Activating Ga0.8Ti0.4Nb0.8O4 cathode for direct electrolysis of CO2via electrochemical switching and infiltration of co-catalyst

Abstract

Solid oxide electrolysis cell (SOEC) can efficiently convert CO2 into CO using renewable energy sources. SOECs that operate at around 800 °C and negative bias for CO2 reduction pose demanding requirements on the stability of the cathode. Here, a non-perovskite niobate, Ga0.8Ti0.4Nb0.8O4 (GTN), is developed as a robust cathode that can be activated under a −1.4 V bias at 800 °C for CO2 splitting. A gradual increase in the current density of the electrolysis cell with GTN cathode is accompanied by the partial reduction of Nb5+ to Nb4+ to produce NbO2 and a pseudorutile phase. The coupling of NbO2 nanoparticles and the defective pseudorutile surface layer serves as a good combination for the electrochemical reduction of CO2 at elevated temperatures: the electrolysis performance is slightly enhanced by ionic infiltration of Ni because the in situ grown metallic NbO2 can serve as the electron reservoir, similar to the metal Ni. The presence of CeO2 can increase the activation of CO2 and provide the ionic transport between the interface of the electrolyte and cathode. This work demonstrates a robust niobate that can be reduced by electrochemical switching to reduce the stubborn Nb5+ to produce a composite functional layer for efficient CO2 splitting.