Dual Inorganic Sacrificial Template Synthesis of Hierarchically Porous Carbon with Specific N Sites for Efficient Oxygen Reduction.

ABSTRACT

It is still a challenge to achieve efficiently controlled preparation of functional oxygen reduction reaction (ORR) carbon electrocatalysts with multi-preferred structures (hierarchically porous networks and specific carbon-nitrogen bonds) from carbohydrate-containing small molecules via simple one-step pyrolysis. Based on the step-by-step spontaneous gas-foaming strategy, we successfully prepare 3D hierarchically porous networks with tunable N sites (NP/NG ≈ 11) by pyrolyzing diverse carbohydrates (glucose, maltose, and cyclodextrin) using nonmetal-metal dual inorganic sacrificial templates. In situ evaporation templates can simplify the procedure of the experiments and avoid the active site loss compared with traditional hard templates. Crucially, dual inorganic sacrificial templates can induce abundant defects and microscopic pore structures (the specific surface area increased from 922.403 to 1898.792 m2·g-1) and tunable N sites compared with single nonmetal sacrificial templates. The regulatory mechanism of dual inorganic templates on N sites (NP/NG ≈ 11) is independent of the polymeric state of carbohydrate precursors or even the carbonization condition of the pyrolysis process. A series of carbon materials prepared by this strategy all have ORR-preferred structures and exhibit low ORR overpotentials compared with Pt/C. For instance, the Zn-air battery with ßCD-DSC-950-1 exhibits an open-circuit potential of 1.51 V and a peak power density of 180.89 mW·cm-2, higher than those of Pt/C (1.47 V, 174.94 mW·cm-2). In general, the conversion of carbohydrate-containing small molecules to functional carbon materials provides a new strategy for the development of carbonaceous electrocatalysts.