Modulating Electrocatalysis on Graphene Heterostructures: Physically Impermeable Yet Electronically Transparent Electrodes.

The electronic properties and extreme thinness of graphene make it an attractive platform for exploring electrochemical interactions across dissimilar environments. Here, we report on the systematic tuning of the electrocatalytic activity toward the oxygen reduction reaction (ORR) via heterostructures formed by graphene modified with a metal underlayer and an adlayer consisting of a molecular catalyst. Systematic voltammetric testing and electrochemical imaging of patterned electrodes allowed us to confidently probe modifications on the ORR mechanisms and overpotential.

Fabrication and Demonstration of Mercury Disc-Well Probes for Stripping-Based Cyclic Voltammetry Scanning Electrochemical Microscopy.

Scanning electrochemical microscopy (SECM) is a rising technique for the study of energy storage materials. Hg-based probes allow the extension of SECM investigations to ionic processes, but the risk of irreversible Hg amalgam saturation limits their operation to rapid timescales and dilute analyte solutions. Here, we report a novel fabrication protocol for Hg disc-well ultramicroelectrodes (UMEs), which retain access to stripping information but are less susceptible to amalgam saturation than traditional Hg sphere-caps or thin-films.

Cyclic Voltammetry Probe Approach Curves with Alkali Amalgams at Mercury Sphere-Cap Scanning Electrochemical Microscopy Probes.

We report a method of precisely positioning a Hg-based ultramicroelectrode (UME) for scanning electrochemical microscopy (SECM) investigations of any substrate. Hg-based probes are capable of performing amalgamation reactions with metal cations, which avoid unwanted side reactions and positive feedback mechanisms that can prove problematic for traditional probe positioning methods. However, prolonged collection of ions eventually leads to saturation of the amalgam accompanied by irreversible loss of Hg.

Electrochemical Imaging of Photoanodic Water Oxidation Enhancements on TiO Thin Films Modified by Subsurface Aluminum Nanodimers.

Detecting metal plasmonic enhancements on the activity of semiconducting photoanodes for water oxidation is often obscured by the inherent electroactivity and instability of the metal in electrolyte. Here, we show that thin TiO photoanodes modified by subsurface Al nanodimers (AlNDs) display enhancements that are consistent with plasmon modes. We directly observed enhancements by mapping the oxygen evolution rates on TiO/AlND patterns using scanning electrochemical microscopy (SECM) while exciting the surface plasmons of the nanodimers.

Emerging scanning probe approaches to the measurement of ionic reactivity at energy storage materials.

Many modern energy storage technologies operate via the nominally reversible shuttling of alkali ions between an anode and a cathode capable of hosting them. The degradation process that occurs with normal usage is not yet fully understood, but emerging progress in analytical tools may help address this knowledge gap. By interrogating ionic fluxes over electrified surfaces, scanning probe methods may identify features that impact the local cyclability of a material and subsequently help inform rational electrode design for future generations of batteries.

Lithium ion quantification using mercury amalgams as in situ electrochemical probes in nonaqueous media.

We report on the quantitative, spatially resolved study of ionic processes for energy materials in nonaqueous environments by in situ electrochemical means at the micro- and nanoscale. Mercury-capped platinum ultramicroelectrodes (Hg/Pt UMEs) were tested as probes for alkali ions in propylene carbonate (PC) in an oxygen- and water-free environment. Anodic stripping voltammetry (ASV) performed at Hg/Pt UMEs displayed a linear response to Li(+) concentration extending from 20 μM to at least 5 mM.

Information content in fluorescence correlation spectroscopy: binary mixtures and detection volume distortion.

When properly implemented, fluorescence correlation spectroscopy (FCS) reveals numerous static and dynamic properties of molecules in solution. However, complications arise whenever the measurement scenario is complex. Specific limitations occur when the detection region does not match the ideal Gaussian geometry ubiquitously assumed by FCS theory, or when properties of multiple fluorescent species are assessed simultaneously.