The Preparation And Electrochemical Performance Of Palladium-based Electrocatalysts

The requirement for renewable and sustainable energy sources has increased due to the gradual decline in traditional fossil fuel resources and the detrimental effects of such fuels on the environment.Fuel cells have received particular attention due to their high energy conversion efficiencies and low pollution.Electrocatalysts play a vital role in improving the performance of fuel cells.This thesis focuses on the synthesis of high-performance Pd-based electrocatalysts.Pd NCNs and Pd-Pt NCNs electrocatalysts with unique nanochain network structure?NCN?are prepared by optimizing synthetic parameters.The electrocatalytic oxidation performance of methanol,ethanol and formic acid are systematically studied.1.Pd NCNs electrocatalysts are prepared by one-step hydrothermal reduction with polyvinyl alcohol as the green reducing agent and stabilizer.The particle size and Pd content were controlled by adjusting the reaction temperature and pH value.The electrocatalytic particles were uniformly dispersed in PVA and the particle diameter was 4.45 nm in the Pd NCNs-1 sample obtained under a weakly acidic condition.Electrochemical test results show that the catalytic oxidation performance of the electrocatalysts increases with the decrease of the pH values.Among all the catalysts,the Pd NCNs-1 electrocatalyst has the largest ECSA?118.4 m2 g-1?and the best electrocatalytic activity of methanol?673.85 A g-1Pd?,ethanol?601.58 A g-1Pd?and formic acid?307.77 A g-1Pd?.The current density was only attenuated by 4.3%after 120 cycles in 1 M methanol solution and the current density remained at 60%after 5000s in 1 M methanol solution.The improvement of catalytic activity and stability is attributed to the introduction of PVA in the preparation process.PVA is not only used as a green reducing agent,but also promotes uniformly dispersion of Pd2+ on the PVA substrate by chelation between hydroxyl groups in the PVA polymers to form a very small particle size and inhibit the agglomeration of the particles.Under the action of the template of the PVA entanglement network,a nano-chain network structure is further formed and its large specific surface area and abundant active sites significantly enhance the electrocatalytic activities of the catalyst for methanol,ethanol and formic acid.2.Palladium chloride?PdCl2?and potassium chloroplatinate?K2PtCl6?are used as the palladium source and platinum source respectively.The Pd-Pt NCNs electrocatalysts were synthesized hydrothermally in the same way.A series of Pd-Pt NCNs catalysts were prepared by adjusting the pH values of reaction solution and the molar ratio of Pd and Pt.Pd4.1Pt1 NCNs-1 shows the highest electrocatalytic activity and stability.The peak current densities of the oxidation reactions of methanol,ethanol and formic acid are 482.14 A g^-1Pd,580.4 A g^-1Pd and 301.5 A g^-1Pa,respectively.