Controlled Synthesis Of Pt-Ni Nanocrystals And Their Electrochemical Eerformance Towards Oxygen Reduction Reaction

Industrial innovation and social economic development will inevitably bring about energy shortages and environmental pollution issues.Proton exchange membrane fuel cells(PEMFCs)with high energy conversion rate,low noise emission,environmentally friendly features,wide application and other advantages,are recognized as one of the most promising energy system in twenty-first Century.However,its extensive popularization is still limited by the catalysts of its cathode oxygen reduction(ORR)-precious metal Pt.The rare and expensive characteristics of Pt greatly hinder its large-scale commercialization process.At present,most researchers mainly focus on two aspects,which are replacing precious Pt with transition metal to cut down the cost and synthesizing specific alloy structure,such as porous,core-shell and multi-branched structure,to enhance the electrochemical performance as well as maximize the use of Pt atoms.Due to the effective improve of utilization of Pt atoms of small particles compared to bulk,single crystals with small-size have aroused great attention from current research.To some extent,in comparison with polycrystals,the grain boundary charge transmission loss existing in nano-structure has been remarkably lowered for single crystals,which in result will benefit the enhancement of electrochemical performance for ORR.Combined with the above work,this paper has prepared porous and multi-footed Pt-Ni single crystal catalysts from the perspective of reducing the cost and improving the performance and stability of catalysts for ORR.The morphology and properties of Pt-based nanocrystals were controlled by capping reagents such as ascorbic acid,glucose,and dodecyltrimethylammonium chloride(DTAC),and their electrochemical performance and durability towards ORR were tested by applying rotating disk electrode.The main contents are as follows:1.This work has demonstrated the successful synthesis of single-crystal Pt3Ni(PSC-Pt3Ni)with porous and big-size characteristics.The mass and specific activities of as-prepared catalysts display 6 and 6.6 times more than that of commercial Pt/C at 0.9 volts versus the reversible hydrogen electrode(RHE),respectively.More importantly,PSC-Pt3Ni prevails against durability test(23.7%loss of mass activity after 10,000 potential cycling)with a small change to porous morphology under harsh experimental conditions.Density functional theory calculations show much less activation energy for PSC-Pt3Ni during the process of dissociation of the oxygen molecule adsorbed on the catalysts surface,which may account for the catalytic activity improvement.The lower series resistance for PSC-Pt3Ni is also verified by electrochemical impedance spectroscopy(EIS)data,resulting from fewer grain boundaries for single-crystals with big sizes.This exciting work brings a new strategy for optimization for electrochemical performance and durability.2.Hollow cubic Pt1.5Ni nanoparticles was successfully synthesized by using glucose as reducing agent.By means of the interaction of glucose and DTAC,the Pt1.5Ni alloy with an average length of 42.5 nm was obtained.It was found that DTAC played a decisive role in the synthesis of this morphology.In the absence of DTAC,we only obtained "darts like"nanoparticles with irregular morphology.The performance test of ORR showed that electrochemical performance of the synthesized hollow cubic Pt1.5Ni nanoparticles was greatly improved.Compared with commercialized Pt/C,the mass activity and specific activity were increased by 7.4 and 9.1 times,respectively.3.Pt-Ni nanocrystals with controllable structure and composition were synthesized by one pot method.It was found that the size and morphology of nanocrystals can be significantly regulated by adjusting the reaction time.The catalysts were formed from quadruped morphology to multiple branched structures,and were accompanied by the growth of average size.The nanocrystals with a composition of PtNi1.25 possessed the most excellent electrocatalytic activity towards ORR.Due to the multiped shaped structure and small size,the utilization of Pt atoms was maximized,and extension of the quadruped shape improved the number of active sites.