Pyrolyzed titanium dioxide/polyaniline as an efficient non-noble metal electrocatalyst for oxygen reduction reaction

doi:10.1016/S1872-2067(14)60223-0

Chinese Journal of Catalysis

Volume 36, Issue 3, March 2015, Pages 414-424

https://doi.org/10.1016/S1872-2067(14)60223-0 Get rights and content

Abstract

To overcome the prohibitive cost and poor durability of conventional Pt-based catalysts, TiO₂/C was prepared by pyrolyzing a novel titanium dioxide/polyaniline (TiO₂/PANI) composite. The prepared catalysts were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, cyclic voltammetry (CV), and linear sweep voltammetry. Interaction between PANI and TiO₂ was found to inhibit the aggregation of TiO₂ and its transformation from anatase to rutile. The catalytic activity of the TiO₂/C first increased with increasing PANI content and then decreased; the optimum was achieved when the PANI/TiO₂ mass ratio was 35/100. CV and i–t curves showed that the prepared composite has a good catalytic stability.

Graphical Abstract

To overcome the prohibitive cost and poor durability of conventional Pt-based catalysts, TiO₂/C was prepared by pyrolyzing a novel TiO₂/PANI composite. This non-noble metal electrocatalyst exhibits good ORR catalytic activity owing to the beneficial interaction between PANI and TiO₂.

Introduction

The preparation of low-cost, efficient, and stable catalysts as fuel cell cathode materials is currently a hot research topic. Groups 4 and 5 metal oxide compounds have been regarded as promising candidates for polymer electrolyte fuel cell (PEFC) cathode catalysts because they are insoluble in acid media [1]. The use of oxides of zirconium [2, 3, 4, 5, 6], tantalum [5, 6, 7, 8, 9, 10], niobium [6], titanium [1, 5], and hafnium [11, 12, 13] as cathode catalysts in oxygen reduction studies has been reported, with varied synthesis methods employed. In particular, TiO₂ is a promising photocatalyst that has received widespread interest [14, 15]. Thorough research has been conducted regarding its synthesis, morphology and crystal phase control, modification, and combination with other materials to prepare composite materials. TiO₂ is often used as the base material for catalysts because of its good stability. Recently, TiO₂ has also been examined as a fuel cell cathode catalyst because it can improve the stability [16] and methanol resistance of cathode catalysts and the selectivity and catalytic activity of 4-electron reactions [17, 18]. Non-stoichiometric TiO₂ has also been used as a base material for cathode catalysts [19].

Notably, TiO₂ is an oxygen reduction catalyst. Zhang et al. [20] prepared a cathode catalyst via the hydrolysis of TiCl₄ followed by heat treatment and used the resulting product in zinc–air batteries. Dam et al. [21] used TiO₂ as a precursor to prepare a titanium carbonitride matrix after calcination at high temperature, and the resulting TiCNO product was a mixture of TiO₂ and TiCN catalysts. The initial oxygen reduction potential and the carrying current of the titanium carbonitride catalyst were significantly improved compared with those of pure TiO₂. Additionally, Chisaka et al. [1] prepared a cathode catalyst, in which the main component was rutile TiO₂, by heat treatment of TiCN. Their studies showed that the residual carbon did not integrate into the TiO₂ lattice to form impurity defects. During heat treatment at elevated temperatures, C was instead incorporated into graphene, which then coated the surface of the TiO₂; the coating played a role in the oxygen reduction electron transfer process. Although part of the N and Ti formed TiN, the N atoms did not influence the oxygen reduction activity because they were not integrated into the TiO₂ lattice. Conversely, both oxygen defects generated in TiO₂ during heat treatment at high temperatures and doped N are known to significantly affect the activity of TiO₂ towards oxygen reduction. Recent studies have indicated that the (110) plane of TiO₂ [1] is more conducive to the adsorption of oxygen. Thus, the (110) facets are favorable for oxygen reduction reactions. Despite the research results achieved to date, further investigations are required to adequately determine the mechanism of oxygen reduction over TiO₂ and its performance as a catalyst or catalyst support.

TiO₂ is a semiconductor, and as such its low conductivity limits its application in terms of oxygen reduction. Based on first-principle calculations, Zheng et al. [22] reported that for low-conductivity materials, the electron transfer efficiency is low, the reaction is limited to a small area on the material interface, and oxygen reduction tends to occur via a two-electron mechanism. The accumulation of the resulting products, H₂O₂ and HO₂⁻ ions, is unfavorable for the reaction to continue. Conversely, the introduction of conductive carbon favors the reduction of oxygen via a four-electron mechanism, thereby improving the oxygen reduction performance of the material. These conclusions have been experimentally confirmed [22]. Chisaka et al. [1] studied TiO₂ prepared via heat treatment of titanium carbonitride at high temperatures in N₂ and H₂ atmospheres. The resulting material exhibited oxygen reduction activity; C was not incorporated into the lattice of TiO₂ but was instead present as a single layer of graphite on the surface of the TiO₂. C played a primary role in electron transportation [23], and the oxygen defects formed during the heat treatment process had a decisive role in improving the performance of the oxygen reduction catalyst.

In this study, we first prepared a novel TiO₂/polyaniline (PANI) complex via a hydrothermal route, and a TiO₂/C catalyst was obtained via subsequent pyrolysis. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the crystal phase composition and morphology of the TiO₂/C, and its electrochemical performance was assessed. Moreover, the influence of the mass ratio of PANI to TiO₂ and the pyrolysis temperature on the oxygen reduction performance of the catalyst was examined to establish optimum synthesis conditions to provide a reference for the future study of oxygen reduction TiO₂ catalysts.

