Resolving the H UPD and H OPD by DEMS to determine the ECSA of Pt electrodes in PEM fuel cells

Abstract

Overpotential deposited hydrogen (H OPD) and underpotential deposited hydrogen (H UPD) are produced together on Pt in acidic media between 0 and 110 mV vs. SHE and cannot be resolved by cyclic voltammetry alone. Differential electrochemical mass spectrometry was demonstrated for the first time to resolve H OPD and H UPD by measuring the H 2 evolved from water by the hydrogen evolution reaction at the cathode (a Pt electrode) of a proton exchange membrane fuel cell (PEMFC). The H UPD at the cathode was thus quantified and determined to form a saturated layer on the Pt surface when the lower potential limit of cyclic voltammetry is below about 70 mV vs. the anode, a dynamic hydrogen electrode. This amount of H UPD can be used to measure the ECSA of a Pt electrode in PEMFC and avoid the error from including H OPD.