Facile Galvanic Replacement Synthesis of Pd-Cu Nanotubes with Improved Electro-Catalytic Activity Toward Methanol Oxidation

Abstract

Direct methanol fuel cells (DMFCs) have been considered to be a promising power source of alternative energy because of their cleanliness and high efficiency and flexibility for mobile, transportation and stationary applications. The methanol electrooxidation plays a significant role in controlling the performance in DMFCs and efficient electrocatalysts for methanol electrooxidation are essential for the practical applications of DMFCs. Carbon–supported Pt have been regarded as the best catalyst for methanol electrooxidation in DMFCs in current catalysis technology. However, the high cost and low reserves as well as low methanol tolerance of Pt for methanol oxidation significantly inhibit its widespread application especially in DMFCs. Among various platinum-free methanol electrooxidation catalysts, palladium has been demonstrated to be an interesting class of highly active methanol oxidation electrocatalyst. Over the past decade, a large number of supportless Pd-based alloy electrocatalysts have been synthesized due to their highly efficient and durable electrocatalysts for methanol oxidation. This abstract mainly focused on a facile synthesis route for as-synthesized palladium-copper alloy nanotubes via the galvanic replacement reaction in a large scale. Utilizing this strategy, we have prepared a series of well-alloyed CuPd alloy nanotubes with a variety of chemical compositions in an aqueous solution containing PdCl2 and copper nanowires as the sacrificial templates at room temperature.This synthesis provides a convenient and environmentally benign route to large-scale production because it does not require high temperature, surfactants and organic solvent, or annealing at high temperatures. Upon adding more and more PdCl2 solution to the synthesis system, we found that the compositions of the as-synthesized CuPd nanotubes were facilely controlled and the alloying extent for these as-synthesized CuPd alloys exceeds 0.98. The morphology and phase structure of the CuPd alloy nanotubes were characterized by transmission electron microscopy, scanning electron microscope and X-ray diffraction, as shown in Fig.1A and B. The results showed that the average diameter of the CuPd alloy nanotubes were in the range of 80–150 nm, and the wall thickness of the CuPd nanotubes was between 20–40 nm. The formation of the CuPd alloy nanotubes may be involved with a Kirkendall and Diffusion Process. The CuPd alloy nanotubes exhibited the excellent methanol electrooxidation activity in an alkaline solution, which is comparable for that of the commercial Pt/C (E-TEK) (Fig.1C). The origin of the enhancement in the methanol electrooxidation activity could be explained by the unique electronic structures in CuPd alloy nanotubes, which can effectively achieve a counterbalance between two opposite effects that revolve with the accelerated methanol oxidation and desorption of oxygenate intermediates like CO on the catalyst during methanol oxidation. This information was important to understand the physical origin of the catalytic activity of palladium-copper alloy nanotubes for methanol electrooxidation. *Corresponding author at :State Key Laboratory of Chemical Resource Engineering, Beijing Key Laboratory of Electrochemical Process and Technology for Materials, Beijing University of Chemical Technology, Beijing 100029, China) E-mail: liujingjun@mail.buct.edu.cn; wangf@mail.buct.edu.cn. This work was supported by National Natural Science Funds of China (Grant Nos. 50972003, 51125007) Figure 1