Size effects of platinum particles@CNT on HER and ORR performance
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Published online 18 August 2020 | https://doi.org/10.1007/s40843-020-1449-2
Size effects of platinum particles@CNT on HER and ORR performance 1
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Zhonghua Ma , Han Tian , Ge Meng , Lingxin Peng , Yafeng Chen , Chang Chen , 2 2,3* 1* 1* 2,3 Ziwei Chang , Xiangzhi Cui , Lianjun Wang , Wan Jiang and Jianlin Shi ABSTRACT Platinum (Pt) is an efficient catalyst for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), but the debate of the relevance between the Pt particle size and its electrocatalytic activity still exist. The strong metal–support interaction (SMSI) between the metal and carrier causes the charge transfer and mass transport from the support to the metal. Herein, Pt species (0.5 wt.%) with various particle sizes supported on carbon nanotubes (CNTs) have been synthesized by a photo-reduction method. The ~1.5 nm-sized Pt catalyst shows much higher HER performance than the counterparts in all pH solutions, and the mass activity of it is even 23–36 times that of Pt/C. While for ORR, the ~3 nm-sized Pt catalyst exhibits the optimal performance, and the mass activity is 3 times and even 16 times that of Pt/C in acidic and alkaline media, respectively. The high HER and ORR performances of the ~1.5 nm- and ~3 nm-sized Pt catalysts benefit from the SMSI between Pt and the CNTs matrix and the higher ratio of face sites to edge sites, which is meaningful for the design of efficient electrocatalysts for renewable energy application. Keywords: size effect, HER, ORR, platinum, strong metalsupport interaction
INTRODUCTION Proton exchange membrane fuel cell (PEMFC) with hydrogen as anode fuel is a kind of clean energy transport system with water as the only product (H2+1/2O2→H2O) [1–3], which can avoid the environmental pollution. The cathodic oxygen reduction reaction (ORR) is sluggish because of the 4e reaction process, which is the rate
controlling step for the cell performance. On the other hand, high-purity hydrogen as anode fuel is necessary to avoid the CO “poisoning” phenomenon of Pt in the anode chamber of PEMFCs. Hydrogen evolution reaction (HER) is a desirable approach to obtain high-purity hydrogen [4,5]. At present, Pt is still the efficient ORR and HER catalysts because of its high electrocatalytic performance. But the amounts of Pt need to reach 20 wt.% and even 20–40 wt.% for using as HER and ORR catalysts, respectively, which limits the practical application due to its limited reserve and high price [6,7]. Although Pt-free electrocatalysts, such as phosphides [8], chalcogenides [9], oxides [10,11], nitrides [12] and carbon based materials [13], have shown promising HER and/or ORR activities, it is rather difficult to completely replace Pt with these catalysts due to the significant gap in performance between the present state-of-the-art Pt-based catalysts and the Pt-free catalysts. Therefore, the challenge is to develop efficient platinum-group-metal-free electrocatalysts, or to greatly decrease the Pt loading amount by enhancing the specific activity of Pt or i
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