Issue 1, 2015

A thermally regenerative ammonia-based battery for efficient harvesting of low-grade thermal energy as electrical power

Abstract

Thermal energy was shown to be efficiently converted into electrical power in a thermally regenerative ammonia-based battery (TRAB) using copper-based redox couples [Cu(NH3)42+/Cu and Cu(II)/Cu]. Ammonia addition to the anolyte (2 M ammonia in a copper-nitrate electrolyte) of a single TRAB cell produced a maximum power density of 115 ± 1 W m−2 (based on projected area of a single copper mesh electrode), with an energy density of 453 W h m−3 (normalized to the total electrolyte volume, under maximum power production conditions). Adding a second cell doubled both the voltage and maximum power. Increasing the anolyte ammonia concentration to 3 M further improved the maximum power density to 136 ± 3 W m−2. Volatilization of ammonia from the spent anolyte by heating (simulating distillation), and re-addition of this ammonia to the spent catholyte chamber with subsequent operation of this chamber as the anode (to regenerate copper on the other electrode), produced a maximum power density of 60 ± 3 W m−2, with an average discharge energy efficiency of ∼29% (electrical energy captured versus chemical energy in the starting solutions). Power was restored to 126 ± 5 W m−2 through acid addition to the regenerated catholyte to decrease pH and dissolve Cu(OH)2 precipitates, suggesting that an inexpensive acid or a waste acid could be used to improve performance. These results demonstrated that TRABs using ammonia-based electrolytes and inexpensive copper electrodes can provide a practical method for efficient conversion of low-grade thermal energy into electricity.

Graphical abstract: A thermally regenerative ammonia-based battery for efficient harvesting of low-grade thermal energy as electrical power

Supplementary files

Article information

Article type
Paper
Submitted
05 Sep 2014
Accepted
18 Nov 2014
First published
18 Nov 2014

Energy Environ. Sci., 2015,8, 343-349

Author version available

A thermally regenerative ammonia-based battery for efficient harvesting of low-grade thermal energy as electrical power

F. Zhang, J. Liu, W. Yang and B. E. Logan, Energy Environ. Sci., 2015, 8, 343 DOI: 10.1039/C4EE02824D

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