Surface Interface Modification And Electrocatalytic Hydrogen Production Performance Study Of Low-Dimensional Molybdate Materials

With the excessive exploitation of coal,petroleum,natural gas and other non-renewable mineral resources,human beings confront the aggravating problems of fossil energy scarcity and ecological environment deterioration.Under the background of the new era,the green and sustainable development strongly requires the development of a new energy to response to the various crises and challenges.Hydrogen,as an eco-friendly secondary energy,is of strategic significance in alleviating energy crisis,ameliorating environment pollution and transforming energy structure.Due to the considerable economic benefits and environmental harmlessness,hydrogen production by water electrolysis is widely recognized and studied,where the platinum and other precious metals are commonly used as electrocatalysts to reduce the overpotential,but the very rare stock is not conducive to the widespread application in industrial water electrolysis equipment.Therefore,developing a cost-effective energy conversion and storage material as efficient as noble-mental material to improve the economy of hydrogen production is the key to achieving the sustainable energy supply model driven by hydrogen energy.Among many developed non-precious metals,molybdate exhibits competitive electrochemical activity for its abundant materials,simple preparation,excellent REDOX ability,adjustable electronic structure and rich metallic catalytic center.However,there are still a large catalytic barrier between molybdate and noble metal.So in this paper,we take the low-dimensional molybdates as the research object,based on the key constraints such as conductivity,catalytic site and reaction energy barrier,and combined with element doping,crystal regulation,defect introduction,interface engineering and other novel surface interface modification strategies,regulating their electronic structure and reaction characteristics coordinatively,and developing a series of high intrinsic active electrocatalysts with abundant catalytic sites for hydrogen production by water electrolysis.In this paper,we focus on the controllable preparation,structural optimization,and performance improvement of self-supporting electrodes with multiphase surface/interface.After discussing the influence of electron transfer process on electrochemical behavior of different composition material,the corresponding structure-activity relationship is concluded and summarized.In addition,we also try to investigate the essential reasons of performance improvement and infer the possible reaction mechanism behind it according to the evolution routine of physical and chemical properties of electrocatalytic material before and after reaction in the subsequent work.Finally,the electrochemical activity and stability of molybdate precursor are improved steadily.Specifically,the molybdate material is modified from following three aspects:1.Given the phenomenon that the electrochemical reactivity of most present low-dimensional molybdate materials is limited by their poor intrinsic conductivity and insufficient active sites,the CoMoO₄ precursor grown on three-dimensional porous nickel foam skeleton is obtained by hydrothermal reaction,and P,S-CoMoO₄/CF with high intrinsic catalytic activity is developed through the chemical modification strategy of low-temperature phosphatization and vulcanization.The dual-anions modification strategy optimizes the conductivity and electronic structure without destroying the overall structure of precursor.In addition,there are strong interfacial electronic effects between Co P and Co₃S₄ new species and CoMoO₄ phase after chemical vapor deposition,which improve the electrocatalytic activity and corrosion resistance of molybdate materials.Under the optimal conditions,the alkaline water electrolyzer of P,S-CoMoO₄/NF requires only 1.66 V to achieve 50 m A·cm^-2,demonstrating excellent bifunction performance and long-term durability.2.The design of interface structure can effectively improve electron conductivity,increase active sites and reduce kinetic energy barrier.According to this,the NiMo O₄/NF precursor are synthesized by hydrothermal,after impregnated in Co²⁺/DMF and phosphatized at low temperature,the cobalt ion is stabilized while the residual DMF on the surface is converted into carbon layer,and C-Co₂P@P-NiMo O₄/NF heterogeneous material is obtained.The coating of carbon layer can optimize the adsorption of reaction intermediates,improve the conductivity and enhance the corrosion resistance of the material,while the construction of heterojunction can provide more catalytic active sites and accelarate electron transfer.Finally,due to the synergistic effect of carbon encapsulation and interface engineering,the optimized C-Co₂P@P-NiMo O₄/NF shows excellent HER performance in 1 M KOH,0.5 M H₂SO₄ and 1 M PBS electrolytes,with overpotentials of 105 m V,107 m V and 177 m V respectively required to drive 100 m A cm^-2,which exceeds those of most reported transition metal-based electrocatalysts.3.Seeking a suitable anode replacement reaction is of great significance to the practical application of water electrolysis technology,and the urea oxidation reaction has incomparable advantages over traditional oxygen evolution reaction in thermodynamics and kinetics,among which Ni³⁺has been proved to be the real active component.Accordingly,in this paper,the hydrothermal synthesized CoMoO₄/CF with high specific surface area is used as the working electrode,and the nickel phosphide particles are electrodeposited on its surface by a three-electrode system.With the hybrization of P modified Ni nanoparticles and CoMoO₄nanosheets,the construction of P-Ni@CoMoO₄/CF heterogeneous material is realized.The heterogeneous interface obtained by in-situ electrodeposition has abundant active components,high epitaxial surface area and excellent electronic structure,which makes the performance of P-Ni@CoMoO₄/CF greatly improved when compared with CoMoO₄.Besides,the urea molecule is introduced to optimize the anodic reaction kinetics.Finally,the P-Ni@CoMoO₄/CF electrode only needs 1.50 V to drive the current density of 100 m A·cm^-2 in the urea-assisted electrolytic cell,which is 170 m V lower than the traditional overall water splitting,realizing more economical hydrogen production.