Fabrication Of Transition Metal (Co/Ni) Based Catalysts And Their High Current-density Electrocatalytic Biomass-related Organics Oxidation Performance

Biomass-related organics electrocatalytic oxidation provides a sustainable,green,and safe method for the efficient use of electrical energy and biomass resources.Due to inherent thermodynamic advantages,these reactions can be used to replace the oxygen evolution reaction（OER）and coupled with the hydrogen evolution reaction（HER）,not only providing energy-saving electrocatalytic hydrogen generation,but also enabling value-added anode production or pollutant degradation.However,these oxidation reactions have sluggish kinetics due to the multiple electrons transferred and complex pathways involved.Furthermore,the low efficiency of biomass-related organics electrocatalytic oxidation,caused by the competition from OER,has severely limited its practical application.Therefore,the key challenge is the design and development of efficient and stable electrocatalysts.This thesis constructs a series of transition metal Co/Ni-based catalysts through a green and simple approach to improve the efficiency and stability of electrocatalytic oxidation of organics.Meanwhile,the corresponding possible reaction mechanisms and structure-function relationships are investigated through relevant in-situ characterization and theoretical calculations,and the mechanism of the reaction is clarified.The main contents of the thesis are shown as follows:（1）Ni（OH）₂@NF and Co-doped Ni（OH）₂（Co Ni（OH）x@NF）catalysts are synthesized in-situ on nickel foam（NF）through a one-step hydrothermal method.Their performance for the glucose electrocatalytic oxidation reaction（GOR）and HER are discussed in order to explore the key factors and active species affecting their electrocatalytic performance.In particular,Co_0.5Ni（OH）x@NF exhibits the optimal GOR performance with the lowest potentials of 1.15 and 1.26 V vs.RHE to reach 10and 100 m A cm^-2,respectively.At the current density of 100 m A cm^-2,the potential is lowered by 330 m V compared to the OER,confirming that the GOR has more favorable thermodynamic dynamics.XPS,In-situ EIS and Raman show that the as-synthesized of Co_0.5Ni（OH）x@NF features reversible structure and recovery process during GOR and the converted Co/Ni（oxy）hydroxides（MOOH,M=Co/Ni）are the real active species.The introduction of Co can enhance the redox performance of Ni（OH）₂@NF,resulting in accelerated production of MOOH and ultimately improved GOR performance.Furthermore,Co_0.5Ni（OH）x@NF is demonstrated to be a promising bifunctional catalyst for HER and GOR.（2）An efficient and low-cost Co-doped Ni₃S₂@NF electrocatalyst is successfully synthesized via a hydrothermal method.The Co_0.4Ni S@NF exhibits an ultralow onset potential（0.9 V vs.RHE）and high current density(497 m A cm^-2 at 1.45 V)for the 5-hydroxymethylfurfural electrocatalytic oxidation（HMFOR）under alkaline conditions.In the HMFOR couple with the cathodic HER system,it delivers the yield rates of 330.4and 1000μmol cm^-2 h^-1 for 2,5-furandicarboxylic acid（FDCA）and H₂,respectively.These are superior to most of reported electrocatalysts and show promise for higher yields of FDCA and H₂.The effects of electrolysis potential,temperature and HMF concentration on HMFOR are also investigated.In-situ Raman analysis reveals that the Co_0.4Ni S@NF surface is rapidly reconstructed into MOOH,effectively lowering the potential threshold,and serving as the actual active sites for HMFOR.（3）P-doped Ni₃S₂/Co₉S₈@NF heterostructure catalyst（P-Ni₃S₂/Co₉S₈@NF）is designed by hydrothermal sulfidation and low-temperature phosphorization strategy,which possesses superhydrophilic and superaerophobic properties and exhibits excellent HER,OER and urea oxidation reaction（UOR）performance.Electrochemical tests show that P-Ni₃S₂/Co₉S₈@NF needs potential of only-63 and 220 m V vs.RHE to drive a current density of 10 m A cm^-2 in the 1.0 M KOH for HER and OER,respectively,and extremely low potentials of 1.20 and 1.39 V vs.RHE to reach 10 and 1000 m A cm^-2 for UOR test,respectively.In addition,the anion exchange membrane flow electrolyzer cell driven by P-Ni₃S₂/Co₉S₈@NF as cathode and anode electrode to couple the HER and UOR,operate at 1000 m A cm^-2 with 180 h of good stability.The temperature-programmed desorption（TPD）and DFT calculations demonstrate that P doping modulates the electronic structure of the bimetallic heterogeneous interface and optimizes the adsorption capacity to the urea molecular groups,thus enhancing the catalytic activity and stability.