Redox reactions involve the transfer of electrons from one substance to another. These reactions always occur in a spontaneous reaction. To represent these reactions, half equations are used. In a reaction there is a reducing agent which donates electrons and an oxidising agent which accepts electrons.
A temperature gradient is established between the flow of charge from the hot electrode to the cold electrode to generate voltage. The generation of potential allows for heat to be converted into electrical potential energy to power wearable devices.