Electrochemistry and thermodynamics of fuel cells

Here M is the net energy of material flowing into the device, W is the net amount of mechanical or electric work performed on the system by the surroundings, and Q is the net amount of heat received from the environment. 

The amount of work performed by the device on its surroundings is -W. Integrated over a period of time, it may be expressed as 

The chemical potential for an electrolyte is an expression of the additional energy of its ions relative to that of the pure solvent. With the electrolyte components labelled as above by i, their contributions may be expressed as 

In case the electrochemical device has a constant volume and the exchange of heat with the environment can be neglected, then the electricity produced must correspond to the loss (conversion) of free energy from the cell. 

This implies that the intensive variables of the small system, which may not even be defined during the process, approach those of the large system 

---