Tiny crystalline grain nanocrystal NiCo2O4/N-doped graphene composite for efficient oxygen reduction reaction

Oxygen reduction reaction (ORR) plays an important role in green energy conversion, although catalysts are necessary for overcoming its sluggish kinetic. Herein, a nanocrystal NiCo 2 O 4 /N-doped graphene composite material showing high ORR electrocatalytic activity is prepared. The resulting NiCo 2 O 4 /N-doped graphene composite (NiCo 2 O 4 -NG/C) combines the advantages of both component materials and shows enhanced ORR electrocatalytic activity (i.e., more positive peak potential and half-wave potential compared with NiCo 2 O 4 ) while having higher diffusion-limited current density values (−5.7 mA cm −2 , 1600 rpm), better tolerance to methanol, and improved stability than 20 wt% Pt/C. NiCo 2 O 4 anchored on N-doped graphene are demonstrated to be nanocrystal with tiny crystalline grain (diameter < 5 nm) and result in large surface area , thereby allowing more active sites to be exposed. Moreover, the potential exposure of high-index planes may be also responsible for the observed high activity of these materials.