Study On The Preparation And Electrochemical Properties Of Pt And PtRu Particles By Electrochemical Deposition

Fuel cell is a device that can turn chemical energy into electrical energy through electrochemical reaction without combustion, which is regarded as one of the most important power resources in the21century. Low temperature fuel cells can work at low temperature with the advantages of quick start and high energy efficiency, which can be potentially used for electric cars, field powerplant and portable equipments. The catalysts for low tempertaure fuel cells are platinum-base catalysts, however, platinum is rare and expensive, which makes the catalysts occupy30-40%of input for low tempertaure fuel cell. This thesis is about using electrochemical method to deposit platinum and exploring the path of improving the utilization ratio of platinum and enhancing the catalytic properties to reduce the cost of fuel cell. Pt and Pt/Ru particles were deposited on boron-doped diamond (BDD) and glassy carbon electrode (GCE) by electro-deposition and chemical deposition. The electro-catalytic property of Pt and PtRu particles as anodes of low tempertaure fuel cells on hydrogen desorption and methanol oxidation was studied. The main contents and conclusions are as follows:1) BDD with different suface morphology (polished BDD, large grain rough BDD and small grain smooth BDD) was applied as the substrate of platinum electrodeposition. The results show that the surface morphology of BDD has an influence on the electro-catalytic property of deposits under the same deposition conditions and extraordinary electro-catalytic property is obtained from the platinum particles on rough BDD substrate.2) Here we demonstrate an ultrasonic treatment on substrate prior to electro-deposition. The roughness of the substrate can be improved and the substrate can also be activated. The results show that an improvement in spatial distribution is seen and the particle size is reduced to50%compared to normal BDD-Pt. The EAS value of modified BDD-Pt is80-85m2/g, which is three times higher than normal one and close to that of a typical electrocatalyst (100-200m2/g Pt) prepared by conventional means. This ultrasonic treatment was also effectively affacted on glassy carbon electrode (GCE). Platinum nanoparticles were observed on GCE. The EAS value of modified GCE-Pt is0.397m2/g, which is higher than the value of normal GCE-Pt (0.29m2/g), and the stability of platinum on modified GCE is three times higher than normal GCE’s.3) Except carbon dioxide, the intermediates, such as formaldehyde and formic acid are observed from methanol oxidation in acid solutions. Pt electrocatalysts are prone to poisoning by the intermediates of methanol oxidation, such as carbon monoxide. As a result, it is better to avoid using single platinum catalyst. In this study, we thus use a potentiostatic method to simultaneous and sequential deposition of Pt-Ru on BDD. The results indicate that the stability of BDD-PtRu electrode from simultaneous deposition is better than the one from sequential deposition. Ruthenium is not stable and tends to dislodge from sequential PtRu deposition. The intermediates of methanol oxidation are less from simultaneous deposition and the electrodes from simultaneous deposition exhibits lower onset potential for methanol oxidization (0.24vs.0.31V) and, consequently, the BDD-PtRu electrodes from simultaneous deposition have better catalytic property.4) In this thesis, we try to explore electroless deposition of platinum on BDD substrate and propose a new novel electroless deposition method which is demonstrated to prepare platinum catalyst on non-catalytic BDD surface. The mechanism of this deposition is a galvanic process along with a chemical process where the iron wire and BDD acts as a galvanic cell and catalytic platinum is firstly deposited by a galvanic process and then the reducing agent reduces the platinum ions from the electrolyte to BDD surface. Pt nanoparticles were co-deposited with iron and phosphorus with sodium hypophosphite as reducing agent. Phosphorus is reduced together with the reduction of platinum by sodium hypophosphite and the exsistence of iron is attributed to the oxidation at high temperature. The limited Pt aggregation by the deposition of phorphous was examined with both AFM and SEM, with diameter of30-50nm and height of3nm. The EAS value of deposit is95.54m2/g as the deposit has more active surface area. High purity platinum particles were obtained using ascorbic acid as reducing agent with a high deposition ratio. Different conditions of platinum deposition on BDD were investigated, such as involving stabilizer into electroless solution, reducing reaction temperature and changing the morphology of substrate. Small nanoparticles size (180nm) and high electrochemical activity towards hydrogen desorption (EAS=4.14) and methanol oxidization were achieved at0℃on ultrasonically treated BDD substrate.