Designing Synergistic Electrocatalysts for H2 Oxidation and Evolution Reactions in Alkaline Media

In this work, we systematically addressed the electrocatalytic activity of different Pt group metals and their alloy catalysts ranging from bulk electrodes and surface-modified electrodes to nanoparticles for the hydrogen oxidation and evolution reactions in alkaline media. Under alkaline conditions, bulk Ir was the best H2 oxidation/evolution catalyst among pure bulk Pt-group metals with the following activity order: Ir > Pt > Rh > Ru > Pd, while Rh/C was the most active one among all carbon-supported pure Pt-group metal catalysts with an activity order: Rh/C > Pt/C > Ir/C > Ru/C > Pd/C due to a nanoparticle size effect. H2 oxidation/evolution kinetics was significantly enhanced on Pt and Ir alloys such as PtRu, IrRu, PtRh, IrRh, PtPd, and IrPd. A synergistic effect for H2 oxidation/evolution reactions on these alloys was observed in which Ru, Rh, or Pd could oxidize adsorbed H atoms at lower potentials due to the oxophilic effect, while Pt and Ir could decrease the H-binding energy, favor H diffusion, and thus enhance the kinetics of adsorbed H oxidation. The catalytic mechanism of hydrogen oxidation and evolution is discussed in terms of oxophilic, electronic, and synergistic effects, based on DFT calculations, kinetic Monte Carlo simulations, surface modification, and differential electrochemical mass spectrometry (DEMS) study of COad stripping. These studies provide a deeper understanding of H2 oxidation/evolution kinetics and mechanism in alkaline media and could thus help tailor and design new active catalysts for alkaline exchange membrane fuel cells (AEMFCs) and alkaline electrolyzers, as well as other electrocatalytic reactions and applications.