Design And Performance Research Of Fe Co Ni Based Catalyst For Electrochemical Water Splitting In Alkaline Electrolyte Solution

Today,with the increasing global pressure to cope with climate change,hydrogen energy,as a clean,safe,efficient and sustainable secondary energy,has attracted worldwide attention.The combustion calorific value of H₂is the highest among all fuels except nuclear fuel,and its reaction product is water,which has no pollutants and greenhouse gas emissions,and can be regenerated to produce hydrogen.It is regarded as the most potential green and clean energy in the 21st century.In China,hydrogen energy was written into the national development program as early as 2019,and the launch of"peak carbon dioxide emissions,Carbon Neutralization"has further promoted the development of hydrogen energy.Hydrogen production from electrolyzed water is considered as the most promising green hydrogen energy supply mode in the future because of its high product purity（>99.7%）and no pollution（expected to achieve zero carbon emission）.Theoretically,at room temperature,hydrogen production by electrolysis of water only needs a voltage of 1.23 V.However,because the anodic oxygen evolution reaction（OER）and cathodic hydrogen evolution reaction（HER）in water decomposition are both spontaneous and have slow kinetics,and the ohmic resistance of electrolytic cell leads to the fact that hydrogen production by electrolysis of water actually needs to apply a higher voltage（1.7～2.4 V）and consume more electric energy.In order to reduce energy consumption and accelerate electrolysis kinetics,catalysts with high activity and good stability are widely used.At present,precious metal catalysts（Pt,Ir,Ru and their oxides）are still the mainstream catalysts,but their further wide application is limited by the characteristics of low earth storage and high price.Therefore,it is of great significance to develop a new generation of catalysts with low price,high activity and high stability that can replace precious metals.Herein,this paper summarizes the research status of alkaline electrolyzed water catalyst in recent years,and systematically analyzes the effective design and performance optimization strategy of alkaline electrolyzed water catalyst.Based on the development of alkaline electrolytic water catalyst with high activity,high stability and low price,from the dynamic process and non-dynamic influencing factors.Among them,the intrinsic activity is optimized by means of multi-element active site design,heteroatom doping,size nanocrystallization,defect control and so on to speed up the kinetic process to solve the usability of the catalyst;Through carbon coating,structural optimization design,hydrophilic and gas-repellent interface construction and other means to overcome the adverse effects of non-dynamic factors to solve the stability problem;Among them,the non-kinetic influencing factors of the catalyst are the focus of our discussion,including the regulation of hydrophilicity and hydrophobicity of the catalyst surface interface,and the evolution behavior of bubbles on the electrode and the influence of hierarchical porous structure are monitored in situ.The exploration of non-kinetic factors is of great guiding significance to the efficient design of electrolytic water catalyst,but there are few related research reports,and this paper will focus on this part.The main research contents of this paper are as follows:（1）BC@Ni-Co₃O₄catalyst constructed by BC-derived carbon and its Overall Water Splitting were studied.The nano-structure of the catalyst is closely related to the catalytic activity and stability of the catalyst.In this chapter,a nano-composite catalyst C@Ni-Co₃O₄with two-dimensional carbon skeleton as the main body and zero-dimensional Ni-Co₃O₄as the active center was constructed by anchoring metal ions with abundant hydroxyl groups of bacterial cellulose（BC）.Through morphological observation,we found that a large number of nano-metal particles were evenly distributed on both sides of the two-dimensional derived carbon,providing rich catalytic active sites,and the staggered intersection between the two-dimensional derived carbon formed a network conducive to electron transport and proton exchange.In alkaline environment,C@Ni-Co₃O₄has excellent water electrolysis performance,and only 80 m V and 270 m V overpotential are needed to realize the current density of 10 m A cm^-2in HER and OER processes.Through the in-depth analysis of its structure-activity relationship,it is found that the HER performance of Ni-Co₃O₄is mainly derived from Ni,while the OER performance is mainly provided by Co₃O₄.At the same time,due to the synergistic effect between Ni and Co₃O₄,the total water-soluble voltage of Ni-Co₃O₄is only 1.63 V.（2）multifunctional carbon-coated nickel nanoparticle are used as electrocatalyst for hydrogen evolution in alkaline electrolyte solution.In the last work,we found that the combination of Ni and C has relatively excellent hydrogen evolution performance,but its activity is not ideal enough to meet the requirements as an industrial hydrogen evolution catalyst.Moreover,the structure-activity relationship between Ni and C is not clear in the last work,which deserves our further exploration.Therefore,in this chapter,a simple bottom-up in-situ polymer encapsulation method was used to prepare nitrogen-doped carbon-coated Ni nanoparticles（NC@Ni NPs）.Thanks to the existence of ultra-thin carbon protective layer,the content of nickel in the obtained catalyst is as high as 89.4 wt%,but the size of Ni nanoparticles is uniform without obvious agglomeration,and the diameter is about8 nm,which is connected into a good network structure under the action of thin carbon.The catalyst HER has excellent catalytic activity,and NC@Ni NPs remains stable even after running at a current density of 1400 m A cm^-2for more than 260 hours in alkaline environment.Interestingly,although the kinetic process is much lower than 20%Pt/C at lower potential,the HER performance of NC@Ni NPs is obviously better than 20%Pt/C at high current density.What is the source of this phenomenon?In order to find out the reason behind this phenomenon,we started with non-dynamic factors and used in-situ detection methods to prove that the mechanical shock effect caused by bubble impact during hydrogen evolution is one of the key reasons for the performance degradation of the catalyst,and the multifunctional carbon protective layer we constructed just effectively alleviated this unfavorable factor;Secondly,the nano-porous network structure connected by thin layers of carbon greatly promotes the increase of the accessible area between electrolyte and catalyst;Finally,the ultra-high metal load ensures the output of high current density.The results show that the effective design of electrolyzed water catalyst should not only pay attention to the kinetic process to improve the catalytic activity,but also pay attention to the non-kinetic influencing factors.（3）Preparation of trace metal-oxide modified Fe OOH self-supporting catalytic electrode and study on its oxygen evolution performance.Although the kinetic processes of HER and OER are different in the same system,they are affected by the same non-kinetic factors.Therefore,guided by the conclusion of the previous work,we further optimize the design from the texture to alleviate the adverse effects of non-kinetic factors,and then develop more efficient OER catalysts.Based on this,at the same time,in order to avoid the natural defect that powder catalyst needs binder,which leads to the increase of contact resistance,in this chapter,we prepared WO₃/Fe OOH@NF three-dimensional self-supporting electrode with needle-like Fe OOH as the main body and trace WO₃modified by simple solution immersion method.The results show that Fe OOH modified by trace WO₃has better OER catalytic activity,and only 220 m V overpotential is needed to achieve a current density of 10 m A cm^-2.XPS results show that the introduction of W makes Fe³⁺shift to a higher valence state,and the optimized electronic structure is more conducive to the OER process.In addition,the results show that Fe OOH has a nano-needle-like microstructure,which is a very good Unzer wetting structure,which is conducive to the rapid emergence of bubbles,which can not only accelerate the catalytic mass transfer process,but also ensure the stability of the electrode.This kind of suitable nano-needle structure and the integrated design of three-dimensional electrode provide the possibility for the rapid migration of bubbles and help to improve the working stability of catalytic electrodes.When this simple synthesis method is extended to other metals（V,Mo,Ce）,excellent electrolytic water catalysts can still be obtained,among which the V-doped modified Fe OOH electrode V-O/Fe OOH@NF has excellent water-dissolving performance,and this method shows high universality.