Temperature, pressure, and adsorption-dependent redox potentials: I. Processes of CO2 reduction to value-added compounds

Abstract

Catalytic conversion of carbon dioxide (CO2) into value-added chemicals and fuels can not only mitigate global warming but also alleviate the energy crisis caused by fossil fuel depletion. Redox potential is a key thermodynamic quantity of CO2 reduction reactions, while currently, only standard reduction potential (25°C, 1 atm, 1 M) is available for application. Herein, it is the first time to report the influence of temperature (0–1000°C), pressure (1–100 atm), and molecular adsorption on the redox potentials of a series of CO2 reduction reactions to form carbon monoxide, formic acid, formaldehyde, methanol, methane, oxalic acid, acetic acid, acetaldehyde, ethanol, ethylene, and ethane. Although almost all gas-phase and aqueous-phase redox potentials decrease with the temperature at an increased rate and increase with pressure at a decreased rate, adsorption-state redox potentials are only sensitive to temperature and no smaller than gas-phase redox potentials. Significant differences of up to 2.35 V with regard to the standard reduction potential would directly affect the thermodynamics and kinetics of reactions. This report will serve as an enriched database of redox potentials for CO2 reduction reactions that allows the use under actual experimental conditions.