Recent progress on metalloporphyrin-based hydrogen evolution catalysis

Designing an energy-efficient and cost-effective system for hydrogen (H2) generation from water or proton source remains as a challenge. Precious and rare earth metals such as platinum as well as iron-dependent hydrogenase enzymes showed high activities and efficiencies for H2 generation at low overpotential. However, Pt-based catalysts are non-affordable for large-scale applications due to limited reserves on earth and high cost. Moreover, hydrogenase enzymes have high molecular weight and relative instability under aerobic conditions. Thus, systematic strategy to design stable molecular catalysts that utilize cheap and earth-abundant transition metals with likely driving force is an attractive approach toward the H2 economy. Accordingly, various transition metal complexes of macrocycles have been extensively reported as catalysts for H2 generation. Metalloporphyrin macrocycles are among the most fascinating organic molecules, which have been employed in the fields of chemistry, materials science and energy relevant catalysis. Most importantly, they have been reported as potential catalysts for H2 generation either in organic solvents or in aqueous solution. Though several porphyrin-based systems have been reported as catalysts under electrochemical or photochemical conditions over decades, there is no an inclusive review and perspective report on the application of metalloporphyrins as catalysts for H2 production. Hence, here in we report the recent progress in potential application of metalloporphyrins as catalysts for H2 evolution under electrochemical and photochemical conditions in aqueous solution or in organic solvents with use of organic acids as proton sources. Moreover, the methods to determine catalytic performance and mechanism of catalysis are discussed in this review.