Date of Award

5-8-2018

Document Type

Dissertation

Degree Name

Doctor of Engineering (DEng)

Department

Materials Science and Engineering

First Advisor

Professor Omowunmi A. Sadik

Abstract

The United Nations formally adopted 17 sustainable development goals (SDGs) at its 2015 summit. Many of these goals addressed issues such poverty, hunger, health, education, climate-change, gender equality, water, sanitation, energy, urbanization, environment and social justice. The seventh SDG seeks to ensure access to affordable, reliable, sustainable and modern energy for all. So among all renewable forms of energy, fuel cells with high efficiency have attracted a lot of attention recently. In particular, the direct ethanol fuel cells (DEFCs) and microbial fuel cells (MFCs) are significant due to their green fuel, less waste generated and environmental friendliness. Hence the overall goal of this work is to develop novel catalysts and electrodes for improving the efficiency of different designs of fuel cells.

Towards achieving this goal, the project was divided into three phases. For the first phase, a new electrode material was prepared for Ethanol Oxidation Reaction (EOR) based on Pt and alloyed PtCr nanoparticles fabricated via electrodeposition on a glassy carbon electrode. The catalyst was tested in acidic media. The typical SEM images showed the near spherical Pt structures with diameters in a range of 50–120 nm. The general size of the PtCr nanoparticles were determined to be around 105 nm and the surface aggregates were from 400 nm to 1µm at 40 cycles. However, the primary challenge has been attributed to the loss of the catalysts into solution. We hereby demonstrate an approach using poly(amic) acid (PAA) films as supporting material in order to improve the stability and inherently the efficiency of the catalysts. This catalyst was created via spin coating of PAA layer (thickness ~4µM) on the surface of electrocatalysts. The PAA/Pt and PAA/PtCr combination permits the diffusion of ethanol towards the surface of the Pt or PtCr nanoparticles resulting in efficient reduction while simultaneously preventing the loss of the catalysts into the solution. Electrode stability of 900 cycles (three days) was recorded at varying potential scan cycles. This electrode coated with PAA was found to be three times as durable when compared with the bare catalysts surface (300 cycles). And this work could allow the widespread use of these combinations for stable and efficient electrochemical reduction of ethanol.

The second phase was focused on the development of a new, easy, fast and green method to synthesize anisotropic Pt nanomaterials for application in EOR. The Pt nanomaterials were formed by combining sugar ligands with PtCl4 in water at room temperature and the reaction occurred immediately. Six types of sugar ligands were tested in this study: N,N'-dilactosylphenylene (LPDA), Lactose+p-aminosalicylic acid (LpAS), D-galactose+(3-amino) propylaniline (44DG), lactose-4,4-ethylenedianiline (L-44EDA), galactose-4,4-ethylenedianiline (G-44EDA) and galactose-4-sulfonyl phenyelendianiline (GPSA). Based on the intrinsic chemical structures and properties of the different sugar ligands, various sizes and shapes of Pt nanomaterials were generated, including uniform tiny nanoparticles and fancy nanoflowers. The electrochemical properties of the sugar ligands were determined using cyclic voltammetry (CV) which showed that LPDA exhibited the greatest electroactive property with two redox couples at 0.28 V and 0.68 V, respectively. And based on the Randles Sevcik equation calculation, the results demonstrated that the redox reaction of LPDA is reversible with two numbers of electrons transferred.

The third and final phase of the project was the development of two different designs of microbial fuel cells. The first design was the traditional one-chamber MFC. So, in order to prove the performance of fuel cell, Pt nanoparticles were electrodeposited onto reticulated vitreous carbon electrode (RVC). Subsequent experiments confirmed that the power density of MFC increased by two times when compared with that containing no Pt catalyst. The second design was a microfluidic-based MFCs using paper as the substrates, which was carried out in collaboration with Choi's research group at BU. Our objective was to develop novel paper-based electrodes for improving the performance of paper MFCs. PAA was employed for the first time as a supporting material for Origami or paper-based design of MFCs due to its hydrophilicity and electrical conductivity.

Overall, this work has shown that different methods had been successfully used to synthesis metallic catalysts and electrodes materials for different types of green fuel cells. Because ethanol is a great alternative green fuel, the electrodeposited Pt and PtCr alloy showed superior performance for EOR, especially after modifying with PAA, the overall efficiency of the DEFCs were increased by three times. Finally, since water has been used as fuel and bacteria as catalysts, the new electrodes materials reported in this work helped to improve the power output and current density of the MFCs compared with previous work. Hence this project could potentially contribute to achieving the seventh SDG of affordable, reliable, sustainable and modern energy for all. (Abstract shortened by ProQuest.)

Available for download on Saturday, November 10, 2018

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