Influence of Acetonitrile on Cu Electrochemical Nucleation and Growth: Preliminary Test of Catalytic Activity for eCO2RR

Abstract

In this study, the nucleation and growth mechanisms of copper on a glassy carbon (GC) electrode from mixed acetonitrile–water (AN/H₂O) solutions were investigated using cyclic voltammetry (CV), chronoamperometry (CA) and scanning electron microscopy (SEM). The mechanism of copper nucleation in the AN and 70:30 AN/H₂O solutions is progressive, whereas for the 50:50, 60:40 and 80:20 AN/H₂O solutions, it is close to the mixed mechanism. The nucleation parameters, including the nucleation rate, nucleation density and average radius of active nuclei centres, were calculated using a three-dimensional electrochemical nucleation model developed by Scharifker-Hills, in accordance with the identified mechanism. The experimental results demonstrated that the average radius of electrodeposited particles could be reduced from 10.8 to 3.2 µm by shifting the applied potential to the negative region, from −0.43 to −0.48 V in a solution of 0.01 M CuCl₂ + 0.5 NaClO₄ + 70:30 AN/H₂O. SEM images of the obtained coatings demonstrated the formation of uniformly distributed “monanthes-like” structures of copper particles. The catalytic activity of the Cu electrocatalysts were determined by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) methods in a 0.5 M NaHCO₃ solution saturated with CO₂ under bulk electrolysis conditions. LSV shows that the Cu catalyst electrodeposited from 50:50 AN/H₂O mixture exhibited the best performance for electrochemical CO₂ reduction reaction (eCO₂RR) with a Tafel slope of 168 mV dec⁻¹, exchange current density of 6.81 \(\times\) 10⁻⁴ A cm⁻² and charge transfer resistance of 9.4 Ω cm². This study may provide an economical approach for developing low-cost and efficient copper-based electrocatalysts for CO₂ electroreduction.

Graphical Abstract