secondary cells and fuel cells.
| Fuels cells | Primary | Secondary | |
| Energy transformation when discharging | chemical --> mostly electrical + heat | chemical --> mostly electrical + heat | chemical --> mostly electrical + heat |
| Energy transformation when recharging | Recharging is not possible | Recharging is not possible | electrical --> mostly chemical + heat |
| Anode during discharge | Site of oxidation (negative) | Site of oxidation(negative) | site of oxidation(negative) |
| Anode during recharge | Recharging is not possible | Recharging is not possible | Site of oxidation(positive) |
| Chemical reactions when discharging | Spontaneous and exothermic | Spontaneous and exothermic | Spontaneous and exothermic |
| Chemical reactions when recharging | Recharging is not possible | Recharging is not possible | Reactions are endothermic as energy is supplied to drive the reactions taking place at the electrodes. |
| Reactants | Constantly supplied | Finite amount present in the battery | Finite amount present in the batter |
| Products | Constantly removed | Stored in the battery away from electrodes | Stored in the battery but in contact with the electrodes |
| Electron flow during discharge (always anode to cathode for all electrochemical cells) | Anode to cathode |
Battery discharging electron flow anode to cathode |
Battery discharging anode to cathode
|
| Electron flow during recharge | Recharging is not possible | Recharging is not possible | Battery recharging anode to cathode
Notice how during recharging the anode becomes the cathode and the cathode becomes the anode. Keep in mind whether its recharging or discharging the electrode where oxidation takes place is always the anode and the electrode where reduction takes place is always the cathode, but the polarity of the anode and cathode change during recharge. |
| Ion flow during discharge | Anions flow to the anode | Anions flow to the anode | Anions flow to the anode |
| Ion flow during recharge | Recharging is not possible | Recharging is not possible | Anions flow to the anode |
| Voltage used to recharge | Recharging is not possible | Recharging is not possible | Greater than the voltage output during discharge. |
| Voltage output | Consistent voltage as reactants are constantly supplied | Drops off as reactants are used up | Drops off as reactants are used up |
