Lawrence Berkeley National Laboratory

Suppressing Ce ³⁺ –Ce ³⁺ pair formation avoids carbon deposition on CeO ₂ -based electrode during CO ₂ electrolysis, found by in operando X-ray photoelectron spectroscopy.

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 CeO ₂ electrodes at LT-SOC operating temperatures (450 °C) in a CO/CO ₂ atmosphere by in operando X-ray photoelectron spectroscopy. In contrast to the general view that CeO ₂ is a carbon tolerant material, significant carbon formation was observed on CeO ₂ during CO ₂ electrolysis, with no other catalyst present. Moreover, carbon deposition on CeO ₂ demonstrated an intriguing threshold onset formation against surface Ce ³⁺ concentration. With the aid of Monte Carlo simulations, we propose the neighboring Ce ³⁺ –Ce ³⁺ pairs to be a critical catalytic structure that facilitates carbon deposition from CO. Finally, we propose mitigation of carbon deposition on CeO ₂ by doping CeO ₂ with non-redox-active cations, and proved this concept using 50% Gd- and 50% Zr-doped CeO ₂ as an example system. These findings provide an in-depth understanding of the mechanism of carbon deposition on CeO ₂ during electrochemical reactions and can guide the design of carbon-resistant CeO ₂ -based electrocatalysts.