Single-component and three-component fuel cells (original) (raw)
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The possible use of mixed ionic electronic conductors instead of electrolytes in fuel cells
Solid State Ionics
Various types of mixed ionic electronic conductors (MIECs) are considered for replacing pure ionic conductors, i.e. solid electrolytes (SEs), in fuel cells (FC). It is shown that a rather high electronic conductivity, which originates from a change in stoichiometry under reducing or oxidizing conditions at the electrodes, can be tolerated provided the FC is operated close to its maximum power output. Thus a MIEC can replace an SE in an FC that is intended to operate under those conditions. The operation conditions in the electrolysis process of water are different. Under these conditions a M1EC cannot replace an SE. The analysis leading to the acceptance of mixed conductivity suggests also that electrodes can be prepared by change of stoichiometry or by doping of the surface region of the SE or MIEC used. The stoichiometry change and the doping will turn the surface regions into semiconductors which can serve as electrodes. The use of a protective thin SE layer on a MIEC is analyzed. It is not needed for an FC operated under maximum power output condition. It may, however, be useful for low-power operation conditions and for electrolysis.
Operation Principles for Fuel Cells with Mixed Ionic Electronic Conductors
Mixed ionic electronic conductors such as doped ceria or δ-Bi 2 O 3 offer the possibility to operate solid oxide fuel cells (SOFC) at lower operating temperatures due to the higher ionic conductivity of these materials compared to yttria stabilized zirconia. On the other hand the mixed ionic electronic conductivity of these materials constraints the operating regime and affects cell and system design. Fuel cells based on ceria solid solutions with Sm or Gd as electrolytes were operated with different electrodes and electrolyte thickness at temperatures between 600 °C and 800 °C. The current-voltage relations and the efficiency of these cells are discussed by a defect chemical model including the mixed conductivity of the electrolyte as well as electrode overpotentials. From this model principles for system operation and cell design are derived. As a consequence of the mixed conductivity a maximum efficiency depending on electrolyte thickness and electrode overpotentials is found.
A fuel cell with a single component functioning simultaneously as the electrodes and electrolyte
Electrochemistry Communications, 2011
A fuel cell device is realized by using a single component of lithium nickel oxide and gadolinium doped ceria (LiNiO 2 -GDC) composite material, a mixture of electronic and ionic conductors, when nickel foam and silver paste are attached to each surface of the single component pellet as current collectors. This simple fuel cell construction with only one component showed the same or even better performances compared to conventional three-component MEA (membrane electrolyte assembly) fuel cell using GDC as electrolyte. The maximum power density of 450 mW/cm 2 has been achieved at 550°C for the single component fuel cell.
Engineering and Operating Aspects of Solid Oxide Fuel Cells with Mixed Ionic Electronic Conductors
Several mixed ionic electronic conductors exhibit a considerable ionic conductivity higher than the one of yttria stabilized zirconia, the most commonly used solid oxide fuel cell (SOFC) electrolyte material. The use of these materials would greatly reduce the internal resistance of solid oxide fuel cells and allow to reduce operating temperatures, however, the electronic conductivity would reduce their electrical conversion efficiency. The tolerable amount of electronic conductivity within an electrolyte, and its influence on system design and performance are derived from electrochemical and defect chemical model. The model is illustrated with the example of a fuel cells using ceria solid solutions as electrolytes. Model calculations for this electrolyte predict an open circuit voltage and a conversion efficiency in SOFCs which depends strongly on the thickness of the mixed conducting membrane and on the performance of the electrodes.
Characteristics of Solid Oxide Fuel Cells based on Mixed Ionic Electronic Conductors
Solid oxide fuel cells (SOFCs) with mixed ionic electronic conductors as electrolytes exhibit fundamentally different current-voltage characteristics compared to fuel cells with pure ionically conducting electrolytes. A model describing mixed conductors as SOFC with a mixed conducting electrolyte with respect of the partial electronic ad ionic currents in such a material is presented and compared with experimental results.
Recent Trends and Comparison in Fuel Cell Technology
The fuel cells are an old technology. Problems have plagued their introduction. Present material science may make them a reality soon in specialized applications. The Solid Oxide Fuel Cell appears to be the most promising technology for small electric power plants over 1 kw. The Direct Alcohol Fuel Cell appears to be the most promising as a battery replacement for portable applications such cellular phones and laptop computers. Fuel cells used as electric power plants may be successful before vehicular ones are. This is because a fuel cell produces electric power which is what is required in this case. In transportation applications the electricity produced must then be converted to mechanical power. It is unclear whether hydrogen fuel will be widely used. This is because solid oxide fuel cells will be become extremely popular and these can cleanly convert renewable hydrocarbon fuels. This paper reviews the advances and typical application of fuel cell comparison in terms of parameters like output, application and advantages.
A REVIEW ON FUEL CELL AND ITS APPLICATIONS
With the increase in the demand of electrical energy now it is the time to think for the alternate source of energy. In order to mitigate the demand of electrical energy and to create pollution free environment the fuel cell acts as an alternate solution. The fuel cells are very much similar to an ordinary dry cell or battery. It has an electrode, some chemical material and an electrical circuit to give the supply to an external circuit. Due to absence of rotating devices they are quite simple and efficient in nature. This paper describes about the working methods of fuel cells and their future and economic growth.
Fuel Cell and Its Applications: A Review
Energy is the most fundamental requirement of today's era. Energy is consumed very rapidly. The energy requirements are very increasing. Our population, abundant energy resources and industrial diversity make our self proficient enough in producing and consuming energy. This will definitely leads in contributing to the national economy. It is the fact that initially there is a cost issue with every new technology but gradually developing mind we can cope up with it. The need for optimization in cost and efficiency can create systems which are cost effective, non-hazardous in nature, commercially available, clean fuel, compete with regular ongoing systems, inherently safe in handling, having renewable power and sustainable to nature. We envision a future where industries can fulfil the growing demands in an environmentally sustainable way. Hydrogen fuel cells have the real potential to be the future technology in terms of applicability. This technology has the solution to the problem of increasing requirements in an environmentally viable option. This review article presents the working operation of Hydrogen Fuel Cell, Classification of fuel cell in a comparable way, applications, new developments, future technologies and economic growth. Fuel cell is very much similar to the electrochemical cell or an ordinary dry cell. There are basically three components in each and every fuel cell. They are cathode, anode and electrolyte. They are connected with the electrical circuit. This construction has no rotating parts in its design. Hence, they are pretty simple and efficient in design. The classification is based on the type of electrolyte used.
The relation between cell voltage (V Cell), applied chemical potential difference (∆µ(O 2)) and cell current (I t) for solid oxide fuel cells (SOFC) based on mixed ionic electronic conductors is derived by considering also the effect of electrode impedance. Four-probe measurements, combined with current interruption analysis are considered to yield the relation between ionic current (I i) and overpotential (η). The theoretical relations are used to analyze experiments on fuel cells with Ce 0.8 Sm 0.2 O 1.9 and Ce 0.8 Gd 0.2 O 1.9 electrolytes with La 0.84 Sr 0.16 CoO 3 or Pt as cathode and Ni/Ce 0.9 Ca 0.1 O 1.9-x or Pt as anode. The electrode overpotentials of these cells determined by current interruption measurements are discussed assuming different models including impeded mass transport in the gas phase for molecular and monoatomic oxygen and Butler-Volmer type charge transfer overpotential.