Electrochemical Reduction of Oxygen at Platinum Electrodes in  KOH  Solutions ‐ Temperature and Concentration Effects

Abstract

Electrochemical reduction of oxygen has been studied in detail employing rotating disk and ring‐disk electrode techniques in aqueous KOH solutions of various concentrations at various temperatures. Analysis of voltammetric results recorded at the rotating disk electrode (RDE) indicates that there are two clearly defined Tafel regions of low (60 mV/decade) and high false(200∼300 normalmV/normaldecadefalse) Tafel slopes. In general, electrode kinetics improves and Tafel slopes of the low‐slope region decreases slightly as the basicity of the electrolyte solution increases. The rotating ring‐disk electrode (RRDE) results were analyzed according to a simple model for oxygen reduction, first proposed by Damjanovic et al. The model is in agreement with experimental results at lower concentrations of KOH . Rate constants for oxygen reduction directly to H2O and H2O2 , and for H2O2 to H2O were calculated at four different disk electrode potentials. The rate constant of direct reduction of oxygen to H2O increases with the overpotential, but the plots of rate constants for oxygen reduction to H2O2 and for H2O2 reduction vs. potential pass through a maximum at about 0.85V vs. DHE. All these rate constants are shown to be slightly dependent on temperature.

Accurate Assessment of the Oxygen Reduction Electrocatalytic Activity of Mn/Polypyrrole Nanocomposites Based on Rotating Disk Electrode Measurements, Complemented with Multitechnique Structural Characterizations

“…The literature survey on ORR at poly-Pt electrode in alkaline solution using the RDE methodology is limited and not consistent [6, 12–14]; therefore a definite comparison between the new developed Mn-PPy material and the state-of-the-art electrocatalysts is not allowed. As a consequence, we have worked to obtain an intralaboratory benchmark (poly-Pt rod) not aiming at proposing a standard RDE curve usable as reference for general activity of poly-Pt (to do that a dedicated work of analysis on the different parameters affecting the ORR activity is necessary, together with interlaboratory testing; this kind of work is actually a challenge especially in alkaline solution) but only at acquiring an internal reference on the basis of which our novel data can be safely evaluated.…”

“…At present, ORR at Pt RDE electrodes of different forms (wires, gauzes, foils, and disks of different areas) has been widely investigated in acid solution [1–3], due to their relevance in polymer electrolyte fuel cells [4]. On the contrary marginal attention has been paid to pure Pt in alkaline solutions (single crystal Pt [5, 6], poly-Pt particles [7], poly-Pt wire [8], poly-Pt thin film [9–11], and poly-Pt rod [6, 12–14]) despite the fact that ORR plays a key role in the chlor-alkali technology and in metal-air batteries [15, 16]. Due to the absence of an interlaboratory benchmark material in alkaline solution and the discrepancies in the few data available at the moment [6, 12–14], we have realized an intralaboratory poly-Pt benchmark against which the data gathered with novel ones can be safely gauged.…”

Oxygen-Containing Nanoclusters on the Surface of Pt-Electrodes and Oxygen Reduction Reaction in Alkaline Medium

“…For example, investigation of ORR in 0.1 M NaOH [34] indicated that change of anodic oxidation potential within 1.0 to 1.5 V (versus RHE) is accompanied by increase of ring/disk current ratio from 10 to 70%. In study [35] it was reported that on Pt-electrodes oxidized at 1.2 V (versus RHE) potential in KOH solutions with concentrations within a range from 0.1 to 6 M the ring/disk current ratio is unchanged parameter with about 7% value. ORR process on Pt-electrode in 0.1 M KOH for cathodic polarization of 1.1 to −0.2 V (versus RHE) is accompanied by ring/disk current ratio within 20-25% interval [36].…”

“…It was experimentally demonstrated (for example, [34][35][36][37]) that quantity of HO 2 − ions detected on the ring depends on surface conditions of polycrystalline Pt-electrode. Preliminary anodic oxidation or cathodic reduction is accompanied by a change of ring/disk current ratio.…”

“…At low values of the current the coefficient is equal to 60 mV per dec on all types of Ptelectrodes (smooth platinum [26,27,35], disperse platinum on carbon substrate [46]). At high current values the various values of coefficient were reported: 120 mV per dec [26,27,46] and 200-300 mV per dec range [35]. On electrodes with platinum nanoparticles on disperse carbon [47] we detected dependence of coefficient from size of platinum nanoparticles.…”