Synthesis And Electrocatalytic Properties Of Noble Metal Pd-based Nanomaterials

With the advantages of high energy conversion efficiency,low environmental pollution and ease of use,fuel cells is considered as a leading alternative of green energy technology,which can effectively alleviate resource exhaustion and increasingly serious environmental problems,with good development prospects and economic benefits.Therefore,it is very important to develop cleaner and more efficient anode catalysts for fuel cells.Due to their unique physical and chemical properties,noble metal nanoparticles have a wide range of applications in energy conversion and storage,cancer treatment,sensing,especially catalysis,etc.It is found that platinum（Pt）and Pt-based nanomaterials are good anode materials for fuel cells,which can greatly improve the electrocatalytic performance.However,the scarcity and expensive of Pt limit its practical application.Therefore,palladium（Pd）is considered to replace Pt.Compared with Pt-based materials,Pd-based nanomaterials have many advantages,such as high catalytic activity,inexpensiveness and excellent anti-CO poisoning ability,etc.,but the economic benefit is still a problem that needs to be noticed.In order to reduce the amount of Pd used in Pd-based catalysts,the introduction of other elements to form bimetallic or trimetallic nanomaterials is considered.Combining Pd with non-precious metals（Co,Fe,Cu,etc.）is considered to be an effective strategy to constructing binary or ternary Pd-based catalysts.In addition,the introduction of oxyphilic metals such as ruthenium（Ru）can effectively convent CO-like poisoning intermediates on Pd into CO₂ at a lower potential,which ultimately improves the electrocatalytic activity of the catalyst.The research shows that the morphology and structure of the catalyst have a great influence on their electrocatalytic performance.At present,Pd-based nanomaterials with linear,rod-like,spherical,core-shell,cube-like and cluster-like shapes have been prepared,and the electrocatalytic performance is good.In this paper,the controlled synthesis of Pd-based precious metal catalysts with different morphologies was further studied,and research the electrochemical activity of fuel cells.The main work includes the following:（1）Hollow and porous octahedral Pd Ru Cu NCs were prepared at room temperature using Cu₂O as the template and PVP as the surfactant through substitution and disproportionation reactions.The morphology of the octahedral Pd Ru Cu NCs can be controlled by adjusting the molar ratio of Pd/Ru/Cu precursors,thus modulating the electrocatalytic performance.The excellent hollow porous structure of the prepared catalysts and the electronic effect between the metals resulted in excellent electrocatalytic activity and significant durability for the formic acid oxidation reaction（FAOR）.Among them,the Pd Ru Cu₅ nanocages（Pd/Ru/Cu precursor ratio of 1:1:5）showed the best catalytic performance for the formic acid oxidation reaction under acidic conditions up to 1229.74 m A mg_Pd^-1,which was 1.9times higher than that of the commercial Pd/C catalyst(636.01 m A mg_Pd^-1).After6000 s durability test,the current density was still higher than that of the other catalysts,and the cyclic retention rate was 86.9%after 400 consecutive cycle scans,with better stability and durability.（2）A series of palladium-ruthenium-tellurium nanowires were prepared by polyol reduction method using tellurium nanowires as a template and by adjusting the introduction of precursors Pd²⁺and Ru³⁺.These catalysts have controlled linear structure,interwoven to form porous mesh structure with lattice defects,high porosity and many active sites,and show high catalytic activity for ethanol oxidation reaction（EOR）under alkaline conditions.Ru is an oxygen-loving metal,and the synergistic effect between metals after the introduction of Ru can effectively improve the electrocatalytic performance of the catalysts,among which the electrochemical active surface area（ECSA）of Pd Ru₂Te NWs is the largest at 93.38 m² g_Pd^-1,and the EOR current density can reach 1110.78 m A mg_Pd^-1,which is better than the existing commercial Pd/C catalysts(189.12 m A mg_Pd^-1).After 6000 s durability test,the current density of Pd Ru₂Te NWs was still higher than that of Pd Te NWs and Pd/C catalysts,and Pd Ru₂Te NWs with good stability,the retention rate of Pd Ru₂Te NWs（96.1%）was higher than that of commercial Pd/C catalysts（63.3%）after 400cycle scans.（3）A highly active and durable Pd Ru Zn hollow nanohexahedral catalyst with a nanoparticle size of about 100 nm was synthesized by a solvothermal method using ZIF-8 as a template.metal organic frameworks（MOFs）with porous structures and large specific surface areas,the introduction of oxygen-loving metal Ru to form an alloy,and the alloying strategy can effectively tune the electronic structure of Pd.The unique hollow porous structure of the catalyst and the synergistic effect between the multi-metals enable the catalyst to have a high active site,which greatly increases the electrochemically active surface area（ECSA）and can be used in direct alcohol fuel cells.In comparison,it can be seen that the trimetallic Pd Ru Zn NBs have smaller charge transfer resistance than bimetallic Pd Zn NBs and commercial Pd/C catalysts,and their EOR maximum current density can reach 1873.67 m A mg_Pd^-1 with good durability and resistance to toxicity.