The metal support of hexagonal boron nitride nanosheets has a significant effect on the electrocatalytic hydrogen evolution reaction, as visualized by scanning electrochemical cell microscopy.

A systematic examination of the microscopic factors affecting the aqueous solvent (electrolyte) window of polycrystalline (p) boron-doped diamond (BDD) electrodes in chloride-containing salt solutions is undertaken by using scanning electrochemical cell microscopy (SECCM) in conjunction with electron backscatter diffraction (EBSD) and Raman microscopy. A major focus is to determine the effect of the local boron doping level, within the same orientation grains, on the solvent window response. EBSD is used to select the predominant (110) orientated areas of the surface with different boron-doped facets, thereby eliminating crystallographic effects from the electrochemical response. Voltammetric SECCM is employed, whereby a cyclic voltammogram is recorded at each pixel mapped by the meniscus-contact SECCM cell. The data obtained can be played as an electrochemical movie of potential-resolved current maps of the surface to reveal spatial variations of electroactivity, over a wide potential range, including the solvent (electrolyte) window.

<div><div><div><p>Outer-sphere electron transfer (OS-ET) is a cornerstone elementary electrochemical reaction, yet microscopic understanding is largely based on idealized theories, developed in isolation from experiments that themselves are often close to the kinetic (diffusion) limit. Focusing on graphene as-grown on a copper substrate as a model 2D material/metal-supported electrode system, this study resolves the key electronic interactions in OS-ET, and identifies the role of graphene in modulating the electronic properties of the electrode/electrolyte interface. An integrated experimental-theoretical approach combining co-located multi-microscopy, centered on scanning electrochemical cell microscopy (SECCM), with Raman microscopy and field emission-scanning electron microscopy, together with rate theory and density functional theory calculations is used to address OS-ET kinetics of hexaamineruthenium (III/II) chloride, [Ru(NH3)6]3+/2+. The experimental methodology allows spatially-resolved electrochemical measurements to be targeted at distinct regions of monolayer, bilayer and multilayer graphene on copper, with high diffusion rates, to reveal ET kinetics in the order: monolayer > bilayer > multilayer. Theoretical and computational methods combining the Schmickler-Newns-Anderson model, transition state theory, and constant potential DFT reveal that the difference in kinetics at monolayer and bilayer graphene can be rationalized in the context of a dominantly adiabatic mechanism, where the addition of subsequent graphene layers increases the contact potential, producing an increase in the effective barrier to electron transfer. This study provides a roadmap for the integration of experiments and theory in order to understand the nature of heterogeneous electron transfer at complex nanostructured electrode materials.</p></div></div></div>