Enabling pure CO2 reduction on Ni{Cu}x-YSZ electrode via an oxide-mediated mechanism

Ni-YSZ-based electrodes are well-known as CO2 reduction cathodes. These electrodes require the presence of safe gases such as H2 or CO in the CO2 inlet stream, adding substantial complexity to the devices. Various reasons such as electrode oxidation and coking have been historically attributed to electrode failure in pure CO2 streams. Using operando Raman spectroscopy and online mass spectroscopy, we have shown that Ni-YSZ electrodes can, in fact, be operated within certain limits. Our measurements reveal that under operation conditions, Ni-YSZ, in fact, oxidizes to NiOx-YSZ. However, it is this oxide that enables the CO2 reduction via a surface oxygen and oxygen vacancy-mediated mechanism. The deactivation of the electrode coincides with strongly reducing conditions where the NiOx is reduced to metallic Ni. Cu-infiltration into Ni-YSZ architecture was demonstrated to mitigate the deactivation issue by modulating the Ni-O-Ni bond strengths and forming a more stable oxide on Ni. This oxide with higher stability to reduction continued to carry out CO2 reduction under strongly reducing conditions. The new electrode also demonstrated improved kinetics and stability against carbon deposition via Boudouard reaction.