Full Length ArticleConcave Pd–Ru nanocubes bounded with high active area for boosting ethylene glycol electrooxidation
Graphical abstract
Introduction
The increasing consumption of traditional fossil fuels coupled with the serious environment crisis have stimulated the rapid development of renewable and clean energy technology [1], [2]. Direct fuel cells (DFCs), with the features of easily-available, high-energy and non-toxic, have attracted an increasing notice for serving as promising energy conversion and storage devices [3], [4]. Among multitudinous fuel cells, direct ethylene glycol fuel cells (DEGFCs) are nowadays considered as advanced energy technologies due to their remarkable features such as higher boiling point (198 °C), higher energy density and less catalyst toxicity etc. [5], [6]. In addition, some previously published researches have demonstrated that the EG can primarily be produced from the cellulose with high yield, all of which make them as safe and attractive energy carrier in the field of DEGFCs [7], [8]. Regardless of these beneficial properties, the lack of cost-efficient catalysts for the electrooxidation of EG still seriously hinder its practical application [9].
Noble metal nanomaterials represent a novel class of catalysts for the electrooxidation reaction in DFCs, but its large-scale commercial application is also impeded by their limited electrocatalytic activity and stability [10]. Update, Pt-based nanomaterials, one of the most effective electrocatalysts used in DFCs, have also met the challenges of scared natural abundance and unsatisfied activity [11], [12]. In order to get over these difficulties, extensive efforts have been paid to engineer the hopefully alternative electrocatalysts with both enhanced activity and durability but less cost. In this regard, many less expensive and more plentiful non-platinum electrocatalysts with satisfactory performances have been widely applied [13], [14]. Especially for Pd and Pd-based materials, which can be widely applied as lead electrocatalysts towards liquid fuel oxidation with comparable or even superior performances to Pt [15], [16], [17]. As for Pd, it has been proved that the catalytic properties of Pd-based electrocatalysts are strongly dependent on their morphologies and compositions [18], [19], [20], [21]. With respect to this, alloying Pd with a secondary metal may be one of efficient strategies to boost the commercial development of DFCs, for which can reduce the usage of noble Pd metal while simultaneously improving performance as compared with that of pure Pd on mass activity [22], [23], [24], [25]. Among a wide range of transition metals, Ru has been undoubtly considered as excellent ligand to form the stable PdRu alloy with greatly enhanced catalytic activity for liquid fuel oxidation reactions due to the Watanabe–Motoo bifunctional mechanisms: Ru atoms provide OHads-like adsorbed hydroxyl groups and serve as the oxidant to oxidize the COads at a much lower potential [26], [27], which are favorable for greatly reducing the CO-poisoning of PdRu electrocatalyst [7], [28].
In addition, tuning and optimizing the exposed surface active area through engineering the morphology and structure is also believed to be a fruitful approach to enhance the electrocatalytic performances [29]. Up till now, many typical nanostructures have been developed to greatly enhance the electrocatalytic performances such as nanowire [30], dendrites [31], nanosphere [32], core–shell [33] and so on. Among these special nanostructures, concave nanocubes have been highly expected to exhibit outstandingly excellent electrocatalytic performances for DEGFCs due to their fascinating properties of high surface area, self-supporting capacity, as well as high surface permeability [34], [35], [36].
Based upon these analyses, we herein designed a novel class of binary PdRu concave nanocubes with abundant exposed surface area and tunable compositions via a facile wet-chemical strategy. Owing to the fascinating concave nanocube structure, synergistic and electronic effects between Pd and Ru, the as-prepared PdRu concave nanocubes exhibited considerable high electrocatalytic activity with the mass activity of 3345 mA mgPd−1, 3.86-fold enhancements than that of commercial Pd/C (866 mA mgPd−1). We confirmedly trust that this proposed plot is important for the fabrication and modification for future metallic catalysts and the as-prepared PdRu concave nanocubes (PdRu CNCs) with outstandingly excellent electrocatalytic performances can be well applied for boosting the development of DEGFCs.
Section snippets
Preparations of electrocatalysts
In the standard synthesis of PdRu CNCs, 40 mg cetyltrimethylammonium bromide (CTAB) was firstly dissolved in 8 mL H2O in a flask. Subsequently, 2.2 mL RuCl3 (19.3 mM) and 2 mL l-ascorbic acid (C6H8O6, 60 mg, 99%) were added dropwise to above mixture under vigorous stirring. The reaction flask was then transferred to an oil bath and heated from room temperature to 85 °C. 1 mL H2PdCl4 (22.6 mM) was also added dropwise to above solution as soon as the temperature raised to 85 °C and kept reacting for 4 h at
Physicochemical characterization
The concave PdRu nanocubes have been synthesized via a facile wet-chemical with the assistance of CTAB. The morphological features of the as-obtained PdRu CNCs were firstly analyzed through TEM. Fig. 1(a)–(c) shows the typical TEM images of Pd1Ru2 CNCs with different magnifications and their size distributions. The results reveal that the as-obtained PdRu nanocrystals with a high yield approaching 100% exhibit a distinct cubic shape with concave structures, indicating that it can be produced at
Conclusions
In summary, a typical wet-chemical method has been developed to successfully synthesize a novel class of binary PdRu CNCs with tunable atomic ratios. A series of characterizations revealed that the as-prepared PdRu nanomaterials showed a fascinating concave nanocube structure with abundant high-density index facets and surface active areas. Benefitting from the unique concave nanocube structure, synergistic effect and electronic effect between Pd and Ru, such PdRu CNCs with optimum component
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant No. 51373111), the Suzhou Industry (SYG201636), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) and the State and Loc-al Joint Engineering Laboratory for Novel Functional Polymeric Materials.
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