Preparation And Electrocatalytic Properties Of Doped Graphene Supported Transition Metal Nanoparticles Composites

The hydrogen evolution reaction（HER）,oxygen evolution reaction（OER）,and oxygen reduction reaction（ORR）serve as the foundation for renewable energy technologies,including electrochemical hydrolysis and metal-air batteries.Such reactions result in energy loss due to high overpotential and slow kinetics,but efficient catalysts can alleviate this problem.Therefore,it is of great significance to develop efficient and stable electrocatalysts to reduce HER,OER,ORR overpotential and reaction kinetic energy barrier.To date,Pt/Ru/Ir metals are still the most efficient electrocatalysts for ORR and HER,while Ir O₂ and Ru O₂ are highly active for OER.However,the scarcity,high cost,and tolerance of these noble metals have severely hindered their large-scale application.Therefore,looking for a well matching base material of Pt,Ru and Ir electric catalytic properties of non-noble metal catalysts are the current challenges.Electrocatalysts composed of various transition metals（Co,Fe,Ni,etc.）have been explored extensively as potential substitutes for precious metals due to their good electrocatalytic activity.To improve the catalytic performance,carbon materials have been widely used as supports to coordinate transition metal atoms and their compounds.This paper mainly developed non-noble metal（Co,Fe,Ni）electrocatalyst materials supported by carbon doped materials,and systematically tested and analyzed the ORR,OER and HER performance of the obtained samples.The main research content and results are as follows:（1）Study of nitrogen-doped graphene supported cobalt nitride(Co_5.47N)nanoparticles for electrocatalytic water splitting performance in alkaline medium.In this study,cobalt nanoparticles were loaded onto the surface of nitrogen doped graphene oxide（NGO）by using chemical reduction method and converted into Co_5.47N nanoparticles using urea as the nitrogen source.Nitrogen doping into GO forms a large number of active sites,and the transition metal nitride has a similar electronic structure to Pt.The synergistic effect of the two compoents makes the catalyst exhibit OER and HER catalytic activity and stability.The Co_5.47N/NGO synthesized at 750°C achieved an overpotential of 352 m V at the current density of 10 m A/cm² in 1.0 M KOH,exhibiting for OER and 104 m V for HER.This can be attributed to the fact that nitrogen doped graphene not only provides abundant anchoring points,but also stabilizes the Co_5.47N nanoparticles.The coupling of Co_5.47N with nitrogen doped graphene can effectively reduce the energy barrier of intermediates to promote the progress of catalytic reactions,and this structure also facilitates the mass transfer process in catalytic reactions.（2）Study of multifunctional electrocatalytic properties of cobalt-carbon nitride nanotube composites.To further investigate the catalytic performance of transition metal composite catalytic materials loaded on carbon materials with different morphologies,NGO loaded with cobalt nanoparticles are usedas the substrate and dicyandiamide as the precursor to grow nitrogen doped carbon nanotubes encapsuled Co particles.And nitrogen doped carbon nanotubes（Co）loaded with Co nanoparticles on the surface were secondary grown（Co/Co@o-NCNT）through chemical reduction method.In this system,the coupling bond Co-N_xformed at the interface between the carbon material coated with nanoparticles and the nanoparticles is widely considered to be a significant electrocatalytic activity center,and such a structure prevents the agglomeration of nanoparticles and improves the conductivity of the electrocatalyst.In this system,the coupling bond Co-N_x formed at the interface between the carbon material coated with nanoparticles and the nanoparticles is widely considered to be a significant electrocatalytic activity center,and such a structure prevents the agglomeration of nanoparticles and improves the conductivity of the electrocatalyst.The carbon material coated with nanoparticles prevents the accumulation of nanoparticles and improves the conductivity of the electrocatalyst by providing an adjustable electronic structure and coordination environment.This encapsulation feature can effectively maintain the stability of nanoparticles and inhibit their aggregation.Meanwhile,the combination of Co,N and C forms a large number of active sites and has a synergistic effect.Therefore,Co-N-C catalyst has the best three-functional catalytic performance of ORR,OER and HER under alkaline conditions.The catalyst（Co/Co@o-NCNT-900）with a half wave potential of 0.86 V in 0.1 M KOH,it has more excellent stability and methanol resistance than commercial 20 w%Pt/C(E_1/2=0.85 V).In 1.0 M KOH,the overpotential was 352 m V for OER and 104 m V for HER at a current density of 10 m A/cm².The results show that Co/Co@o-NCNT-900 is an efficient and stable three-functional electrocatalyst for ORR,OER and HER.The fexible Zn-air batteries（F-ZABs）are assembled with Co/Co@o-NCNT-900 act as the air cathodes exhibits an open cicuit voltage of 1.46V and a power density of 36.51 m W/cm².（3）Study of nitrogen doped graphene supported Fe-Ni bimetallic phosphide and its electrocatalytic water splitting performance.Fe and Ni nanoparticles were loaded onto NGO by sodium borohydride reduction method,and then sodium hypophosphite was used as the phosphorus source.The bi-functional electrocatalyst((Fe_xNi_1-x)₂P/NGO)supported by Fe₂P and Ni₂P was successfully prepared in a tube furnace by annealing at high temperature.When the current density of the catalyst(Fe_0.2Ni_0.8)₂P/NGO prepared at 1.0 M KOH reached10 m A/cm²,the OER overpotential required 228 m V,almost equivalent to that of commercial Ru O₂（overpotentialη=227 m V）,and the HER overpotential required 160 m V.When(Fe_xNi_1-x)₂P/NGO is used as the cathode and anode of the electrolytic cell,the current density of 10m A/cm² can be reached at a voltage of 1.66 V,shows excellent stability.This work simplifies the synthesis of nickel-iron phosphide,and the flake NGO reduces the agglomeration of nanoparticles,providing a large number of active sites.This simple strategy can be extended to the development of other metallic phosphates for electrochemical applications..