Enhancing the Understanding of Hydrogen Evolution and Oxidation Reactions on Pt(111) through Ab Initio Simulation of Electrode/Electrolyte Kinetics

The hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) play an important role in hydrogen based energy conversion. Recently, the frustrating performance in alkaline media raised debates on the relevant mechanism, especially on the role of surface hydroxyl (OH*). We present a full pH range electrode/electrolyte kinetics simulation for HER/HOR on Pt(111), with the potential-related rate constants been calculated with density functional theory methods. The polarization curves agree well with the experimental observations. The stability of OH* is found to be unlikely an effective activity descriptor since it is irrelevant to the onset potential of HOR/HER. Degree of rate control analyses reveal that the alkaline current is controlled jointly by Tafel and Volmer steps, while the acidic current solely by Tafel step, which explains the observed pH-dependent kinetics. Therefore, it is also possible to reduce the overpotential of alkaline HER/HOR by accelerating the Tafel step besides tuning the hydrogen binding energy.