Hierarchically porous nitrogen-doped graphene aerogels as efficient metal-free oxygen reduction catalysts.

Nitrogen-doped graphene aerogels with hierarchically porous architectures (N-Gs) are fabricated through the co-assembly of graphene oxide and o-phthalonitrile in a solvothermal process and the thermal treatment of the obtained composites at different temperatures. The structural characterizations indicate that both mesopores and macropores exist in the monolithic N-Gs. More importantly, the architectures, porosities and compositions show obvious dependence on the thermal treatment temperature. As the metal-free catalyst for oxygen reduction reaction in basic media, the sample thermally treated at 750°C shows the best catalytic performances among the three N-Gs, which is owing to its advantages in the surface areas and content of active N species.

A hybrid-assembly approach towards nitrogen-doped graphene aerogel supported cobalt nanoparticles as high performance oxygen reduction electrocatalysts.

As a novel electrocatalyst for oxygen reduction reaction (ORR), nitrogen-doped graphene aerogel supported cobalt nanoparticles (Co-NGA) is archived by a hybrid-assembly of graphene oxide (GO), o-phthalonitrile and cobalt acetate and the following thermal treatment. The hybrid-assembly process successfully combines the ionic assembly of GO sheets and Co ions with the coordination between o-phthalonitrile and Co ions, which can be converted to nitrogen doped carbon and Co nanoparticles in the pyrolysis process under nitrogen flow. Remarkable features of Co-NGA including the macroporous graphene scaffolds, high surface area, and N/Co-doping effect can lead to a high catalytic efficiency for ORR. As the results, the composites pyrolyzed at 600°C (Co-NGA600) shows excellent electrocatalytic activities and kinetics for ORR in basic media, which are comparable with those of Pt/C catalyst, together with superior durability.

Heteroatom doped mesoporous carbon/graphene nanosheets as highly efficient electrocatalysts for oxygen reduction.

The high cost of platinum (Pt) based catalysts for oxygen reduction reaction (ORR) has restricted the widespread commercialization of fuel cells. Heteroatom (N, B, P, S or Se) doped carbon materials have been regarded as the promising metal-free catalysts for replacing Pt based catalysts owing to their high efficiencies, good stability and relative low cost. In this work, we present a cost-effective synthesis approach for heteroatom (N and S) doped mesoporous carbon/graphene (HMCG) nanosheets by using nano-casting technology with mesoporous silica/graphene nanosheets (MSG) as hard templates, and four different amino acids (alanine, serine, arginine and cystine) as heteroatom (N, S) and carbon precursors. The resulting catalysts exhibited excellent electrocatalytic activity for ORR in alkaline media. In particular, HMCGAla with alanine as precursors showed the highest electron transfer numbers and durability. These results indicated the attractive potential of HMCGs as metal-free catalysts in practical fuel cells.