Phase-Inversion Induced 3D Electrode for Direct Acidic Electroreduction CO2 to Formic acid

Direct electrochemical CO2 reduction to formic acid (FA) instead of formate is a challenging task due to the high acidity of FA and competitive hydrogen evolution reaction. Herein, 3D porous electrode (TDPE) is prepared by a simple phase inversion method, which can electrochemically reduce CO2 to FA in acidic conditions. Owing to interconnected channels, high porosity, and appropriate wettability, TDPE not only improves mass transport, but also realizes pH gradient to build higher local pH micro-environment under acidic conditions for CO2 reduction compared with planar electrode and gas diffusion electrode. Kinetic isotopic effect experiments demonstrate that the proton transfer becomes the rate-determining step at the pH of 1.8; however, not significant in neutral solution, suggesting that the proton is aiding the overall kinetics. Maximum FA Faradaic efficiency of 89.2% has been reached at pH 2.7 in a flow cell, generating FA concentration of 0.1 m. Integrating catalyst and gas-liquid partition layer into a single electrode structure by phase inversion method paves a facile avenue for direct production of FA by electrochemical CO2 reduction.

Automated summary

A 3D porous electrode (TDPE) is prepared by a simple phase inversion method, enabling electrochemical reduction of CO2 to formic acid (FA) in acidic conditions. TDPE with interconnected channels, high porosity, and suitable wettability improves mass transport and creates a higher local pH micro-environment for CO2 reduction compared to other electrode designs. The proton transfer is identified as the rate-determining step at pH 1.8, while not significant in neutral solution, indicating that protons aid the overall kinetics. FA Faradaic efficiency of 89.2% is achieved at pH 2.7 in a flow cell, producing a concentration of 0.1 m. The integration of catalyst and gas-liquid partition layer into a single electrode structure by the phase inversion method provides a facile approach for direct production of FA through electrochemical CO2 reduction.