Hydrogen Oxidation Reaction on Pt and Pt Alloys and the Role of Cations in Alkaline Media

Abstract

Hydrogen oxidation/evolution reactions (HOR/HER) are the main key for the hydrogen economy in thefuture. The control of an efficient hydrogen generation from water and of its reverse reaction, particularlyin fuel cells, is still insufficient. For instance, very low Pt loadings are required for the HOR in protonexchange membrane fuel cells,1 whereas the HOR kinetics change tremendously in alkaline media andbecome at least two order of magnitudes slower.2 To design catalyst materials with improved HOR/HERperformance in alkaline conditions, a deeper understanding about the reaction mechanism and kinetics isneeded. This includes to uncover the significant role of cations during the HOR in alkaline media.3 Firstly, we have studied the effect of monovalent cations on the HOR kinetics on polycrystalline and nanosizedplatinum in different alkaline solutions (MOH, M = K+, Na+, Li+). Depending on the cations, weobserved a significant change of the HOR activity and activation energy for the Pt. More precisely, theHOR activity of Pt increases in the order of K+ < Na+ < Li+, respectively, while the activation energysimultaneously decreases in the same order. We suggest that the catalytic properties of the Pt are stronglyinfluenced by non-covalent interactions of the hydrated cations with the adsorbed hydrogen by the hydrogenbond formation. In the second part, various Pt-Co alloys were investigated for the HOR/HER in alkalinemedia using rotating disc electrode set up. Our results show that the HOR/HER performance can be tunedby variation of atomic Pt & Co arrangements like core-shell, segregation and alloy nanoparticles. Wedeveloped a multi-dimensional matrix to clarify the relationship between structural parameters and catalyticHOR activities for the Pt-Co nanoparticles.The combination of both works allows to provide a deeper understanding about the mechanism and kineticsof the HOR/HER for Pt and Pt alloys in alkaline media.