Pd Nanocatalyst Supported On CoFe-LDHs/NF And Their Catalytic Oxidation Performance For Ethanol

Direct ethanol fuel cells（DEFCs）are a potential renewable energy conversion and storage technology.Due to its strong resistance to the toxicity of oxidative intermediates(mostly CO_ads)and its ability to increase the kinetics of the ethanol oxidation process（EOR）in an alkaline environment,palladium（Pd）has been widely used as an efficient catalyst for EOR in DEFCs.However,the high cost,scarcity and easy aggregation of Pd limit its application and development.In this thesis,based on the controllability of laminate cations and“outer confinement”effect of layered double hydroxides（LDHs）materials,and oriented to optimize the key scientific issues such as the optimal dispersion of active components and electron/ion conductivity.A hydrothermal approach was used to create LDHs nanoarrays supported Pd nanocatalysts on nickel foam（NF）substrates,and the structure-activity link between the catalyst structure and the performance of the ethanol oxidation reaction was examined.The following are the key research contents and findings:（1）CoFe-LDHs materials（Co₁Fe₃-LDH/NF）were synthesized on NF substrate by hydrothermal method,and Pd nanoparticles were loaded on Co₁Fe₃-LDH/NF by electrodeposition method to prepare Pd/Co₁Fe₃-LDH/NF composite material,and its electrocatalytic efficacy for ethanol oxidation was also investigated.The results showed that the cyclic voltammetry（CV）peak current density of Pd/Co₁Fe₃-LDH/NF was as high as 676.0 m A·cm^-2 with a specific activity of 17.46 m A·cm^-2 and the j_f/j_r of 1.92under alkaline conditions,and the relatively high current density was maintained after a stability test of 8000 s.X-ray absorption fine structure（XAFS）and X-ray absorption spectroscopy（XAS）proved the strong interfacial interaction of Pd nanoparticles with the carrier material through the Pd-O-Co（Fe）bridges.The findings of high performance liquid chromatography（HPLC）and ¹H nuclear magnetic resonance（¹H NMR）revealed that the creation of Pd-O-Co（Fe）brideges facilitated charge transfer,significantly accelerates the catalytic rate during the electrocatalytic process,which is a key factor in determining the evolution of EOR towards carbon-carbon bond（C-C）cleavage.（2）The ternary CoFeAl-LDH/NF was synthesized by the hydrothermal method and used as a precursor,and the Al ion vacancies were regulated by the alkali etching method,so that the Pd nanoparticles were anchored in the vacancies generated by the alkali etching,and the Pd/D-CoFeAl-LDH/NF catalyst was obtained.When the etching solution concentration was 4 M,Pd/D-CoFeAl-LDH/NF performed superiorly in EOR catalysis.The peak current density was up to 968.0 m A·cm^-2,the specific activity was45.28 m A·cm^-2,the j_f/j_r was 3.39 under alkaline conditions,and the corresponding current density(120.0 m A·cm^-2)at 8000 s was 7.8 times that of Pd/Co₁Fe₃-LDH/NF(15.3 m A·cm^-2).The D-CoFeAl-LDH/NF support with the Al ion defects structure increased the dispersion of Pd nanoparticles.X-ray photoelectron spectroscopy（XPS）and electrochemical characterizations revealed that the Pd anchored on the defect sites was coordinated with Co（Fe）via Pd-O bonds,where its strong metal-support interaction force and oxygen vacancies and metal defects had a strong promoting effect on the catalytic reaction of ethanol.