钯基电催化剂的制备及其电化学性能研究

【作者】 李娟；

【导师】 张亚彬； 孙建东；

【作者基本信息】 天津工业大学 ， 材料工程（专业学位）， 2019， 硕士

【摘要】 由于传统化石燃料资源的逐渐减少以及此类燃料对环境的不利影响,对可再生和可持续能源的需求日益增加。燃料电池因其高能量转换效率和环境友好性而受到特别关注,而电催化剂是改善燃料电池性能的关键。本论文以合成高活性Pd基电催化剂为目的,通过优化工艺路线制备了具有独特纳米链网络状结构的Pd NCNs和Pd-Pt NCNs电催化剂,系统研究了它们对甲醇、乙醇及甲酸的电催化氧化性能。1.采用聚乙烯醇作为绿色还原剂和稳定剂,一步水热还原制备出Pd NCNs电催化剂,通过调节反应温度、pH值实现了对催化剂颗粒尺寸以及Pd金属含量的调控。在弱酸性条件下所得样品Pd NCNs-1中,电催化剂颗粒均匀分散在PVA中,粒径为4.45 nm。电化学测试结果表明,电催化剂的催化氧化性能均随着溶液pH值减小而升高,其中,Pd NCNs-1电催化剂的电化学活性比表面积最大（118.4 m2 g-1）,且对甲醇（673.85 A g-1Pd）、乙醇（601.58 A g-1Pd）和甲酸（307.77 A g-1Pd）的电催化活性最佳。在1M甲醇溶液中循环120圈后,电流密度的衰减率仅为4.3%,在1 M甲醇溶液中反应5000 s后电流密度的保持率仍达到60%。催化剂活性和稳定性的改善得益于制备过程中PVA的引入,PVA不仅作为绿色还原剂,而且PVA聚合物中的羟基还通过螯合作用使Pd2+均匀分散在PVA基底上,形成粒径非常小的Pd纳米颗粒并抑制了颗粒的团聚。在PVA聚合物缠结网络的模板作用下,进一步形成纳米链网络状结构,其较大的比表面积和丰富的活性位点显著增强了催化剂对甲醇、乙醇和甲酸的电催化活性。2.分别以氯化钯（PdCl2）和氯铂酸钾（K2PtCl6）作为钯源和铂源,采用同样的方法一步水热合成了Pd-Pt NCNs电催化剂。通过调节反应溶液的pH值和Pd、Pt的摩尔比制备了Pd-Pt NCNs系列催化剂样品,其中Pd,4.4Pt1 NCNs-1表现出最高的电催化活性和稳定性,其催化甲醇、乙醇和甲酸氧化反应的峰值电流密度分别为482.14 A g^-1Pd、580.4 A g^-1Pd和301.5 A g^-1Pd。更多还原

【Abstract】 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.更多还原