On the Origins of Intrinsic Limitations of Electrocatalytic Hydrogen Evolution in Alkaline Media

Electrocatalytic hydrogen evolution reaction (HER) in alkaline media was investigated in comparative relationship to HER in acidic media. Experimentally obtained adsorption free energies for 13 d-metals were used to study the impact of intermediate coverage on HER activity trends, and how activity trends relate to trends in activation energies and preexponential frequency factors. A mechanistic picture of water discharge and adsorbed intermediate formation was analyzed in the light of recent experimental findings with the goal of creating a more comprehensive picture of HER electrocatalysis in alkaline media. Hydrogen evolution reaction in alkaline media is analyzed using: activation energies, preexponential factors, experimentally obtained values of free energies of hydrogen intermediate formation and hydrogen intermediate coverages. Reaction mechanism is proposed suggesting that besides water dissociation and optimal bonding of adsorbed hydrogen intermediate there has to exist at least one more parameter that controls activity tends. image