EFFECTS OF PRECURSOR TYPE ON CATALYTIC FUNCTION OF PLATINUM INSERTED IN NATA-DE-COCO ON FUEL CELL

• Main Author: Fonda Aritonang, Henry
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/33620
• Institution: Institut Teknologi Bandung

The short supply of fossil fuels has encouraged scientists to seek alternative energy sources such as fuel cells. At present direct methanol fuel cell (DMFC) is widely developed due to its advantages in terms of methanol availability in Indonesia. Platinum (Pt) is often used in fuel cell as catalyst. In order to improve the catalytic activity of Pt, its content should be optimum, its dimension should be nano-sized and its distribution in the electrode should be homogeneous. Some researchers have already used nata-de-coco as matrix for the synthesis of Pt nanoparticles. However, fundamental studies on the preparation of this composite has not been done yet. One of the important parameter to be investigated is the type of precursor as the starting material for Pt source. Therefore, the objectives of this research are to study the effects of precursor type on the dimension, content and distribution of Pt particles in nata-de-coco as matrix as well as the catalytic function of the resulting Pt. The types of the precursors are limited to Pt (II) and Pt (IV), by using K2PtCl4 and PtCl4, respectively. This work consists of several stages, namely the synthesis of nata-de-coco, synthesis and characterization of Pt particles and catalytic functional test. Nata- de-coco has been obtained from the fermentation of coconut water by Acetobacter xylinum with fermentation time varied from 3 to 12 days. Nata-de-coco was then made into membranes; the morphological observation and the size of membrane cavity were done using SEM method. From the experiments it has been found that the optimum condition for the preparation of nata-de-coco was 6 days where the cavity size was relatively small (44 nm) and its distribution was more homogeneous compared to other fermentation time. The nata-de-coco prepared by this optimum condition was further used as matrix for Pt particles synthesis. The effects of precursor concentration on the content and dimension of Pt particles has been studied in the next stage. The XRD and SEM-EDS analysis proved that all of Pt precursors have been reduced to Pt particles; this was also supported by Pt database from ICSD No. 76951. Besides that, it was found that the particle size of Pt was affected by both type and concentration of Pt precursor. At a concentration of 30 mM, Pt particle size obtained from K2PtCl4 precursor ranged between 130 nm and 350 nm, while the PtCl4 precursor yielded Pt ranging from 40 nm to 1000 nm. The content of Pt particles obtained from both precursors also increased with the increase of precursor concentration. On the other hand, the effect of precursor type on the Pt content was not significant. The experiments showed that the optimum precursor concentration was 20 mM and was used for the next stage of the synthesis. The effect of Multiwall Carbon Nanotubes (MWCNT) inserted in nata-de-coco on the characteristics of the resulting Pt has been studied in this stage. Several characterizations such as XRD, SEM-EDS, TGA, TEM and electrical conductivity have been realized. Besides that, the catalytic function of Pt particles have been measured using cyclic voltammetry, while the performance of Pt catalyst was tested in the cathode of a single cell of DMFC using 1 M CH3OH at 40-80 ºC. The experiments were carried out through two insertion routes: firstly, the insertion of Pt particles was done before MWCNT and secondly, the insertion of Pt particles was done after MWCNT. The study of the insertion route revealed the best method to obtain a high content of Pt particles with a small dimension and homogeneous distribution. The various characterizations mentioned above revealed that the first route was better than the second one, because it produced Pt particles with good characteristics in terms of content and dimension of Pt particles as well as electrical conductivity. Pt particles produced from K2PtCl4 precursor had a crystal size of 5.01 nm with its content of 28.95% (mass) based on EDS data and 1.02 mg/cm2 based on TGA data. Pt particle size ranged between 4 and 35 nm with Pt particle size average of 11 ± 6 nm, while the electrical conductivity was 0.552 ± 0.001 S/cm. Conversely, Pt particles produced from PtCl4 precursor had a crystal size of 4.88 nm with its content of 50.63% (mass) based on EDS data and 1.80 mg/cm2 based on TGA data. Pt particle size ranged between 2 and 9 nm with an average size of 3 ± 1 nm and its electrical conductivity was 1.092 ± 0.002 S/cm. This can be explained by the mechanism of Pt formation from the two precursors. When PtCl4 precursor was used, it formed [PtCl4(OH)(H2O)]- anion in aqueous solution and interacted with the cellulose (nata-de-coco). Additionally, these anions have octahedral structures which are relatively more bulky than the [PtCl4]2- anions which have a flat rectangular structure. Therefore, when hydrogen gas was passed, the anions were reduced and Pt particles adhered on the surface of the cellulose, resulting in a homogeneous distribution. Meanwhile, the K2PtCl4 precursor did not form anions as shown in PtCl4 precursor and hence, the Pt particles formed agglomerated. Therefore, the performance of Pt particles from PtCl4 precursor showed good catalytic activity, indicated by a current density measured by cyclic voltammetry of 9.38 µA/cm2 and an optimum power of a single DMFC of 0.11 mW/cm2 at a current of 1.01 mA/cm2. Furthermore, the Pt catalytic activity against Pt particle mass obtained from the two types of Pt precursor is relatively the same. However, Pt particles of PtCl4 precursor were more efficient as catalyst compared to the Pt particles of K2PtCl4 precursor.