Direct electrochemical identification of rare microscopic catalytic active sites

Abstract

Local voltammetric analysis with a scanning electrochemical droplet cell technique, in combination with a new data processing protocol (termed data binning and trinisation), is used to directly identify previously unseen...

Multiscale Analysis of Electrocatalytic Particle Activities: Linking Nanoscale Measurements and Ensemble Behavior

“…Among tools for SEE, scanning electrochemical cell microscopy (SECCM) is proving to be a particularly powerful and versatile technique that enables correlative structure–function studies in (electro)­materials science. , In SECCM, the meniscus cell formed at the end of a fluidic scanning probe (composed of a glass micropipet or nanopipet) is brought into contact with a target entity (i.e., an area of an electrode surface) to perform local electrochemistry with high spatiotemporal resolution. Employed in tandem with complementary, colocated high-resolution spectroscopy/microscopy in a correlative multimicroscopy approach , SECCM has previously been used to probe the activity of single step edges (e.g., transition-metal dichalcogenides − and sp 2 carbon − ), nanoparticles (e.g., metal , and metal oxides ,, ), inclusions, , grains − and grain boundaries, , etc. Two very recent SECCM studies on complex electrode materials demonstrate single-entity behavior that would not be readily predicted from bulk electrochemistry alone: (1) individual LiMn 2 O 4 particles exhibit facile Li + (de)­intercalation at rates that are orders of magnitude higher than macroscopic composite electrodes of the same material and (2) individual conductive domains of poly­(3-hexylthiophene) (P3HT) retain facile electron-transfer rate capability when blended with nonconductive poly­(methyl methacrylate) (PMMA), despite apparently ultrasluggish electron transfer at the macro-scale .…”

Evaluating Analytical Expressions for Scanning Electrochemical Cell Microscopy (SECCM)

“…Sequentially positioning the nanopipette at an array of points across the substrate surface and performing an electrochemical characterization at each point creates a nanoscale electrochemical map. SECCM is used to quantify reactions and processes at a wide variety of electrochemical interfaces with nanoscale spatial resolution, − including corrosion, − phase formation, − surface defect detection, − battery materials, − and electrocatalytic reactions (e.g., hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, etc.) on single particles. − …”

Practical guidelines for the use of scanning electrochemical cell microscopy (SECCM)

“…Furthermore, refinements in SECCM methodology have notably expanded its capabilities, particularly in the realm of characterising the (sub) nanoscale structural heterogeneities (e.g., defects) that are inherent to electrode surfaces. [12][13][14] Since its inception, SECCM has been employed to analyse and characterise structurally heterogeneous surfaces in a local regime (i.e., µm to nm scale) to investigate electron-transfer kinetics at a diverse range of electrode materials including, highly oriented pyrolytic graphite (HOPG), 15 boron-doped diamond (BDD) 16 and polycrystalline metals, such as platinum. 17 More recently, SECCM investigations were extended into corrosion science, which aim to correlate local corrosion rates with the underlying materials composition and structure (e.g., crystallographic orientation, phase, inclusions etc.).…”

“…For example, a robust linear relationship of the probe resistance with puller power and the multiplicative inverse of the probe diameter was previously observed, indicating that probe size can be estimated (and controlled) without the need for electron microscopy. 13 While filling the probe with electrolyte, the formation of bubbles near the taper of the capillary is a regular occurrence, which if not removed, will physically obstruct the flow of current between the working electrode (i.e., electrode surface area wetted by the SECCM droplet cell) and QRCE. These bubbles are relatively large and can be observed using a standard optical microscope at low magnification.…”

“…For example, a robust linear relationship of the probe resistance with puller power and the multiplicative inverse of the probe diameter was previously observed, indicating that probe size can be estimated (and controlled) without the need for electron microscopy. 13…”