CHAPTER 1INTRODUCTION1.1 Background of StudySolid oxide fuel cell (SOFC) is an energy conversion system that convert chemical energy to electrical energy and gives least impact to the environment. It is a new technology invented that has been discussed worldwide because it could give many advantages over traditional energy conversion systems (Zhijie Yang, 2012). SOFC can be divided into two types which are oxide-ion based solid oxide fuel cell (O2- SOFC) and proton conducting solid oxide fuel cell (H+-SOFC) also known as Proton Conducting Fuel Cell (PCFCs).
SOFC is a type of fuel cell that operates relatively at high operating temperature in the range between 800°C to 1000°C which then lead to high fabrication cost and limit its practical application (Zhijie Yang, 2012). In order to cut cost, the SOFCs must be able to operate at lower temperature so that less expensive material could be used in SOFCs systems. Therefore, several years ago more attention is given to H+-SOFC compared to conventional O2- SOFC due to its advantages including high efficiency of energy conversion and low activation energy for proton transport (Zhang et al.
, 2013). Besides, PCFC have receive much interest since it can give effective way to lower the operating temperature of SOFC that show good electrical performance at intermediate temperature (Lei Bi E. F., 2011). The advantages of proton conductors over the3oxide ion conductors are simpler fuel-recycling instrument, being able to avoid the dilution of fuel and reduce active energy of proton transport (R-h. Yuan, 2017).
The typical three main components of PCFC are anode, cathode and electrolyte. Anode is where the proton are generated and will transfer to the cathode through the electrolyte. The main purpose of the cathode is to produce the reaction between the reactant which is the oxygen and the electrolyte, without itself being consumed or corroded.
A cathode also shows the characteristic as a catalyst in the oxygen reduction. Electrolyte act as transfer medium while at the cathode site, the mechanism between protons from anode and O2 happen, producing water and electricity. The water is generated at cathode. Among the parts in fuel cell anode is where the electrochemical reaction occur for oxidation of the fuel. Anode must be stable in the reducing environment of the fuel and should be electronically conducting so that it could provide passage of electron.
Furthermore, an anode should exhibit high catalytic activity towards fuel oxidation. There is various type of material that used as anode such as iron, cobalt, platinum and nickel. Nickel (Ni) is preferable among of them and usually pair with an ion-conducting to form a composite anode. Ni offers good chemical stability, high catalytic performance in hydrogen oxide and inexpensive. Also, Ni has high electronic conductivity of the nickel constituent and good electro catalytic property for electrochemical oxidation of hydrogen in the anode. Ni material might suffers from considerable mismatch in thermal expansion as it has poor binding with YSZ electrolyte but instead it has good compatibility with LSCF-BCZY electrolyte.
4There are 3 types of PCFC which are anode supported, electrolyte supported and cathode supported cell. Effectiveness of each supported cell are vary as such for anode supported cell it operate at low temperature. Recently, anode supported button cell has been well extensively developed to achieve a good performance by using Ni material as anode since it has excellent catalytic activity toward the hydrogen oxidation, high electronic conductivity of Ni constituent and low cost. Many investigations have shown that anode supported button cell could show good performance due to reducing of electrolyte thickness and ohmic losses (L.P. Sun).
Various techniques of fabrication were introduced in order to prepare anode supported button cell. For examples, screen printing, tape casting, dry pressing, spray coating, dry pressing and spin coating (Tan et al., 2014).
In this work, an anode composite of NiO:BCZY with ratio 60:40 and 70:30 will be synthesized using NiO-BCZY as anode, BCZY as electrolyte and LSCF-BCZY as cathode which will be prepared by sol-gel method. The fabrication process of anode supported button cell NiO-BCZY|BCZY|LSCF-BCZY by dry pressing assisted with spin coating technique will be discussed and the performance of the anode supported button cell at intermediate temperature will be evaluated.51.2 Problem StatementThe performance of a single cell at the intermediate temperature for SOFC application is strongly affected by the ratio of NiO:BCZY used at anode for anode supported button cells.
Although, there are a lot of works have been devoted for finding and evaluating promising material for intermediate temperature SOFC cell components to enhance its performance but less literature discussing on the ratio of NiO:BCZY composite anode of anode supported button cell using the ratio of 60:40 and 70:30. Thus, this research will be conducted to give more information on the anode supported button cell with the different ratio of NiO:BCZY composite anode at intermediate temperature range.1.3 Significance of studyThe outcomes of this study may contribute to a significant knowledge in developing anode supported button cell with different ratio of NiO:BCZY (60:40 and 70:30) composite anode towards increasing the performance of anode supported button cell for PCFC application at intermediate temperature.61.4 Objective of studyThe aim of this study is to evaluate the performance of anode-supported button cell of intermediate temperature with different ratio of NiO:BCZY composite anode.
The specific objectives for this study are1. To fabricate anode-supported button cells using the prepared composite anode by dry-pressing assisted spin-coating technique.2.
To evaluate the electrochemical performance of the fabricated anode-supported button cells using electrochemical impedance spectroscopy (EIS) at intermediate temperature.