A Thermoelectrochemical Converter Using High-Temperature Polybenzimidazole (PBI) Membranes for Harvesting Heat Energy

To meet the rising energy demand and efficiently utilize a larger amount of waste heat energy from various devices and systems, here we report an innovative thermoelectrochemical converter which utilizes the electrochemical potential of a hydrogen pressure differential applied across a proton conductive membrane. The amount of energy available to the external load is the difference in electrical potential between that generated during a high-temperature expansion stage and that required during a low-temperature compression stage. In this work, various phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes, DiOH-PBI, para-PBI, and m/p-PBI, are prepared via the poly­(phosphoric acid) (PPA) process and investigated to understand how the membrane chemistry affected device performance. When operating a laboratory scale device at 20 °C/200 °C and a pressure ratio of 770, DiOH-PBI exhibited the best performance (maximum current density of 43 mA/cm², peak power density of 0.52 mW/cm², and net efficiency of 17.1%) as compared with the other two PBIs due to its high proton conductivity. Further increases in temperature or pressure differentials are expected to significantly improve the device output. All the reported results are consistent with the Nernst equation and thus further confirm the working principle of the thermoelectric conversion technique. This transformational approach may allow for efficient generation of electricity from many diverse forms of waste heat.