Preparation And Performance Optimization Of Iron-Group Electrocatalysts For Electrocatalytic Oxidation Of Small Organic Molecules

In order to effectively solve the energy crisis and environmental problems caused by traditional fossil fuel consumption,it is necessary for us to develop new environment-friendly energy sources.Among them,hydrogen has received widespread attention due to its no pollution and high energy density.Due to its flexible installation,low contamination and high product purity,water electrolysis technology is considered an ideal hydrogen production route.Traditional water electrolysis techniques typically combine cathodic hydrogen evolution（HER）with anodic oxygen evolution（OER）.However,OER involves four-electron transfer reaction mechanism,which makes the electrolysis of water require high overpotential and high energy consumption.Fortunately,electrocatalytic oxidation of small organic molecules such as urea,benzyl alcohol,and glycerol can be used as an alternative reaction to OER due to their low starting potential,which can not only reduce the overall energy consumption in the hydrogen production process,but also achieve the purpose of wastewater treatment or product value-added.However,these anodic reactions all involve a multi-electron transfer process.Therefore,there is an urgent need to develop cheap and efficient multifunctional electrocatalysts to achieve the comprehensive goals of hydrogen production and wastewater treatment or product value-added.At present,although cheap iron-group materials have good stability,they also have the problems of insufficient number of active sites and poor conductivity.In order to get the utmost out of the advantages of iron-group materials,we modify them by different methods and prepare iron-group catalysts with multifunctional catalytic effects.The specific research contents are as follows:1.Cobalt,iron co-doped Ni（OH）₂multiphase（CFN MP/CC 2:4:10）was prepared by electrochemical deposition and hydrothermal method on carbon cloths（CC）.The structural characterization showed that the catalyst was a nanosheet with a thickness of 5-6 nm,which can be exposed to more active sites and improve the catalytic activity of the catalyst.X-ray powder diffraction（XRD）showed that the prepared catalyst was a mixed phase ofα-Ni（OH）₂andβ-Ni（OH）₂,and transmission electron microscopy（TEM）further confirmed that there is a continuous phase interface between the two phases,which can effectively reduce the potential energy barrier of charge transport and further accelerate the charge transfer process under the synergistic effect between the two phases.At the same time,the uniform doping of Fe and Co can effectively adjust the electronic structure of the original catalyst and induce the formation of more active Ni³⁺,so that the number of catalytic sites and intrinsic activity of the catalyst can be effectively improved.The results of electrochemical tests showed that the mixed phase catalyst shows excellent catalytic activity in OER and urea oxidation reaction（UOR）.The sample requires only 1.42 V vs.RHE in OER to achieve a current density of 10 mA cm^-2,while the same current density in UOR requires only 1.30 V vs.RHE.Meanwhile,the sample also showed good stability in the constant voltage test,the OER current retention rate can reach 96.8%,and the UOR current retention rate can reach 92.1%.At the same time,in the test of electrocatalytic oxidation of benzyl alcohol,the catalyst also showed good catalytic activity.By electrocatalytic oxidation test at 1.43 V vs.RHE,the conversion rate of benzyl alcohol reached 95.34%,the selectivity of benzoic acid was 96.78%,and the Faraday efficiency（FE）reached 92.70%.The catalyst has similar properties to benzyl alcohol oxidation electrocatalysts such as NiOOH/Ni Fe OOH and Co_0.83Ni_0.17/AC reported in the literature.This study provides theoretical possibilities and technical guidance for the design of highly active multifunctional catalysts for OER,UOR,and oxidation of small organic molecules.2.NiO/CoO nanosheets（NiO-C-CoO/CC 1:1）linked to carbon shells were successfully prepared on carbon cloth by using sulfonated polystyrene microspheres as templates.XRD shows that the phase of the catalyst is a mixed phase of NiO and CoO.Scanning electron microscopy（SEM）can observe three-dimensional（3D）carbon spheres deposited with NiO nanosheets evenly distributed on two-dimensional（2D）nanosheets composed of NiO and CoO.This stereohierarchical structure not only gives the sample a large surface area,but also provides more active sites for the catalytic reaction.On the one hand,more open void structure can enhance the mass transfer ability of the sample in the catalytic reaction process.On the other hand,the open pore structure can release the stress accumulated due to repeated oxidation-reduction processes in constant voltage tests,further optimizing the long-term operational stability of the catalyst.The results of TEM and EDS spectroscopy showed that the nanospheres in the hierarchical structure are hollow carbon spheres.It is precisely because of the existence of the hollow carbon shell that not only can the stability of the catalyst be improved,but also its good conductivity can greatly accelerate the electron transport between different phases,promote better synergy between NiO and CoO phases,and show faster reaction kinetic behavior,which is further confirmed by electrochemical test results.The catalyst exhibits excellent electrocatalytic performance for UOR,requiring only 1.31 V vs.RHE to achieve a current density of 10 mA cm^-2,and its current retention rate reached 97.4%in the constant voltage test of 80 h,showing extremely high stability.More importantly,the catalyst also exhibits versatile electrocatalytic oxidation properties.By selective oxidation of glycerol under constant voltage,the selectivity of reaction to formic acid can reach 95.4%,the Faraday efficiency can reach 91.6%.Selective oxidation of benzyl alcohol,the conversion rate of benzyl alcohol can reach 98.4%,the selectivity of benzoic acid reached 94.9%,and the FE is as high as91.8%.In this study,a multifunctional electrocatalyst for UOR and oxidation of small organic molecules is proposed,which provides the possibility to realize energy conversion and anode electrocatalytic value-added at the same time.