Optimal Design And Electrocatalytic Performance Research Of Pt-Based Nanocatalysts

The sustainable supply of energy is the core of the energy problem.Due to the increase in consumer demand and the limitation of reserves,fossil fuels are no longer the guaranteed energy source.In future renewable energy systems,proton exchange membrane fuel cell has become an important energy conversion device.From traditional internal combustion engines to proton exchange membrane fuel cells,major breakthroughs have occurred in both energy structure and environmental protection.Proton exchange membrane fuel cells have many advantages,such as environmental protection,fast start-up at room temperature,simple structure and high energy density.However,the overall efficiency of the battery is also limited due to the high overpotential caused by the slow dynamics of the electrochemical reaction.Pt-based nanocatalysts can alleviate this problem.In this paper,different strategies are used to optimize the design and synthesis of high-performance Pt-based nanocatalysts,and discuss their electrocatalytic properties.The specific research contents are as follows:(1)Fuel cells are one of the promising energy-conversion devices due to their high efficiency and zero emission.Despite tremendous research works in past decades,there remains a tough challenge in realizing the commercial applications of fuel cell technologies.Therefore,the development of highly efficient and stable fuel cell electrocatalyst is the top priority for practical fuel cells.As we all know,the small-size nanoparticles always have high specific surface area,which can provide more active sites to enhance the catalytic activity,while the one-dimensional nanowires usually own high structural stability.It may provide a possibility for the design of a novel bimetal Pt-based alloy nanostructure by combining the structural superiority of both,which can maintain the high stability and maximize the catalytic activity at the same time.Driven by these purposes,a novel nanostructure constructed by Pt-Ni alloy nanoparticles with a one-dimensional chain structure was designed to balance the contradiction between the activity and stability due to the size effects(the smaller the size,the higher the activity,and the worse the stability of the nanocatalyst;and vice versa).Here,a simple one-step solvothermal method has been adopted to produce the novel nanostructures constructed by the chain-like Pt-Ni nanoparticles(Pt-Ni CNPs)with Pt-rich crystal faces and alloy nature.The structure,component and catalysis were investigated by the combination of x-ray diffraction,transmission electron microscopy,x-ray photoemission spectra,and electrochemical measurements.The results show that the as-synthesized Pt-Ni CNP is constructed from a nanowire(with a diameter of about 3 nm and a length of several hundred nanometers)and the nanoparticles(with an average diameter of about 10 nm).This nanostructure is cleverly integrated the structural advantages of one-dimensional nanowires and zero-dimensional nanoparticles,which can significantly enhance the catalytic activity and stability for the methanol oxidation reaction(MOR)in acidic environment.Specially,the mass activity and specific activity of as-prepared Pt-Ni CNPs are 5.7 and 7.6 times higher than those of the commercial Pt/C,respectively.After 1000 cycles of cyclic voltammetry(CV)measurement,Pt-Ni CNPs still retain 91.2% of the specific activity,while the commercial Pt/C undergoes a drastic loss of MOR activities,retaining only 4.4% of the initial activity.It is particularly noteworthy that this nanostructure of Pt-Ni CNP solves the problem of agglomeration of nanoparticle catalysts in the reaction,and provides a new approach to obtain Pt-based nanocatalysts with high catalytic activity and stability at the same time.Our finding will provide insight into more rational designs of Pt-based bimetallic nanocatalysts with one-dimensional architectures,which is expected to promote the further development and large-scale industrial application of the direct methanol fuel cell.(2)Direct formic acid fuel cell is one of the typical proton exchange membrane fuel cells.It is technical and scientific to understand the reaction mechanism of formic acid electrooxidation and improve catalyst performance.Using a simple method assisted by ultrasound,Pt Au alloy nanocatalysts(Pt Au/Co C NF)supported on a cobalt carbon nanoframe(Co C NF)was designed and synthesized to catalyze the FAO reaction.Without using any surfactant,Pt Au/Co C NF series catalysts were synthesized by uniformly and densely supporting Pt Au alloy nanoparticles on a pre-synthesized cobalt carbon nanoframe(Co C NF)in an ethanol/water solvent.The Pt/Au controllable ratio can be achieved by simply adjusting the dosage of the precursor.Characterize theprepared samples,including physical characteristics such as morphology,composition,crystal structure and electronic structure,and study their catalytic properties for formic acid oxidation(FAO).The most excellent specific activity of the synthesized samples reached commercial Pt/C 6.4 times.The excellent FAO catalytic properties are attributed to the unique Co C NF carrier which promotes the electron transfer between the carrier and the loaded particles and the optimized synergy of Pt and Au provided by the appropriate Pt/Au atomic ratio.This provides a meaningful reference for optimizing the design strategy of Pt-based nanocatalysts by alloying method and durable support substitution method.