Controllable Preparation Of Hydroxyl Compound Nanoelectrodes And Electrolytic Water Performance Study

The realization of carbon neutrality and carbon peaking requires the renewable energy with high energy density and low environmental impact.As a new energy source with great development potential,green hydrogen plays a pivotal role in the process of achieving carbon peaking and carbon neutrality.Generally,green hydrogen is obtained by electrolysis of water and methane reforming,among which electrocatalytic decomposition of water is a way to produce hydrogen with low environmental impact and high efficiency.Electrocatalytic decomposition of water consists of two half-reaction processes:oxygen precipitation reaction（OER）at the anode and hydrogen precipitation reaction（HER）at the cathode.However,compared with the HER process,the OER process involves a multi-electron process,which requires a large amount of energy to overcome the resistance of the electron transfer process,resulting in an unpromising efficiency of hydrogen production,hence searching for an efficient electrocatalyst is expected to improve the hydrogen production rate from electrolytic water.Since many years,researchers have devoted to the research of advanced catalysts and have achieved remarkable results in hydrogen production from electrolytic water,but the complex preparation steps and long preparation cycle have limited the development of hydrogen production from electrolytic water.In this paper,we intend to solve the problems of poor catalytic activity of hydroxyl compounds in water by electrocatalytic decomposition,preparation process involving high temperature and high pressure,and long preparation cycle,and to prepare electrolytic water catalysts with high efficiency of hydrogen production by different methods.The specific research of this thesis is as follows.（1）In situ synthesis of hydroxyl compound by solution plasma for the performance of electrocatalytic splitting water.（Oxy）hydroxide materials are of vital importance for efficient electrolytic water low carbon hydrogen production technology,nevertheless,it is still a great challenge to prepare（oxy）hydroxides in a fast,environmentally friendly and low carbon way.In this chapter,we report a method to form（oxy）hydroxides on nickel foam by solution plasma treatment at room temperature and pressure with no chemical reagents added.This green and environmentally friendly preparation method not only avoids changing the morphology or surface area of nickel foam,but also ensures rapid electron transfer and exhibits excellent allolytic performance in alkaline electrolytes.Specifically,the Fe Ni OOH catalyst required only 257m V overpotential to achieve a current density of 50 m A cm^-2 during HER and 320 m V overpotential to achieve a current density of 50 m A cm^-2 during OER.when Fe Ni OOH was used as a total water dissolution catalyst in a full cell,the applied voltage was only 1.81 V was required to achieve a current density of 50 m A cm^-2,and the catalytic activity barely decreased after 50 h of durability performance test.The DFT theoretical calculations show that Fe Ni OOH accepts partial electron transfer,reduces the occupancy of the d orbitals,has less unpaired electron density in the d_xz,d_yz and d_z² orbitals,endows the reaction intermediates with a milder binding strength,and the synergistic interaction between the closed reaction center of Fe-Ni and the metal stabilizes the reaction intermediates,causing an enhancement of the intrinsic activity.This work provides an effective strategy to create new opportunities for finding more advanced materials.It is expected that solution plasma modified high surface area nickel foam has the potential to be applied to various electrocatalytic processes.（2）Rapid in situ synthesis of hydroxyl compound by room temperature impregnation for the performance of electrocatalytic splitting water.（Oxy）hydroxide materials have great importance in advancing the electrolysis of water for hydrogen production,and yet it remains a huge challenge to prepare（oxy）hydroxides in an efficient,energy-efficient,time-saving and economical method.This chapter reports the in situ synthesis of（oxy）hydroxides using nickel foam as a conductive substrate in five minutes at ambient temperature and pressure.This ultrafast preparation method forms an S-doped（oxygen）hydroxide layer on the surface of nickel foam,which has a porous continuous interconnected structure and good hydrophilicity with excellent total hydrolysis performance in alkaline electrolytes.In particular,S-Fe Ni OOH achieved an overpotential of 248 m V for HER and 293 m V for OER at a current density of 100 m A cm^-2 when used as HER and OER catalysts.When S-Fe Ni OOH was used as a catalyst for decomposing water in a full cell,a current density of 100 m A cm^-2 was achieved at a low voltage of 1.81 V.S After the endurance performance test for 100 h,the catalytic activity of S-Fe Ni OOH hardly decreased.DFT theoretical calculations showed that S-Fe Ni OOH shows the strongest electron delocalization and the best conductivity,which is favorable for electron transport.S doping can optimize the reaction energy barrier of the reaction intermediate,while the synergistic effect between the two metals stabilizes the reaction intermediate.The S-Fe Ni OOH structure weakens the OH*species adsorption,hence optimizing the Gibbs free energy barrier for the whole process and providing an ideal reaction interface for its catalytic reaction.This work provides a simple and rapid preparation strategy and offers new insights into the search for more advanced materials for electrocatalytic splitting water.（3）Preparation of spitball-like hydrotalcite nanomaterials by chemical exfoliation and study of electrocatalytic splitting water properties.Utilization of sunlight for water decomposition to produce green hydrogen is essential for sustainable development,but the enhancement of sunlight utilization remains a major challenge.This chapter reports an efficient Zn Al-LDH catalyst for light-assisted electrocatalytic splitting water.The prepared Si-Zn Al-LDH amorphous nanosheet material not only improves the absorption wavelength of sunlight but also enhances the light capture ability,and the amorphous nanosheet material with suitable energy band structure for electrocatalysis also meets the requirements of photocatalysis.The amorphous nanosheets obtained by large-area chemical exfoliation are abundant in catalytically active phases,thereby improving the catalytic performance.Specifically,Si-Zn Al-LDH exhibited good hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）performance in the photo-assisted electrocatalytic splitting water.Under the light-assisted conditions,a current density of 10 m A cm^-2 was achieved with an overpotential of 108 m V for HER and 260 m V for OER.Si-Zn Al-LDH achieved a current density of 10 m A cm^-2 at a low voltage of 1.673 V when employed as a total solution water catalyst in a full cell.The DFT theory was performed to calculate the differential charge density,the projected density of states and the effective energy band of the catalyst under the light and dark reaction conditions.The results revealed that the introduction of Si can effectively enhance the catalytic performance of the material by changing the charge distribution of the system,which in turn adjusts the local electronic structure of the active site,the photoreaction process,decreases the excitation energy required for electron leap,and increases the degree of hybridization of the atomic orbitals,which in turn enhances the overall catalytic performance.This work provides a novel preparation strategy for the synthesis of LDH nanosheets with good photoelectric response.