Bio-inspired design: bulk iron–nickel sulfide allows for efficient solvent-dependent CO2 reduction

Abstract

The electrocatalytic reduction of carbon dioxide (CO₂RR) to valuable bulk chemicals is set to become a vital factor in the prevention of environmental pollution and the selective storage of sustainable energy. Inspired by structural analogues to the active site of the enzyme CODH_Ni, we envisioned that bulk Fe/Ni sulfides would enable the efficient reduction of CO₂. By careful adjustment of the process conditions, we demonstrate that pentlandite (Fe_4.5Ni_4.5S₈) electrodes, in addition to HER, also support the CO₂RR reaching a peak faradaic efficiency of 87% and 13% for the formation of CO and methane, respectively at 3 mA cm⁻². The choice of solvent, the presence of water/protons and CO₂ solubility are identified as key-properties to adjust the balance between HER and CO₂RR in favour of the latter. Such experiments can thus serve as model reactions to elucidate a potential catalyst within gas diffusion electrodes.