Synthesis Of Platinum-based Super Nanostructures And Their Electrocatalysis

Nowadays,electrocatalysis plays a critical role in green and renewable energy systems such as fuel cells and water electrolyzers.Platinum（Pt）based catalysts have been widely applied in the field of electrocatalysis for enhancing hydrogen oxidation reactions（HOR）,water splitting,and oxygen reduction reaction（ORR）,as well as methanol oxidation reaction（MOR）due to their efficient electrochemical activity.These reactions are vital for energy system.However,the intrinsic limitation of prohibitive cost and poor stability contributes to the bottleneck of large-scale application of green and renewable energy systems.Therefore,improving the utilization of precious metals is one of crucial challenges in the field of electrochemical energy conversion catalysis.Tuning precious metal structure to expose active sites is an effective strategy to reduce the amount of precious metal loading.To address this issue,in the thesis,a simple sequential reduction strategy to synthesize Pt-Co super nanostructure catalyst was developed and investigated their electrocatalysis for hydrogen evolution reaction（HER）and ORR.The resultant Pt-Co super nanostructures exhibited better electrochemical performance and stability.Firstly,Pt-Co hollow nanospheres with ultra-thin shell were synthesized via a sequential reduction strategy using amorphous Co-B-O complex as the key spheres-forming intermediates and co-reduction with Pt under reductant Na BH₄.The modulation mechanism of Pt-Co hollow nanospheres formation was established by investigating critical factors such as order of reactants,type of reductant,and different ratio of precursor.The optimized Pt-Co hollow nanospheres with the Pt/Co molar ratio of 1:1 is characterized by the average diameter of around 30 nm and the shell thickness of 2.3 nm.They display superior performance for enhanced hydrogen evolution reaction（HER）in the aspect of activity and stability in 0.5 M H₂SO₄,in which the mass activity of the Pt-Co hollow spheres exhibits 2.93 times higher than that of Pt Co nanoparticles prepared via co-reduction and even 2.82 times as much as commercial Pt/C,and its stability also has a significant enhancement.The outstanding activity of the Pt-Co hollow nanospheres for HER is mainly attributed to its highly accessible electron/mass transport path,expose active sites on the ultra-thin shells and strain effect induced by the hollow sphere structure.This hollow nanospheres with ultra-thin shell provides a promising way to develop highly efficient precious metal based electrocatalysts.Secondly,Pt-Co nanochains were prepared by the similar sequential reduction strategy using hydrazine hydrate as reducing agent instead of sodium borohydride used in the synthesis of Pt Co hollow nanospheres.The formation mechanism was estabilished by investigating the factors such as strong reducing agent,the precursor ratio of Pt and Co,etc.Pt-Co nanochains are composed of Pt-Co particles with the average particle size of 15.5 nm,which are crosslinked together to form a three-dimensional network structure.The structure shows excellent ORR activity and good stability,wherein its mass activity(0.55A·mg_Pt^-1)at 0.9 V vs.RHE in 0.1 M HCl O₄ for ORR is 4.23 times higher than commercial Pt/C(0.13 A·mg_Pt^-1),and after 20000-cycle stability test(0.38A·mg_Pt^-1),it can retain 70%of initial activity.Three-dimensional network structure provides large specific surface area,which is conductive to expose abundant active sites for improving catalysis performance.In a word,the sequential reduction method proposed in this study provides a new synthetic approach to rapid preparation of platinum-based superstructures and is expected to be applied to the preparation of other precious metal materials.