Electrochemical hydrogen pump using SnO2-stabilized CsH2PO4 proton transport membrane: A performance evaluation at 250°C

• Demonstrated a stably functional electrochemical hydrogen pump based on a new SnO 2 -stablized CsH 2 PO 4 (CDP) proton conducting membrane. • Identified degradation mechanisms of the membrane under high current density and low partial pressure of water vapor. • Identified the best working condition for high efficiency and selective hydrogen separation with the new SnO 2 -stabilized CDP based electrochemical hydrogen pump. Proton transport membrane (PTM) based electrochemical cells are a more efficient way to separate hydrogen than conventional porous membrane-based technologies. Herein, we report an investigation on the performance (e.g., hydrogen yield, Faradaic efficiency and stability) of an electrochemical hydrogen pump (EHP) based on super-protonic CsH 2 PO 4 (CDP) and 18wt%SnO 2 -stabilzied CDP (CS-18) PTM under different current densities, voltages, water contents, electrode compositions and H 2 concentrations. The results show that both CDP and CS-18 cells perform well under 10 mA/cm 2 and 0.38 atm of partial pressure of water vapor (p(H 2 O), while under lower p(H 2 O)=0.20 atm, only CS-18 cells can stably operate. Under higher 25 mA/cm 2 and p(H 2 O)=0.20 atm, CS-18 cell also fails to retain its original performance, exhibiting degradation. The reason for the instability under either high current density or low p(H 2 O) is fundamentally rooted in dehydration of the membrane induced by either low p(H 2 O) or electrochemical splitting of H 2 O inside the membrane at potentials higher than 1.23 V. We show that operation at a constant 1 V is a safe way to avoid CDP’s internal water splitting and ensure stable operation. Overall, this work has demonstrated technical feasibility and favorable operating conditions for using CDP, particularly the SnO 2 -stabilzied CDP, to electrochemically separate H 2 from different H 2 -containing sources.