Mass Transfer Resistance in Fuel Cells

As we have mentioned earlier, one of the fuel cell voltage losses is the mass transfer loss or concentration loss caused by lower reactant gas concentration distribution at the reaction sites. Mass transport establishes reactant gas concentration distributions in gas supply channels and in the electrodes of a fuel cell, and hence in the distribution of local current densities. The gas supply rates to the anode-membrane and cathode-membrane interface must be sufficient enough to meet the gas consumption rate given by the electrochemical reaction rates. Any insufficient supply of gas to reaction sites may cause sluggishness in the reactions and cause mass transfer loss and reduction in fuel cell output voltage. 

Major factors that contribute to the mass transfer loss are as follows  

Convective mass transfer resistance in the gas flow channel 

Transport of different species such reaction gas, electrons, and ions to/from the electrode-electrolyte interface 

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