The Preparation Of Vanadium-involved Materials For High-performance Electrocatalysis

Due to the aggravation of energy crisis and environmental problems,reforming the energy infrastructure and establishing a sustainable new energy system is essential for the long-term development of human society.Most clean energy conversion processes involve series of electrochemical reactions.To overcome the energy barriers and to obtain efficient kinetics,it is desirable to develop high-efficiency and low-cost electrocatalysts.Currently,most non-precious metal catalysts are iron-,cobalt-,and/or nickel-based materials.Compared with cobalt and nickel,vanadium shows a higher abundance in the earth's crust and has more empty d-orbitals,which is conducive to be incorporated into other transition metal-based materials to modify the overall or local electronic structure,and thus offering electrocatalytic materials with high intrinsic activity.However,V-based materials have rarely been investigated as electrocatalysts.Therefore,in order to explore the application prospects of vanadium-containing materials as electrocatalysts,we develop vanadium-containing catalysts with high intrinsic activity for electrocatalytic hydrogen evolution reaction(HER),oxygen evolution reaction(OER),and oxygen reduction reaction(ORR).At the same time,through nano-synthesis methods,the morphology with high specific surface area is constructed,which efficiently increases active sites and improves the overall activity of the catalysts.The contents of this dissertation are divided into three parts as following.(1)Based on Ni₅P₄,a highly active HER catalyst,vanadium-doped Ni₅P₄(V-Ni₅P₄)porous microspheres with high specific surface area are constructed on the surface of nickel foam via a two-step hydrothermal treatment and subsequent calcination method.Theoretical calculation results show that V doping can effectively modulate the electronic structure of Ni₅P₄,modify the hydrogen binding strength of Ni₅P₄,and push Ni₅P₄ closer to the optimal?G_H*value,thereby enhancing its intrinsic HER activity.V-Ni₅P₄ exhibits excellent HER catalytic activity and stability in acidic,neutral and alkaline media,demonstrating a wide p H range for various applicaitons.Especially in the alkaline media,the overpotential(?₁₀)of V-Ni₅P₄at a current density at 10 m A cm^-2 is only 13 m V,and the overpotential(?₁₀₀₀)at a current density at 1000 m A cm^-2 is 295 m V,which is superior to Ni₅P₄(?₁₀=148 m V,?₁₀₀₀=409 m V),and even Pt(?₁₀=37 m V,?₁₀₀₀=372 m V).In the neutral media,V-Ni₅P₄(?₁₀=94 m V,?₁₀₀=260 m V)also shows a comparable performance as Pt(?₁₀=121 m V,?₁₀₀=259 m V).The material achieves a Pt-like HER performance,and a high current density up to 1 A cm^-2 under alkaline or acidic conditions,then greatly reduces the cost for synthesizing high-efficiency HER catalysts and propels the application of non-precious HER catalysts.(2)Based on Co₃O₄ spinel oxide,vanadium-doped Co₃O₄(V-Co₃O₄)mesoporous nanorods with high specific surface area are prepared by a simple solvothermal-calcination method.V doping effectively modifies the electronic structure of Co₃O₄ and optimizes the electron filling number of the e_g orbital of Co³⁺at the octahedral site(close to 1),thereby balancing the adsorption strength of oxygen-containing intermediates and exhibiting excellent ORR and OER bifunctional intrinsic activity.Benefit from the mesoporous structure,V-Co₃O₄ has a high specific surface area and plenty of channels for efficient mass transfer,which is beneficial to enhance the overall activity of the catalyst.Compared to Co₃O₄,V-Co₃O₄ shows more excellent ORR and OER bifunctional activity and reversibility,and can be used as a positive electrode catalyst for rechargeable Zn-air batteries.The liquid-state Zn-air battery(ZAB)based on V-Co₃O₄ exhibits high charge and discharge activity,high open circuit voltage(?1.45 V),high specific capacity(814 m Ah g _Zn^-1,about 99.3%of the theoretical value),high energy density(951 W h kg _Zn^-1,about 78.1%of the theoretical value),and excellent stability.When operated at charge-discharge cycle test for 4100 cycles(>57 days),V-Co₃O₄ demonstrates excellent structural stability and durability,which enables the stable long-term operation of rechargeable ZABs.In addition,based on the increasing demands of flexible devices,a cable-type all-solid-state flexible rechargeable ZAB is designed and assembled.The flexible ZAB based on V-Co₃O₄ exhibits high open circuit voltage(?1.39 V)and high maximum power density(40.6 m W cm^-3),outperforming that based on Co₃O₄(?1.30 V,14.0 m W cm^-3).Meanwhile,the flexible battery shows excellent mechanical deformation capabilities by stretching,folding and twisting,and is expected to be used as a flexible power source in the next generation of electronic devices.This work provides a useful reference for adjusting the electronic structure of spinel oxide,and a new strategy for designing high-performance ORR and OER bifuntional catalysts for rechargeable ZABs.(3)Based on V₂O₃,V₂O₃/Mn S composite is synthesized by a hydrothermal-calcination method.The theoretical calculation results show that a small amount of Mn S can effectively modify the electronic structure of V₂O₃ at the V₂O₃/Mn S interface,then improve its intrinsic activity of ORR and OER,and enhance the stability of V₂O₃.V₂O₃/Mn S shows excellent bifunctional catalytic activity,especially a desirable ORR activity with a half-wave potential of 0.835 V,which is close to that of commercial Pt/C(0.856 V).The liquid-state rechargeable ZAB based on V₂O₃/Mn S exhibits high charge and discharge activity,high specific capacity(808 m Ah g _Zn^-1,about 98.5%of theoretical value),high energy density(970 W h kg _Zn^-1,about 80.0%of the theoretical value),and excellent stability.During the charge-discharge stability test for 4000 cycles(>55 days),V₂O₃/Mn S demonstrates excellent structural stability and durability,and its energy efficiency is maintained around 60.0%,showing great potential as an efficient and stable catalyst for long life-span rechargeable ZAB.At the same time,the layered sandwich-type all-solid-state flexible ZAB based on V₂O₃/Mn S exhibits high open circuit voltage(?1.40 V),high specific capacity(?760 m Ah g _Zn^-1)and high energy density(?772 Wh kg g _Zn^-1),superior to the control samples and most of the reported flexible ZAB.The flexible ZAB also shows desirable flexibility,giving a good potential for application.This work reports a novel electrocatalyst,and also offers a reference for the interfacial design of highly active electrocatalytic materials.