Molecular Catalysts for the Hydrogen Evolution Reaction: A First-Principles Study.

Molecular catalysts can be used in solution to promote the hydrogen evolution reaction (HER) through electrolysis and photocatalysis. We study the HER from first-principles for four different molecular catalysts, each composed of a transition metal atom and two organic ligands: Co-(bpy)2, Co-(PyDAT)2, Ni-(PyDAT)2, and Cu-(PyDAT)2. By computing the Gibbs free energy from density functional theory (DFT) at every step of the HER, we identify the protonation sites and the most favorable catalytic pathway on the different catalysts. We compare the efficiency of the different catalysts from their energetic span and from their potential-pH diagrams, showing the operating conditions that make the HER spontaneous. We find that both the nickel- and copper-based systems offer a viable alternative for HER molecular catalysts free of precious metals.