Fabrication Of Doped Co₃O₄ Nanoarrays And Investigation Of Their Non-enzymatic Glucose Sensing Performance

At present,with the increase of diabetes patients in the world,the demand for glucose sensors is increasing.Due to the fact that commercial enzyme sensors are always vulnerable to environmental factors such as humidity,acidity and alkalinity,the development of enzyme-free glucose electrochemical sensors has attracted much attention.Electrode material is one of the key factors to determine the performance of enzyme-free glucose electrochemical sensor.Therefore,the fabrication of electrode material with simple synthesis process,high sensitivity,good selectivity and stability is the research focus of enzyme-free glucose sensor.Transition metal oxides（such as cobalt,copper,nickel,etc.）are considered to be one of the most promising electrode materials for enzyme-free glucose sensor due to their excellent catalytic performance for glucose oxidation.Cobalt tetroxide（Co₃O₄）has abundant reserves,simple preparation method and controllable morphology.However,due to the defects of poor conductivity and slow electron transfer rate,the comprehensive sensing performance of electrode materials needs to be further improved.In this paper,based on the design thought of constructing high specific surface area nanoarrays and doping modification to adjust electronic structure,two kinds of transition metal element doped Co₃O₄ nanoarrays were fabriated via one-pot method by introducing transition metals ceriumcerium（Ce）or iron（Fe）respectively into the reaction systems during in-situ growth of Co₃O₄ nanoarrays,and the electrode material with high electrocatalytic activity and excellent sensing property were obtained.It provides experimental and theoretical basis for the development of electrode materials for enzyme-free glucose electrochemical sensor.The main research results are as follows:（1）Ce doped Co₃O₄ nanowire arrays were in-situ grown on FTO in a one-step hydrothermal synthesis by adding cerium source.The results show that the electronic structure of Ce doped Co₃O₄ nanowire arrays can be effectively controlled by changing the amount of Ce doping,so as to optimize their electrochemical activity and sensing performance.The 0.45-Ce-Co₃O₄/FTO electrode sample has the best enzyme-free electrochemical sensing performance of glucose with a sensitivity of 637 μA·mM-1·cm-2 which was 5 times of that of the undoped sample.The linear range was 0.0002～0.8 mM,and the detection limit was as low as 70 nM.In this work,the mechanism of Ce doping on the sensing performance was further investigated by electrochemical activity surface area,electrochemical impedance spectroscopy and catalytic rate constant tests.The results show that the electrochemical activity specific surface area and catalytic rate constant increases significantly,while the charge transfer resistance decreases.The improvement of sensing performance can be attributed to the high coordination number and flexible coordination mode of doped Ce,which can easily induce distortion to Co₃O₄ lattice and produce oxygen vacancies.On the one hand,oxygen vacancies can act as electron charge carriers to promote electron transport,on the other hand,they can provide additional active sites for redox reaction.（2）Fe doped Co（OH）₂ nanosheet arrays were constructed in situ on FTO by electrochemical deposition,and the Fe-doped Co₃O₄ nanosheet array was obtained by heat treatment.The results show that the morphology and electronic structure of Co₃O₄ nanosheets can be effectively regulated by controlling the amount of Fe doping,and the electrochemical activity and sensing performance of Co₃O₄ nanosheets can be improved.The 5.0-Fe-Co₃O₄/FTO electrode has the best electrochemical performance.The sensitivity of the electrode is 625 μA·mM-1·cm-2,which is 3 times of that of the undoped sample.The linear range is 0.0002～2.5 mM,and the detection limit is as low as 100 nM.Via electrochemical impedance spectroscopy and catalytic rate constant test,this work explored the mechanism of action that how Fe doping influences the per formance of the electrochemical sensing,and the results show that the catalytic rate constant of the doped electrode increases significantly and the charge transfer resistance decreases,which can be attributed to the introduction of electrons into the conduction band of Co₃O₄ by Fe doping,which increases the concentration of free electrons and reduces the resistance of Co₃O₄.At the same time,the defects introduced by grain refinement and doping also significantly increase the active sites and thus enhance the electrocatalytic activity of the electrode materials.