Optimization of electrochemical reduction of high-pressure CO2 to hydrocarbon (methane) at nickel electrode in cold methanol

Abstract

Electrochemical reduction of CO2 in conventional aqueous electrolytes is often limited by low CO2 solubility and the competing hydrogen evolution reaction (HER). To address these challenges, we investigated CO2 electroreduction on a Ni electrode in a nonaqueous methanol/LiCl electrolyte under high CO2 pressure (1.0 MPa) and low-temperature conditions (258–288 K). The combined effects of temperature and applied potential on electrochemical behavior, product distribution, and reaction selectivity were systematically evaluated. Cyclic voltammetry (CV) revealed pronounced temperature-dependent changes in reduction characteristics, indicating significant modifications in interfacial charge-transfer processes and CO2 activation kinetics. Product analysis confirmed HCOOCH3, CH4, and CO as the primary carbon-containing products, with their formation strongly influenced by both temperature and cathodic potential. Lower temperatures substantially enhanced carbon-product generation while suppressing the competing hydrogen evolution reaction, leading to maximum faradaic efficiencies of approximately 15% for HCOOCH3 at 258 K and −1.8 V and 13% for CH4 at 258 K and −2.0 V. The improved performance is attributed to enhanced CO2 solubility and availability in the methanol-based electrolyte under high-pressure, low-temperature conditions, together with favorable modulation of interfacial reaction pathways. These findings demonstrate that simultaneous control of pressure, temperature, and electrolyte environment provides an effective strategy for tuning CO2 reduction selectivity in nonaqueous systems. This work offers valuable insights into the mechanistic aspects of pressure- and temperature-assisted CO2 electroreduction and highlights methanol/LiCl electrolytes as promising media for selective CO2-to-fuel conversion.