Advanced bifunctional catalysts for energy production by electrolysis of earth-abundant water

Hydrogen production employing non-carbon materials has tremendous promise toward the sustainable Future. Conventional technology relies on water splitting (WS) for hydrogen generation, yet the process of electrochemical water splitting falls short of efficient H-2 production. In order to address this challenge, there is an urgency to engineer cost-effective and highly efficient bifunctional catalyst materials. These catalysts are pivotal in replacing precious metal-based catalysts in the electrochemical WS process. This manuscript elaborately reviews the development of bifunctional catalysts, analyzing their roles as both anode and cathode catalysts in the electrochemical WS process. The historical context of hydrogen production, hydrogen, and oxygen evolution reactions in both acidic and alkaline electrolytes, and the electrochemistry of water splitting reactions are discussed. The current landscape of WS electrolyzers and their limitations is also presented. In the pursuit of enhanced catalysis for water splitting reaction, diverse materials have emerged, including noble metal-based catalysts, carbon-encapsulated catalysts, and non-precious transition metal-based catalysts with various heteroatom dopants. This review encompasses their design strategies, synthetic methods, and associated challenges. The significance and advantages of organic-based macrocycles is also mentioned. To summarize, the review sheds light on the challenges posed by bifunctional catalysts for WS reactions related to materials' design, development, and future prospects. This review offers insights into design, fabrication and efficiency of advanced catalysts for renewable hydrogen energy and water splitting reactions."