Enhanced performance of a PtCo recombination catalyst for reducing the H 2 concentration in the O 2 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 H 2 concentration in O 2 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 H 2 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 H 2 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 H 2 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 H 2 concentration in O 2 of about 2.3 %, almost constant through most of the current density range