Hydrogen Oxidation and Evolution Reaction Kinetics on Carbon Supported Pt, Ir, Rh, and Pd Electrocatalysts in Acidic Media

The hydrogen oxidation and evolution reaction (HOR/HER) behavior of carbon supported metal (Pt, Ir, Rh, Pd) nanoparticle electrocatalysts is studied using the H 2 pump approach, in a proton exchange membrane fuel cell (PEMFC) setup. After describing the best method for normalizing the net faradaic currents to the active surface area of the electrodes, we measure the HOR/HER kinetic parameters (exchange current densities and transfer coefficients) in a temperature range from 313 K to 353 K and calculate the activation energy for the HOR/HER process. We compare the measured kinetic parameters with those extracted from different mass-transport limitation free setups in literature, to evaluate the hydrogen electrocatalysis on these most active surfaces. The HOR/HER activity scales with the following: Pt > Ir ≫ Rh > Pd. The anodic and cathodic transfer coefficients are similar for all metals (ca. 0.5), leading to Tafel slopes of ca. 140 mV/decade at 353 K (except for the anodic branch of Pd and the cathodic branch of Rh). The lowest activation energies are found for Pt and Ir (≈20 kJ/mol). For Rh and Pd, higher activation energies are found (≈30 kJ/mol), and attributed to the formation of surface oxides and hydride phase, respectively.