Self-supported ultrathin NiCo layered double hydroxides nanosheets electrode for efficient electrosynthesis of formate

Abstract

Electrochemical CO₂ reduction into energy-carrying compounds, such as formate, is of great importance for carbon neutrality, which however suffers from high electrical energy input and liquid products crossover. Herein, we fabricated self-supported ultrathin NiCo layered double hydroxides (LDHs) electrodes as anode for methanol electrooxidation to achieve a high formate production rate (5.89 mmol h⁻¹ cm⁻²) coupled with CO₂ electro-reduction at the cathode. A total formate faradic efficiency of both anode for methanol oxidation and cathode for CO₂ reduction can reach up to 188% driven by a low cell potential of only 2.06 V at 100 mA cm⁻² in membrane-electrode assembly (MEA). Physical characterizations demonstrated that Ni³⁺ species, formed on the electrochemical oxidation of Ni-containing hydroxide, acted as catalytically active species for the oxidation of methanol to formate. Furthermore, DFT calculations revealed that ultrathin LDHs were beneficial for the formation of Ni³⁺ in hydroxides and introducing oxygen vacancy in NiCo-LDH could decrease the energy barrier of the rate-determining step for methanol oxidation. This work presents a promising approach for fabricating advanced electrodes towards electrocatalytic reactions.