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A low-cost, novel carbon-based electrocatalyst for oxygen reduction reaction (ORR), nitrogen-doped carbon xerogel (N-CX) was synthesized via a sol-gel polymerization method followed by a pyrolysis process. The N-CX catalyst exhibited a high activity for ORR, and a good stability in acid media. A high performance with a maximum power density of 360 mW cm À2 was achieved on a single PEM fuel cell with N-CX as the cathode electrocatalyst.As one of the key materials of PEM fuel cells, the electrocatalyst for oxygen reduction reaction (ORR) in particular plays a critical role in determining cell performance, cost and durability. The platinumbased carbon-supported electrocatalysts (e.g. Pt/C) have been considered as the most effective elecrocatalysts for ORR in PEM fuel cells due to their high activities and good stabilities. 1-9 However, the issues of high cost, scarce sources and long-term durability limit their large-scale production and hinder the commercialization of PEM fuel cells. [10][11][12][13][14] In order to decrease the cost of electrocatalysts and eliminate their dependence on noble metals, various non-noble metal catalysts have been explored recently as alternatives to the Pt-based electrocatalysts, which include chalcogenide catalysts, 15-19 transition metal macrocyclic compounds, 20-22 transition metallic oxides 23-27 and carbon-based catalysts. [28][29][30][31][32][33][34][35] In particular, carbon-based catalysts doped with the heteroatoms such as nitrogen (N) or boron (B) have been paid much attention and been proposed as typical non-noble metal catalysts for ORR 36-38 in alkaline media. Especially, since Gong et al. 37 reported the superior activity and stability of nitrogen doped carbon nanotube in alkaline solution, the heteroatom doped carbon materials have been expected to be promising alternative Pt-based catalysts. The doped carbon-based catalysts demonstrate tailored physico-chemical properties, such as structure, electrical conductivity, surface properties and oxidation stability, depending on the amount of the incorporated heteroatoms. It is also reported that the incorporated heteroatoms in the carbon structure contribute to the catalytic activities for many reactions 39-41 including the ORR in alkaline media. However, the activities and stabilities of these catalysts in acidic media are still challenging.Recently, carbon xerogels have been reported as the electrode materials for capacitors and electrocatalyst supports because of their controllable structures, high electronic conductivities, good anticorrosion properties, facile preparations and low costs. 42-51 However, they are almost inactive towards the ORR in PEM fuel cells. In this paper, a nitrogen-doped carbon xerogel (N-CX) was developed by incorporating nitrogen into the carbon xerogel and employed as an electrocatalyst for ORR in PEM fuel cells. Broader contextDue to their advantages such as fast response, high efficiency, environmental friendliness, etc., PEM fuel cells are considered as the most promising power sources for t...

a b s t r a c tCarbon supported Pt (Pt/C) with various average particle sizes ranging from sub 3 nm to 6.5 nm were in situ prepared and characterized at the cathode of proton exchange membrane fuel cells (PEMFCs). A clear Pt particle size effect on both the catalytic activity for oxygen reduction reaction (ORR) and the durability of the electrocatalyst was revealed. With the Pt particle size increase, both the surface specific activity and the electrochemical stability of Pt/C improved; however, the mass specific activity of Pt/C is balanced by the electrochemical surface area loss. The reduced occupation of corner and edge atoms on the Pt surface during the Pt particle size increase is believed to weaken the adsorption of the oxygenated species on Pt, and thereafter releases more available active sites for ORR and also renders the Pt surface a stronger resistance against potential cycling. It is therefore proposed that by designing the Pt microstructure with more face atoms on the surface, cathode electrocatalyst with both improved activity and enhanced durability would be developed for PEMFCs.