Interfacial pH Measurements Using a Rotating Ring‐Disc Electrode with a Voltammetric pH Sensor

Abstract

Dedicated to Professor Wolfgang Schuhmann on the occasion of his 65 th birthday and his eminent contributions to physical and analytical electrochemistry.Electrochemical reactions in which H + or OH À ions are produced or consumed, affect the pH near the electrode surface. Probing the pH locally is therefore highly desired to understand and model the reaction environment under operando conditions. We carried out interfacial pH measurements under mass transport control using a rotating ring-disc electrode (RRDE) coupled with our recently developed voltammetric pH sensor. The interfacial disc pH is detected by functionalizing the gold ring with a hydroxylaminothiophenol (4-HATP)/4-nitrosothiophenol (4-NSTP) redox couple. As protons only have to interact with a monolayer containing the 4-HATP/ 4-NSTP, the sensitivity and time resolution that can be achieved are superior to potentiometric sensors. We used hydrogen evolution as a model reaction and performed measurements in buffered and unbuffered electrolytes. The effects of the current density, potential, the buffer capacity of the electrolyte and rotation rate on the local pH were investigated. This work shows a reliable and sensitive method for accurately probing the reaction environment under well-defined mass transport conditions, over a wide pH range.

The Effect of Temperature on the Cation‐Promoted Electrochemical CO2 Reduction on Gold

“…have shown that for low current densities (<4.33 mA/cm 2 at 1600 rpm) no significant local pH changes are observed. On the other hand, recent experiments in our group have shown that even at relatively low current densities, the local pH at rotating electrodes can be significantly different from the bulk pH [62] . However, as the change in bulk pH and buffer capacity are minor, we do not expect the pH to dominate the temperature effect observed in Figure 1.…”

“…On the other hand, recent experiments in our group have shown that even at relatively low current densities, the local pH at rotating electrodes can be significantly different from the bulk pH. [62] However, as the change in bulk pH and buffer capacity are minor, we do not expect the pH to dominate the temperature effect observed in Figure 1. The local pH can change because the current densities are higher, but this is then the result of the increased activity, instead of the cause.…”

Role of Electronic Structure on Nitrate Reduction to Ammonium: A Periodic Journey

“…Phosphate-mediated HER (Figure 1a, black dashed lines) is observed as a mass-transfer limited peak at potentials less cathodic than water dissociation (Figures S1 and S2), where protons are easier to extract from phosphate anions than from water. 31 The comparable mass-transfer limited current density (ca. 2 mA/cm geo 2 ; Figure S1) across TMs indicates similar roughness (ratio of actual and geometric surface areas) except for the lower-roughness Ag and Co.…”

Versatile DIY Route for Incorporation of a Wide Range of Electrode Materials into Rotating Ring Disk Electrodes

“… 8 The RRDE ring electrode can also be used as a pH sensor to detect pH changes resulting from reactions on the disk. 9 , 10 …”