Dear interested reader,
In the following we would like to describe to key components of the project D2Service. There will be no room for Details concerning the project but a brief description of fuel cells and their field of use.
One step ahead of fuel cells is the concept of the galvanic element:
A galvanic cell is an electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell. It generally consists of two different metals connected by an ion bridge, or individual half-cells separated by a porous membrane.
Reduction and oxidation extend spatially separated in a half-cell.
Galvanic cells are systematically into three groups Divided, in primary, secondary and tertiary cells.

A primary cell is a battery that is designed to be used once and discarded, and not recharged with electricity and reused like a secondary cell (rechargeable battery). In general, the electrochemical reaction occurring in the cell is not reversible, rendering the cell unrechargeable. As a primary cell is used, chemical reactions in the battery use up the chemicals that generate the power; when they are gone, the battery stops producing electricity

A secondary cell or accumulator is a type of electrical battery which can be charged, discharged into a load, and recharged many times. It is composed of one or more electrochemical cells. The term "accumulator" is used as it accumulates and stores energy through a reversible electrochemical reaction. Several different combinations of electrode materials and electrolytes are used, including lead–acid, nickel cadmium (NiCd), nickel metal hydride (NiMH), lithium ion (Li-ion), and lithium ion polymer

Fuel cells also referred to as tertiary cells. These galvanic cells do not store the chemical energy’s carrier in the cell, but provided externally continuously available flow. This type of feed allows continuous and in principle perpetual operation.

What are fuel cells?
Fuel cells are galvanic cells, where anode and cathode are separated by ion-conducting electrolytes, which is impermeable for gases and electrodes. The function of a fuel cell is the reversed process of electrolysis. While water is separated to hydrogen and oxygen during electrolysis by adding electrical energy the fuel cell gains energy by letting those parts react.
In the fuel cell the electrolyte prevents the individual constituents to react with one another or with the ambient air. These cells provide a voltage of about one volt.
For technical applications these cells have to be stacked. In this way they are capable of providing a much larger voltage.
Of particular importance are the fuel cells in the NASA. With a very compact size the hydrogen and oxygen flow is generated and the "waste product" water served some astronauts (Apollo, Space Shuttle ... ) as drinking. Early 2000s these fuel cells already had an electrical efficiency of approximately 60 %
The technical development is currently focused on 5 types of fuel cells.

•  PEFC (“Polymer Electrolyte Fuel Cells")
  In this fuel cell the electrolyte consists of Teflon -like rigid plastic film, which behaves as an acid. The cell is divided in the anode powered by hydrogen and the cathode powered by oxygen.
  The cell will run on pure hydrogen or hydrogen from reformed natural gas. It should be noted that carbon monoxide radicals which can damage platinum in the electrodes.
  This cell offers a simple structure un low working temperature (about80°C)

•  PAFC ("Phosphoric Acid Fuel Cells")
  The electrolyte consists of water with diluted phosphoric acid which is incorporated in a fibrous matrix. The electrodes are porous asbestos and graphite plates or silicon carbides. Because of its high operating temperature of 170-200 ° C, the CO desorption is reinforced at the electrodes, so that sufficient a CO purification to 1% is enough.

•  MCFC („ Molten Carbonate Fuel Cells " )
  The electrolyte consists of a mixture of potassium and lithium carbonate.
  The melting point of this carbonate mixture is at about 480°C. At an operating temperature of 650°C, the molten salt is highly conductive for carbonate ions. The Ions walk through the melt and react at the anode to form carbon dioxide. The Cell must be maintained at operating temperature in order to achieve a long service life the equipment. A Temporary “off” is therefore harmful to the durability. Another problem of these systems is the hot molten electrolyte "crawls". This is countered by careful placement of nickel and aluminum parts.

•  SOFC ("Solid Oxide Fuel Cells")
  In this cell, the electrolyte is made from Zirkooxid with a Yitrium doping. The doping allows a good transfer of ions at temperatures greater than 800°C, because of the high operating temperature the cell can be powered with liquefied and the coupling of a gas turbine is possible.

•  AFC ("Alkaline Fuel Cells")
  The electrolyte consists of a 30% strength potassium hydroxide solution, through which the ions migrate to the anode. The cell is unpressurized at about 80°C. At the cathode, oxygen or purified air is supplied. Natural gas and other carbon rich gases must first be prepared. These cells are suitable because of their sensitivity only in environments where anyway worked with pure oxygen. Space Shuttle and submarines are common carriers. Economically these cell types are present rather uninteresting.