Farid Taherkhani, Fabian Mauss
A novel analytical expression for the surface coverage of metal hydrogen has been derived as a function of the Gibbs free energy of the Tafel step, electrical overpotential, chemical reaction rate constant, and activation energy of the Tafel step for the hydrogen evolution reaction (HER) in alkaline media. Analytical solutions for the surface coverage of metal-hydrogen have been obtained in both the low- and high-temperature limits in terms of the same key parameters. An asymptotic limit of surface coverage as a function of applied overpotential is observed, even at elevated temperatures under alkaline conditions. The HER performance of Ir-Pt nanoalloys supported on different substrates has also been studied in alkaline media. The sensitivity of metal-hydrogen surface coverage to kinetic parameters on three different substrate materials CNTs, Ti sheet, and stainless steel for the Ir-Pt nanocatalyst has been analyzed with respect to overpotential for the HER in water electrolysis in alkaline media by a theoretical approach. The computational results indicate that the sensitivity of surface coverage is closely related to the water dissociation reaction on the catalytic surface, specifically the formation of adsorbed hydrogen on the metal surface and the concurrent release of hydroxide ions. The exchange current density of Ir-Pt nanoalloys in the hydrogen evolution reaction (HER) during water electrolysis in acidic media has been systematically investigated via DFT calculations. The DFT calculation results show that doping Pt with Ir to form Ir-Pt nanoalloys makes a significant contribution to the exchange current density. The DFT results show that the exchange current density of Ir-Pt nanoalloys exhibits a nonmonotonic dependence on Ir content. The calculated DFT exchange current densities for Ir, Pt, and Ir-Pt nanoalloys are in good agreement with available experimental data.