Electrical power production from low-grade waste heat using a thermally regenerative ethylenediamine battery

Thermally regenerative ammonia-based batteries (TRABs) have been developed to harvest low-gradewaste heat as electricity. To improve the power production and anodic coulombic efficiency, the useof ethylenediamine as an alternative ligand to ammonia was explored here. The power density of theethylenediamine-based battery (TRENB) was 85 ± 3 W m2-electrode area with 2 M ethylenediamine,and 119 ±4Wm2 with 3 M ethylenediamine. This power density was 68% higher than that of TRAB. Theenergy density was 478 Wh m3-anolyte, which was ~50% higher than that produced by TRAB. Theanodic coulombic efficiency of the TRENB was 77 ± 2%, which was more than twice that obtained usingammonia in a TRAB (35%). The higher anodic efficiency reduced the difference between the anodedissolution and cathode deposition rates, resulting in a process more suitable for closed loop operation.The thermal-electric efficiency based on ethylenediamine separation using waste heat was estimated tobe 0.52%, which was lower than that of TRAB (0.86%), mainly due to the more complex separationprocess. However, this energy recovery could likely be improved through optimization of the ethylenediamineseparation process.