Synthesis Of Pd-Based Nanostructures Control And Their Applications As Electro-catalysts In Fuel Cells

For the commonly used Pt-based catalysts,although showing high performances in both acidic and alkaline fuel cells,their cost has always been an issue in limiting the development of hydrogen-oxygen fuel cell.An objective of the current research on electrocatalysts is to reduce the use Pt membrane electrode assembly?MEA?,e.g.designing Pt alloy catalysts with unique morphologies and structures such as core-shell nanostructures,or finding non-platinum materials with excellent performance for substitution.The Pd-based catalysts have demonstrated good performance in oxygen reduction reaction?ORR?.However,there has yet to be a breakthrough for such catalysts.Therefore,it has become a hot area to design high-performance Pd-based electrocatalysts towards the ORR.This thesis is based on Pd-based alloys.Through the composition and nanostructure design,as well as surface treatment and other ways,catalytic ability is enhanced.The specific research content is as follows:1)PdNi nano-particles are synthesized as core materials and PtCo,PtFe and PtNi are formed as shells to obtain the core-shell nano-catalysts.The PdNi@PtNi catalysts which show superior ORR catalytic activities,is selected to carry out the structural optimization.We find that the PdNi@Pt₁Ni₁/C prepared under ultrasonic horn shows the catalytic activity of 0.40 A/mg_Pt,more than twice that of commercial Pt/C under acidic conditions.2)Surface acid-treatment and doping strategies are performed based on the PdCuNi ternary alloy catalyst.The acid-treated catalyst induces the enhancement in the mass activity.Specifically,the treatment with the sulfuric acid solution enables the PdCuNi/C catalyst to achieve a mass activity of 0.24 A/mg_{Pd or Pt},nearly 2 times that of commercial Pt/C catalyst in alkaline medium.However,the surface doing with W and Mo elements,which induced enhancement for Pt-based alloy catalysts,does not enhance the catalytic activity.It can be inferred from TEM images that this may be due to the fact that the doping may form a certain coating layer on the surface of the nanocrystals.The catalytic activity of the catalyst is reduced and the catalytic activity is reduced.3)An oxidative surface treatment protocol is developed for the PdCuNi ternary alloy catalysts.The PdCuNi-AB-t/C catalyst with excellent performance in alkaline environment is prepared by using different combinations of ascorbic acid and benzoic acid as reducing agents to regulate the size and nanostructures of PdCuNi nanocrystals.The PdCuNi-AB-t/C catalyst prepared after the oxidation treatment had a 30 mV shift in half-wave potential.The mass activity reaches 5-time and 2.4-time of commercial Pt/C and Pd/C,respectively.The enhancement,induced by the oxidative treatment,originates from the atomic arrangement from the sub-surface layers.In this thesis,by preparing core-shell type,surface-doped type,and surface treated type Pd-based nanocatalysts,the catalytic properties of some Pd-based catalysts have been explored in acidic or alkaline.For the surface-treated PdCuNi catalysts,the Pd-rich surface and unique sub-surface structure can greatly enhance the catalytic activity.This also provides a new strategy for the design of Pd-based nanocrystalline alloy catalysts.