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Development of Novel Non-precious Cathode Electrocatalysts for Alkaline Exchange Membrane Fuel Cells

Development of Novel Non-precious Cathode Electrocatalysts for Alkaline Exchange Membrane Fuel Cells
Jakkid Sanetuntikul
DGIST Authors
Jakkid Sanetuntikul; Shanmugam, Sangaraju
Shanmugam, Sangaraju
Han, Oc Hee
Issue Date
Degree Date
2015. 8
Access Rights
The original item will not be provided upon request from the author
Non-precious catalystElectrocatalystOxygen reductionDurabilityAlkaline fuel cells
Polymer electrolyte membrane fuel cells (PEMFCs) are considered one of the most promising alternative energy conversion devices. They are low emission, lightweight, highly efficient, and scalable devices that utilize hydrogen, which can be produced from a variety of sources to generate electricity. Despite its many benefits, PEMFCs technologies have failed to reach wide commercialization due to limited fuel cell materials stability and the high cost of electrocatalyst. Fuel cells use platinum (Pt) as a state-of the art catalyst used for both the oxygen reduction and hydrogen oxidation reactions. However platinum is very rare and expensive. Therefore, there is significant ongoing research focus to discover inexpensive catalysts with activity comparable to platinum. This thesis explores to develop non-precious inexpensive catalysts, metal coordinated with nitrogen doped carbon (M-N-C), which were synthesized by a direct pyrolysis method. Three different kinds catalysts were synthesized catalysts were active for the oxygen reduction reaction (ORR). The first experiment utilized Cobalt amino acid chelate complex (CoAAC), which contains metal, nitrogen and carbon in a single solid precursor resulting in an active ORR electrocatalyst after direct pyrolysis process. The CoNPC-71 was found to have a highly porous structure, active ORR and better stability as compared with a reference Pt/C cathode in an alkaline medium. In the next part of thesis, utilized Iron (III) diethylene triaminepentaacetate (Fe-DTPA) as a single solid precursor for iron, nitrogen and carbon. Fe-DTPA was chosen due to its ability to form larger amounts of nitrogen content on the carbon surface and nitrogen-bonding with the metal (Fe-Nx) after pyrolysis process. The catalysts were pyrolyzed at difference temperatures in a Swagelok cell without any inert gas. Heat-treatment effects to prepare an active catalyst led to different levels of catalyst graphitization, heteroatom content and activity. The ORR onset potential of the HNCS71 catalyst was high, up to 0.97 V, and half-wave potential was only 20 mV lower than Pt/C. An alkaline exchange membrane fuel cell made with HNCS71 as cathode catalyst tested in a H2-O2 single cell showed a maximum power density of ~68 mW cm-2. This study determined that the success of using a single precursor was essential to the synthesis of active materials, without surface modification of the precursor prior to the pyrolysis. The final part of thesis, describes the properties of M-N-C catalysts with Iron (II) acetate or Cobalt (II) acetate, which were mixed with melamine precursors and functionalized carbon (VXC-72R). The catalyst precursor was heat-treated at 900°C and characterized through electrochemical tests for the ORR. These experiments allowed for important realizations regarding the nature of the M-N-C catalysts and allowed for a huge improvement in onset and half-wave potentials. Single fuel cell measurements using Fe-N-C catalysts as cathodes produced power density ~75 mW cm-2 which was comparable to the reference Pt/C, and over 100 h of stability was observed. These inexpensive non-precious catalysts appear to be a promising new class of non-precious catalyst for alkaline exchange membrane fuel cells applications. ⓒ 2015 DGIST
Table Of Contents
1.Introduction 1 -- 1.1Motivation 1 -- 1.2Polymer electrolyte membrane fuel cell (PEMFC) 6 -- 1.3Electrochemistry of fuel cell 10 -- 1.4Performance of fuel cell 11 -- 1.5Oxygen reduction reaction (ORR) 15 -- 1.6Non-precious catalysts 19 -- 1.7Objectives of the research 28 -- 1.8Organization of thesis 29 -- 2.Characterization 30 -- 2.1 Physical characterization analysis 30 -- 2.1.1Scanning electron microscope (SEM) 30 -- 2.1.2Transmission electron microscopy (TEM) 31 -- 2.1.3X-Ray Diffraction (XRD) 33 -- 2.1.4Raman spectroscopy 34 -- 2.1.5X-Ray Photoelectron Spectroscopy (XPS) 35 -- 2.1.6Nitrogen Adsorption Analysis 36 -- 2.1.7X-ray Absorption Spectroscopy (XAS) 38 -- 2.2 Electrochemical characterization analysis 41 -- 2.2.1Catalyst ink preparation 41 -- 2.2.2Calibration of SCE and conversion to RHE 42 -- 2.2.3Linear sweep voltammetric (LSV) 43 -- 2.3Membrane Electrode Assembly Testing 47 -- 3.Cobalt and nitrogen co-doped hierarchically porous carbon as electrocatalyst for oxygen reduction 48 -- 3.1Introduction 48 -- 3.2Experimental 50 -- 3.3Results and discussion 52 -- 3.4Summary 71 -- 4.Investigation of hollow nitrogen-doped carbon spheres as non-precious Fe-N4 based oxygen reduction catalyst 72 -- 4.1Introduction 72 -- 4.2Experimental 74 -- 4.3Results and discussion 75 -- 4.4Summary 101 -- 5.Highly active and stable non-precious electrocatalyst via high pressure pyrolytic synthesis for alkaline exchange fuel cells 102 -- 5.1Introduction 102 -- 5.2Experimental 105 -- 5.3Results and discussion 106 -- 5.4Summary 128 -- 6.Conclusions 129 -- 7.Reference 132
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Energy Science and EngineeringThesesPh.D.

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