A broad parameter range for selective methane production with bicarbonate solution in electrochemical CO2 reduction

Abstract

This study demonstrated the previously unrecognised capability of potassium bicarbonate (KHCO₃) aqueous solutions to assist in the selective generation of methane (CH₄) over a wide range of reaction parameters during electrochemical CO₂ reduction over a bulk polycrystalline Cu catalyst. Compared with the results obtained with potassium chloride (KCl) electrolytes, a 0.5 M KHCO₃ solution maintained a higher faradaic efficiency (FE) for CH₄ production at higher current densities. This trend was further emphasised upon increasing the CO₂ pressure from near-ambient to 3 atm and incorporating stirring. The result was a FE above 50% over a range of current densities from 90 to more than 330 mA cm⁻². The maximum FE reached 80% at 0 °C, while maintaining a broad peak structure when plotted against current density, even over 300 mA cm⁻². The buffering ability of KHCO₃ appears to play an important role in increasing both the reaction rate and the selectivity for CH₄, especially when combined with an optimised CO₂ supply to the electrode and an ideal reaction temperature.