Preparation And Electrochemical Properties Of Cobalt Or Nickel Based Phosphides And Oxides

Electrochemical oxidation reaction shows great application prospects in energy conversion,pollutant treatment,and biomass upgrading.However,the slow electron transportation,high oxidation overpotential,and low conversion for electrode materials result in the energy consumption increase and seriously hinder the improvement of oxidation performance.Based on these critical scientific questions,we have employed element doping,construction of heterojunction,defect regulation,and laser machining means to fabricate a series of cobalt and nickel based metal phosphides and oxides.Furthermore,improving the carrier density,promoting surface reconstruction,and fabricating oxygen defects of catalytic materials are implemented to realize the efficient electrocatalytic oxidation of pollutants and5-hydroxymethylfurfural（HMF）.Meanwhile,we have revealed the correlation between the structural composition,the elements’coordination environment,surface phase transition,and electrochemical performance for electrode materials.The main results are as follow:（1）Co and CoFe precursors have been grown on the carbon film with sintering polyimide as the substrate,and Co P/C and Co Fe P/C composites are prepared,follow by low-temperature phosphorization.Sea urchin-like Co P possesses a fast electron transfer rate leading to the overpotential of hydrogen evolution reaction,which is only 42 m V with 10 m A cm^-2.The coordination environment around the Co atom is regulated and increases the carrier density for the material via doping Fe,increasing the electro-Fenton reaction rate.Employing Co Fe P/C as electrode of electro-Fenton reaction,methylene blue with 10 m L 25 ppm can be almost completely degrading in only 20 min（degradation rate is more than 91%）,confirming the high-efficiency electrocatalytic oxidation performance of organic pollutants in water.The distribution of H⁺concentration is explored in the flow electrochemical reactor by numerical simulation calculation.The role of the flow electrochemical reactor is studied in the catalytic reaction.The effect of Fe doping on the intrinsic activity of the catalyst is explored by density functional theory（DFT）calculation.（2）Ni and NiCo precursors are transferred to Ni₂P and Ni Co P employing a low-temperature phosphorization strategy.Ni OOH is easier to reconstruct in materials surface via Co substitution,which makes the interaction between Ni OOH and Ni Co P improve the conversion of 5-hydroxymethylfurfural(300 mmol L^-1).The voltage is only 1.46 V with 100m A cm^-2 when Ni Co P has employed the electrolyzer’s anode and cathode.The conversion rate of HMF(300 mmol L^-1),the yield of 2,5-furanedioic acid（FDCA）,and the Faraday efficiency reach 98.7%,98.8%,and 96.1%,respectively when the voltage is 1.46 V after1802.3 C.Additionally,the space-time yield of the flow-through electrochemical reactor is34.9 g L^-1 h^-1 at 1.46 V.The numerical simulation results show that 300 mmol L^-1 HMF is almost completely transformed into FDCA after three reaction units,which provides a basis and reference for optimizing the continuous flow electrochemical reaction process.（3）CoOOH is grown on the surface of CoP to form heterojunction（Co P-Co OOH）by electrochemical deposition.The results show that Co P in Co P-Co OOH is a p-type semiconductor,which promotes electrons accumulate on its surface,and Co OOH is an n-type semiconductor,which is easy to accumulate holes.Employing Co P-Co OOH as electrodes to oxidize 150 mmol L^-1 HMF requires 1.14 V voltage.The conversion of HMF,the selectivity of FDCA and Faraday efficiency are 98.3%,96.3%,and 96.3%,respectively when the charge of reaction is 854 C.Theoretical calculation（DFT）shows that the electron density at the heterojunction interface increases sharply,which makes Co P-Co OOH possess a lot of the effective electron in the electrocatalysis process.In a flow reactor,150 mmol L^-1 HMF is oxidized at 1.42 V,the Faraday efficiency and selectivity of FDCA are 98.2%and 99.4%,respectively.（4）The nano nickel oxide with oxygen-rich defects is fabricated by UV pulsed laser sinter nickel plate strategy.The results show that the material possesses low valence Ni,and the oxygen defect content in the material is the largest at 38 A laser current.In 100 mmol L^-1HMF,the oxidation initiation potential of V_o-Ni O as electrode material is only 1.26 V,and the HMF conversion,FDCA selectivity,and Faraday efficiency after consuming 668 C are99.7%,99.2%,and 85.7%,respectively.DFT results show that there are more electron transfer numbers in V_o-Ni O,which has greater adsorption energy for HMF.V_o-Ni O has a strong infrared adsorption effect on C=O and C-OH species in HMF.Meanwhile,the conversion of HMF,the selectivity of FDCA,and the Faraday efficiency are 98.4%,97.7%and 83.3%,respectively in the flow electrochemical reactor with 1.50 V DC power.