Hydrogen Electrooxidation under Conditions of High Mass Transport in Room-Temperature Ionic Liquids and the Role of Underpotential-Deposited Hydrogen

Abstract

The hydrogen oxidation reaction (HOR), an electrocatalytic reaction of fundamental and applied interest, is studied in the protic ionic liquid (PIL) diethylmethylammonium trifluoromethanesulfonate, [dema][TfO], at Pt electrodes using rotating disk electrode (RDE) and ultramicroelectrode (UME) voltammetry. A steady-state HOR current is observed during RDE voltammetry at overpotentials >50 mV but an additional plateau is observed in the overpotential region 50–200 mV when using UMEs. The difference in voltammetric responses is attributed to higher rates of mass transport to the UMEs than to the RDE. Three models have been used to fit the experimental data. The first is a dual-pathway model, which assumes that the Tafel–Volmer and Heyrovsky–Volmer pathways are both active over the potential range of interest and no blockage of catalytic sites occurs during the reaction. The second is a dual-pathway model, which assumes that reaction intermediates block access of H2 to catalytic sites. The third is based on t...