Non-precious-metal or metal-free catalysts with stability are desirable but challenging for proton exchange membrane fuel cells. Here we partially unzip a multiwall carbon nanotube to synthesize zigzag-edged graphene nanoribbons with a carbon nanotube backbone for electrocatalysis of oxygen reduction in proton exchange membrane fuel cells. Zigzag carbon exhibits a peak areal power density of 0.161 W cm−2 and a peak mass power density of 520 W g−1, superior to most non-precious-metal electrocatalysts. Notably, the stability of zigzag carbon is improved in comparison with a representative iron-nitrogen-carbon catalyst in a fuel cell with hydrogen/oxygen gases at 0.5 V. Density functional theory calculation coupled with experimentation reveal that a zigzag carbon atom is the most active site for oxygen reduction among several types of carbon defects on graphene nanoribbons in acid electrolyte. This work demonstrates that zigzag carbon is a promising electrocatalyst for low-cost and durable proton exchange membrane fuel cells.

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Effects of yttrium and erbium additions on glass-forming ability (GFA), thermal stability and mechanical properties of glassy Zr 55 Al 10 Ni 5 Cu 30 alloy were studied. (Zr 0:55 Al 0:10 Ni 0:05 Cu 0:30 ) 100Àx RE x (RE = Y, Er and x ¼ 0; 0:5; 1; 2; 3; 5 at%) metallic glasses were formed by melt-spinning and copper mold casting. It was found that the addition of Y or Er greatly enhanced the glass-forming ability, thermal stability and mechanical properties of Zr 55 Al 10 Ni 5 Cu 30 alloy. The alloys containing 1-3 at% Er can be cast into glassy rods with a diameter of 15 mm, which is larger than the critical diameter (10 mm) of the base alloy in the present work. With the addition of 1 at% Y, supercooled liquid region ÁT x of the base alloy was extended from 89 to 102 K, compressive strength was increased from 1650 to 1800 MPa and plastic strain reached a value as high as 3.5%.

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