Nanograin-Boundary-Abundant Cu2O-Cu Nanocubes with High C2+ Selectivity and Good Stability during Electrochemical CO2 Reduction at a Current Density of 500 mA/cm2

Surface and interface engineering, especially the creation of abundant Cu⁰/Cu⁺ interfaces and nanograin boundaries, is known to facilitate C₂₊ production during electrochemical CO₂ reductions over copper-based catalysts. However, precisely controlling the favorable nanograin boundaries with surface structures (e.g., Cu(100) facets and Cu[n(100)×(110)] step sites) and simultaneously stabilizing Cu⁰/Cu⁺ interfaces is challenging, since Cu⁺ species are highly susceptible to be reduced into bulk metallic Cu at high current densities. Thus, an in-depth understanding of the structure evolution of the Cu-based catalysts under realistic CO₂RR conditions is imperative, including the formation and stabilization of nanograin boundaries and Cu⁰/Cu⁺ interfaces. Herein we demonstrate that the well-controlled thermal reduction of Cu₂O nanocubes under a CO atmosphere yields a remarkably stable Cu₂O-Cu nanocube hybrid catalyst (Cu₂O(CO)) possessing a high density of Cu⁰/Cu⁺ interfaces, abundant nanograin boundaries with Cu(100) facets, and Cu[n(100)×(110)] step sites. The Cu₂O(CO) electrocatalyst delivered a high C₂₊ Faradaic efficiency of 77.4% (56.6% for ethylene) during the CO₂RR under an industrial current density of 500 mA/cm². Spectroscopic characterizations and morphological evolution studies, together with in situ time-resolved attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies, established that the morphology and Cu⁰/Cu⁺ interfacial sites in the as-prepared Cu₂O(CO) catalyst were preserved under high polarization and high current densities due to the nanograin-boundary-abundant structure. Furthermore, the abundant Cu⁰/Cu⁺ interfacial sites on the Cu₂O(CO) catalyst acted to increase the *CO adsorption density, thereby increasing the opportunity for C-C coupling reactions, leading to a high C₂₊ selectivity.

Molecular dynamics simulations of nanoindentation and scratch in Cu grain boundaries

The dynamic nanomechanical characteristics of Cu films with different grain boundaries under nanoindentation and scratch conditions were studied by molecular dynamics (MD) simulations. The type of grain boundary is the main factor in the control of the substrate atoms with respect to the size of dislocations since the existence of the grain boundary itself restricts the movement associated with dislocations. In this work, we analyzed the transverse and vertical grain boundaries for different angles. From the simulation results, it was found that the sample with a transverse grain boundary angle of 20° had a higher barrier effect on the slip band as compared to samples with other angles. Moreover, the nanoindentation results (i.e., indentation on the upper area) of the vertical grain boundary showed that the force was translated along the grain boundary, thereby producing intergranular fractures.