Tuning Active Sites By In-Situ Self-Sacrificing Strategy For The Preparation Of High-Efficiency Multifunctional Cobalt-Based Electrocatalysts

Fuel cell,metal-air battery and electrochemical water splitting device are favored by new energy research because of their green,environmentally friendly,high efficiency and long life.These advanced energy devices enable efficient conversion of chemical energy and electrical energy.But how to improve their efficiency and achieve large scale production remains a huge challenge.Among these devices,oxygen reduction reaction(ORR),oxygen evolution reaction(OER),and hydrogen evolution reaction(HER)play an important role.They are also the key to the kinetic sluggishness and insuf-ficient activity.Therefore,it is particularly important to prepare the corresponding high-efficiency and durable electrocatalysts.Noble metal-based electrocatalysts(i.e.,Ru/Ir oxides and Pt/C)are considered as the most efficient electrocatalysts for above electrochemical processes to date.However,the scalable applications of noble metal based electrocatalysts are heavily impeded by their scarcity,high cost,and insufficient durability.Therefore,nonprecious metal electrocatalysts(NPMCs)are widely explored to be substitutes for noble metal.It’s worth noting that the electrocatalysts need the integration of different reactions within one device.Therefore,the development of efficient trifunctional electrocatalysis is highly desired.This paper study the synergistic effects of different active sites.In-situ self-sacrificial templates were used to prepare porous nano-porous carbon materials with large specific surface area.First of all,single atom catalysts with high atomic utilization rate are ideal catalysts in reactions.On the other hand,Co9S8 nanoparticles also show great potential in electrocatalysis due to their unique structure.Herein,the single atom CoN4 sites were combined with Co9S8 nanoparticles to obtain a high-efficiency trifunctional electrocatalyst.Hollow carbon nanotube integrated single cobalt atoms with Co9S8 nanoparticles(CoSA+Co9S8/HCNT)is fabricated by one-step pyrolysis an in-situ self-sacrificing precursor.ZIF-67 was grown on ZnS nanorode and further coated with polydopamine to form the precursor.During the pyrolysis process,ZnS was used as a self-sacrificial template to create a hollow structure with abundant porosity.The conversion of the polydopamine coating to highly graphitized carbon greatly improves the conductivity and stability of CoSA+Co9S8/HCNT.It exhibits excellent catalytic performance and stability in ORR,OER and HER.CoSA+Co9S8/HCNT shows a remarkable half-wave potential of 0.855 V(RHE)in ORR.It requires a low potential of 1.56 V(RHE)to attain a 10 mA cm"2 current density in OER while HER over-potential for this current density is only 0.25 V.Zn-air batteries based on CoSA+Co9S8/HCNT exhibit excellent power density of 177.33 mW cm-2.Moreover,the overall water splitting device assembled with CoSA+Co9S8/HCNT achieves current density of 10 mA cm-2 at a low voltage of 1.59 V.Secondly,ZIF-8 nanocrystals were prepared and then sulfurized under the condition of heating refluxes to convert the ZIF-8 into ZnS,which was used as an in-siut self-sacrificial template,and then epitaxial growth of ZIF-67 on it.A large number of cross-linked top seal carbon nanotube structures could be generated after carbonization at high temperature.The product can efficiently catalyze both ORR and OER.It exhibits an excellent half-wave potential of 0.85 V(RHE)in ORR and requires a low potential of 1.56 V(RHE)to achieve a 10 mA cm-2 current density in OER.