Electrocatalytic And Photoassisted Electrocatalytic Performance Of Porous Nickel-based Hierarchical Nanostructure

Hydrogen energy is a kind of clean energy which has attracted wide attention,and its combustion has high calorific value and pollution-free properties.One of its important preparation methods is electrochemical water splitting.However,the best catalysts for electrolysis are some precious metals,such as iridium dioxide and ruthenium dioxide for the anode,and platinum or platinum-carbon for the cathode.Because these precious metals are rare and expensive,limit their large-scale applications.A low-cost catalyst with high activity and stability is urgently needed.Another method to prepare high purity hydrogen is photocatalytic water splitting,which not only has the advantage of energy-free,but also has disadvantages of small photoelectric current and slow catalytic reaction.Combining two methods can reduce energy consumption and enhance the electrocatalytic activity.Among numerous catalysts,the nickel-based catalyst are extremely promising ones.Our designing rules for nickel-based catalysts are based on the principles of multiple active sites,multi-functionality,high conductivity and robust structural stability.the self-template method can effectively control morphology of hierarchical nanostructure,and effectivity built complex hierarchical nanostructures.Firstly,MoO3@Ni?OH?2 hierarchical core-shell nanotubes were synthesized using MoO3 nanorods as self-templates.Secondly,the Ni1-xCox glycerine solid spherical template was prepared by hydrothermal method,and then obtained the Ni_1-x-x Co_x yolk-shell oxyhydroxide precursor by hydrolyzing Ni_1-xCo_x glycerine solid spherical template.The precursors of nickel-based hierarchical nanostructures with large specific surface area were prepared by using the self-template method,and then obtained the ideal catalysts through further treatments.NiMoO₄ hierarchical hollow nanotubes were synthesized by annealing the MoO3@Ni?OH?2 hierarchical core-shell nanotubes in air.The NiMoO4 hierarchical hollow nanotubes have a surface area of 128.5 m² g^-1.The NiMoO₄ hierarchical hollow nanotubes have excellent catalytic activity because of more active sites and robust hierarchical structure.The cobalt source was introduced in the process of preparation of the precursor of NiMoO4 hierarchical hollow nanotubes,then synthesized CoMoO4-NiMoO4 hierarchical hollow nanotubes by annealing the precursor.The structural of characterization shows that CoMoO₄-NiMoO₄ hierarchical hollow nanotube has a specific surface area of 186.7 m² g^-1,which is larger than NiMoO4 hierarchical hollow nanotubes.The electrochemical test show that the overpotential of CoMoO₄-NiMoO₄ hierarchical hollow nanotubes only was 300 mV when the current density was 10 mA cm^-2,which is lower than NiMoO₄ hierarchical hollow nanotubes.The electrocatalytic activity of CoMoO4-NiMoO4 hierarchical hollow nanotubes has a significant gain after light irradiation.After heating NiMoO4 hierarchical hollow nanotubes,and NH3/Ar flow,then obtained NiMoN hierarchical hollow nanotubes.NiMoN hollow nanotubes have more outstanding bifunctional catalytic properties than NiMoO₄ and CoMoO₄-NiMoO₄.For NiMoN-550,the overpotentials of OER and HER were 295 mV and 89 mV on the current density of 10 mA cm^-2 respectively.The voltage was 1.596 V when NiMoN-550 were assembled to two-electrode.Its electrocatalytic activity and kinetics have been improved after light irradiation owe to its strong absorption in the ultraviolet visible range.By doping iron into MoO3@Ni?OH?2 hierarchical core-shell nanotubes at room temperature,after heating the Fe-doped MoO₃@Ni?OH?₂ hierarchical core-shell nanotubes under an NH3/Ar flow,then obtained Ni-Fe-MoN hollow hierarchical nanotubes.The electrochemical test shows that the overpotentials of OER and HER were 228 mV and 55 mV on the current density of 10 mA cm^-2 respectively.The voltage was 1.513 V when Ni-Fe-MoN NTs were assembled to two-electrode.A significant improvement is found in both OER and HER after the light irradiation.In addition,spherical structures have more robust structure than other shapes.Ni_1-xCo_x yolk-shell oxyhydroxide precursor were mixed with sodium hypophosphite,and the mixture was annealed under an Ar flow,and then obtained Ni1-xCox-P yolk-shell hierarchical porous microspheres.The electrochemical test shows that Ni_1-xCo_x-P yolk–shell hierarchical porous microspheres have better catalytic activity than monometallic phosphides in OER and HER.A significant improvement is found in both OER and HER after the light irradiation,which is owing to the light absorption in the ultraviolet visible range.