Scanning electrochemical cell microscopy as a tool for the evaluation of electrocatalytic activity at the nanoscale

Im Rahmen dieser Arbeit wurde ein elektrochemisches Rasterzellmikroskop (SECCM) aufgebaut und dazu benutzt, die Aktivität von Elektrokatalysatoren zu untersuchen. Die Konzeption und die folgende Optimierung (inclusive Hardware, Software und Rauschisolierung) sind ausführlich beschrieben. Das SECCM wurde verwendet, um geringe Mengen an Katalysatorpartikel mit hoher Präzision auf den empfindlichen Membranen von Flüssigzellen-Transmissionselektronenspektroskopie (LC-TEM) Chips zu immobilisieren. Das eröffnet die Möglichkeit, LC-TEM in der Forschung von Elektrokatalysatoren zu benutzten. Mittels des SECCM wurde weiterhin die Aktivität von Katalysatornanopartikel für die Sauerstoffentwicklungsreaktion in alkalischer Lösung untersucht. Dabei wurde ein Os-Komplex als interner Standard eingesetzt, um die Potentialdrift zu berücksichtigen und die tatsächlich gemessene aktive Oberfläche zu bestimmen. Dadurch konnte die Aktivität einzelner Katalysatorpartikel ermittelt werden

Calibrating SECCM measurements by means of a nanoelectrode ruler

Scanning electrochemical cell microscopy (SECCM) is increasingly applied to determine the intrinsic catalytic activity of single electrocatalyst particle. This is especially feasible if the catalyst nanoparticles are large enough that they can be found and counted in post-SECCM scanning electron microscopy images. Evidently, this becomes impossible for very small nanoparticles and hence, a catalytic current measured in one landing zone of the SECCM droplet cannot be correlated to the exact number of catalyst particles. We show, that by introducing a ruler method employing a carbon nanoelectrode decorated with a countable number of the same catalyst particles from which the catalytic activity can be determined, the activity determined using SECCM from many spots can be converted in the intrinsic catalytic activity of a certain number of catalyst nanoparticles

Scanning electrochemical cell microscopy investigation of single ZIF-derived nanocomposite particles as electrocatalysts for oxygen evolution in alkaline media

"Single entity" measurements are central for an improved understanding of the function of nanoparticle‐based electrocatalysts without interference arising from mass transfer limitations and local changes of educt concentration or the pH value. We report a scanning electrochemical cell microscopy (SECCM) investigation of zeolitic imidazolate framework (ZIF‐67)‐derived Co−N‐doped C composite particles with respect to the oxygen evolution reaction (OER). Surmounting the surface wetting issues as well as the potential drift through the use of a non‐interfering Os complex as free‐diffusing internal redox potential standard, SECCM could be successfully applied in alkaline media. SECCM mapping reveals activity differences relative to the number of particles in the wetted area of the droplet landing zone. The turnover frequency (TOF) is 0.25 to 1.5 s$^{−1}$ at potentials between 1.7 and 1.8 V vs. RHE, respectively, based on the number of Co atoms in each particle. Consistent values at locations with varying number of particles demonstrates OER performance devoid of macroscopic film effects

A universal nano‐capillary based method of catalyst immobilization for liquid‐cell transmission electron microscopy

A universal nano‐capillary based method for sample deposition on the silicon nitride membrane of liquid‐cell transmission electron microscopy (LCTEM) chips is demonstrated. It is applicable to all substances which can be dispersed in a solvent and are suitable for drop casting, including catalysts, biological samples, and polymers. Most importantly, this method overcomes limitations concerning sample immobilization due to the fragility of the ultra‐thin silicon nitride membrane required for electron transmission. Thus, a straightforward way is presented to widen the research area of LCTEM to encompass any sample which can be externally deposited beforehand. Using this method, Ni$_x$B nanoparticles are deposited on the μm‐scale working electrode of the LCTEM chip and in situ observation of single catalyst particles during ethanol oxidation is for the first time successfully monitored by means of TEM movies