Preparation And Oxygen Reduction/precipitation Properties Of Carbon-supported Transition Metal Selenium And Sulfides

Energy crisis and environmental pollution are serious challenges facing the world at present.Under this environmental situation,electrochemical energy storage technology(including metal-air battery system)stands out among many new energy technologies due to its high energy density,long working life and relatively low self-discharge rate.Therefore,the development of efficient electrochemical energy storage systems has always been a research hotspot in the energy field.For metal-air battery systems,it is the oxygen reduction(ORR)and oxygen evolution(OER)reaction efficiencies that are decisive for the energy efficiency and stability.Usually,ORR/OER require catalysts to improve the slow reaction kinetics and poor stability,while commercial precious metal catalysts have problems of poor economy and stability,which directly limit the development of this technology.Therefore,the development of efficient,stable and inexpensive ORR/OER catalysts is the key to realizing the application of metal-air batteries in various fields.The research and preparation of bifunctional electrocatalysts for ORR and OER with high efficiency and long-term stability are targeted.In this paper,inexpensive carbon materials and single-metal nickel selenide and double-metal nickel-iron sulfides(Ni₃Se₄and Ni-Fe-S)in non-precious metal chalcogenides are selected as the objects and X-ray diffraction,nitrogen adsorption/desorption,scanning electron microscopy and other methods to study the physicochemical properties of the material.In addition,the ORR and OER electrocatalytic performance and reaction mechanism of the catalysts were explored by rotating ring and rotating ring disk electrode tests.In this study,three-dimensional flower-like Ni₃Se₄ coated by ultrathin carbon-layer(UNCs)as bifunctional catalyst(Ni₃Se₄/UCL-x).The content of supported carbon is controlled to tune the structure and catalytic performance of Ni₃Se₄/UCL-x.The obtained Ni₃Se₄/UCL-3 composites possess three-dimensional curd morphology and excellent ORR/OER catalytic activity.Ni₃Se₄/UCL-3(the mass ratio of Ni Cl₂·6H₂O and UNCs is3)has an excellent half-wave potential of 0.82 V(E_1/2,ORR)and an excellent overpotential of 1.58 V at 10 m A cm^-2(OER),?E(E_j=10(OER)-E_1/2(ORR))is 0.76 V.Ni₃Se₄/UCL-3 only negatively shifted 12 m V for E_1/2 after 5000 cycles(ORR)and a current density decline of only 6.99%after 6 h test(OER).For ORR,the integrated structure of Ni₃Se₄/UCL-3 causes strong electronic interaction between Ni₃Se₄(Ni²⁺)and UCL(N species)to achieve efficient charge transfer at interfaces.For OER,in situ X-ray diffraction tests verified the presence of active?-Ni OOH during OER.In addition,the bimetallic nanocages with 3D porous hollow structure and anchored N-doped carbon quantum dots are synthesized by using selective etching and self-assembly methods to obtain the Ni-Fe-S/NCQDs as bifunctional ORR/OER catalysts.Ni-Fe-S/3NCQDs exhibits a promising half-wave potential of 0.85 V(E_1/2,ORR)and an excellent overpotential of 1.525 V at 10 m A cm^-2(OER).Ni-Fe-S/3NCQDs has a negative shift of only 12.8 m V for E_1/2 after 5000 cycles(ORR)and a current density decline of only 7.05%after 20 h tests(OER).For ORR,the strong oxygen-adsorption affinity of Ni-Fe-S improves the ORR efficiency,while the N-species on NCQDs enhances the charge transfer and ORR activity.For OER,the in situ formed Ni/Fe oxyhydroxide on hollow structure mainly contributes to the excellent OER activity and stability.Synergistic effects between bimetallic sulfide and NCQDs lead to the promising bifunctional activity(?E=0.675 V)in oxygen electrocatalysis.In this paper,electrocatalytic materials based on transition metal sulphides and selenides loaded with carbon were constructed with excellent bifunctional catalytic activity,indicating the potential of such catalysts for electrocatalytic applications and provides a promising reference for the future development of sulfuror selenide-based electrocatalysts provides a promising reference.