Threshold catalytic onset of carbon formation on CeO2 during CO2 electrolysis: mechanism and inhibition

Abstract

Carbon deposition from CO and other carbon-containing fuels is a major cause of the performance degradation of catalysts and electrocatalysts in many energy conversion devices, including low-temperature solid oxide cells (LT-SOCs). In this work, we present direct observation of carbon deposition on thin-film CeO₂ electrodes at LT-SOC operating temperatures (450 °C) in a CO/CO₂ atmosphere by in operando X-ray photoelectron spectroscopy. In contrast to the general view that CeO₂ is a carbon tolerant material, significant carbon formation was observed on CeO₂ during CO₂ electrolysis, with no other catalyst present. Moreover, carbon deposition on CeO₂ demonstrated an intriguing threshold onset formation against surface Ce³⁺ concentration. With the aid of Monte Carlo simulations, we propose the neighboring Ce³⁺–Ce³⁺ pairs to be a critical catalytic structure that facilitates carbon deposition from CO. Finally, we propose mitigation of carbon deposition on CeO₂ by doping CeO₂ with non-redox-active cations, and proved this concept using 50% Gd- and 50% Zr-doped CeO₂ as an example system. These findings provide an in-depth understanding of the mechanism of carbon deposition on CeO₂ during electrochemical reactions and can guide the design of carbon-resistant CeO₂-based electrocatalysts.