Almost all batteries contain chemical energy that releases electrons whenever the battery is attached to a circuit. The reactants are made up of atoms just like everything ells. Those atoms are orbited by smaller particles called electrons; some atoms and molecules are called ions because they either have too many electrons or not have enough electrons.
When a lead acid battery cell is fully charged it has two electrons that are made up of dissimilar metals and the acid or electrolyte. They are called dissimilar because one attracts a positive cation and one attracts a negative anion. The crazy part is that when the battery is fully charged the negative electrode is composed of sponge lead (Pb), the positive electrode is composed of lead peroxide (PbO2) and the electrolyte is (H2O) and sulfuric acid (H2SO4). When the battery is fully discharged the negative electrode becomes lead sulfate, the positive one looses the oxygen atoms and turns into lead sulfate as well and the electrolyte turns into water (H2O); “but I wouldn’t drink it”.
This whole thing is explained by the fact that the sulfuric acid breaks down in the water and (H2SO4) turns into two (H) atoms and one (SO4) molecule. The (SO4) anions have a charge of –2 and the (H) cations have a charge of +1. When the lead acid cell discharges the sulfate ions are attracted to the lead at the negative electrode and the lead turns into lead sulfate as the sulfate molecule releases two electrons that have a negative charge. At the same time the positive electrode loses its negative oxygen atoms to four positive hydrogen atoms the positive electrode now has a charge of +4. The electrons travel through the circuit that starts your car or whatever the circuit does and eventually they make it to the positive electrode. Two negative electrons and one negative sulfate anion with a charge of –2 neutralize the positive electrode having the charge of +4. Eventually the sulfuric acid turns into water (H2O) and both of the electrodes turn into lead sulfate (PbSO4) and the cycle is complete. When you charge the battery the opposite happens.
| A picture can make a whole book worth of gibberish make sense so hear is a picture. |
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The lead at the negative electrode gives up 2 electrons and gets a charge of +2 at the same time the lead sulfate at the positive electrode loses 2 oxygen’s to 4 hydrogen’s and gets a charge of +4.
The positively charged lead at the negative electrode attracts a sulfate ion and becomes neutral lead sulfate. At the positive electrode the lead has a charge of +4 and is neutralized by 2 negative electrons and a negative sulfate ion becoming lead sulfate. At the negative electrode the reaction looks like this Pb+SO4=PbSO4+2 e- at the positive electrode 2e- +PbO2+2(H2)+SO4=2(H2O)+PbSO4.
Lead acid cells are extremely heavy to send into space so on the Apollo moon flights they used a hydrogen oxygen H2-O2 fuel cell instead. The fuel cell weighed 500 pounds and lasted 11 days.
The reaction for a fuel cell looks like this at the negative electrode (Anode) 2(H2)+4(OH)=4(H2O)+ 4e- and at the positive electrode (Cathode) 4e- +O2+2(H2O)=4(OH) the 4(OH) at the cathode is the same 4(OH) used at the anode.