Visualization of Chlorine Evolution at Dimensionally Stable Anodes by Means of Scanning Electrochemical Microscopy

Abstract

Scanning electrochemical microscopy (SECM) has been used to detect and visualize the local electrocatalytic activity of dimensionally stable anodes (DSA) for Cl(2) evolution from brine. The sample generation-tip collection (SG-TC) mode of SECM shows limitations arising from complications connected with the reduction of Cl(2) at the SECM tip due to the presence of a significant amount of nondissolved Cl(2) gas. Because only dissolved Cl(2) can be electrochemically reduced at the tip, a large amount of the Cl(2) gas which is produced at active spots of the DSA is not detected. Additionally, a decrease of the cathodic current at the tip may occur owing to the adhesion of gas bubbles and blocking of the electrode surface. To overcome this limitation, the redox competition mode of SECM was extended and applied to the local visualization of Cl(2) evolution from highly concentrated brine solutions. High concentrations of Cl(2) produced at the sample can cause inhibition of the same reaction at the tip by accumulation of Cl(2) in the proximity of the SECM tip. In this way the tip current is decreased, which can be used as a measure for the catalytic activity of the sample underneath the tip.

Controlling Selectivity in the Chlorine Evolution Reaction over RuO2‐Based Catalysts

“…From a thermodynamic point of view, the oxygen evolution reaction (OER: equilibrium potential U o = 1.23 V) is preferred over the chlorine evolution reaction (CER: equilibrium potential U o = 1.36 V). However, since the CER constitutes a twoelectron process and the OER a four-electron process, the kinetics of the CER are much faster than that of the OER, so that the CER prevails above 1.36 V. A mixture of RuO 2 with SnO 2 or TiO 2 has been shown to improve both the stability of the electrode [6] and the selectivity of the anodic reaction towards the CER, [7] although the underlying chemistry is not well understood on a molecular level.Over the past decade, theory [8][9][10][11][12][13][14] has increased our molecular understanding of electrocatalytic reactions through the use of ab initio thermodynamics. [15] Ab initio Pourbaix diagrams [9] reveal stable surface structures under (suppressed) reaction conditions, and universal scaling relationships [3] have been employed to identify the optimum adsorption properties of the electrode material for the reaction under consideration.…”

“…From a thermodynamic point of view, the oxygen evolution reaction (OER: equilibrium potential U o = 1.23 V) is preferred over the chlorine evolution reaction (CER: equilibrium potential U o = 1.36 V). However, since the CER constitutes a twoelectron process and the OER a four-electron process, the kinetics of the CER are much faster than that of the OER, so that the CER prevails above 1.36 V. A mixture of RuO 2 with SnO 2 or TiO 2 has been shown to improve both the stability of the electrode [6] and the selectivity of the anodic reaction towards the CER, [7] although the underlying chemistry is not well understood on a molecular level.…”

Rapid screening of silver nanoparticles for the catalytic degradation of chlorinated pollutants in water

“…Fortunately, new electroanalytical techniques have been recently introduced to improve this screening step. In particular, the scanning electrochemical microscopy (SECM) [34,35] has demonstrated its utility as a rapid and high throughput technique in screening electrocatalyts [36] for processes A c c e p t e d M a n u s c r i p t 5 such as the oxygen reduction reaction (ORR) [37][38][39][40][41][42], methanol interference during ORR [43], chlorine evolution [44] and oxygen evolution reactions (OER) [45,46], formic acid oxidation (FAOR) [47,48] and methanol oxidation reactions (MOR) [48].…”

Die Elektrochemie des Sauerstoffs als Meilenstein für eine nachhaltige Energieumwandlung

“…[163,235,236] Darüber hinaus sind die räumliche Verteilung der aktiven Zentren und die Vermeidung von Oberflächensegregation von großer Bedeutung für die Leistungsfähigkeit gasentwickelnder Elektroden. [237][238][239] Eine direkte Überwachung der lokalen Aktivität für die OER an der Fest-flüssig-Grenzfläche wird notwendig, um diese nanostrukturellen Effekte eindeutig zu zeigen. [240,241] Abbildung 8.…”