Influence of the Polymerization Method on the Oxygen Reduction Reaction Pathway on PEDOT

Abstract

The influence of the polymerization method of poly(3,4-ethylenedioxythiophene) (PEDOT), namely vapor-phase polymerization (VPP-PEDOT) or electrodeposition (EP-PEDOT), on the electrocatalytic properties is herein reported. Rotating disk electrode and rotating ring-disk electrode studies in alkaline conditions have shown that as the electrode potential is scanned in the negative direction the oxygen reduction reaction (ORR) on VPP-PEDOT undergoes a transition from a 2-electron pathway to a 4-electron pathway at −0.45 V (vs Ag/AgCl). In contrast, the ORR proceeds only by the 2-electron pathway on EP-PEDOT.Poly(3,4-ethylenedioxythiopene) (PEDOT) has emerged as an alternative cathode catalyst material to platinum since the discovery by Winther-Jensen et al. of its ability to effectively catalyze the oxygen reduction reaction (ORR). 1 Here it was shown that PEDOT catalyzes the ORR most effectively under alkaline conditions, making it particularly attractive for alkaline fuel cells (AFCs) and metal-air batteries. It was suggested that the ORR followed a 4-electron pathway, however, a report was recently published in 2012 stating that the ORR proceeds via the 2-electron process on electrodeposited PEDOT. 2 The ORR is able to proceed via two overall pathways; the 'direct' and the 'series' pathways. The direct pathway sees the complete reduction of oxygen via a 4-electron step to form hydroxides in basic media (Eq. 1)The 'series' pathway in basic media involves two successive 2-electron processes, which proceed via a hydrogen peroxide anion intermediate to give hydroxides (Eqs. 2 and 3).Both the choice of counter-ion present during electrodeposition 3,4 and the electrodeposition potential 5,6 have been shown to play an important role in regards to the structure and properties of electrodeposited films. However, there are no reported works to date that have investigated the influence of the polymerization technique on the pathway of electrocatalytic reactions on conducting polymer electrodes. ExperimentalAll voltammetric experiments were performed using a Biologic VMP3/Z multi-channel potentiostat and a RRDE-3A rotating ringdisk electrode (RRDE) apparatus (ALS Co., Ltd, Japan). The RRDE and RDE measurements were taken with an electrode composed of a Pt ring (0.188 cm 2 area) electrode and a glassy carbon (GC) disk electrode (4 mm diameter, 0.126 cm 2 area). A Pt wire counter electrode and Ag/AgCl (NaCl(aq), 3 mol dm −3 ) (both from ALS Co., Ltd, Japan) reference electrode were used throughout. All potentials are stated in reference to Ag/AgCl. Deionized water (Millipore SuperQ system, resistivity 18.2 M cm) was used to prepare all electrolyte solutions. All voltammetric experiments were performed at 20 ± 1 • C.The solution for PEDOT electrodeposition was prepared by dissolving 3,4-ethylenedioxythiophene (EDOT, Yacoo) to a concentration of 5 × 10 −2 mol dm −3 in a water-ethanol (60:40) solution containing sodium para-toluenesulfonate (NaPTS, 0.1 mol dm −3 , Aldrich) as * Electrochemical Society Active Member. z E-mail: Rober...

Enhancement of the Electrocatalytic Activity of Thienyl‐Substituted Iron Porphyrin Electropolymers by a Hangman Effect

“…This points to a more inhomogeneous distribution of electronic accessibilities and overall lower electron transfer efficiency of FeH3ThP/PEDOT films compared to FeT3ThP/PEDOT films. For PEDOT alone, a value for n of 1.5±0.04 was obtained indicating incomplete reduction of oxygen to hydrogen peroxide as has been observed earlier for electrodeposited PEDOT . Bi‐potentiostat measurements with amperometric reduction of oxygen by the catalyst at −0.6 V and simultaneous detection of produced hydrogen peroxide at a platinum electrode at +0.6 V underlined the results from Koutecky‐Levich analysis (Figure S5 in the Supporting Information).…”

Energetic Control of Redox‐Active Polymers toward Safe Organic Bioelectronic Materials

“…The ORR yields either H 2 O 2 (two‐electron process) [ 20 ] or water (H 2 O) (four‐electron process), [ 21,22 ] as well as charging (oxidation) of the OMIEC that acts as the catalyst. The four‐electron reaction (O 2 + 2H 2 O + 4e − → 4OH − , E 0 = 1.23 V versus reversible hydrogen electrode (RHE), pH ≥ 7) is thermodynamically favorable over the two‐electron reaction ( E 0 = 0.76 V versus RHE, pH > 7) as shown in Figure .…”

Role of the Anion on the Transport and Structure of Organic Mixed Conductors

“…Several studies have documented that oxygen reduction reactions (ORRs) in PEDOT can occur in an acidic environment. [58][59][60] The oxidation of the polymer can be facilitated by a two-or four-electron process as shown in Supporting Information Equations S3 and S4, where one reaction product is hydrogen peroxide (H2O2) and the other is water (H2O). [59] Whether the ORR in PEDOT occurs via a two-or four-electron process is beyond the scope of this study characterizing p(g2T-TT).…”