Unitized regenerative fuel cell

Reversible fuel cells ( engl. reversible fuel cell RFC) are fuel cells, whose energy -supplying labor process is reversible.

Example, hydrogen fuel cell

A hydrogen fuel cell uses hydrogen ( H2) and oxygen ( O2) to produce electricity and water ( H2O); as reversible fuel cell, it must now resume production by electrolysis of water, hydrogen and oxygen. For this purpose, an electrolyser with the fuel cell is combined.

Reversible process in a hydrogen fuel cell:

To reduce the complexity of the system and reduction also reversible fuel cells are investigated that can work both as an electrolyser as well as fuel cell ( unitized regenerative fuel cell, short URFC ). Polymer electrolyte fuel cells are currently being used mainly for this purpose.

Together with a fuel tank, a reversible fuel cell to replace a battery, whereby a significantly lower and more favorable power ratio can be achieved, but with less efficiency.

Fundamentals of Thermodynamics

Since, according to the energy conservation law ( first law of thermodynamics ) can not vanish and energy in chemical reactions always occur entropy, a reversible fuel cell has this entropy can be compensated for by a reversible heat or energy transport across the system boundaries of the cell away.

As a prerequisite, we must demand that the fuel cell makes its maximum reversible work in the combustion reaction. It is at a known temperature of the cell according to the second law of thermodynamics:

Since, according to the first law of thermodynamics for the reaction enthalpy of the following applies:

Follows by combining the above two equations for the reversible work:

Thus, the reversible work depends not only on the actual enthalpy of reaction directly on the temperature and the change in entropy of reaction.