Growth of copper-nickel (Cu-Ni) dual atom catalysts over graphene variants as active anodes for clean oxygen generation: Integrative experimental and computational validation

Abstract

The development of atomically precise metals on the surface of graphene has led to superior electrocatalytic properties for the clean oxygen production. In this study, Cu single-atom and NiCu dual-atom catalysts supported on different graphene variants were effectively developed as electrocatalysts for the production of clean oxygen. Various techniques, including XRD, SEM, Raman, HR-TEM, EXAFS and XPS, were used to characterize these synthesized electrocatalysts. The extent of reduction in graphene oxide (GO) support was confirmed using Raman analysis which demonstrated a greater ID/IG-apparent intensity ratio, indicating that the GO (ID/IG=0.9) has more sp3-hybridized carbon with respect to the rGO (ID/IG= 0.6). The HR-TEM analysis with EDX and STEM data confirmed the dispersion of Cu and NiCu dimer over the surface of graphene variants. XPS and EXAFS studies revealed predominant metallic nature of Cu and NiCu dimer with the synergistic interplay between the constituent atoms. Copper-nickel dimer catalyst supported on reduced graphene oxide (CuNi/rGO) demonstrated the best electrocatalytic performance, where a lower overpotential of 320 mV was observed to reach a current density of 10 mA cm−2 with lowest Tafel slope of 110 mV/dec for oxygen evolution reaction. Good stability was observed after 1000 CV cycles and 50 h of electrolysis in 1.0 M KOH electrolytic solution at an oxidation potential of 1.62 V (vs RHE). Control experiments were also performed using borosilicate pyrex glass and Teflon made electrochemical cells in order to over rule the probable involvement of leached out impurities in OER reaction under extreme alkaline conditions. The calculations obtained from Density Functional Theory (DFT) suggest that the dual-atom catalysts have lower overpotential (0.33 V at Cu-site) with respect to the single-atom catalysts, which agreed well with the experimental results. Also, the Cu-site OER was found to have lower overpotential (0.33 V) than the Ni-site (0.47 V). Thus, this study can provide valuable insights into developing low-cost dual-atom electrocatalysts, where the synergism between constituent elements in the dimer and their stabilization by graphene matrix can be exploited for various electrochemical reactions.