Development of an efficient high temperature solid oxide fuel cell

W.J. Oosterkamp

Introduction

Fuel cells convert chemical into electrical energy and can be compared with batteries.
The difference is that in fuel cells the reactants (fuel and oxygen) are supplied externally,
and in a battery they are generated internally using electricity. Possible applications for
fuel cells are:

-Large scale electricity production
-Cars, aeroplanes and ships (auxiliary power units)
-Small scale combined heat and power

Low temperature fuel cells work with hydrogen. It is possible to produce hydrogen in combination
with a fuel cell using oil or natural gas. This is however a complex process. A number of systems
for small scale combined heat and power are being developed based on the Ballard process. They are
big and expensive. They have a relatively low efficiency ( 30 -35 %).

Electricity is produced in the high temperature fuel cells by the transport of oxygen ions through
a membrane. In these solid oxide fuel cells all conventional fuels can be used. The cells have a
high electrical efficiency (50 %). In Westervoort (Netherlands) a system of 400 kW from Westinghouse-
Siemens) has operated for 18 month. There are however problems with the commercial introduction.

Inventions

In my inventions the fragile membrane material is kept under compression. This prevents (similar
to pre-stressed concrete) the growth of fissures. Application of the US patent 7,041,410 B2
(European patent pending) will reduce the membrane thickness by a factor of five. This results
in less resistance and a higher current density. The size of the system can be reduced significantly
and as a result the costs will be much lower. A second related invention (Netherlands patent 1026285,
US and European patent pending)) "Method for the production of an electrochemical cell and cell stack
obtained in this way" simplifies the production significantly and makes it possible to put the cells
in series thereby reducing the required material for conductors. The cells so produced have a higher
efficiency than the Ballard cells and lower production costs than the Westinghouse-Siemens cells.

Development

The development of such a cell start with the demonstration of a simple cell, constructed according
the inventions. This could be done by a university or a research centre (ECN or TNO in the Netherlands).
A high temperature autoclave is required. The important parameters are the occurrence of fissures and
the amount of oxygen bypassing the membrane. This first phase will costs about 100 000 $ (Euro). Then
complete systems have to be designed and built. This will cost about 1 million $ (or Euro). Subsidies
of about 50 % of the development costs are available.

Market introduction

Small scale combined heat and power units offer a good opportunity for the introduction of these cells.
Two thirds of the heat and one half of the power requirement of a one family house in Europe can be
supplied by a fuel cell delivering 3 kW electrical and 3 kW thermal energy. The electrical grid needs
to be used used as a buffer. The cost for such a unit are estimated to be about 5 000 Euro.

A niche market is formed by auxiliary power units in sail boats. Owners of these boats are willing to
pay a premium for a silent highly efficient electricity generator.

Batteries in electric cars do not have the capability to store large amounts of energy and to have a
high power output. Proton exchange membrane fuel cells are being developed as an alternative. Hydrogen
storage is however complex and the safety implications are not yet fully explored. On board reforming
of diesel fuel or gasoline require high temperatures and sophisticated catalysts. Solid oxide fuel cells
are a more logical choice when high temperatures are used. With organically produced alcohol a sustainable
solution for automotive applications is obtained.

A power package, based on these fuel cells, of 50 kW will have an active volume of 100 l. With heat
exchangers and auxiliary equipment it is estimated that the volume will be about 300 to 500 l.

Thermal cycling should be avoided and the cells should be preferably kept at the operating temperature.
Thermal isolation is therefore important. This seems to be possible as batteries for electric vehicles
have been operated routinely at about 300 degrees for the last ten years.

These improved solid oxide fuel cells are therefore an attractive alternative to the proton exchange
membrane fuel cells and worth of further development.

back