A novel design concept of a three-dimensional graphene shell encapsulated cobalt nanostructure as a new route to tune the work function of graphene for enhanced ORR.

Recently, nonnoble‐metal catalysts such as a metal coordinated to nitrogen doped in a carbon matrix have been reported to exhibit superior oxygen reduction reaction (ORR) activity in alkaline media. In this work, Co2P nanoparticles supported on heteroatom‐doped carbon catalysts (NBSCP) are developed with an eco‐friendly synthesis method using bean sprouts. NBSCP can be easily synthesized through metal precursor absorption and carbonization at a high temperature. It shows a very large specific surface area with various dopants such as nitrogen, phosphorus, and sulfur derived from small organic molecules. The catalyst can exhibit activity in various electrochemical reactions. In particular, excellent performance is noted for the ORR. Compared to the commercial Pt/C, NBSCP exhibits a lower onset potential, higher current density, and superior durability. This excellent ORR activity and durability is attributable to the synergistic effect between Co2P nanoparticles and nitrogen‐doped carbon. In addition, superior performance is noted on applying NBSCP to a practical anion exchange membrane fuel cell system. Through this work, the possibility of applying an easily obtained bio‐derived material to energy conversion and storage systems is demonstrated.

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Atomically dispersed metal atoms on supporting materials inherit the merits of both heterogeneous and homogeneous catalysts, such as the easy separation and high durability of a heterogeneous phase and the well-structured catalytic active sites and tunable activity of a homogeneous phase. [6][7][8] The isolated metals in SACs are located on neighboring surface atoms (metal oxide, metal nitride, and carbon atoms) or coordinated with heteroatoms, such as nitrogen, sulfur, and phosphorus. [7,[9][10][11] The metal centers and their surrounding atoms can be thought of as molecular catalytic sites that proceed down a highly selective reaction pathway. [12][13][14][15][16] For a decade, a variety of synthesis strategies have been developed to realize highly active SACs. [7,[17][18][19] One of the most widely applied methods is the defect engineering strategy. [1,[20][21][22] Preformed defects on supporting materials can alter the surrounding electronic state and have been used as effective "traps" to capture metal precursors and anchor metal atoms during post-treatment. [8,23] Another popular synthetic method is the spatial confinement strategy. Despite considerable development in the field of single-atom catalysts (SACs)on carbon-based materials, the reported strategies for synthesizing SACs generally rely on top-down approaches, which hinder achieving both simple and universal synthesis routes that are simultaneously applicable to various metals and nanocarbons. Here, a universal strategy for fabricating nanocarbon based-SACs using a flash bottom-up arc discharge method to mitigate these issues is reported. The ionization of elements and their recombination process during arc discharge allows the simultaneous incorporation of single metal atoms (Mn, Fe, Co, Ni, and Pt) into the crystalline carbon lattice during the formation of carbon nanohorns (CNHs) and N-doped arc graphene. The coordination environment around the Co atoms of Co 1 /CNH can be modulated by a mild post-treatment with NH 3 . As a result, Co 1 /CNH exhibits good oxygen reduction reaction activity, showing a 1.92 times higher kinetic current density value than the commercial Pt/C catalyst in alkaline media. In a single cell experiment, Co 1 /CNH exhibits the highest maximum power density of 472 mW cm −2 compared to previously reported nonprecious metal-based SACs.