| With the depletion of fossil fuel and the deterioration of global environment,a clean and sustainable alternative energy is in urgent need for the sustainable economic and social development.Hydrogen,as an environmentally benign energy resource,has advantages of low density,high energy density and renewability,which is deem to one of the most promising energy as an alternative to fossil energy in 21st century.Electrolytic water splitting is a directly electrolytic process of water for pure hydrogen,showing a bright prospect for practical application.In the process of water splitting,electrocatalysts play an important role in the aspect of efficiency and stability.In most electrocatalytic systems,carbon-based materials are generally used as substrates of electrocatalysts in virtue of high specific surface area and good conductivity.However,they are liable to suffer from corrosion in the environment of electrolytic water splitting,causing the decrease in pore size and porosity of carbon-based supports and leading to a negative influence on water splitting.Transition metal nitrides are drawing a tremendous attention as emerging substrates due to their high conductivity,chemical stability and resistance to corrosion.However,their specific surface area and pore structures are not comparable to carbon-based materials,which restrict their further development and practical application.In this thesis,vanadium nitride(VN)with high specific surface area and porous structure was designed and prepared.And then the applications of vanadium nitride as substrates in electrolytic water splitting were explored.The main research contents are as follows:(1)Aiming at the poor conductivity of PBAs,by a facile coprecipitation method,CoFe-PBAs were in-situ grown on the surface of highly conductive vanadium nitride(VN)particles.CoFe-PBAs/VN manifests a remarkably enhanced electrocatalytic activity for oxygen evolution reaction(OER)(lower overpotential of 290 mV at 10 mA·cem-2 and a smaller Tafel slope of 39.72 mV·dec-1 than CoFe-PBAs),which is superior among PBAs and PBAs-derived materials reported as electrocatalysts for OER.The close contact between CoFe-PBAs layer and VN substrates facilitates the electron migration in CoFe-PBAs endowed by the excellent conductivity of VN.Besides,the strong interaction between CoFe-PBAs and VN modulates the electron structure of electrocatalysts and increases the proportion of active sites Co2+in CoFe-PBAs.This study provides a novel strategy using VN substrates to support PBAs-based catalysts so as to obtain highly active and stable electrocatalysts towards practical applications.(2)In order to improve the electrocatalytic performance of Ni2P for hydrogen evolution reaction(HER),Ni2P nanoparticles were respectively supported on N-doped reduced graphene oxide(N-RGO),carbon black(C),carbon nanotubes(CNTs)and VN through hydrothermal process and phosphorization.The prepared Ni2P/N-RGO with well dispersive and ultrafine Ni2P nanoparticles demonstrates a superior electrocatalytic activity in 0.5 M H2SO4 solution with a low onset overpotential(80 mV)and small Tafel slope(93.1 mV·dec-1).In virtue of the high specific surface area of N-RGO(450.60 m2·g-1),supported Ni2P particles shows alleviative aggregation and decreased particle size of 2.94 nm in average.Doped N in RGO endows the substrate with the electronic interaction with Ni2P,which increases the proportion of Ni2+and promotes the process of adsorption of H+on the surface of catalytic active sites.VN substrate accelerates the electrocatalytic reaction kinetics of Ni2P and improves its stability for HER,while the insufficient specific surface area of VN leads to the severe aggregation and restricts the activity of supported electrocatalyst.Besides,the comparison among Ni2P supported on four substrates was conducted and their influence on supported electrocatalysts in the perspective of specific surface area,conductivity and electronic interaction was investigated,which provides the guidance for the optimization of VN.(3)In order to improve the insufficient specific surface area,VN with an enlarged specific surface area(VN(CTAB))was successfully prepared by a soft template method.Then,MoS2 nanoplates were vertically grown on VN(CTAB)via a facile hydrothermal reaction for the first time.The synthesized MoS2-VN(CTAB)as an electrocatalyst for HER performs a lower overpotential(180 mV at 10 mA·cm-2)and a smaller Tafel slope of 53.31 mV·dec-1,as well as superior stability compared with commercial MoS2.Besides the benefits from higher conductivity(106 S·m-1)and greater stability of VN(CTAB)beyond the traditional carbon-based substrates,the expanded interlayer spacing(1.00 nm)and extra defects,along with the lower valence states of Mo and S due to the stronger electron interaction between VN(CTAB)and MoS2 also effectively contribute to the excellent catalytic performance of MoS2-VN(CTAB).This work proves that the VN with a designed structure is able to be an efficient substrate of electrocatalysts for HER and show a bright prospect in electrocatalysis.(4)For further optimization of VN substrate for better application,the preparation method in work(3)was improved.The mixed templates of CTAB and SDS were used together in modified template method.Prepared mesoporous VN exhibits larger specific surface area of 172.48 m2·g-1,which surpasses all of other VN materials reported at present.Then,P doped MoS2 supported on prepared VN was successfully synthesized,delivering a more uniform distribution of MoS2 nanoplates.P-MoS2-VN(CS)performs excellent activity(lower overpotential of 155 mV at 10 mA·cm-2 and a smaller Tafel slope of 58.35 mV-dec-1)and long-term durability for HER in 0.5 M H2SO4 solution.DFT calculation demonstrates that the doped P and VN substrate effectively modulate the electron structure of MoS2,optimize the free energy for hydrogen on edge active sites and increase the occupied state of electrocatalyst near fermi level,which improves the activity and conductivity of electrocatalyst.This work achieves further improvement of VN substrate and unveils the its effect mechanism on electrocatalyst by theoretical calculation,which provides the inspiration of theory and method for further application of non-carbon substrate,particularly of transition metal nitrides substrates in in electrocatalysis. |
