Study On Electrocatalytic Performance Of Spiky Au-Pd Nanoparticles Assisted By Near-infrared Light

Developing new clean energy technologies(such as fuel cell)is one of the main ways to solve the future energy shortage.Palladium(Pd)-based catalysts are widely used in direct alcohol fuel cells(DAFCs).However,for most Pd-based catalysts,breaking C-C bonds in alcohol molecules and converting them into CO2(CO2 generation pathway)is challenging,leading to low utilization efficiency of DAFCs and limiting their further commercial application.Fortunately,in alkaline media,OH-ions adsorbed on the surface of Pd-based catalysts can be converted into OHads species,which can then be further converted into OH radicals with the assistance of external light sources.Therefore,the oxidation of alcohol catalyze by Pd-based catalysts in alkaline media is high likely to be carried out through the CO2 generation pathway with the assistance of external light source.Meanwhile,it would be more ideal to introduce Near-infrared(NIR)light as an external light source,because the low energy of NIR light is not easy to destroy the stability of the whole system.Based on the above problems,the main objective of this thesis is to investigate the catalytic performance enhancement by using NIR light to assist spiky Au-Pd nanoparticles.Firstly,the possible growth mechanism of spiky Au NPs is explored to further regulate the size of intermediate spherical nucleus.Secondly,spiky Au@AuPd NPs with ultrathin AuPd shell are prepared by using small sized spiky Au NPs as cores.Their catalytic performance towards mono alcohols oxidation reaction is studied with the assistance of NIR light,and the possible mechanism of performance improvement is proposed.Then,the catalytic performance of oxygen reduction reaction(ORR)of spiky Au@Au11.8Pd88.2 NPs with or without the assistance of NIR is further investigated,and the effect of the introduction of NIR on the catalytic performance is analyzed.Finally,the effect of L-spiky Au@Au15.3Pd84.7 NPs assisted by NIR on the oxidation pathway of glycerol is investigated.The specific research contents are as follows:In Chapter 2,We first investigate the influence of different types of gold nanorods(Au NRs)as seeds(Au NRs with different aspect ratio,Au NRs with the same aspect ratio but different lengths and widths)on the morphology of the resulting spiky Au NPs,including the average number of spikes and core size.Then,we extensively characterize the total surface area,{111} facet ratio and individual complete {111} facet area of traditional spherical Au nanoparticles,a series of spherical intermediates during the growth of spiky Au NPs and TOH Au NPs.This study aims to explore the possible growth mechanism of spiky Au NPs with an average number of spikes less than or equal to 6,and proposes a formula to estimate the number of spikes on the surface of spiky Au NPs.Finally,using the synthesis of spiky Au NPs with the smallest size as an example,we examine the influence of various reaction factors in the growth solution on the number and length of spikes on the surface of spiky Au NPs,further demonstrating the generality of the synthesis of spiky Au NPs.In chapter 3,spiky Au-Pd NPs with different content of Pd are firstly prepared by adjusting the concentration of Pd(Ⅱ)with smallest size spiky Au NPs as the core.Then,the surface composition and structure of the as-prepared spiky Au@AuPd NPs are characterized,and the composition is identified as spiky Au@Au9.2Pd90.8 NPs.Next,the catalytic performance of spiky Au@Au9.2Pd90.8 NPs assisted by NIR(NIR-spiky Au@Au9.2Pd90.8 NPs)towards EOR in alkaline media is investigated.The mass activity of NIR-spiky Au@Au9.2Pd90.8 NPs with ultrathin AuPd alloy shell can be up to 33.2 A mgpd-1 in the 0.5 M KOH solution containing 0.5 M ethanol,which is about 158 times higher than that of commercial Pd/C catalysts(0.21 A mgpd-1)and is better than those of the state-of-the-art Pd-based catalysts reported so far in the literature thus far,to the best of our knowledge.Moreover,their highest mass activity can be further improved to 118.3 A mgpd-1 in the 1.5 M KOH solution containing 1.25 M ethanol.Finally,on the basis of a series of controlled experiments,the possible mechanism of ethanol oxidation reaction(EOR)catalyzed by NIR-spiky Au@Au9.2Pd90.8 NPs is proposed.In other words,spiky Au@Au9.2Pd90.8 NPs can convert the OH-ions adsorbed on its surface into OH radicals by surface plasmon resonance effect(SPR)in alkaline media after the introduction of NIR light,and these OH radicals can break the C-C bond of ethanol molecules.In Chapter 4,spiky Au@AuPd NPs with ultrathin AuPd shell are prepared using the synthesis method described in Chapter 3,and confirms their composition as spiky Au@Au11.8Pd88.2 NPs.Subsequently,the catalytic performance for oxygen reduction reaction(ORR)with or without the introduction of NIR is investigated.Under alkaline conditions,NIR-spiky Au@Au11.8Pd88.2 NPs exhibits excellent ORR catalytic performance.For example,their onset potential and half-wave potential(Econset and E1/2)are determined to be 1.068 V and 0.954 V(vs.RHE),which are 55 mV and 71 mV higher than those of commercial Pt/C catalysts(1.013V and 0.883V),respectively.Finally,by comparing the results with EOR,the possible reasons for the modest improvement of ORR catalyzed by NIR-spiky Au@Au11.8Pd88.2 NPs are analyzed.In Chapter 5,firstly,spiky Au@AuPd NPs with ultrathin AuPd shell and longer spikes(Lspiky Au@AuPd NPs)are synthesized using the methods described in Chapters 2 and 3.The composition of these nanoparticles is determined as L-spiky Au@Au15.3Pd84.7 NPs.Subsequently,the catalytic performance of L-spiky Au@Au15.3Pd84.7 NPs assisted by NIR(NIR-L-spiky Au@Au15.3Pd84.7 NPs)for the oxidation of polyhydric alcohols(glycerol)in alkaline medium is further investigated.The NIR-L-spiky Au@Au15.3Pd84.7 NPs shows excellent catalytic activity of 28.3 A mgpd-1,which is 176.8 times higher than that of commercial Pd/C catalysts(0.16 A mgpd-1).Finally,according to the results of glycerol oxidation reaction(GOR)in the literature and EOR in Chapter 3,the possible causes and reaction pathways of the variation of the performance of GOR catalyzed by NIR-L-spiky Au@Au15.3Pd84.7 NPs are preliminarily explored and analyzed.In Chapter 6,the above works have been summarized and prospected.In summary,this thesis investigates the growth mechanism of spiky Au NPs to achieve the rational synthesis.Subsequently,spiky Au@AuPd NPs and L-spiky Au@AuPd NPs with an ultrathin AuPd shell are synthesized,utilizing the smallest-sized spiky Au NPs as the core.Finally,the catalytic properties of small molecular alcohols(ethanol,glycerol)and ORR with the assistance of NIR are studied,and the possible mechanisms of their catalytic performance improvement are proposed.