Preparation And Electrocatalytic Performance Of Cobalt-based Oxide/Selenide Catalysts

The anodic oxygen evolution reaction（OER）of electrocatalytic water splitting is a multi proton and electron transfer process,resulting in slow kinetics and high overpotential,seriously hindering the application of OER.In addition,hydrogen peroxide（H₂O₂）is widely used in various industries.The electrocatalytic oxygen reduction（ORR）to H₂O₂ is a clean and pollution-free method used to reduce dependence on energy intensive anthraquinone processes.Precious metals are highly effective catalysts for the above two electrochemical reactions,but their high cost and low reserves limit their wide application.Therefore,it is crucial to develop non noble metal catalysts with high activity,selectivity,and stability.Co based materials is a kind of electrocatalytic raw materials with abundant reserves,good conductivity,and high selectivity.Based on this,this paper designed and synthesized cobalt-based oxides and selenides with various structures,and combined theoretical calculations and experiments to explore the effects of the defects and heterostructures on the electrochemical performance of OER and ORR.The main content is divided into the following three parts:Firstly,the Co_3-xO₄ with metal defects was selected as an electron-acceptor carrier,and Co_3-xO₄/Ni O with rich surface Ni³⁺active sites was synthesized using a hydrothermal calcination method.The results showed that Co_3-xO₄/Ni O had low overpotentials of 240 m V and 320 m V at 10 m A/cm² and 100 m A/cm²,respectively,a low Tafel slope of 64 m V/dec and the electrochemical active area（ECSA）of 1033.3cm².In addition,after 60 h stability testing at a current density of 10 m A/cm²,Co_3-xO₄/Ni O still had high activity.Combining experimental and theoretical calculations,the high activity and stability of Co_3-xO₄/Ni O were attributed to the adjustable electronic structure,which meant that more electrons were transferred from Ni O to Co_3-xO₄,resulting in more Ni³⁺active sites on the surface of the catalyst.Co_3-xO₄/Ni O with rich Ni³⁺sites could effectively regulate the binding energy of oxygen containing intermediates（OH*,O*,and OOH*）with appropriate binding energy,reduce the Gibbs free energy change of the rate-limiting step,and accelerate the OER reaction kinetics.Secondly,the preparation method in the previous chapter is relatively complex and requires the use of adhesives,which cannot fully expose the active sites and reduce the conductivity and stability of the catalyst.Therefore,this chapter used a simple and rapid one-step cyclic voltammetry（CV）electrodeposition method to prepare amorphous/crystalline phase Fe doped Co Se catalysts（Fe₁Co₄Se/NF）as a cheap Fe Co bimetallic OER self-supporting electrocatalyst,and explored the influence of Fe/Co ratio on OER performance.When the Fe/Co ratio was 1:4,the Fe₁Co₄Se/NF catalyst had the most excellent OER performance.The overpotentials were 269 m V and 280 m V at 50 m A/cm² and 100 m A/cm²,the Tafel slope was 38 m V/dec,and the electrochemical active area was 720 cm².It could operate stably for 135 h at a high current density of 100 m A/cm².Through characterization analysis,the synergistic effect of Fe doping and amorphous/crystalline phase structure were conducive to the formation of high valence Co³⁺and Fe³⁺in Fe₁Co₄Se/NF,greatly improving the OER reaction activity.Thirdly,based on the excellent electrocatalytic properties of cobalt-based materials explored in the previous two chapters,this chapter used a simple hydrothermal method to synthesize Co Se₂ with abundant Se deficiency,in which the addition of Na BH₄ induced the orthogonal phase Co Se₂（o-Co Se₂）to a cubic phase Co Se₂（c-Co Se₂）.Abundant Se deficiency could effectively regulate the electronic structure of the surface of c-Co Se₂,and provide suitable binding energy for OOH*and*O intermediates.It had high activity,selectivity and long-term stability for the preparation of H₂O₂ by acidic 2e^-ORR.The onset potential was as low as 0.73 V,the selectivity for H₂O₂ was 84%（0 V vs.RHE）,and the average electron transfer number was about 2.3.In addition,the H₂O₂ yield measured using a flow cell was as high as115.9 mmol/g_cat./h and the Faraday efficiency was 70% at 0 V（vs.RHE）.