Surface And Interface Engineering Of Pd-Based Nanocrystals For Electrocatalysis

Noble metal nanomaterials have been widely used in many fields of energy conversion,industrial catalytic,information storage and biological analysis,due to their unique physical and chemical properties.However,the scarce storage and expensive price limit their further development.Researchers have devoted lots of effort to elevating the catalytic performance and lowering the cost of noble metal nanomaterials.In this thesis,we focus on the surface and interface engineering of Pd-based nanomaterials to improve their catalytic properties for alcohol oxidation,oxygen reduction and hydrogen evolution.The control experiments and theoretical calculations are carried out to uncover the mechanism of the excellent activity.Our work will provide the guidance to design and synthesize high-activity catalysts.The main contents and conclusions of this thesis are summarized as following:1.We develop an efficient method for the morphology transformation between Pd nanosheets?NSs?and Pd nanotetrahedra by controlling the reaction temperature.The Pd NSs are primary products at low temperature,while Pd nanotetrahedra are the dominant products at high temperature.The key of determining the morphology of Pd nanocrystals is that whether the energy of the reaction system can overcome the strong confining effect of CO.Moreover,under similar synthesis conditions,the as-prepared Pd nanocrystals are the ideal models for investigating the effect of the morphology on catalytic performances.The Pd NSs show better methanol oxidation and oxygen reduction activity than Pd nanotetrahedra and commercial Pd/C because of the large specific surface area and high atomic utilization.The fabrication method provides a new pathway for controlling the synthesis of noble metal nanocrystals and studying their shape-dependent properties.2.We develop a facile seed-mediated strategy to synthesis Pd-Pt bimetallic heterostructures.The Pt nanoparticles?NPs?modified on two distinct Pd-Pt heterostructures possess the similar crystalline structures?size,morphology and crystal facets?,except for the seating position of Pt NPs on the Pd NSs.Different growth positions represent different interfacial structures of Pd?100?-Pt interface and Pd?111?-Pt interface.Such unique interfacial structures offer a platform for elucidating the effect of the interfacial facets on the catalytic activities.Density functional theory calculation and X-ray photoelectron spectroscopy characterization revealed that the work function difference defines the flow direction of charge transfer and the interfacial facet structure decides the amount of charge transfer,which in turn affect the catalytic performance of hydrogen evolution and alcohol oxidation.These investigations provide guidance to synthesize high-activity catalysts by controlling the interfacial crystal facets.3.We develop a facile one-pot method,using n-butylamine as a bifunctional agent,to synthesize a series of ultrathin wrinkle-free PdCu NSs.Tunable compositon can be facilely achieved by changing the ratios of Pd/Cu precursors.The small size and wrinkle-free feature endow the Pd₄Cu₁ NSs with the highest electrochemically active surface area among all of the reported PdCu nanocrystals.The density functional theory calculations and experimental results show that quantum confinement and entrapment effects of ultrathin sheet-like structure render the d-band center far away from the Fermi level that weaken the adsorption of poisoning specious on the surface during the reaction.The modification of electronic structures enhances the catalytic activity and stability of methanol oxidation.Our study not only represents a method to synthesize wrinkle-free NSs,but also demonstrates the origin of the remarkable activities of ultrathin alloy NSs.4.We develop an efficient strategy to interstitially modulate H atoms into RhPd alloy nanoparticles to boost the alkaline HER performances.The as-prepared catalysts show the high stability at both room temperature and during the HER process.H atoms increase the electronic density,enlarge the bond distance and lower the coordination number of the Pd and Rh atoms.These modifications of crystal and electronic structures lead to the RhPd-H NPs exhibiting excellent alkaline HER performance,exceeding that of most reported noble metal-based electrocatalysts.Density function theory calculations reveal that the interstitial H atoms trigger the activity of Pd,Rh and H sites for water dissociation and thus accelerate the H₂production.The RuPd-H NPs and RuRhPd-H NPs were also successfully obtained and exhibit much better alkaline HER activities than those of commercial Pt/C.This work not only highlights the importance of H atom modulation but also opens a new path for tuning the catalytic performance of electrocatalysts.