Complexes of earth-abundant metals for catalytic electrochemical hydrogen generation under aqueous conditions

Growing global energy demands and climate change motivate the development of new renewable energy technologies. In this context, water splitting using sustainable energy sources has emerged as an attractive process for carbon-neutral fuel cycles. A key scientific challenge to achieving this overall goal is the invention of new catalysts for the reductive and oxidative conversions of water to hydrogen and oxygen, respectively. This review article will highlight progress in molecular electrochemical approaches for catalytic reduction of protons to hydrogen, focusing on complexes of earth-abundant metals that can function in pure aqueous or mixed aqueous–organic media. The use of water as a reaction medium has dual benefits of maintaining high substrate concentration as well as minimizing the environmental impact from organic additives and by-products.