Herein, a N, S co-doped carbon encapsulating Co 9 S 8 nanoparticles (Co 9 S 8 @N, S-C) catalyst is successfully synthesized by a new precursor of Co-pyridine coordinated-polymer consisting of 2,6-diacetylpyridine and 4,4′-dithiodianiline. Benefiting from the abundant pore-structure (average pore-size ≈25nm) and unique electronic-properties of the Co 9 S 8 and N, S-C layer, the as-prepared Co 9 S 8 @N, S-C exhibits rapid oxygen reduction reaction (ORR) kinetics with high electron transfer number of ≈3.998 and demonstrates a low overpotential of 304 mV for the oxygen evolution reaction (OER). It exhibits a small potential difference of 0.647V for overall ORR/OER activity, outperforming most of the non-precious metal-catalysts previously reported. The rechargeable Zn-Air battery test further demonstrates its excellent activity and stability, in which the battery delivers a maximum power density output of 259 mW cm −2 , a specific capacity of 862 mAh g Zn −1 , and after continuous 110 h operation the charge-discharge round-trip efficiency only reduces by 4.83%. Theoretical calculation studies show that the surface N, S-C layers and Co 9 S 8 can adjust each other's Fermi levels, so that the adsorption energy of Co 9 S 8 @N, S-C on O intermediate is more favorable than using Co 9 S 8 and N, S-C alone. This study reveals the structure-function relationship of coated-nanostructures with multifunctional electrocatalytic properties, and provides a feasible strategy for the design of non-noble metal-catalysts.

Electrochemical water-splitting reactions (hydrogen evolution reaction (HER) and oxygen evolution reaction (OER)) and oxygen redox reactions (oxygen reduction reaction (ORR) and OER) are core processes for electrochemical water-splitting devices, rechargeable metal–air batteries, and regenerative fuel cells. Developing highly efficient non-noble multifunctional catalysts in the same electrolyte is an open challenge. Herein, efficient Co–N–C electrocatalysts with a mixed structure comprising Co–N moieties and Co nanoparticles encapsulated in a N-doped carbon layer were prepared via pyrolysis of a new structure of Co-coordinated bis­(imino)­pyridine polymer constructed by 2,6-diacetylpyridine and 3,3′-diaminobenzidine. Results demonstrate that Co ion sources have a remarkable impact on the final Co–N–C performance. The Co–N–C catalyst prepared using cobalt acetate as a precursor displays remarkable overall multifunctional performance. It needs only a cell voltage of 1.66 V (obtained from the half-cell test) for the water-splitting reaction (HER/OER) to reach 10 mA·cm–2 in 1.0 M KOH, and the overall oxygen redox activity (OER/ORR) is 0.72 V in 0.1 M KOH, outperforming the reported nonprecious metal catalysts. The excellent activity is attributable to the synergistic effects between active sites with encapsulated metallic Co for HER and OER and Co–N moieties for ORR.

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Developing transition-metal excluding iron and cobalt−nitrogen−carbon (M−N−C) electrocatalysts for the oxygen reduction reaction (ORR) is critical to substantially promote the development of precious-metal-free metal−air batteries and fuel cells. In the work, Mn−N−C nanoparticles with atomically dispersed MnN x moieties were synthesized by pyrolyzing Mn-ion−dual-pyridine coordinated complex, which was obtained via a simple condensation reaction between 2,6-diamino-pyridine and 2,6diacetyl-pyridine with MnCl 2 as the Mn source. The precursor features with a characteristic structure of dual-pyridine ligand, which possesses a strong coordinating capability for Mn 2+ , facilitating the formation of highly dispersed nitrogen-coordinated Mn sites (MnN x ). Attributed to the highly active atomic MnN x sites, hierarchical pore structure, and high surface area of the Mn−N−C derived from the new precursor, it exhibits outstanding ORR performance in 0.1 M KOH with an almost direct fourelectron reaction path and high selectivity of O 2 into H 2 O (low H 2 O 2 production <3.5%). The half-wave potential of Mn−N−C is 0.88 V vs RHE, which is 20 mV higher than that of commercial Pt/C catalyst and reaches to the level of Fe−N−C catalyst obtained by the same method. Meanwhile, the feasibility of Mn−N−C for practical application is validated by its higher-performance power output in Zn−air battery with a maximum power density of 132 mW cm −2 compared to that of Pt/C (121 mW cm −2 ) using the same catalyst loading of 1.0 mg cm −2 . This work develops a convenient route to develop non-Fe or Co−N−C electrocatalyst for the ORR.

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