catalyst development and deployment is ensured by highlighting the significance of Life Cycle Assessment (LCA) and Techno-Economic Analysis (TEA) in assessing environmental sustainability and economic viability. The review closes with a call for multidisciplinary research and innovation to improve electrochemical water-splitting technology and accelerate the transition to an enduring hydrogen economy.