| In recent years,more and more countries,institutions and companies have declared zero emissions,China has also included carbon peaking and carbon neutrality into the 14th Five-Year Plan.Hydrogen energy is regarded as the ideal alternative fuel for traditional fossil energy,electrolytic water will become the core technology of hydrogen production industry in the future.However,the high electromotive force hinders the water splitting.It is necessary to develop efficient,high-quality and cheap catalysts to speed up the hydrogen evolution reaction.The thesis mainly includes the following five parts:The study of preparation and properties of CoSe2/MoSe2 heterostructured hydrogen evolution catalysts.The electronic structure of MoSe2 is significantly affected by layer spacing,and the stress effect of heterojunction can be used to effectively optimize the electronic structure of MoSe2 catalyst.We prepared CoSe2/MoSe2 heterostructure with hollow microtubule morphology composed of stacked nanosheets.The strong interfacial coupling between CoSe2 and MoSe2 compresses the layer spacing of MoSe2,both XAS and XPS indicate the charge transfer between CoSe2 and MoSe2.The descending d-band center weakens the binding energy between Mo atom and adsorbed hydrogen in MoSe2,thus the electrocatalytic activity was improved.In addition,the rough surface morphology of hollow microtubules helps to provide more active sites.Based on the above advantages,the overpotential of CoSe2/MoSe2 only 119 mV at the current density of 10 mA cm-2,these results indicate that CoSe2/MoSe2 heterogeneous catalysts have better performance than other similar catalysts.The study of preparation and properties of Co9S8/MoS2 heterostructured hydrogen evolution catalysts.Fabricating transition metal sulfide heterojunction can combine their respective characteristics to realize the charge redistribution and high conductivity,so the overall electrocatalytic performance improved.In this paper,we synthesized 3D microspheroidal CoMo-LDH precursors with the morphology of cross-linking nanosheets,We prepared the microspheres Co9S8/MoS2 heterostructure hydrogen evolution catalysts by vulcanization,which composed by the large quantity of nanosheets.After the heterojunction formed,the obvious electron transfer happened between Co9S8 and MoS2,which could optimize the charge redistribution.The formation of heterojunction weakened the hydrogen adsorption and make the value of ΔGH*approach to zero.In addition,the increase of state density which near the Fermi level and the enhanced adsorption of water molecules all contributed to the improvement of HER performance.Due to these results,the overpotential of the heterojunction catalyst prepared in this paper is better than that of most reported Co9S8/MoS2 related HER electrocatalysts,the overpotential was 118 mV at the current density of 10 mA cm-2 in 1 M KOH.The study of preparation and properties of CoP/CoMoP2 heterostructured hydrogen evolution catalysts.The synergistic effect between heterogeneous structures of phosphide can significantly improve its catalytic activity and accelerate the hydrogen evolution reaction process.There are many reports for phosphide heterostructure HER catalysts,but the studies for CoP/CoMoP2 are limited.The microspheres surface morphology of the prepared CoP/CoMoP2 coverd with the dense nanoporous phosphorus structure,which not only limited the aggregation of active sites,but also provided H2 transport channels and a large number of active sites.Compared to CoP and CoMoP2,CoP/CoMoP2 has the largest electrochemically active surface and the smallest impedance,exhibit the excellent stability.The DFT calculations proved that Fermi level of CoP/CoMoP2 has strong electron state density,the optimized electron structure is beneficial to the electron transport and improve HER performance.CoP/CoMoP2 showed excellent HER activity in 1 M KOH,the required overpotential was 93.6 mV at the current density of 10 mA cm-2.The study of preparation and properties of CoP/MoS2 heterostructured hydrogen evolution catalysts.Many studies have shown that heterojunction catalysts constructed by the anionic compounds from different main groups have higher HER activity than those constructed by the anionic compounds from the same main group.Phosphide and sulfide heterojunction CoP/MoS2 was prepared and evaluated by experiment and theoretical calculation.Meanwhile,the hydrogen evolution properties of CoP/MoS2 were compared with phosphide heterojunction CoP/CoMoP2 and sulfide heterojunction Co9S8/MoS2.The results show that CoP/MoS2 has better hydrogen evolution performance than CoP/CoMoP2 and Co9S8/MoS2.When the current density reached to 10 mA cm-2,the overpotential of CoP/MoS2 is only 88 mV.Meanwhile,CoP/MoS2 showed the best hydrogen adsorption free energy(0.16 eV)and water absorption energy(-1.43 eV).According to various characterization and DFT calculation results,the heterostructure which hybridized by phosphide and sulfide have better synergistic effect and higher HER activity.The study of the preparation and properties of Ni2P/(Co,Ni)OOH heterostructured hydrogen evolution catalysts.The multiple levels of hierarchy structures can offer considerable area for active sites loading,both beneficial for HER and the substance transportation.Here,using the two-step method,we prepared the Ni2P/(Co,Ni)OOH heterointerface with a three level hierarchy morphology.Meanwhile,the strong charge transfer at the Ni2P/(Co,Ni)OOH heterointerface eliminates the spin asymmetry and achieves the neutral adsorption of active H species.Moreover,the resulted Coulomb attraction stacks the two materials firmly facilitating the stability.DFT and in-situ Raman measurements reveal the sufficient Ni atoms acting as the active sites.With these merits,the Ni2P/(Co,Ni)OOH exhibits much better HER activity than the separate Ni2P or(Co,Ni)OOH,affording a current density of 100 mA/cm2 at an overpotential of 169 mV when tested in 1 M KOH electrolyte.This paper provides inspiration for optimizing the intrinsic HER activity utilizing multiple-level hierarchy structures. |
PDF Full Text Request