Activating Ga0.8Ti0.4Nb0.8O4 cathode for direct electrolysis of CO2 via electrochemical switching and infiltration of co-catalyst

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, Ga_0.8Ti_0.4Nb_0.8O₄ (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.