Elsevier

Applied Surface Science

Volume 492, 30 October 2019, Pages 617-625
Applied Surface Science

Full length article
Pd-Ru-Bi nanoalloys modified three-dimensional reduced graphene oxide/MOF-199 composites as a highly efficient electrocatalyst for ethylene glycol electrooxidation

https://doi.org/10.1016/j.apsusc.2019.06.228Get rights and content

Highlights

  • PdRuBi@rGO/MOF-199 catalyst was fabricated by hydrothermal and impregnation method.

  • The catalyst exhibits excellent electrocatalytic activity and durability for EGOR.

  • Peak current of the catalyst for EG oxidation is 7.23 times higher than that of Pd/C.

  • The unique 3D structure and strong synergistic effect improve catalytic durability.

Abstract

Well-dispersed trimetallic Pd-Ru-Bi alloy nanoparticles (NPs) were successfully embedded in the three-dimensional (3D) rGO/MOF-199 by a facile hydrothermal and in situ impregnation-reduction method. Among the mono-, bi- and tri-metal@rGO/MOF-199 electrocatalysts, the trimetallic PdRuBi@rGO/MOF-199 exhibited the highest catalytic activity and durability towards ethylene glycol oxidation reaction (EGOR) under the alkaline condition, as high as 213.93 mA cm−2, is about 7.23 times higher than that of commercial Pd/C. The outstanding electrocatalysis oxidation performance of the PdRuBi@rGO/MOF-199 is attributed to the unique 3D structures with trimetallic composition and strong synergistic effects of Pd, Ru and Bi nanoalloys that providing plenty of interfaces and achievable reaction active sites. Furthermore, the introduction of GO in MOF-199 matrix conduces to the superior electron transfer and large surface area, which are beneficial to improve the catalytic ability of the catalyst. The study on the new composites offers a conception and applicable way to develop the advanced Pd-based electrocatalysts for high performance direct ethylene glycol fuel cells.

Introduction

Currently, direct alcohol fuel cell is considered as the next generation power sources for efficient and non-polluting energy conversion [[1], [2], [3]], in which the development on direct ethylene glycol fuel cell (DEGFC) have increased tremendously, owing to ethylene glycol's low toxicity, available in supply chain, inflammability, high boiling point, and superior energy density or high theoretical capacity [[4], [5], [6]]. The investigations of electrochemical kinetics and reaction mechanism show that the electrooxidation of ethylene glycol illustrates high activity under alkaline conditions [7]. Accordingly, the application of highly electro-active and durable catalysts for ethylene glycol oxidation reaction (EGOR) is still a challenge.

The exploitation of efficient electrocatalysts for ethylene glycol (EG) could be designed through two pathways: the support features and metallic phase composition [8]. Graphene is considered to be the most promising carrier material for fuel cell electrode catalysts due to its good electrical conductivity and special structural properties [9]. A single layer of hexagonally close-packed carbon atoms has characteristics of stable structure, large specific surface area, fast electron conduction speed and corrosion resistance, which possess the basic conditions as a fuel cell catalyst carrier [[10], [11], [12], [13]]. Graphene oxide (GO) is a soft two-dimensional nanomaterial containing a large number of oxygen-containing functional groups such as epoxy groups and carboxyl groups [14,15]. Moreover, reduced graphene oxide (rGO) possesses unique ability to anchor metal NPs through its inherent residual oxygen containing functional groups [16,17]. Additionally, the defect sites on rGO sheet act as anchoring sites for the metal NPs, which can restrict free mobility of the NPs and improve the catalytic efficiency and stability [18].

MOFs-based structures offer many advantages, such as high surface areas, tunable pore sizes, huge porosity, functionality, structural diversity and flexibility [19,20]. Based on these characteristics, MOFs have been applied as solid catalysts or catalyst supports for a various of organic transformations [21]. This specific structural feature favors the attachment of the graphene layers to the MOFs units and the subsequent growth of the crystal. GO can be easily dispersed in water because of its hydrophilic character, this will lead to the formation of new pore space at the interface between the MOFs blocks and GO, which can increase the dispersive forces and effectively retain the guest molecules. MOF/GO composites can combine the advantages of MOFs and the dense graphene layers of GO [[22], [23], [24]], the incorporation will enhance the stability, porosity and electron-conductive properties of MOFs [25]. With the loading of metal NPs, the new composites will be beneficial to increasing metallic loading quantity, reducing size, enabling uniform distribution and the enhancement of catalytic activity of nanoalloys.

