Facet‐Resolved Electrochemistry of Polycrystalline Boron‐Doped Diamond Electrodes: Microscopic Factors Determining the Solvent Window in Aqueous Potassium Chloride Solutions

Abstract

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.

Interrogating the Surface Intermediates and Water Oxidation Products of Boron‐Doped Diamond Electrodes with Scanning Electrochemical Microscopy

“…Scanning electrochemical microscopy (SECM) is a powerful tool to spatially and temporally resolve local reactivity at interfaces [18] and has been recently applied to heterogeneous electron transfer at BDD electrodes. [19] Various SECM modes have been used to determine outer sphere reactivity in single crystal [20] and polycrystalline [21] BDD electrodes, collect H 2 O 2 and other ROS as water oxidation products, [22] and determine solvent windows of differently doped and terminated facets. [14] Here, we employ the collection mode of SECM to qualify water oxidation products and how they change with pH and electrolyte.…”

Nanoscale electrochemistry in a copper/aqueous/oil three-phase system: surface structure–activity-corrosion potential relationships

“…For polycrystalline surfaces, SECCM measurements are powerfully combined with co-located electron backscattered diffraction (EBSD), to elucidate nanoscale structure-activity, as exemplified by studies of various electrochemical processes at a range of polycrystalline materials, including Pt, [23][24][25][26] Au, 27 Pd, 28 low carbon steel, [29][30][31] Zn 32 and boron-doped diamond. 33 In addition to its high spatiotemporal resolution, the meniscus cell configuration of SECCM facilitates rapid reactant/product exchange with the surrounding environment, mimicking a gas diffusion electrode, with an enhanced flux of gases into the meniscus cell (i.e., at the threephase boundary). 24,27,34 When operated in air, SECCM emulates the configuration of atmospheric corrosion, with gas exchange (e.g., oxygen, O 2 ) taking place across the liquid/gas interface of the meniscus in contact with a surface of interest.…”

High pressure high temperature synthesis of highly boron doped diamond microparticles and porous electrodes for electrochemical applications

“…This treatment minimized solution spreading from the pipet onto the sample surface during SECCM measurements (vide infra). 29 The nanopipette was filled with solution containing 10 mM Ru(NH3)6Cl3 and 10 mM KNO3 and an AgCl-coated Ag wire quasi-reference-counter electrode (QRCE) inserted into the back of the nanopipette. A relatively low concentration of supporting electrolyte was used to prevent KNO3 crystallization during measurements.…”

“…Immediately upon meniscus contact with the substrate (but no contact of the pipette), the voltammetric scan commenced, at a fast rate of 10 V s -1 to prevent significant wetting on the timescale of the scan, given the hydrophilic nature of oxygen terminated BDD. 29 For the compact, at the start of the scan (1 V vs QRCE), the current is close to zero, but as the potential is scanned cathodically, a reduction current begins to flow at approximately -0.3 V and increases monotonically as the potential is scanned further in the negative direction. At -1.0 V vs QRCE, the scan direction is reversed and the current decreases in magnitude towards 0 nA, before an anodic peak is observed in the potential range -0.2 V to +0.5 V. Notably, the reduction current magnitudes for the HPHT electrode (Fig.…”