Construction And Electrocatalytic Properties Of Nitrogen-doped Carbon Nanotube Confined Nickel-based Catalysts

With the increasing demand for energy and environmental protection and the consumption of traditional fossil fuels,the development of sustainable and clean energy production and storage and transformation technologies has become more and more important.As a clean energy,hydrogen can be obtained by electrolysis of water and urea solution.Meanwhile,metal air cell and fuel cell devices can meet energy storage and conversion.These new technologies mainly involve hydrogen evolution reaction（HER）,oxygen evolution reaction（OER）,urea oxidation reaction（UOR）and oxygen reduction reaction（ORR）.The key to the development of these electrochemical reactions lies in the construction of highly active electrocatalysts.Traditional noble metal catalysts（Pt,Ru,Ir,Rh,etc.）greatly increase the cost and complexity of the device due to their high cost,scarce resources and selective catalysis.Therefore,the research and development of cheap,easily available,highly active and stable non noble metal catalysts are of great significance to reduce costs and promote their commercialization.Through the investigation and analysis of relevant papers,the current research on non-noble metal electrocatalysts mainly involves transition metal compounds.Among them,the nickel-based catalyst confined in nitrogen doped carbon nanotubes（NCNT）has flexible structure,excellent electronic properties,excellent performance and outstanding stability,which is conducive to electrocatalytic reaction.It is a potential ideal catalyst to meet the requirements of commercial applications.Therefore,different Ni based catalysts are constructed to obtain and study excellent electrocatalytic performance through design strategies such as material morphology control,heteroatom doping to regulate electronic structure,metal doping to construct bimetallic synergistic effect,designing heterogeneous interface and synthesizing single atomic high-efficiency exposure active sites.The main contents are as follows:1.Firstly,we synthesize a series of nickel nanoparticles（Ni NPs）embedded nitrogen doped carbon nanotubes（Ni@NCNT）and study the effect of nitrogen dopants on UOR catalytic activity.According to experiments and the density functional theory（DFT）calculation,nitrogen dopants also promote the in-situ conversion of Ni³⁺species from Ni,thereby facilitating UOR catalysis.Simultaneously,the nitrogen dopants can weaken the binding strength between CO₂ species and active sites resulting in alleviation of CO₂ poisoning,and promote the desorption of CO₂ from the active site of Ni and improve the activity of UOR.Moreover,nitrogen dopants also improves Ni@NCNT-3HER catalytic activity.Subsequently,the overall UOR catalysis for Ni@NCNT requires only 1.56 V to achieve current density of 10 m A cm^-2and display excellent stability.This work offers useful information for designing a stable and efficient electrocatalyst for not only UOR but also electrochemical generation of H₂ from wastewater.2.Based on the Ni@NCNT electrocatalyst to excellent selective catalytic activity for UOR,the cobalt（Co）metal doping engineering is employed to further improve the UOR performance of the Ni@NCNT catalyst.Construction of bimetallic catalyst system（Co Ni@NCNTs）by introducing Co into the Ni@NCNT catalyst and investigating the effects of different Co metal doping on its UOR and HER performance.It is found that more Co doping can effectively promote the conversion of Ni to Ni³⁺,which improves the catalytic activity of UOR.The DFT calculation results show that Co Ni bimetallic system has lower binding energy for CO₂ adsorption and Co Ni alloying can promote CO₂desorption.Meanwhile,Co doping also improved HER performance for the Co Ni@NCNTs due to introducing more active sites.In addition,the assembled overall UOR device only requires 1.51 V to reach catalytic current density of 10 m A cm^-2 and exhibit excellent stability.3.Rational design of highly active and durable noble metal free electrocatalyst is extraordinarily important for the industrializations of rechargeable zinc air batteries（ZABs）and water splitting.Herein,we employ heteroatom doping and heterogeneous engineering strategies to prepare a novel tri-functional electrocatalyst,N,P co-doped carbon nanotubes confined WN-Ni heterostructured nanoparticles（WN-Ni@N,P-CNT）via one-pot pyrolysis.Owing to the advantages of N,P-dual doped carbon nanotube structure and the synergistic effect of WN-Ni heterostructure,WN-Ni@N,P-CNT-800exhibited excellent trifunctional catalytic performance toward ORR,OER and HER as well as robust durability in alkaline electrolyte.Meanwhile,the performance and stability of the assembled aqueous and all-solid-state rechargeable ZABs for WN-Ni@N,P-CNT-800 outperforms Pt/C||Ir O₂.Moreover,WN-Ni@N,P-CNT-800 shows a comparable water splitting performance than that of Pt/C||Ir O₂.This work offers a novel strategy for constructing alternative non-noble metal multifunctional electrocatalysts towards sustainable energy applications.4.Herein,we report a one-step pyrolysis method to synthesize Pt single atoms（Pt-SAs）coordinated with metallic Ni nanoparticles（Pt-SAs@Ni）encapsulated into nitrogen doped carbon nanotubes（Pt-SAs@Ni/NCNT）by constructing the strategy of Pt single atoms dispersion.Due to the strong electronic interplay between Pt-SAs and metallic Ni nanoparticles,d band center of Pt is downshifted;thereby,the hydrogen binding strength is balanced;as a result,Pt-SAs@Ni/NCNT ensures efficient HER catalysis in acidic and alkaline mediums with mass activities of 350.7 A mg _Pt^-1 and 90.6 A mg _Pt^-1 at overpotential of 150 m V,respectively,corresponding to 146 and 70 times higher than that of commercial 20%Pt/C.In alkaline medium,owing to the presence of Ni nanoparticles with efficient water splitting of water ability,a better alkaline HER activity is achieved for Pt-SAs@Ni/NCNT than commercial Pt/C,Pt-SAs@NC and Pt₃Ni/C.In-situ Raman spectroscopy test also reveals that nickel nanoparticles enable water dissociation and Pt-SAs capture the generated hydrogen ions to release gaseous hydrogen in alkaline electrolyte.