Enhanced performance of a PtCo recombination catalyst for reducing the H2 concentration in the O2 stream of a PEM electrolysis cell in the presence of a thin membrane and a high differential pressure

Abstract

High electrochemical efficiency at elevated current densities and low H2 concentration in O2 can be achieved in PEM electrolysis using thin membrane and integrated recombination catalyst. An enhanced PtCo alloy recombination catalyst was synthesized and used at the anode of a membrane-electrode assembly (MEA). This allowed reducing the H2 concentration in the oxygen stream during electrolysis operation with a thin 50 μm perfluorosulfonic acid (PFSA) Aquivion® membrane. Both dual-layer and composite anode configurations (PtCo/IrRuOx) were investigated. The electrochemical performance of the MEAs containing the recombination catalyst was better than a bare MEA while producing a decrease of the H2 content at the anode. This allowed extending the partial load operation down to 5% at 55 °C under a differential pressure of 20 bar. The effects of the cathodic pressure and cell temperature (including evaluation of intermediate temperature operation at 140 °C) on both electrochemical performance and H2 concentration in the anode stream were investigated. An excellent performance of 4 A cm−2 at 1.75 V, at 140 °C, 20 bar cathode pressure, 5.5 bar anode pressure, with 0.6 mg cm−2 overall precious metal catalysts content was recorded. At 140 °C, the MEA also showed a moderate H2 concentration in O2 of about 2.3%, almost constant through most of the current density range.