Edges of Layered FePSe3 Exhibit Increased Electrochemical and Electrocatalytic Activity Compared to Basal Planes.

Transition metal trichalcogenphosphites (MPX3), belonging to the class of 2D materials, are potentially viable electrocatalysts for the hydrogen evolution reaction (HER). Many 2D and layered materials exhibit different magnitudes of electrochemical and electrocatalytic activity at their edge and basal sites. To find out whether edges or basal planes are the primary sites for catalytic processes at these compounds, we studied the local electrochemical and electrocatalytic activity of FePSe3, an MPX3 representative that was previously found to be catalytically active. Using scanning electrochemical microscopy, we discovered that electrochemical processes and the HER are occurring at an increased rate at edge-like defects of FePSe3 crystals. We correlate our observations using optical microscopy, confocal laser scanning microscopy, scanning electron microscopy, and electron-dispersive X-ray spectroscopy. These findings have profound implications for the application of these materials for electrochemistry as well as for understanding general rules governing the electrochemical performance of layered compounds.

Catalyst Formation and In Operando Monitoring of the Electrocatalytic Activity in Flow Reactors.

Flow reactors are of increasing importance and have become crucial devices due to their wide application in chemical synthesis, electrochemical hydrogen evolution reaction (HER), or electrochemical waste water treatment. In many of these applications, catalyst materials such as transition-metal chalcogenides (TMCs) for the HER, provide the desired electrochemical reactivity for the HER. Generally, the flow electrolyzers' performance is evaluated as the overall output, but the decrease in activity of the electrolyzer is due to localized failure of the catalyst. Herein, we present a method for the spatially resolved (tens of micrometers) In Operando analysis of the catalytic activity under real operation conditions as well as the localized deposition of the catalyst in an operating model flow reactor. For these purposes, scanning electrochemical microscopy was applied for MoSx catalyst deposition and for localized tracking of the TMC activity with a resolution of 25 µm. This approach offers detailed information about the catalytic performance and should find broad application for the characterization and optimization of flow reactor catalysis under real operational conditions.

Scanning Electrochemical Microscopy of Electrically Heated Wire Substrates.

We report a new configuration for enhancing the performance of scanning electrochemical microscopy (SECM) via heating of the substrate electrode. A flattened Pt microwire was employed as the substrate electrode. The substrate was heated by an alternating current (AC), resulting in an increased mass transfer between the wire surface and the bulk solution. The electrochemical response of the Pt wire during heating was investigated by means of cyclic voltammetry (CV). The open circuit potential (OCP) of the wire was recorded over time, while varied heating currents were applied to investigate the time needed for establishing steady-state conditions. Diffusion layer studies were carried out by performing probe approach curves (PACs) for various measuring modes of SECM. Finally, imaging studies of a heated substrate electrode surface, applying feedback, substrate generation/tip collection (SG/TC), and the competition mode of SECM, were performed and compared with room temperature results.

Methodical studies of the simultaneous determination of anions and cations by IC×CE-MS using arsenic species as model analytes.

The separation of the constituents of complex sample mixtures is a challenging task in analytical chemistry. Multidimensional separation systems are widely used to enhance the peak capacity. The comprehensive hyphenation of ion chromatography (IC) and capillary electrophoresis (CE) is promising because the two most important instrumental techniques in ion analysis are combined. In this report a new configuration for capillary anion chromatography is presented enabling the simultaneous IC×CE analysis of anions and cations using a switching valve. Electrospray ionization mass spectrometry (MS) was used for detection. A mixture of organic and inorganic arsenic species served as a model system. The coupling of anion chromatography to CE-MS was done via a modulator enabling periodical injections of the IC effluent into the CE. The injection parameters of the modulator were studied taking into account the complex transport situation. Graphical abstract ᅟ.