| Summary: | 博士 === 國立臺灣大學 === 生物產業機電工程學研究所 === 103 === This main research direction of this dissertation is to develop novel palladium (Pd) based nanocatalysts for alkaline glucose electrooxidation. The different carbon materials for Pd nanoparticle decoration are investigated to obtain a proper catalyst support for Pd decoration. The one-pot poly method and two-stage polyol synthesis process were proposed to obtain palladium-bismuth (Pd-Bi) bimetallic catalysts and palladium-nickel core-shell catalysts (Pd-Ni), respectively. The prepared carboxylated multi-walled carbon nanotubes (cMWCNT) supported Pd-based bimetallic catalysts aim to improve the active surface, catalytic performance, and catalysis durability toward glucose oxidation reaction (GOR). The electrochemical and physicochemical properties are comprehensively characterized and discussed to find out the idea Pd-based catalyst for the further discussion. The objective of this study is to develop Pd-based anode catalysts for the application of direct glucose fuel cell with the advantages of a low-cost, a high efficiency, and an improved stability.
At first, a series of investigation was discussed on different carbon materials supported Pd nanocatalysts. The carbon materials used in this study are pristine multi-walled carbon nanotubes (pMWCNT), carboxylated MWCNT (cMWCNT), amine-modified MWCNT (nMWCNT), hydroxyl-modified MWCNT (oMWCNT), XC72 carbon black (XC72), and carboxylated graphene (cGraphene). Nanosized Pd particles were decorated on these carbon supports by an alkaline one-pot polyol method via the reduction of palladium chloride hydrate (PdCl2). The electrochemical behaviors of alkaline GORs on the prepared Pd nanocatalysts were studied in this part to understand the influences of carbon functionality. Among the functionalized MWCNTs, cMWCNT shows a 6.2-fold higher GOR current density and a 100 mV lower over-potential compared to pMWCNT. In addition, cMWCNT supported Pd nanocatalyst has the lowest Tafel slope of 92 mV dec-1 and the highest stability of The 500 continuous GOR cycles in this study. The results indicate that cMWCNT will be a promising carbon support for the decoration of Pd nanoparticles by a polyol method. In this part, cMWCNT had been known as an idea catalyst support material for the further studies of Pd-based catalysts catalyzed GOR.
In the second part, the palladium-bismuth decorated cMWCNT catalysts (Pd-Bi/C) were prepared via a one-pot polyol method. The XRD data shows that Bi elements existed in the Pd-Bi/C are amorphous phase as Bi oxides. It was found that Pd-Bi/C (1:0.14) can significantly enhance the electrocatalytic activity on GOR about 40% times higher than Pd decorated cMWCNT (Pd/C) and as well as has a 3.7-fold lower poisoning rate. Moreover, the in-use stability of Pd-Bi/C (1:0.14) is remarkably improved. The effects of the operating temperature and the concentration of glucose and NaOH electrolyte on Pd-Bi/C were further investigated in this study. In this part, the highest Pd-Bi/C catalyzed GOR current density of 29.5 mA cm-2 is attained in alkaline medium.
In the third part, the cMWCNT supported palladium-nickel bimetallic catalysts (Pd-Ni/C) with a core-shell structure were employed to increase the utilization of Pd nanocatalysts. The PdshellNicore catalysts decorated cMWCNT were prepared by a facile two-stage polyol method. High resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscope (STEM) were used to identify the core-shell structure and analyze the elemental distribution of Pd-Ni nanoparticles. From the results of the electrocatalytic studies, the prepared PdshellNicore can obviously improve the GOR electrocatalytic activity and catalyst stability. The electrochemical results indicate that Pd-Ni/C (1:0.06) exhibits the highest electrochemical active surface area of 78.0 m2 g-1 which is 4.5 times higher than that of Pd/C and as well as has a 1.5-fold higher GOR current density of 21.2 mA cm-2. In this part, the highest Pd-Ni/C (1:0.06) catalyzed GOR current density of 42.5 mA cm-2 is attained in 0.5 mol L-1 glucose and 1.0 mol L-1 NaOH alkaline medium at 313 K.
The prepared Pd-based catalysts (Pd-Bi/C and Pd-Ni/C) coated glassy electrodes were applied to be anodes in the home-made direct glucose fuel cells. A platinum-niobium (Pt-Nb) cathode electrode and a Nafion® 117 proton exchange membrane were employed in this fuel cell system. In this study, 0.5 M mol L-1 glucose and 1.0 mol L-1 NaOH was used as a fuel in anode electrolyte and oxygen is used as an oxidizing agent. The power out of the constructed batch type direct glucose fuel cells and membrane electrode assemblies (MEA) were investigated in this study. From the results of the low-scan rate linear sweep voltammetry (LSV) investigation, the maximum power output of 3.0 mW cm-2 was attained in the Pd-Bi/C anode based batch type DGFC in this study.
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