The two-electron reduction of inorganic acids (Hþ) to hydrogen gas (H2) is efficiently
catalyzed by the hydrogenase enzymes in biology . However, the best nonbiological,
heterogeneous catalyst is Pt metal, which serves as the universal standard for
electrochemical potentials in the Normal Hydrogen Electrode (NHE). A longstanding
research goal in the catalysis of multielectron redox processes involving
small gaseous molecules like O2, H2, and N2 has been to discover molecular catalysts
whose activity exceeds that of the best available heterogeneous catalyst and
approaches that of the relevant enzymes .