A dual-cathode study on Ag-Cu sequential CO2 electroreduction towards hydrocarbons

Abstract

Electroreduction of CO2 to high value-added products such as hydrocarbons provides a promising way to create a carbon neutral circular economy. Copper (Cu) is the most effective metal catalyst with selectivity towards hydrocarbons but Cu catalyst alone generally produces hydrocarbons at low selectivity and yield. Operando surface enhanced infrared absorption spectroscopic (SEIRAS) analysis reveals that the low hydrocarbon yield is attributed to the poor ability of Cu to produce carbon monoxide (CO), which is a crucial intermediate for hydrocarbon formation. In the current study, an Ag-Cu dual-cathode CO2RR device is developed, which allows separate control of electrode potential. This dual-cathode cell shows increased hydrocarbon yield (83 % for methane and 106 % for ethylene) and a 200 mV lower onset potential for C2H4, compared to electrolysis with a single Cu cathode. The CO produced by the Ag cathode transfers to Cu and increase its CO coverage, facilitating methane formation as well as promoting CC coupling to form ethylene. This study also reveals a mismatch of optimum electrode potential between Ag and Cu, which results in compromised performance of the two components in an Ag-Cu bimetallic electrocatalyst, but poses no challenge in the dual-cathode cell. To optimize the performance of the dual-cathode cell, we propose the use of a single-pass dual-gas-diffusion-cathode reactor with enhanced mass transfer for maximum hydrocarbon production. This work verifies that splitting the complex CO2RR process into two separate steps is a feasible method to improve the overall efficiency and rate of advanced products while reducing the energy input.