(Physical and Analytical Electrochemistry Division David C. Grahame Award) Kinetics of the Hydrogen Oxidation in Alkaline and Acid Electrolytes

Abstract

The development of fuel cells based on alkaline membranes (AMFCs) is one of the options to reduce the required amount of platinum, whereby the strong CO2sensitivity of alkaline membranes is a significant challenge. However, while there are several non-noble metal catalysts for the oxygen reduction reaction in alkaline electrolytes which match the activity of platinum, the only currently known hydrogen oxidation catalysts are based on platinum or palladium. Furthermore, the activity of platinum is orders of magnitude lower than in acidic electrolytes [1,2,3], so that ultra-low platinum loading anodes which can be used in acidic electrolytes (PEMFC) are not feasible in alkaline electrolytes. Therefore, the challenge to catalysis research for alkaline membrane fuel cells is to develop more active hydrogen oxidation catalysts. In our presentation, we will compare the kinetics of the H2 oxidation/evolution reaction (HOR/HER) on carbon supported platinum-group metal electrocatalysts in alkaline and acid electrolytes, determined by rotating disk electrode measurements in liquid electrolytes and hydrogen-pump measurements in fuel cells. The so far proposed causes for the »100-fold lower HOR/HER kinetics in alkaline electrolyte are an increased H/metal bond strength [1,4], a change of the reaction mechanism from H+ to H2O activation requiring more oxophilic catalyst surfaces [5], and/or a change of the water configuration at the metal/electrolyte interface [6]. The consistency of these hypotheses with the HOR/HER kinetics on different metal electrodes will be discussed.