The significance of supporting electrolyte on poly (vinyl alcohol)–iron(II)/iron(III) solid-state electrolytes for wearable thermo-electrochemical cells

Thermo-electrochemical cells (known as thermocells) can convert heat energy into electrical power through redox reactions driven by the presence of a temperature gradient. Low-grade heat from the human body can be harvested using thermocells containing a suitable electrolyte, such as the iron(II)/iron(III) chloride redox couple housed in poly (vinyl alcohol) described here. However, conventionally the thermo-electrochemical performance of gelled electrolytes is poor, due to slow ionic transport and high charge transfer resistance. In this report, hydrochloric acid has been found to synergistically decrease the charge transfer resistance of the redox reaction, whilst doubling the tensile properties of the gel housing. Moreover, individual thermocells can be connected in parallel to enhance current output.