Total Efficiency of Fuel and Electrolytic Cells

Generally, the total efficiency, 4, of an electrochemical energy conversion system is defined as a product of thermodynamic efficiency, 4th. voltage efficiency, 4v. and current (or Faradaic) efficiency, 4 - 

The current efficiency, 4 , is defined by Faraday s law. In a fuel cell, the amount of fuel or oxidizer can never be smaller than the theoretically calculated amounts using 

Faraday s law based on the measured current as a function of time. The ratio of the calculated and measured amount of chemical is the fuel cell current efficiency, 

In an electrolytic cell, the amount of chemicals produced can never be larger than the theoretically calculated amounts using Faraday s law based on the measured current as a function of time. The ratio of the measured and calculated amount of chemical is the current efficiency of the electrolytic cell. The current efficiency of either fuel or electrolytic cells is expected to be above 0.95 in the properly operating electrochemical energy conversion system. 

The voltage and thermodynamic efficiencies of an electrolytic cell are defined as follows  

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