A graphene-directed assembly route to hierarchically porous Co–N_x/C catalysts for high-performance oxygen reduction

Abstract

The development of non-precious metal catalysts for efficient oxygen reduction is of significance for many advanced electrochemical devices such as fuel cells and metal-air batteries. Herein, we develop a graphene-directed assembly route to synthesize hierarchically nanoporous Co-Nx/C materials with a macro/meso/microporous structure, high specific surface area (i.e. 512 m 2 /g) and excellent conductivity using graphene oxide (GO) supported zeolitic imidazolate frameworks nanocrystal arrays as a catalyst precursor, followed by carbonization and acid leaching process. In this route, GO acts as a structure-directing agent to construct ZIF nanocrystal arrays supported on GO nanosheets. During the carbonization process, the resulting reduced graphene oxide functions as a binder and electrical conductor to connect individual ZIFderived carbon nanoparticles into the macroporous structure and increase the overal conductivity. ZIF nanocrystals themselves are also converted into meso/microporous carbon nanoparticles without using any other template. The hierarchically porous Co-Nx/C materials exhibit high ORR catalytic activity, superior stability and good methanol tolerance in both alkaline and acidic conditions.

Metal‐Organic Framework‐Based Nanomaterials for Electrocatalysis

“…Wei et al, developed Co-N-C on 2D graphene sheets with a high surface area of 512 m 2 /g using Co-ZIF-67 crystals in the initial precursor along with GO. [68] The developed catalysts not only show excellent capacity in the alkaline solution but also show superior onset potential (0.83 V vs RHE) in the acidic electrolyte. In contrast to other approaches where MOFs were coated onto flexible/hard substrates, an interesting approach describes the coating of amorphous Co x S y on ZIF-67 crystals to obtain yolk-shelled Co-C@Co 9 S 8 doubleshelled nanocages for highly efficient ORR catalysis.…”

Zeolitic Imidazolate Framework/Graphene Oxide Hybrid Nanosheets as Seeds for the Growth of Ultrathin Molecular Sieving Membranes

“…[8] Anumber of their composites such as ZIF-67/GO, [9] silicalite/GO, [10] MOF-5/GO, [11] HKUST-1/GO, [12] MIL-100/GO, [13] MIL-53/ GO, [14] and ZIF-8/GO [15] have been reported by our group and many others.C aro and co-workers [2g] showed the effectiveness of using GO to seal MOF crystal gaps to improve gas selectivity of MOF membranes.T hese studies demonstrate that it is feasible to prepare GO hybrid nanosheets from different MOFs and zeolites to build up ultrathin molecular sieving membranes.…”

The structure-dependent enhancement of the oxygen reduction reaction performance of Co-based low Pt catalysts through Au addition

“…On the other side, for the non-precious metal catalysts (NPMC), Co has shown promising enhancement for ORR activity and is one of the most studied catalysts in ORR application. [6][7][8][9][10] As summarized in the literature, [11][12][13][14][15][16] those NPMC are metal macrocycles, oxides, carbonitrides or chalcogenides and have shown promising results in the ORR application either in the acidic or alkaline electrolytes as their catalytic activity can be optimized by changing the chemical compositions and structures. However, the alloys of the non-precious metals have seldom been investigated.…”