Research On Ni-based Ceria Composite Hydrogen Evolution Reaction Electrode Prepared By Electrodeposition Method

Hydrogen was mainly used as an important chemical raw material, and thehydrogen energy has received more and more attention as new green energycandidate. The method to get hydrogen by electrolysis was historic. Many studieswere focused on this electrolysis method recently, because of its clean andsustainable characteristics. Cathodic hydrogen evolution reaction （HER） materialsplayed an important role in this process. It was possible to improve the energyconversion efficiency and reduce cost by designing and preparing new cathodicHER electrodes. In this thesis, the electrochemical co-deposition method suitable toindustry application was employed; the new Ni-based CeO₂composite electrodematerials were prepared; the different sized CeO₂particles were used in theco-deposition process. The scanning electron microscopy （SEM）, X-ray diffraction（XRD）, thermo gravimetric and differential scanning calorimetry （TG-DSC） andX-rays photoelectron spectroscopy （XPS） were used to characterize the compositeelectrodes, the HER catalysis activity and corrosion resistance of the compositeelectrodes were studied by electrochemical analysis method, such as linearpolarization, Tafel curve analysis, and electrochemical impedance spectroscopy（EIS）. It was focused on the HER synergetic effects between CeO₂particles and theNi matrix.Firstly, Ni/CeO₂composite coatings were prepared by electrochemicaldeposition， using the micro-CeO₂（5-10μm） and nano-CeO₂（10-30nm） particles.The results showed the Ni/CeO₂composite coatings had a good thermal stability.The different sized co-deposited CeO₂particles can improve the hardness and thesurface roughness of the nickel coating, make the fining effect on the Nielectrocrystallization, and change the preferred orientation of the nickel coating. Themicro-CeO₂particles inhibited the nickel deposition, but the nano-CeO₂decreasedthe Ni polarization. A good HER catalysis activity can be observed on the Ni/CeO₂composite electrodes, i.e. the HER charge-transfer resistance on the Ni surfacedecreased and the HER exchange current density increased obviously with the CeO₂particles addition. When the micro-CeO₂concentration was15g/L, the HERexchange current density on the Ni/CeO₂composite was70times higher than thaton the Ni coating, meanwhile, the HER total resistance on the composite coatingwas30times lower than that on the nickel coating. And the composite electrodescan keep a good stability during the HER process. The good HER activity oncomposite coating can be attributed to the synergetic effects between CeO₂particles and the Ni matrix. The H atom reduced on the nickel surface can be adsorbed on theCeO₂particles which have empty d and f orbits. The result showed the low-contentCeO₂composite coating had a better corrosion resistance.And then, Ni-based alloy CeO₂composite coatings were prepared by alloydeposition method. HER activities on the alloy composite coatings were studied.During Ni-S/CeO₂composite coatings investigation, it was found that the additionof different sized CeO₂particles increased the sulfur content in the Ni-S alloycoatings. The HER activity on the Ni-S/CeO₂composite coatings was higher thanthat on the Ni-S alloy coating. When the micro-CeO₂concentration was10g/L, theHER exchange current density on the Ni-S/CeO₂composite was2.2times higherthan that on the Ni-S coating. It was considered the HER activity on the Ni-S/CeO₂composite coatings were affected by the sulfur content in the Ni-S alloy coating, thesynergetic effects between CeO₂particles, and the Ni-S alloy coating. DuringNi-Zn/CeO₂composite coating investigation, it was worth noting that the Ni-Znalloy was consisted by some intermetallic compound. The Ni-Zn alloy coatingshowed an instinctive high HER activity. However, the HER activity can be furtherimproved with a proper CeO₂content embedded. The addition of the CeO₂particlescan change the microstructure and element composition of the Ni-Zn alloy coating.According to the Ni-Zn anomalous co-deposition mechanism and the CeO₂influence on the intermediate in the Ni-Zn co-deposition, the alloy elementcomposition of the Ni-Zn/CeO₂composite coatings was explained. Meanwhile, thecorrosion resistance of the Ni-Zn alloy coating can be improved with a lower CeO₂particles content.At last, the parameters of HER kinetics on the Ni/CeO₂composite coatingswere calculated. The results showed different sized CeO₂particles addition canincrease the specific surface area of the Ni coatings, and decrease the HERactivation energy on the Ni surface. When the micro-CeO₂concentration was15g/L,the HER activation energy on the Ni/CeO₂composite coating surface was only20.69kJ mol-1, much lower than that on the Ni surface. The HER rate constants onthe Ni and Ni/CeO₂surface were calculated, and then the adsorbed hydrogen atomscoverage was obtained at different overpotential. It was found that the addition ofthe CeO₂particles can accelerate the adsorption of the reduced hydrogen atoms,increase the value of adsorbed hydrogen atoms coverage as the hydrogen evolutionwas stable. It further confirmed the synergetic effects between CeO₂particles andthe Ni matrix.