On the other hand, palladium-based catalysts exhibited good catalytic effects on alcohol electrooxidation in alkaline medium [26]. Moreover, Pd is a cheaper and more abundant metal than Pt in nature. For these reasons, the research on Pd-based catalysts in recent years has a rapid development. For instance, many Pd-based bimetallic catalysts including PdPb NCs [27], Pd-Sn/Pd-Ni/CNT [28], Pd-Cu [29] and trimetallic catalysts Pd-Ag-Au [30], Pd-Pt@Pt/rGO [31], Pd-Au-Ni/C [32], Pt-Pd-Ni/rGO [33] and Pd-Co-Ni/G [13] have been reported. Apart from these, Pd-Ru/C was found that Ru can form RuxOHy at low potential and weak CO adsorption on Pd3Ru/C under the alkaline condition [34]. Almir Oliveira Neto et al. [35] reported that Pd/C catalyst through Bi-modified can improve catalytic activity towards ethanol oxidation. Yiyin Huang et al. [36] found that PdCuBi/C core-shell catalysts exhibited enhanced catalytic activity for EG electrooxidation, owing to Cu and self-adsorbed Bi providing oxygenated species on the catalyst surface. Yaxi Pan et al. [37] studied the three-dimensional catalyst RuPdBi/SiO2-NG using for EG oxidation in alkaline media, and found that the addition of Ru and Bi in Pd/SiO2-NG can obviously promote catalytic activity, but the highest current density was only 52.4 mA cm−2. Tengfei Li et al. [38] reported that the Ru-Bi modified Pd/N-graphene had a high electrocatalytic performance on EG, but the peak current density was only 157.3 mA cm−2. Consequently, using the low cost materials while improving the activity and stability of the catalysts is alloying noble metals, the alloy formation between the active component Pd and other metals alters the electronic structure of the Pd-based electrocatalysts and is beneficial to increase their synergistic effect as well as tolerance of poison species.

In this work, a simple and efficient route to prepare Pd-Ru-Bi nanoalloys embedded in the novel three-dimensional rGO/MOF-199 by a facile hydrothermal and in situ impregnation-reduction method was demonstrated. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brauner-Emmett-Teller (BET) specific surface area, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) were used to study the physical and chemical properties of all electrocatalysts. The electrochemical behavior of the trimetallic PdRuBi@rGO/MOF-199 catalyst was evaluated by cyclic voltammetry (CV), chronoamperometry (CA), electrochemical impedance spectroscopy (EIS) towards EG oxidation in the alkaline solution, compared with Pd/C, Pd@rGO/MOF-199, PdRu@rGO/MOF-199 and PdBi@rGO/MOF-199.

Section snippets

Preparation of catalysts

Graphene oxide (GO) was prepared by the modified Hummer's method and preserved in water [11,13,39]. The GO/MOF-199 support was prepared as follows: take 0.0168 g of the above-obtained graphene oxide by sonication for 1 h, the mixture of Cu(NO3)2·3H2O (0.1247 g, 0.515 mmol) and 1,3,5-benzenetricarboxylic acid (H3BTC) (0.0672 g, 0.3189 mmol) and the above graphene oxide were dissolved in the mixed solution of N,N-dimethylformamide (DMF, 3 mL), ethanol (4 mL) and water (2 mL). The mixture was

Physicochemical characterization

Fig. 1 shows the XRD patterns of five different composites GO/MOF-199, Pd@rGO/MOF-199, PdBi@rGO/MOF-199, PdRu@rGO/MOF-199 and PdRuBi@rGO/MOF-199. From Fig. 1A, it is obvious that the main diffraction peaks of the support GO/MOF-199 at 2θ = 6.56°, 9.38°, 11.72°, 13.37°, 17.38°, 18.99°, 26.02°, 29.31°, 34.93° and 39.20° are well consistent with XRD pattern of MOF-199 reported in the literature. Moreover, all four catalysts contain the diffraction peaks of MOF-199, which indicate that the presence

Conclusions

In summary, a three-dimensional reduced graphene oxide/MOF-199 decorated Pd-Ru-Bi nanoalloys electrocatalyst with high activity and durability towards EGOR have been successfully prepared by hydrothermal and liquid impregnation method. The PdRuBi@rGO/MOF-199 catalyst is used as an anode catalyst for EGOR, the current density (213.93 mA cm−2) is 7.23 times as much as that of commercial Pd/C (29.57 mA cm−2). The result reveals that the introduction of reduced graphene oxide/MOF-199 support into

Acknowledgements

This project was supported by the Natural Science Fund for Creative Research Groups of Hubei Province (2014CFA015) of China. This work was also supported by the Hubei College Students' Innovation Training Program of China (201510512030).

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