Direct Atmospheric Pressure Plasma Jet (APPJ) Synthesis of Nanosized CuOx-Ag Composites for Efficient Electrochemical CO2 Reduction to Multi-Carbon Products

Abstract

Atmospheric pressure plasma jet (APPJ) is an emerging technique capable of synthesising ligand-free nanosized composites with controllable configuration ratio. Here, APPJ is used to synthesise and directly deposit CuOx-Ag for electrocatalytic CO2 reduction reaction (CO2RR). The morphology of CuOx-Ag composites evolves from Janus-type to core-shell with higher Cu:Ag precursor ratio. When applied in CO2RR catalysis, the nanoparticles configuration appears to matter more than the exact Cu:Ag composition. The core-shell arrangement is found to have higher C2+ production over Janus-type, predicted due to better Cu retention that remains encircling Ag core after CO2RR. Thorough pre- and post- catalysis electron microscopy investigations revealed that Cu-Ag pairing likely resulted in selective oxidation of Cu, resulting in strained Cu2O-Ag epitaxial relationship that can be retained in the reduced Cu-Ag during CO2RR. On the use of electrochemical methods as convenient “probes” to rationalise CO2RR activity, we found ECSA and EIS measurements to be ineffective in predicting CO2RR product selectivity. Instead, surface charge estimated using modified pulse voltammetry technique is a more suitable probe, where distinct behaviour between Ag and Cu-containing catalysts can be observed. Due to severe reconstruction during catalysis, having a core-shell configuration is found to be more beneficial to the catalysis performance than initial composition. Beyond Cu-Ag, we believe the findings are relevant to many other multi-component catalysts with immiscible constituents.