Synthesis of AuCu nanoalloy and investigation on its electrocatalytic proton reduction and CO2 reduction activity

Identifying efficient catalysts for the H2 evolution reaction and CO2 reduction, which can operate at low overpotential in a neutral or near-neutral pH aqueous solution, represents a significant challenge. This work reports the synthesis of an AuCu nanoalloy in the form of spherical nanoparticles with an average size of ~16.7±0.3 nm. The morphology, crystal structure, and chemical composition of AuCu nanoparticles were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution - high angle annular dark field - scanning transmission electron microscopy (HR-HAADF-STEM), and energy dispersive X-ray (EDX) analysis. The use of AuCu nanoparticles as a catalyst for the H2 evolution and CO2 reduction reactions in a 0.1 M KHCO3 (pH 6.8) solution was investigated. It was found that AuCu nanoparticles catalysed the reduction of CO2 to CH4 at a low cathodic potential of -0.2 V vs. Reversible hydrogen electrode (RHE) with a Faradaic efficiency of 7.1%. However, at low cathodic potentials ranging from -0.2 to -0.5 V vs. RHE, H2 evolution was more favourable than CO2 reduction reactions. Conversely, at higher cathodic potentials, e.g. -0.6 V vs. RHE, the reduction of CO2 to CO was more favourable. The AuCu nanoparticles demonstrate superior CO2 reduction selectivity compared to Au and Cu nanoparticle catalysts. A discussion on potential reaction pathways contributing to the CO2 reduction selectivity is also proposed.