Fuel Cell

Here as a start for you:

The increase in the internal energy of a system is equal to the amount of energy added to the system by matter flowing in and by heating, minus the amount lost by matter flowing out and in the form of work done by the system.

This is the first law of thermodynamics for an open thermodynamic system.

Type how does a fuel cell work into Google

http://www.google.co.uk/search?q=how+does+a+fuel+cell+work&sourceid=ie7&rls=com.microsoft:en-gb:IE-SearchBox&ie=&oe=&rlz=1I7GGLT_en&redir_esc=&ei=QxeuTLf2ApaSjAfriqha

from above

http://www.youtube.com/watch?v=QBk1sDculpM Video