The Effect of Anions and pH on the Activity and Selectivity of an Annealed Polycrystalline Au Film Electrode in the Oxygen Reduction Reaction‐Revisited

Abstract

Aiming at a better understanding of correlations between the activity and selectivity of Au electrodes in the oxygen reduction reaction (ORR) under controlled transport conditions, we have investigated this reaction by combined electrochemical and in situ FTIR measurements, performed in a flow cell set‐up in an attenuated total reflection (ATR) configuration in acid and alkaline electrolytes. The formation of incomplete reduction products (hydrogen peroxyde/peroxyls) was detected by a collector electrode, the onset of OHad formation was probed by bulk CO oxidation. Using an electroless‐deposited, annealed Au film on a Si prism as working electrode and three different electrolytes for comparison (sulfuric acid, perchloric acid, sodium hydroxide solution), we could derive detailed information on the anion adsorption behavior, and could correlate this with the ORR characteristics. The data reveal pronounced effects of the anions and the pH on the ORR characteristics, indicated e. g., by a grossly different activity and selectivity for the 4‐electron pathway to water/hydroxyls, with the onset ranging from ca. 1.0 V in alkaline electrolyte to 0.6 V in sulfuric acid electrolyte, and the selectivity for the 4‐electron pathway ranging from 100 % (alkaline electrolyte, low overpotentials) to 40 % (acidic electrolytes, alkaline electrolyte at high overpotentials). In contrast, the effect of the ORR on the anion adsorption characteristics is small. Anion effects as well as correlations between anion adsorption and ORR are discussed.

Probing the Effects of Acid Electrolyte Anions on Electrocatalyst Activity and Selectivity for the Oxygen Reduction Reaction

“…The identity of electrolyte ions is also known to affect ORR performance; however, acid electrolyte effects on the ORR have been mainly studied on Pt surfaces. [8,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] For example, activity on Pt has been shown to decrease with the following anion trend: ClO À 4 > HSO À 4 =SO 2À 4 > H 2 PO À 4 > Cl À > Br À . [16][17][18]20,21] These differences in the ORR performance have generally been attributed to anions, at or near the surface, blocking active sites (competitive adsorption) and/or in some way altering binding energy of oxygen intermediates.…”

“…In addition to investigating the ORR performance of weak oxygenbinding Ag in various acid electrolytes, we also investigate the role of acid electrolyte anion identity on Pd and examine if the anion effects in acid electrolytes seen on Pt apply to also strong oxygen-binding Pd. [8,[14][15][16][17][18][19][20][21][22][23][24][25][26][27]35] We evaluate ORR performance and material stability in six different acid electrolytes (HClO 4 , HNO 3 , H 2 SO 4 , H 3 PO 4 , HCl, and HBr at pH 1) with combined electrochemical and physical characterization methods and compare the activity trends to those previously seen on Pt. [14][15][16][17][18][19][20][21][22][23][24][25][26][27] For both Ag and Pd we find activity to follow the trend:…”

“…[8,[14][15][16][17][18][19][20][21][22][23][24][25][26][27]35] We evaluate ORR performance and material stability in six different acid electrolytes (HClO 4 , HNO 3 , H 2 SO 4 , H 3 PO 4 , HCl, and HBr at pH 1) with combined electrochemical and physical characterization methods and compare the activity trends to those previously seen on Pt. [14][15][16][17][18][19][20][21][22][23][24][25][26][27] For both Ag and Pd we find activity to follow the trend:…”

Elucidating Pt-Based Nanocomposite Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Gas Diffusion Electrode Measurements

“…It is widely accepted that IrO2 is not a good catalyst for the ORR. Au on its own also performs badly for the ORR in acidic conditions, with H2O2 or HO2being the final product of the reaction [39][40][41] . However, in previous studies it was reported that Pt-Au core-shell structures 42 , Pt-Au alloy structures 15 , and Au-modified Pt structures 43 can not only increase the ORR rate but also the stability.…”

A Fishery Water Quality Monitoring and Prediction Evaluation System for Floating UAV Based on Time Series

“…Its rapidity, high selectivity, superiority, corrosion resistance, commercial availability, and low power consumption [ 36 ] make it an excellent choice for fishery water quality detection. The pH composite electrode is shown in Figure 8 a, and the specific principle is provided in other reports [ 37 , 38 ]. The structure of the dissolved oxygen sensor probe is shown in Figure 8 b, and the specific principle is described in [ 39 ].…”