Probing Oxygen-to-Hydrogen Peroxide Electro-Conversion at Electrocatalysts Derived from Polyaniline.

Yaovi Holade,Sarra Knani,Marie-Agnès Lacour,David Cornu,Teko W Napporn,Sophie Tingry,Julien Cambedouzou

doi:10.3390/polym14030607

Abstract

Hydrogen peroxide (H2O2) is a key chemical for many industrial applications, yet it is primarily produced by the energy-intensive anthraquinone process. As part of the Power-to-X scenario of electrosynthesis, the controlled oxygen reduction reaction (ORR) can enable the decentralized and renewable production of H2O2. We have previously demonstrated that self-supported electrocatalytic materials derived from polyaniline by chemical oxidative polymerization have shown promising activity for the reduction of H2O to H2 in alkaline media. Herein, we interrogate whether such materials could also catalyze the electro-conversion of O2-to-H2O2 in an alkaline medium by means of a selective two-electron pathway of ORR. To probe such a hypothesis, nine sets of polyaniline-based materials were synthesized by controlling the polymerization of aniline in the presence or not of nickel (+II) and cobalt (+II), which was followed by thermal treatment under air and inert gas. The selectivity and faradaic efficiency were evaluated by complementary electroanalytical methods of rotating ring-disk electrode (RRDE) and electrolysis combined with spectrophotometry. It was found that the presence of cobalt species inhibits the performance. The selectivity towards H2O2 was 65–80% for polyaniline and nickel-modified polyaniline. The production rate was 974 ± 83, 1057 ± 64 and 1042 ± 74 µmolH2O2 h−1 for calcined polyaniline, calcined nickel-modified polyaniline and Vulcan XC 72R (state-of-the-art electrocatalyst), respectively, which corresponds to 487 ± 42, 529 ± 32 and 521 ± 37 mol kg−1cat h−1 (122 ± 10, 132 ± 8 and 130 ± 9 mol kg−1cat cm−2) for faradaic efficiencies of 58–78%.

Highlights

Hydrogen peroxide (H2O2) is one of the most important chemicals in the chemical and medical industries
We chose not to apply ohmic drop correction, even though the ohmic resistance was in the range of 5–6 Ω as determined by the electrochemical impedance spectroscopy (EIS), indicating an ohmic drop in potential of 25–30 mV at an absolute current of 5 mA
We investigated the applicability of materials derived from the conducting polymer polyaniline (PANI) for oxygen-to-hydrogen peroxide electro-conversion in an alkaline medium

Summary

Introduction

Hydrogen peroxide (H2O2) is one of the most important chemicals in the chemical and medical industries. To address the high and increasing demand (application for disinfection, textile bleaching, wastewater treatment and renewable energy storage), the four possible methods to produce H2O2 include the traditional anthraquinone process, direct synthesis, photocatalysis and electrocatalysis [3,4,5]. The electrocatalytic [3,6,7,8,9,10] (or even photoelectrocatalytic [11,12]) pathway, the so-called Power-to-X approach, is seen as a promising option where electrical energy from any source (ideally renewable) would allow the intelligent and elegant production of hydrogen peroxide from naturally available reactants, either by the partial oxidation of water (2H2O → H2O2 + 2H+ + 2e−) or the partial reduction of atmospheric oxygen (O2 + 2H+ + 2e− → H2O2). We need highly selective electrocatalysts to circumvent the four-electron pathway that reduces the faradaic efficiency (portion of the used electrical energy to make a targeted electron transfer reaction)

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