Electrocatalytic Conversion of CO2 to Formate on a Pb–Graphite Composite Electrode

Abstract

Among the different approaches for CO₂ emanation alleviation and climate change mitigation, recycling CO₂ into added-value products through electrochemical reduction is promising. This study highlights the conversion of CO₂ to formate using a composite electrode of Pb-graphite in an H-type cell. Different composite electrodes with variable wt % of Pb and graphite were investigated. Electrode characterization using energy dispersive X-ray and Scanning electron microscope provided a porous surface with partially flaky crack morphology and a homogeneous distribution of Pb in the graphite matrix. Absorption of CO₂ by 0.1 M KHCO₃ at 25°C and 1 atm provided a value of 1.434 g/L (30.66 mol/L). Adsorption of the dissolved CO₂ by 50 wt % Pb electrodes demonstrated a saturation capacity of 590 mg/g. Cyclic voltammetry showed a distinct reduction peak of CO₂ at –0.62 V (vs. Ag/AgCl). This peak has increased with an increased amount of absorbed CO₂ in 0.1 M KHCO₃. Linear Sweep Voltammetry provided an irreversible conversion of CO₂ to formate with a peak current of 32.5 mA at a scan rate of 0.1 V/s and 1 M KCO₃. Electrode kinetic analysis proved a Butler–Volmer reduction constant of \(\beta = 0.62\) at 298 K, leading to a differential change in reaction constant with the potential 77.89 \({{{\text{V}}}^{{ - 1}}}{{\;}}{{{\text{s}}}^{{ - 1}}}\). The corresponding current efficiency was varied with a variation of KHCO₃ concentration to yield a value of 96% obtained using 1 M KHCO₃ and 25°C. Therefore, the composite Pb-graphite electrode demonstrated high surface area, minimum mass transfer, and diffusion resistance of the dissolved CO₂ to the electrode surface.