This work evaluates the impact of the reduction potential (E_R) on the pulse-mediated formation of high-index facet structures on Cu(111) and 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 have performed a comprehensive voltammetric analysis across a broad range of stepped single crystal electrodes, demonstrating that blank CVs of the Cu | 0.1 M NaCl interface effectively decouple terrace and step contributions on copper. Our study revealed that while chloride tends to induce structures comprising (100) terraces and (111) or (110) steps under oxidation–reduction potential pulse conditions, the deposition rate, determined by the E_R, controls the length of the generated (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 behaviour. Low-coordinated sites promote oxidation of HMF, whereas (100) terraces adjacent to steps decrease 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.

Electrochemical oxidation-reduction processes on copper electrodes and in the presence of different electrolyte anions have been widely explored for the preparation of tailor-made catalysts. Nevertheless, the effect of the electrode surface structure and electrolyte on the growth of new crystalline domains on copper remains under discussion. In this work, we have modified a Cu(111) single crystalline electrode with chloride by using the square-wave potential method, aiming to reach a higher control on the formation of shape structures. In particular, we have modified the single-facet surface by applying potential pulses with a frequency of 1 Hz and between -1.3 V and 0.5 V vs SCE. Then, we evaluated the formation of new structures with scanning electron microscopy after different times of applied potential pulses. The morphology analysis revealed the formation of hexagonal micro and nanoclusters homogeneously distributed on the surface. These clusters were similar to tetrahexahedral particles embedded in the (111) plane. Moreover, we also observed a shape transformation from a hexagonal particle to a triangular pyramid, showing that crystal growth and evolution are time and structure dependent. Herein, we provide experimental insights on the preparation of (n10) micro and nanostructures of copper using the square-wave potential method. The present work offers a straightforward approach that enables precise control over the rational preparation of copper surfaces.

Electrolyte effects play a fundamental role in electrocatalysis, influencing reaction kinetics, selectivity and catalyst stability by altering interfacial interactions and charge distribution. Here we report recent advances to rationalize non-covalent interactions between electrolyte and surface adsorbates in electrocatalysis. Three main schools of thought have rationalized the effect of electrolyte–adsorbates–surface interactions on the reaction kinetics, each based on different descriptors. The first suggests that non-covalent interactions with the electrolyte modify the binding energies of the adsorbed intermediates. The second highlights the role of charge and electric fields near the electric double layer, shaped by the potential of zero charge, in stabilizing the polar adsorbates and governing proton transfer. The third focuses on energy barriers arising from the restructuring of the water solvation spheres of both electrolyte and reactants. We critically examine the main arguments and limitations of each framework, with a focus on hydrogen evolution and carbon dioxide reduction, and outline experimental challenges and future directions for elucidating electrolyte effects in electrocatalysis.

Here, we highlight 35 global researchers approximately under the age of 35. This third annual cohort was self-generated by initial seed invitations sent by the editorial team, with each contributor suggesting two more in a nominally supervised self-selecting pyramid-like scheme. The final collection reflects both the diversity and excitement across the field of materials science.

Copper is an active electrocatalyst for various energy conversion reactions, but its performance depends on the structure of the active surface sites. In this work, we propose a simple strategy to tailor both the roughness and the active site's geometry of copper. To modify the surface of copper, we oxidize and reduce a copper polycrystalline electrode in 0.1 M solutions containing both sodium fluoride and sodium chloride with different chloride/fluoride molar ratios: (0.1-x) M NaF+x M NaCl. To address the anion effect on the changes in surface geometry, we recorded the voltammetric fingerprints of the modified electrodes using lead underpotential deposition (UPD). The voltammetric analysis suggested that while chloride induces (n10) sites, fluoride promotes an increase in the active surface area and the growth of low-coordinated sites with (110) or (111) geometry. Solutions containing both fluoride and chloride anions induced (n10) motifs covered by nanometric clusters, as observed by scanning electron microscopy, forming a highly defect-rich surface. Our work provides a direct link between electrochemical response and ex-situ structural characterization, and compares, in detail, the effect of chloride and fluoride on the surface nanostructuring of copper.