Temperature-Dependent Pathways in Carbon Dioxide Electroreduction

Abstract

Temperature affects both the thermodynamics of intermediate adsorption and the kinetics of elementary reactions. Despite its extensive study in thermocatalysis, temperature effect is typically overlooked in electrocatalysis. This study investigates how electrolyte temperature influences CO₂ electroreduction over Cu catalysts. Theoretical calculations reveal the significant impact of temperature on *CO and *H intermediate adsorption thermodynamics, water microenvironment at the electrode surface, and the electron density and covalent property of the C–O bond in the *CH–COH intermediate, crucial for the reaction pathways. The theoretical calculations are strongly verified by experimental results over different Cu catalysts. Faradaic efficiency (FE) toward multicarbon (C₂₊) products is favored at low temperatures. Cu nanorod electrode could achieve a FE_C2+ value of 90.1% with a current density of ~ 400 mA cm^− 2 at − 3°C. FE_C2H4 and FE_C2H5OH show opposite trends with decreasing temperature. The FE_C2H4/FE_C2H5OH ratio can decrease from 1.86 at 40°C to 0.98 at − 3°C. Introduction Electrochemical CO₂ reduction reaction (CO₂RR) into high-value products stands as one of the most promising strategies for mitigating CO₂ emissions through the utilization of renewable electricity^1–2. CO₂RR is a complex process involving multiple reaction pathways that harvest a diverse array of chemical products^3–4. However, the simultaneous occurrence of various CO₂RR routes alongside the hydrogen evolution reaction (HER) can diminish the selectivity toward desired products^5–8. The adsorption behavior of carbonous intermediates and the intricate water microenvironment at the electrode surface are pivotal factors for influencing these reaction pathways, thereby dictating the distribution of products^9–12. By far, researchers have developed a wide range of electrode materials and electrolytes tailored to finely control intermediate adsorption and the water microenvironment on the electrode surface^13–16. These advancements hold significant promise for steering the CO₂RR pathway toward desired product with enhanced efficiency and selectivity. The adsorption or dispersion of intermediates, as well as the water microenvironment, are significantly influenced by temperature since they are thermodynamically controlled^17–19. For instance, both C₂H₄ and C₂H₅OH share the same precursor *CH–COH, leading to their simultaneous production^20–23. The kinetics of their distinct reduction pathways can be influenced by temperature, offering a feasible means to control the ratio of C₂H₄ to C₂H₅OH. Hence, adjusting the temperature of the electrolyte to regulate both thermodynamic and kinetics processes emerges as a potent method for steering the CO₂RR pathway. Consequently, a comprehensive investigation into the relationship between performance and temperature is crucial, providing invaluable insights and guiding significance for optimizing CO₂RR performance^{4, 24}. CO₂RR experiments are typically conducted at room temperature, which can vary, for example from − 3°C to 40°C, depending on seasons and regions. The environmental temperature, typically indicated by the electrolyte temperature, can significantly influence the performance of CO₂RR, yet it is often ignored in CO₂RR studies^25–28. In this study, we systematically investigated the impact of temperature on CO₂RR performance. We initiated our study with theoretical calculations, including density functional theory (DFT) and molecular dynamics (MD) simulations, to explore the impact of temperature on intermediate adsorption and kinetics of elementary reactions in CO₂RR. Subsequently, Cu catalysts were synthesized and employed for CO₂RR at various temperatures. The theoretical findings aligned well with experimental observations, indicating that lower temperatures favor C₂₊ production and promote the formation of C₂H₅OH over C₂H₄. For instance, a Faradaic efficiency toward multicarbon products (FE_C2+) of 90.1% was achieved with a current density of ~ 400 mA cm^− 2 at − 1.3 V vs RHE over a Cu nanorod (Cu-NR) electrode at − 3°C. Moreover, the FE_C2H4/FE_C2H5OH ratio decreases gradually from 1.86 to 0.98 in 1 M KOH as the temperature decreases from 40°C to − 3°C. Further characterizations, including in situ surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), in situ Raman spectroscopy and electrochemical analysis, provide a comprehensive understanding of the temperature effect on CO₂RR performance.