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(CoS_(2)YSS)are prepared and modified with amino groups as nucleation sites for coupling highly-conductive needle-like nitrogendoped carbon via a facile solvothermal method(CoS_(2)YSS@NC).The as-marked CoS_(2)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 CoS_(2).CoS_(2)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,CoS_(2)YSS@NC-0.5 shows a better overpotential(244 mV at 10 mA/cm^(2))and Tafel slope(135 mV/dec)than RuO2.Zinc-air battery with CoS_(2)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 CoS_(2)effectively lowers the charge transfer resistance to obtain extraordinary ORR/OER activities.It indicates that the integration of highly-conductive carbon onto pyritetype sulfides is an effective strategy to acquire durable bifunctional ORR/OER catalysts.