Emergence of Potential-Controlled Cu-Nanocuboids and Graphene-Covered Cu-Nanocuboids under <i>Operando</i> CO₂ Electroreduction.

Abstract

The electroreduction of CO₂ (CO₂RR) is a promising strategy toward sustainable fuels. Cu is the only Earth-abundant and pure metal capable of catalyzing CO₂-to-hydrocarbons conversion with significant Faradaic efficiencies; yet, its dynamic structure under <i>operando</i> CO₂RR conditions remains unknown. Here, we track the Cu structure <i>operando</i> by electrochemical scanning tunneling microscopy and Raman spectroscopy. Surprisingly, polycrystalline Cu surfaces reconstruct forming Cu nanocuboids whose size can be controlled by the polarization potential and the time employed in their <i>in situ</i> synthesis, without the assistance of organic surfactants and/or halide anions. If the Cu surface is covered by a graphene monolayer, smaller features with enhanced catalytic activity for CO₂RR can be prepared. The graphene-protecting layer softens the 3D morphological changes that Cu-based catalysts suffer when exposed to aggressive electrochemical environments and allows us to track the kinetic roughening process. This novel strategy is promising for improving Cu long-term stability, and consequently, it could be used as a platform to ultimately control product selectivity.