Electrocatalytic Investigation On Platinum Single Particle Through Nano-collision Electrochemistry

With the massive consumption of fossil fuel,the globe is up against an increasingly serious energy and environmental problems;therefore,developing renewable energy is urgent for social sustainable development.Electrocatalysis achieves an efficient conversion between electrical energy and chemical energy by boosting the process of heterogeneous electrochemical reaction at the electrode/solution interface,and has become a key technology for the renewable energy conversion and utilization.At the basic level,the core mission of electrocatalysis is to explore the relationship between material's property and performance.Due to the ensemble effect,the traditional modified electrode electrochemical method obtains the average information of massive particles,which cannot reveal the intrinsic catalytic activity of the catalyst.Recently,the single particle electrochemical method has provided a new perspective to study the structure-activity correlation.Different from traditional method,single particle electrochemical provides information of single entity,which favors the exploration of electrocatalytic mechanism and the intrinsic electrochemical activity,as a result,favors the construction of structure-activity relationship in a reliable way.In this dissertation,Pt nanoparticle and its aggregates are employed as a model system,based on the nano-collision electrochemical method,the hydrogen evolution reaction,the oxygen reduction reaction and the dynamic evolution of polymer-nanoparticle aggregates are extensively studied.The concrete content is summarized as follows:(1)Dynamics investigation of hydrogen evolution reaction on a single platinum nanoparticle.Based on the Derjaguin-landau-Verwey-Overbeek(DLVO)and Brownian motion theory,the effect of proton concentration on the stability of colloidal particles in solution is studied indetails.It is found that by controlling the proton concentration,the particle agglomeration in the solution can be effective lessened,and thereby the electrocatalysis study is performed at single-particle level.With nano-collision electrochemical method,it is found that HER behavior,which originates from a single particle,displays a transition from spikey to step,and depends on the polarized potential.Conditional experiments suggest that this transition behavior is jointly affected by the proton and hydrogen concentration on the platinum surface,and supposed to result from the shift in the equilibrium potential caused by the dynamic evolution of proton and hydrogen.Further,the mechanism of hydrogen evolution reaction on platinum under different atmospheres is studied,the polarized curve of hydrogen evolution reaction is obtained by reconstructing the cyclic voltammetry curve.It is found that under hydrogen atmosphere,Pt nanoparticle suffers from a hydrogen evolution deactivation,which is proposed to result from hydrogen adsorption/absorption,thereby,inhibiting its catalytic activity.(2)Electrocatalytic investgation on the size and ligand effect of platinum single particle towards oxygen reduction reaction.Platinum nanoparticles with different size are prepared by seed-growth strategy.Based on the nano-collision electrochemistry,the relationship between the electrocatalytic activity and the particle properties(size and surface state)are studied in details.The oxygen reduction polarization curve on single platinum particle is obtained.It is found that the intrinsic electrocatalytic activity depends on the Pt size,and the nanoparticle with a smaller size exhibits the best catalytic activity.Further,polyvinylpyrrolidone,cetyltrimethylammonium bromide and citrate are used as model ligand molecules to reveal the ligand effect on the catalytic activity with ligand-replacement method.The reconstructed polarized curve reveals that the ligands occupy the active platinum surface and therefore inhibit its catalytic activity.(3)Revaling the dynamics evolution process of polymer-nanoparticle aggregates.The system(denoted as Pt-Nafion)comprised of 4 nm platinum particle and Nafion molecule is used as model platform to mimic the fuel cell membrane electrode ink,and the dynamic evolution of the ink is tracked.It is found that due to the intramolecular polarity difference,Nafion self-assemble and form sphere micelles in an aqueous solvent.Nafion has a rapid adsorption for nanoparticles and form the Pt-Nafion aggregation,the adsorption process is proposed to cause by the van der Waals interaction and the bridging effect between polymer and particle.The Pt-Nafion aggregation was characterized by TEM and DLS in a long time scale,it is found that the aggregation suffered thermodynamic unstable and underwent a dynamic evolution process,which was proposed to be effected by the swelling behavior of Nafion molecules.