Pulse-Mediated Refaceting of Copper. Influence on 5-Hydroxymethylfurfural Electrocatalysis

This work evaluates the impact of the reduction potential (ER) on the pulsed-mediated formation of high-index facet shaped structures on Cu(111) and on a copper polycrystalline electrode in sodium chloride (NaCl) electrolyte. Cyclic voltammetry (CV), electron backscatter diffraction (EBSD), and scanning electron microscopy (SEM) were combined to correlate grain orientation and surface morphology changes with experimental conditions that drive shape formation. Furthermore, we performed a comprehensive voltammetric analysis across a broad range of stepped single-crystal electrodes, demonstrating that blank cyclic voltammograms in NaCl effectively decouple terrace and step contributions on copper. Our results revealed that while chloride tends to form structures comprising (100) terraces and (111) or (110) defects when oxidation-reduction pulses are applied to refacet copper, the deposition rate, determined by the ER, controls the length of the created (100) terraces and defect density. The oxidation and reduction of 5-hydroxymethylfurfural (HMF) were investigated as model structure-sensitive reactions to probe how variations in the terrace-to-defect ratio affect catalytic behavior. Low-coordinated sites promote oxidation of HMF, whereas (100) terraces adjacent to steps lower the onset potential for HMF reduction. By identifying the active surface facets, this work demonstrates that surface structure engineering is a powerful approach to advance electrocatalysis on copper.