Functionally Regulating the Oxygen Defects in High-Entropy Oxide Catalysts for Reverse Water–Gas Shift Conversion

Oxygen defects play a pivotal role in many catalytic processes, particularly the reverse water–gas shift (RWGS) reaction. It is widely acknowledged that the quantity of oxygen defects has a direct impact on the catalyst’s performance. We show here that the functional modulation of the oxygen defects may be more significant than the quantity adjustment. Cr was employed to elicit the structural evolution of high-entropy oxide (HEO) catalysts. At 350 °C, the obtained spinel@rock salt core@shell catalyst achieves a high CO2 conversion of 28.9%, close to the thermodynamic equilibrium conversion of 30%. We demonstrate that two types of oxygen defects, separately responsible for adsorbing CO2 and catalyzing CO2 dissociation, coexist on the HEO’s surface. The incorporation of Cr effectively optimizes the ratio between these two oxygen defects.