The hydrogen liberated at the cathode would coat the electrode so polarises the cell. And manganse (IV) oxide is used as a depolariser. I got an equation in my notes: 2MnO2 + 3H2 --> 2MHO(OH) + 2H2O. But evidently the oxygen doesn't balance. I tried looking on the internet but still no equation. Can someone help? (also the overall equation does not contain hydrogen at all, can someone explain that?) Thanks.