Energy efficiency, current conditions

Fig. 3. Current efficiency for hydrogen separation. Calculated overall energy efficiency vs. current density of hydrogen purification for conditions of Table 1 including reversible work O excluding reversible work.

However, under working conditions, with a current densityj, the cell voltage E j) is lower than eq - see Equation 1.7 - so that the practical energy efficiency, for a DEFC working at 0.5 V and 100 mAcm with complete oxidation to CO2, would be - see Equation 1.9... 

Energy efficiency. Electrochemical processes are amenable to work at low temperatures and pressures, usually below ambient conditions. Electrodes and cells can also be designed to minimize power losses due to poor current distribution and voltage drops. In some instances, the required equipment and operations are simple and, if properly designed, can be made relatively inexpensively. 

The current efficiency increases with increasing anode-cathode distance, because for a longer anode-cathode distance there is less convection, less interaction between gas bubbles and the metal, and more stable conditions. It was found that the current efficiency is independent of the anode-cathode distance above a certain distance. However, the ohmic drop in the electrolyte increases with the interpolar distance, so the cell voltage increases. These two factors influence the energy efficiency in an opposite manner. Furthermore, the heat balance of the cell sets limits to the variation of the anode-cathode distance. 

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