Temperature characteristics of a copper/zinc thermally-regenerative ammonia battery

Abstract

Bimetallic thermally-regenerative ammonia battery (B-TRAB) is a new way to harvest low-grade waste heat as high-power electricity. Among B-TRABs, copper/zinc thermally-regenerative ammonia battery (Cu/Zn-TRAB) shows the most cost-effective and a relatively high discharge voltage. Within a temperature range of 10–40 °C, the maximum power density of Cu/Zn-TRAB is promoted from 389 W m−2 to 723 ± 45 W m−2 with a linear slope of 12.25 W m−2 °C−1. There is an intense drop in power generation as the operating temperature reaches 45 °C, while ion diffusion and reaction kinetics are not negatively affected by high temperature, indicating that self-discharge caused by ion cross-contamination is the main reason. The cyclic voltammetry tests show that the cathode reaction during discharging is more susceptible to ion cross-contamination at high temperatures. The net energy density first increases and then decreases with the increase of temperature and varies with discharge current, and a maximum of 635 W h m−3 is achieved at 35 °C and a current density of 100 A m−2, with a thermoelectric conversion efficiency ηt of 0.37% (the Carnot-relative efficiency ηt/C is 3.52%). From the simulation results, the condenser temperature has a crucial influence on the energy conversion efficiency, and the ηt can be improved from 0.37% to 1.28% (ηt/C = 12.3%) by reducing the condenser temperature from 43 °C to 21 °C. The highest ηt/C of 14.6% is received at 45 °C.