Electrochemical Preparation And High Performance Of Palladium Nanocatalysts With Special Wettability

The three-phase interface is exist in heterogeneous catalysis reaction,So the catalyst surface wettability is impact of its catalytic performance.Therefore, in addition to control morphology, size, crystal structure, andto build a hybrid structure, the performance of catalyst can be enhancedby controlling the surface wettability.Surface wettability is governed bythe microstructure and surface energy of a solid, thus the surfacewettability can be designed and constructed by manipulating chemicalcompositions and surface roughness.In this thesis, we have developed an electrochemical method tocontrol the surface structure and wettability, and prepared successfullycatalysts of palladium film with tetrahedral, flower, thorn morphology.The study has illustrated the relationship between the wettability of thecatalyst and its catalytic activity, and to deepen the understanding of themulti-phase catalytic reaction process, and to improve the catalyticactivity and stability of the catalyst. The main results are as follows:1. A variety of Pd films with different wettability have been prepared bythe electrochemical deposition method in ITO electrode. Theelectrochemical experiment proved that the Pd film with differentwettability in the oxygen reduction reaction and oxidation of formic acidexhibit different catalytic activity. The hydrophilic Pd film exhibit1.5times higher catalytic activity than that of hydrophobic Pd film towardselectrocatalytic reduction of oxygen in terms of current density. In theformic acid catalyzed reaction, the hydrophilic Pd film show the formicacid oxidation peak current is5.9mA·cm^-2and2times higher catalytic activity than the hydrophobic Pd film. The related mechanistic studiesindicate that the hydrophobic electrode conducive diffusion andadsorption of the gas molecules; the hydrophilic electrodes is conduciveto the adsorption of small polar molecules and the desorption gas productin the active site of the catalytic process.2. Super-hydrophilic Pd electrode with flower structure were preparedthrough the rules that hydrophilic surface can enhanced the catalyticactivity of hydrogen peroxide reaction and applied to the sensordetector,the detection limit was60nM and the sensitivity was221（uA/ug）/mM.3. Pd-Au catalyst with a core-shell structure and different wettability wasprepared by underpotential deposition technology combined with thedisplacement reaction. this methode to obtain specific wettability surfaceincreasing the catalytic activity and enhanced the stability of the materialat the same time. For the contact angle of16°Pd-Au film electrode, aftera constant potential catalytic reactions2h in O₂saturated0.1M KOH+1.0M CH₃OH solution,it’s reduction current were decay of16.4%, while thecontact angle of130°Pd-Au film decay of24.9%.