Preparation Of Non-precious Metal Micro/nano Materials And Their Performance In The Field Of Energy Storage And Conversion

Fossil fuels will emit fumes or acid rain during the combustion process,such as CO₂ or SO₂,which will adversely affect the environment.Due to the environmental problems and energy crisis caused by the burning and consumption of fossil fuels,there is an urgent need to develop a green and sustainable development path,that is,the storage and conversion of clean energy.In the storage of clean energy,hybrid supercapacitors have attracted widespread attention.For water-based hybrid supercapacitors,the focus is on using transition metal sulfides,selenides or phosphides for energy storage to increase the energy and power density of such supercapacitors.In the process of clean energy conversion,the use of electrocatalysts and photocatalysts to split water to produce hydrogen is also a current research focus.Under acidic conditions,only the Gibbs free energy of hydrogen adsorption(?G_H*)is considered for the electrocatalytic splitting of water for hydrogen evolution.Under alkaline conditions,the reaction needs to consider not only the hydrolysis barrier,but also the balance between the adsorption of hydrogen(H*)and the adsorbed hydroxide(OH^-).Therefore,the hydrogen evolution reaction mechanism under alkaline conditions is complicated and worthy of in-depth study.At present,transition metal chalcogenides,phosphides,carbides and nitrides are being studied as good electrocatalysts.Two-dimensional(2D)carbon nitride semiconductor materials have limited absorption of a wide range of visible light,which hinders their practical application of photocatalytic splitting water to produce hydrogen under visible light irradiation.Therefore,it is very important to modify the 2D carbon nitride material to expand it for light absorption to visible light absorption spectrum.Based on above these,our subject is mainly focused on using non-precious metal micro/nano materials as energy storage or conversion components to systematically study their performance in energy storage and conversion.The main research contents are as follows:1.Using Ni-MOF as the precursor,and subjecting it to simultaneous selenization and phosphating reactions,a mixed anion Ni_0.85Se|P hollow yolk shell structure with carbon-embedded phosphorus doped on the surface of Ni_0.85Se was prepared.The obtained Ni_0.85Se|P shows a high specific capacity of 506 C g^-1 at 1A g^-1 due to the high Ni²⁺/Ni³⁺ratio and high crystallinity,and up to 5000 cycles current charges/discharge(GCD)cycle stability.The assembled Ni_0.85Se|P//AC liquid hybrid supercapacitor has an energy density of 20.7 Wh kg^-1 and a power density of 798.7 W kg^-1 at 1A g^-1.In addition,the Ni_0.85Se|P electrode also exhibits good electrocatalytic hydrogen evolution performance with a low Tafel slope of 90 m V dec^-1 under alkaline electrolyte.The dual function of Ni_0.85Se|P in the field of energy storage and conversion is realized.2.Co-based NS-p/CNTs prepared by hydrothermal method were used as precursors for high-temperature phosphating reaction,and 2D cobalt phosphide(Co P)nanosheets grafted with 1D carbon nanotubes(CNTs)(namely Co P NS/CNTs)was prepared.Co P NS/CNTs have more and better interfaces,as well as more excellent hydrophilicity,so that they show extremely low and negligible onset overpotential in the alkaline hydrogen evolution reaction,an overpotential of low 68 m V vs.RHE which reaching-10 m A cm^-2,a Tafel slope of low 57 m V dec^-1 and good cyclic stability for at least 24 h.3.Ultra-thin 2D carbon nitride nanosheets(CNs)were annealed at high temperature in the Se vapor atmosphere to prepare Se-doped ultrathin g-C₃N₄nanosheets(Se-CNs).From the experimental characterization results combined with theoretical calculation analysis,it can be concluded that due to the synergy of Se and nitrogen vacancies,the light absorption edge of CNs has been greatly expanded.Therefore,under the irradiation of visible light,Se-CNs with 3 w%Pt as a cocatalyst,and with triethanolamine(TEOA)and methanol(Me OH)as sacrificial agents,respectively,achieved up to the rate of photocatalytic splitting water to produce hydrogen of 2555 and 2037?molh^-1 g^-1.In addition,Se-CNs can also achieve high hydrogen production rates of 466 and 377?molh^-1g^-1 for photocatalytically splitting water with respectively TEOA and Me OH as sacrificial agents without a cocatalyst.