High performing triple-conductive Pr2NiO4+δ anode for proton-conducting steam solid oxide electrolysis cell

The development of proton-conducting solid oxide electrolysis cells for the intermediate-temperature range application is largely hindered by the limited choice of adequate anode materials. In this study, the popular solid oxide fuel cell cathode material Pr2NiO4+δ (PNO) is investigated as the anode for the electrolysis cell, considering its proton-conducting ability. The introduction of protons into the PNO lattice is confirmed through insertion-induced conductivity variation measurements. Good chemical compatibility is verified between PNO and BaZr0.2Ce0.6Y0.2O3−δ (BZCY) proton-conducting electrolyte. Excellent catalytic activity towards water splitting is observed for the PNO–BZCY composite anode, 0.52 Ω cm2 for 550 °C, 0.057 Ω cm2 for 700 °C. The water-splitting process is disclosed by impedance spectroscopy measured under different conditions. Due to proton conduction in PNO, the PNO surface is activated for electrochemical reactions. The non-charge transfer processes account little to the electrode resistance. The performance of the PNO–BZCY anode is determined by two charge transfer processes whose kinetics are governed the electrolyzing potential. This charge transfer-limiting nature is relatively benign since the electrode resistance has been found to exponentially reduce with increasing overpotential. Cathode-supported Ni–BZCY//BZCY//PNO–BZCY thin film electrolyte single cells are fabricated and characterized. ∼95% current efficiency is confirmed. At 700 °C, a current density of 977 mA cm−2 is achieved at a 1.3 V electrolyzing potential, e.g. 0.37 V overpotential, which is one of the best performances of proton-conducting steam electrolysis cells so far. The PNO–BZCY anode accounts only for 16% of the overall polarization resistance at 700 °C. These findings prove that the triple-conductive PNO is a promising anode material for proton-based steam electrolysis cells.