Section snippets

Catalyst preparation

First, 2.282 g ammonium persulfate (APS, AR, Tianjin Damao Chemical Reagent Factory, Tianjin, China) was dissolved in HCl (36%, AR, Beijing Chemical Plant, Beijing, China) solution (0.1 mol/L) and held in an ice-water bath. Then, 0.3411 g of cetyltrimethylammonium chloride (CTAC, AR, Tianjin Guangfu Chemical Plant, Tianjin, China) dissolved in HCl solution (0.1 mol/L) was added to a three-necked flask. After adding 0.92 mL aniline (AR, Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), the

Influence of the mass ratio of PANI to TiO₂ on the performance of the TiO₂/C composites

TEM images of the synthesized PANI before and after its combination with TiO₂ are shown in Fig. 1. The HCl doped PANI had a fiber-like structure with rough spiculations on its surface, as shown in Fig. 1(b). Fig. 1(a) shows that the TiO₂ nanoparticles were closely and uniformly adhered to the surface of the PANI nanofibers.

The effect of the PANI on the phase composition of the TiO₂ was investigated by XRD. The presence of PANI in the composites was found to change the phase composition and

Conclusions

We prepared TiO₂/C cathode catalysts and examined the influence of the PANI-to-TiO₂ mass ratios on the properties of the resulting composite materials. The influence of high-temperature treatment on the properties of the composite materials was also investigated. The results show the presence of bonding between the amidogen (or imido) of PANI and the hydroxy groups on the surface of TiO₂ in the composite materials. The presence of this interaction prohibits the anatase-to-rutile TiO₂

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Nanostructured energy materials for electrochemical energy conversion and storage: A review
2016, Journal of Energy Chemistry
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The current electrocatalysts are mainly classified into three groups: precious metals, non-precious metals, and carbon-based materials. Pt and its alloys are most well studied and active electrode for ORR [202–206]. Additionally, non-precious metals compounds which are composed of non-precious metal and nitrogen-contained organic compounds are also promising electrocatalysts for ORR [156,207–210].
Nanostructured materials have received tremendous interest due to their unique mechanical/electrical properties and overall behavior contributed by the complex synergy of bulk and interfacial properties for efficient and effective energy conversion and storage. The booming development of nanotechnology affords emerging but effective tools in designing advanced energy material. We reviewed the significant progress and dominated nanostructured energy materials in electrochemical energy conversion and storage devices, including lithium ion batteries, lithium–sulfur batteries, lithium–oxygen batteries, lithium metal batteries, and supercapacitors. The use of nanostructured electrocatalyst for effective electrocatalysis in oxygen reduction and oxygen evolution reactions for fuel cells and metal–air batteries was also included. The challenges in the undesirable side reactions between electrolytes and electrode due to high electrode/electrolyte contact area, low volumetric energy density of electrode owing to low tap density, and uniform production of complex energy materials in working devices should be overcome to fully demonstrate the advanced energy nanostructures for electrochemical energy conversion and storage. The energy chemistry at the interfaces of nanostructured electrode/electrolyte is highly expected to guide the rational design and full demonstration of energy materials in a working device.
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Nitrogen-doped carbon materials exhibiting high oxygen reduction reaction activity were prepared via the pyrolysis of a poly-p-phenylenediamine/carbon black composite. The as-synthesized catalyst showed excellent catalytic activity in alkaline solution, and outperformed commercial Pt/C in KOH solution (0.1 mol/L), as demonstrated by the higher current density and the more positive half-wave potential. Scanning electron microscopy and N₂ adsorption-desorption analyses indicated that a composite structure, in which the N-rich surface of the poly-p-phenylenediamine had an increased active center concentration and the high external surface area of the carbon black was conducive to the mass transport, is highly beneficial in terms of promoting the oxygen reduction reaction. However, the activity of this catalyst underwent an obvious decrease following exposure to air for 30 d. X-ray photoelectron spectroscopy showed that the oxygen content in the catalyst was increased by prolonged air exposure. O 1s spectrum showed increases in the C=O and C–O components, suggesting that atmospheric oxygen reacted with the catalyst. This oxidation leaded to the deactivation of active center, thus the catalytic activity decreased. Based on these results, the stability in air of nitrogen-doped carbon materials must be taken into consideration when assessing applications as alternatives to platinum-based materials.

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Published 20 March 2015

This work was supported by the National Natural Science Foundation of China (21001037, 21071037, and 91122002), the Special Fund for Harbin Technological Innovation Talent (2013RFLXJ011), and the Research Fund for Talent Introduction of Huazhong University of Science and Technology (2014036).

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ArticlePyrolyzed titanium dioxide/polyaniline as an efficient non-noble metal electrocatalyst for oxygen reduction reaction

Abstract

Graphical Abstract

Introduction

Section snippets

Catalyst preparation

Influence of the mass ratio of PANI to TiO2 on the performance of the TiO2/C composites

Conclusions

Electrochim Acta

Int J Hydrogen Energy

Electrochim Acta

J Power Sources

Electrochim Acta

Electrochim Acta

Electrochim Acta

Chin J Catal

J Power Sources

Electrochim Acta

Int J Hydrogen Energy

J Mol Catal A

Carbon

Article
Pyrolyzed titanium dioxide/polyaniline as an efficient non-noble metal electrocatalyst for oxygen reduction reaction

Influence of the mass ratio of PANI to TiO₂ on the performance of the TiO₂/C composites