Controllable Construction Of Palladium-based Alloy Nanomaterials And The Electrocatalytic Performance Investigation Of Alcohol Oxidation

The development and utilization of new energy technologies are crucial measure to address the current energy crisis and environmental issues.Electrochemical alcohol oxidation is a green and pollution-free catalytic technology,in which complete oxidation of alcohol molecules can serve as the anodic half-reaction for direct alcohol fuel cells.Additionally,its partial oxidation can be used to prepare various high value-added organic chemicals,making it of great theoretical and practical significance.However,alcohol oxidation faces challenges such as low activity,poor stability,and selectivity,and the design and development of high-performance electrocatalysts are essential for enhancing the industrial application of alcohol oxidation.The noble metal Pd and Pd-based materials are currently one of the most effective and extensively studied catalytic materials due to their excellent electrocatalytic activity in alcohol oxidation.However,the relatively high cost of Pd hinders the practical application of the catalysts,and the activity and resistance to poisoning of the catalysts still need to be further improved.In this thesis,Pd-based alloy nanomaterials were prepared by alloying Pd with free-noble-metal elements to reduce the amount of Pd used.By controlling the morphology,composition,and dimensions of these nanomaterials,the performance of electrocatalytic alcohol oxidation was improved,revealing the inherent relationship between catalyst structure and performance.Furthermore,the improvement mechanism of catalysts performance for alcohol oxidation was elucidated through density functional theory（DFT）calculations.The main research contents are as follows:（a）Pd Sb binary alloy nanoparticles with different branched structures were prepared by a simple wet chemical method using Pd（acac）₂ and Sb Ph₃ as metal precursors and controlling the amount of Mo（CO）₆.The formation mechanism of Pd Sb alloy and its branched structure was revealed through analysis of the morphology,structure,and elemental composition of the nanomaterials under different preparation conditions.The ethanol oxidation performance of different branched Pd Sb alloys under alkaline conditions was studied using various electrochemical testing techniques,and the results showed that Pd Sb alloy had better ethanol oxidation reaction（EOR）activity and stability than commercial Pd/C and branched Pd catalysts.Among them,highly branched Pd Sb alloy had the best EOR performance due to its larger specific surface area,with a specific activity of 109 m A cm^-2 and a mass activity of 2.42 A mg_Pd^-1.DFT calculations showed that the introduction of Sb optimized the electronic structure of the Pd catalytic site,lowered the energy barrier of the rate-determining reaction step,and thus improved the electrocatalytic performance of alcohol oxidation.（b）Three-component Pd Sb Bi alloy nanoparticles with different compositions were synthesized using Pd（acac）₂,Sb Ph₃and Bi Ph₃ as raw materials.By adjusting the ratio of Sb and Bi precursors,nanoparticles with different compositions were prepared,and their characterization showed similar branched structures and particle sizes.The Pd Sb Bi nanoparticles with different compositions were loaded onto carbon black to prepare catalysts,and their EOR performance was electrochemically tested under alkaline conditions.Results showed that the three-component Pd Sb Bi alloy had better performance than binary Pd Sb,Pd Bi alloys,and commercial Pd/C,with the Pd₇₆Sb₁₇Bi₇/C nanoparticles owning the best EOR activity and stability.Using Pd₇₆Sb₁₇Bi₇/C as the anode catalyst and platinum mesh as the cathode catalyst,a mixed electrolysis system for the oxidation of ethanol and the production of hydrogen was assembled,which could simultaneously produce high-value-added acetic acid and hydrogen with high efficiency and low energy consumption.DFT calculations showed calculations the presence of Sb and Bi can be favored for the adsorption OH^-in the EOR rate-limiting step as well as for the removal of reaction intermediates at the Pd site.（c）Using 2D ultrathin Pd Mo bimetallene as a template,Pd Mo Sb trimetallene with a thickness of about 1.5 nm and a highly curved and 2D ultrathin structure was prepared by alloying with Sb.Pd Mo Sb trimetallene was loaded onto reduced graphene oxide（r GO）as a catalyst for alcohol oxidation,with very high Pd utilization rate.Electrochemical tests showed that Pd Mo Sb/r GO had better activity and stability than Pd Mo/r GO and commercial Pd/C for the oxidation of various small alcohols such as ethanol,methanol,and glycerol under alkaline conditions.The enhancement of Pd Mo Sb trimetallene performance was not only due to the high specific surface area of the 2D ultrathin nanostructure,but also due to the presence of Sb which enhances both the adsorption of OH^-in the AOR reaction-intermediate pathway and the tolerance of CO in the poisoning-intermediate pathway.（d）Monodisperse and uniform Pd₂Ga nanorods were prepared using a colloid method with Pd（acac）₂ and Ga（acac）₃ as raw materials.Pd₂Ga combined with carbon black as a catalyst for the EOR reaction exhibited excellent activity and stability,with mass activity and specific activity reaching 1.97 A mg_Pd^-1 and 164 m A cm^-2,respectively.Furthermore,it showed electrocatalytic hydrogen evolution reaction（HER）performance in alkaline media containing ethanol that was close to commercial Pt/C.Using Pd₂Ga as both the anode EOR and cathode HER catalysts,a two-electrode electrolysis system was assembled to simultaneously produce acetic acid and hydrogen at a low voltage.The electrolysis system achieved a current density of 10 m A cm^-2 with only about0.62 V,making it an economical and efficient mixed electrolysis device.DFT calculations revealed that the high performance of the coupled system benefited from the electronic and bifunctional effects of Ga.