Elsevier

Materials Letters

Volume 264, 1 April 2020, 127309
Materials Letters

Template-mediated growth of tungsten oxide with different morphologies for electrochemical application

https://doi.org/10.1016/j.matlet.2020.127309Get rights and content

Highlights

  • Length to width ratios of WO3 can be mediated via CNT templates.

  • CNT bundles exhibit good prospects in regulating the morphologies of nanomaterials.

  • SR-WO3/CNTs displayed excellent hydrogen oxidation properties and high stability.

  • Excellent performance is attributed to the conductive CNTs and good dispersion of WO3.

Abstract

The morphology of tungsten oxide (WO3) was effectively mediated by carbon nanotubes (CNTs) as templates. The grown direction of WO3 on the CNT bundle surfaces could be controlled, which mainly depended on the distribution state of tungsten acid (H2WO4) precursor in the reaction system. After thermal treatment of H2WO4/CNTs under nitrogen gas flow, WO3 with different morphologies (plates, short rods, and long rods) and sizes (10–1000 nm) supported by CNT bundles were finally obtained. The results indicated CNT bundles as templates can play an important role in regulating the morphologies of WO3. Moreover, the study shows that CNT bundles exhibit excellent prospects in the tailor-synthesis of micro/nanostructured materials with different dimensions. According to the peak current density for the 1000th electrochemical cycle in 0.5 mol L−1 H2SO4 and 0.5 mol L−1 CH3OH electrolyte solution, short rod-like WO3/CNTs exhibited higher peak current density (43.2 mA cm−2) than long rod-like WO3/CNTs (23.68 mA cm−2), plate-like WO3/CNTs (15.63 mA cm−2), CNTs (2.25 mA cm−2), and commercial WO3 (3.19 mA cm−2). The results demonstrated the potential application of short rod-like WO3/CNTs materials for hydrogen oxidation reaction of methanol fuel cells and in other related fields.

Graphical abstract

The CNT templates played a vital role in regulating the grown direction of H2WO4 precursors, and ultimately determined the morphologies and sizes of WO3. The WO3 short rods deposited on the CNT bundles exhibit excellent hydrogen oxidation performance, which indicates great potential application as electrocatalyst for DMFCs and in other related fields.

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Introduction

Nanostructured WO3 has attracted increasing attention due to its excellent electrochromic [1] and hydrogen oxidation reaction (HOR) performance [2], and significant potential application for catalyst support or catalyst for direct methanol fuel cells (DMFCs) [3]. Cathode and anode peaks are due to the redox that occurs during hydrogen insertion/detachment in WO3. H+ from an acid solution receives an electron and embeds into WO3 during the cathode reaction process, whereas the reduced H is oxidized by losing an electron forming H+ during the anode reaction process, which is similar to the catalytic activity of metallic Pt to hydrogen insertion/detachment [4], [5], [6]. Therefore, the developed WO3 nanomaterials with novel structure and improved performance have good prospects as catalyst supports or catalysts [7], [8], [9]. However, the morphology and grain size of WO3 are mainly affected by its precursor. Further enhancement of the unique properties of WO3 is necessary. The most common method for the synthesis of WO3 is the template method, which is efficient in influencing, modifying, and adjusting the morphology, size, and structure of the target material, with the aid of specific templates [10], [11], [12], such as carbon nanotubes (CNTs), graphene, and metal organic frameworks (MOFs).

Bestowed with high specific surface area and unique network structure, CNTs have been widely used as a template to mediate the morphology of micro/nanomaterials and further enhance their specific properties [13], [14]. After the deposition of an appropriate metallic precursor on the surface of CNT bundles, metal oxide with high dispersion, specific morphology, and small size can be obtained after the direct calcination of the precursor [15], [16]. To the best of our knowledge, studies on the preparation of micro/nanomaterials with different morphologies using CNT templates are rare. Herein, we report the synthesis of WO3 with different morphologies by tuning the mole ratios of CNT templates to H2WO4 seeds. The CNTs were prepared according to the literature reported by ZiPing Wu et al. [17]. The obtained micro/nanostructured WO3 materials with different morphologies and sizes exhibited different hydrogen oxidation performances and stabilities.

Section snippets

Materials and methods

Na2WO4 aqueous solution was added to CNTs/ethylene glycol suspension, and then concentrated hydrochloric acid was gradually added dropwise in the mixed solution above under well-controlled pH and temperature conditions. The tungsten precursor/CNTs composites were controlled by setting CNTs to Na2WO4 ratios of 1:1, 1:4, and 1:14; the obtained products were noted as TP-1, TP-2, and TP-3, respectively. The composites above were calcined at 600 °C under nitrogen gas at a ramp rate of 6 °C min−1 for

Results and discussion

As shown in Fig. 1, TP-1 with a plate-like structure (the average size was 50 to 100 nm) deposited on CNT bundles (Fig. 1a) and showed green color (Fig. S1d). As presented in Fig. S1e, TP-2 exhibited short rod-like structure (length of 50 nm with widths of 20 nm) that was deposited on CNT bundles (Fig. 1b) and gray color. The long rods of H2WO4 transformed into long nanorods (length of over 200 nm and width of 50 nm) (Fig. 1c) and showed light blue (Fig. S1f) when the mole ratio of CNTs to Na2WO

Conclusions

WO3 materials with different morphologies (plates, short rods, and long rods) were successfully synthesized via a CNT template-based method. WO3 with a short rod-like structure and good dispersion that was deposited on the conductive CNTs templates demonstrated improved electrochemical performance and higher stability. These results show that the synthesized SR-WO3/CNTs has promising potential in application as electrocatalyst for DMFCs and likely in other related fields.

Author contribution statement

(1) Yanhong Yin, Chunfa Liao and Qiulin Zhang designed experiments and supplied substantial contributions to conception.

(2) Zhen Tong and Min Wen carried out experiments and collected experimental data.

(3) Xianbin Liu, Yesheng Li and Changqiang Yu analyzed and interpreted experimental data.

(4) Yanhong Yin drafted the article and revised it critically for important intellectual content.

(5) Yanhong Yin and Ziping Wu give general supervision of the research group.

(6) Dionysios D. Dionysiou

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the China Scholarship Council [201908360233]; Postdoctoral Science Foundation of China [2018M632591].

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