Selective electro- or photo-reduction of carbon dioxide to formic acid using a Cu–Zn alloy catalyst

Abstract

A copper-and-zinc (Cu–Zn) alloy material was synthesized using a vacuum sealing method, in which evaporated zinc was reacted with copper film or nanoparticles to form a homogeneous Cu–Zn alloy. This alloy was evaluated as an electrocatalyst and/or cocatalyst for photocatalysis to selectively reduce carbon dioxide to formic acid. Based on the optimised alloy composition, the Cu₅Zn₈ catalyst exhibited efficient electrochemical CO₂ reduction. Furthermore, we constructed a photoelectrochemical (PEC) three-electrode system, in which the Cu₅Zn₈ film functioned as the cathode for CO₂ reduction in the dark and strontium titanate (SrTiO₃) served as the photoanode for water oxidation. The PEC system also selectively reduced CO₂ to formic acid with a faradaic efficiency of 79.11% under UV-light and the absence of an applied bias potential. SrTiO₃ particles decorated with nanoparticles of the Cu–Zn alloy also photocatalytically reduced CO₂ to formic acid under UV-light. Isotope trace analysis demonstrated that water served as the electron donor to produce oxygen and organic molecules under UV light, similar to photosynthesis in plants. The Cu–Zn alloy material developed in the present study is composed of ubiquitous and safe materials, and can catalyse CO₂ conversion by means of various kinds of renewable energies.