Synthesis Of Gold-based Noble-metal(Au-M)Ultra-small Nanoparticles And Study On The Electrocatalytic Performance

The development of fuel cell and water electrolysis technology is an important part of building a low-carbon economy.The design and preparation of electrocatalysts with enhanced property is one of the key to realize the commercial development.Noble metal nanoparticles with specific size,structure and composition have shown great potential in electrode reactions such as HER,ORR and FAOR at present.Due to the higher surface area/volume ratio,small-sized nanoparticles can provide more surface active sites.In addition,it was found that ultra-small nanoparticles(USNPs)with an average size between 2-3 nm will have both enhanced mass activity and high stability.Meanwhile,in the core-shell structured gold-platinum nanoparticles(CS Au-Pt NPs),the presence of Au not only improves their stability,but also cultivates their activity due to the electronic effect between Au and Pt.However,most of the CS Au-Pt NPs reported were made by a two-step method and the size is relatively large.Therefore,to combine the advantages of USNPs and CS structures,it is important to devise a one-pot route to synthesize CS Au-Pt USNPs.Mostly,the catalytic activity of the pure Pt catalysts towards FAOR is relatively low.This is because the Pt surfaces have strong adsorption energy for the COads,which is prone to CO poisoning,resulting in the loss of active sites.Recently,the Pt-based catalysts with a discrete Pt atomic outer layer structure,which can weaken the adsorption energy of CO,were reported broadly.Therefore,the preparation of Pt-based catalysts with a discrete shell structure(CSD)can further expand the commercial application in the field of FAOR catalysis.In addition,the ternary noble metal nanoparticles can balance the adsorption/desorption energy between the catalysts and the intermediate products due to the electronic effect and synergistic effect between different metal atoms,thereby improving its performance,effiencially.For example,towards HER,iridium(Ir)catalysts have a weaker adsorption energy for its intermediate product(Hads)than that of Pt,so it is beneficial to balance the strong adsorption energy of the Pt catalysts and promote the release of H2,accordingly achieving the improvement of catalytic activity.Based on the above problems,an innovative synthesis strategy was proposed in this thesis to synthesize several core-shell structured gold-based noble metal ultra-small nanoparticles(Au-M USNPs).And by adjusting the structure and composition of those ultra-small nanoparticles,their electrocatalytic performance was improved effiencially.The full text is divided into five chapters(Chapter 1 is the introduction),and the main contents are as follows:In Chapter 2,firstly,a simple but efficient strategy was presented to synthesize high yield CS Au-Pt USNPs via Fe(?)-assisted one-pot co-reduction of Au(?)ions and Pt(?)ions in the citrate solution.Among them,the average diameter of CS Au38.4@Au9.3Pt52.3 USNPs was 2.3±0.5 nm.And then,the electrocatalytic performance of CS Au38.4@Au9.3Pt52.3 USNPs loaded on carbon black(CS Au38.4@Au9.3Pt52.3-USNP/C)as catalysts towards the HER and ORR was investigated in acidic media.Towards the HER,the as-prepared CS Au38.4@Au9.3Pt52.3-USNP/C catalysts exhibit a lower overpotential of 16 mV at-10 mA cm-2,showing an enhanced HER activity.Strikingly,their mass activity is nearly 13.1 times higher than those of Pt/C catalysts.In addition,they also showed improved ORR activity,as the Eonset and E1/2 were 1.015 V and 0.896 V,respectively,which were positively shifted by nearly 28 mV and 21 mV than those of commercial Pt/C(0.987 V,0.875 V),respectively.Finally,they also showed a better long-term durability towards HER and ORR.In Chapter 3,Au-Pt ultra-small nanoparticles with a discrete shell structure(denoted as CSD Au-Pt USNPs)were firstly synthesized by reducing the Pt(?)ions concentration in the reaction mixture solution.The average particle size of the as-prepared CSD Au61.2@Au27.3Pt11.5 USNPs was 2.3±1.0 nm.And then,their FAOR electrocatalytic performance in acid medium was tested.The results showed that the mass normalized current density(6.91 AmgPt-1)of the CSD Au61.2@Au27.3Pt11.5-USNP/C catalysts was 16.8 times higher that of the commercial Pt/C(0.4 A mgPt-1),showing an enhanced electrocatalytic activity.In addition,they also exhibited a better long-term durability.In Chapter 4,on the basis of the above two Au-Pt USNPs,Ir elements were introduced to prepare CS Au-Pt/Ir USNPs and CSD Au-Pt/Ir USNPs.The average particle sizes were 2.3±.0 nm and 2.3±1.1 nm,respectively.And then,the electrocatalytic properties towards HER,ORR and FAOR in acid medium were tested.It was found that the introduction of a small amount of Ir elements in the Au-Pt USNPs can improve the catalytic activity towards HER and FAOR,but it is not conducive to the catalytic activity towards ORR.Specifically,in the HER test,when the content of Ir elements was 17.9 at.%,the overpotential of CS AuPt/Ir-USNP/C catalysts was only 9 mV at-10 mA cm-2,which is the lowest overpotential among the Pt-based catalysts reported in the literature such far.In the FAOR test,when the content of Ir elements was 3.63 at.%,the current density of the CSD AuPt/Ir-USNP/C catalysts under acidic conditions was 9.69 A mgPt-1,which was 1.4 times higher than that of CSD Au61.2@Au27.3Pt11.5-USNP/C catalysts.Chapter 5 is a summary and prospect of current research work.In summary,in this thesis,several core-shell structured gold-based(Au-M)ultra-small nanoparticles were successfully prepared,and the electrocatalytic performance towards HER,ORR and FAOR was improved in acidic medium.