Mukhopadhyay (Banerjee), Madhumita
(2012)
Development Of Planar Solid Oxide Fuel Cell Using
Cermet Anode Prepared By Electroless Technique.
PhD thesis, Central Glass & Ceramic Research Institute.
Abstract
Solid Oxide fuel cell (SOFC) is a very promising electrical
conversion device owing to its high efficiency and low gas emissions. In light of the present world scenario relating to the energy sector, research and development works on alternate energy sources viz. fuel cells, solar, hydro etc.
holds special drive and attention. Among various classifications of ceramic fuel cells (SOFCs), the present
research work is based on the flat planar design owing to its ease of fabrication and potential for providing high power densities compared to other cell configurations. Till date, nickel (Ni) -8 mol % yttria stabilized zirconia (YSZ) [Ni-YSZ] cermet has been evolved out as the most widely
accepted anode for SOFC application. However, such Ni-ceramic composite posseses certain shortcomings owing to which the commercialization of SOFC is limited. The endeavour of the present research is based on the development of Ni-YSZ functional anode materials by novel ‘electroless technique’ and its application for SOFC fabrication. Generation of unique core (YSZ)-shell
(discreet Ni nanoparticulates around the YSZ core) microstructure in a patterned manner through process optimization is one of the major accomplishment of such electroless technique. Sensitization of YSZ particulates
by high energy ultrasonification forms the catalytic Pd0 particulates in-situ in the redox reaction bath. The adsorption of such Pd0 onto YSZ core governs the
deposition of Ni around YSZ during electroless technique and hence the microstructure. Optimization of process parameters initially involve mathematical modeling which is followed by experimental validation. The developed electroless anode is found to exhibit the required electrical conduction (~ 500 Scm-1) at much lower Ni content (28 vol %) compared to other conventional cermets. The major drawbacks of thermal incompatibility and poor redox tolerance associated with such Ni-YSZ anode is rectified using the functional electroless anode. Efforts have been exerted to determine the length of triple phase boundary (active sites for electrochemical reactions) and
reaction sequences through mathematical modeling approach.
The second phase of the present research work is focussed on the fabrication of SOFCs using such functional anodes in assorted configurations. Electroless cermet is configured as anode-support structure, multilayered anode or anode active layer (AAL). The various factors affecting
electrochemical activity of single cell such as: a) thickness and sintering temperature of the half cell b) rate of NiO reduction to metallic Ni, c) effect of
moisture in fuel and c) type of oxidant used at the cathode side are studied thoroughly during the course of this research work. The load bearing competence of the fabricated SOFCs with the developed anodes are also
examined for a considerable period of time to determine the corresponding degradation rates. The experimental results support the superiority of electroless anodes, which showed the highest cell performance of 3.7 Acm-2 at 800oC without any significant degradation and lowest polarization from the
associated factors. The experimental outcome of electrochemical reactions are correlated with: a) optical microstructures, b) elemental mapping, c) NiO reduction equilibrium, d) pore-size distribution in anodes, e) effect of moisture in the fuel, f) variation in oxidant type etc. The influence of polarization/resistive factors is also studied in terms of both mathematical approach and
electrochemical impedance measurements. Therefore, the entire effort of the present research work is exerted
towards the development of functional Ni-YSZ anode by novel ‘electroless’ technique encompassing its potential to act as new-generation anode for ITSOFC application.
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