Yolk shell-structured pyrite-type cobalt sulfide grafted by nitrogen-doped carbon-needles with enhanced electrical conductivity for oxygen electrocatalysis

Pyrite-type sulfides (PTS) exhibit promising intrinsic activities for oxygen reduction and evolution reactions (ORR/OER). However, their poor electrical conductivities may limit the charge transfer rate to inevitably lower activity. Here, yolk-shell structured cobalt-pyrite nanospheres (CoS₂ YSS) are prepared and modified with amino groups as nucleation sites for coupling highly-conductive needle-like nitrogen-doped carbon via a facile solvothermal method (CoS₂ YSS@NC). The as-marked CoS₂ YSS@NC-0.5 shows a gap between yolk and shell, and an obvious exterior layer of grafted NC, which can provide an integrated structure, an interior place, and three exposed surfaces on CoS₂. CoS₂ YSS@NC-0.5 reveals higher ORR activity (half-wave potential of 0.88 V) and methanol resistance than commercial Pt/C. Due to in-situ formation of highly-active CoOOH, CoS₂ YSS@NC-0.5 shows a better overpotential (244 mV at 10 mA/cm²) and Tafel slope (135 mV/dec) than RuO₂. Zinc-air battery with CoS₂ YSS@NC-0.5 air-cathode exhibits good open circuit potential (1.44 V), specific capacity (772.5 mAh/g) and cycling stability. Needle-like NC layer coated on the yolk-shell structure of CoS₂ effectively lowers the charge transfer resistance to obtain extraordinary ORR/OER activities. It indicates that the integration of highly-conductive carbon onto pyrite-type sulfides is an effective strategy to acquire durable bifunctional ORR/OER catalysts.