Nanoporous Graphitic-C3N4@Carbon Metal-Free Electrocatalysts for Highly Efficient Oxygen Reduction - Zheng, Y.; Jiao, Y.; Chen, J.; Liu, Jian; Liang, J.; Du, A.; Zhang, W.; Zhu, John; Smith, S.; Jaroniec, M.; Lu, G.; Qiao, S. (American Chemical Society, 2011)