A bimetallic thermally regenerative ammonia-based battery (B-TRAB) using inexpensive materials efficiently converts low-grade thermal energy into electricity with high power density. Through thermal regeneration of the anolyte, the B-TRAB system realized high-voltage discharge (1.38 V) with redox couples [Cu(II)/Cu and Zn(NH₃)₄ ²⁺/Zn] and low-voltage charge (0.72 V) with Zn(II)/Zn and Cu(NH₃)₄ ²⁺/Cu. Adding 2 M NH₃ to the anolyte of a Cu/Zn-TRAB produced a peak discharge power density of 525 W m⁻²-electrode (120 W m⁻²-membrane), and the voltage (or current) and peak power could be doubled by connecting two cells in series (or parallel). In successive regeneration cycles, a maximum power density of 115 W m⁻²-electrode (26 W m⁻²-membrane) and a net energy density of 714 W h m⁻³ were produced at a constant current density of 100 A m⁻². The power density was enhanced to 515 W m⁻²-electrode (118 W m⁻²-membrane) and maintained in successive cycles by adding acid to the regenerated catholytes, with a net energy density of 299 W h m⁻³ (discharged at a constant load of 12 Ω and charged at a constant current density of 100 A m⁻²). A thermal-electricity conversion efficiency of 0.95% (10.7% relative to the Carnot efficiency) was achieved.

Thermally regenerative ammonia batteries (TRABs) show viable potential for harvesting abundant low-grade waste heat as high-power electricity. However, the ammonia brings about a large pH difference between the catholyte and anolyte, leading to self-discharge and severe energy decay. Here, an electrolyte decoupling strategy is proposed for ammonia batteries to restrain the self-discharge and enhance energy density as well as power generation at high temperatures. The self-discharge by ion cross contamination is observed visually as a colour evolution of the interlayer solution, and a transition of the principal cathodic reactant from Cu²⁺ to Cu(NH₃)₄ ²⁺ exists during discharging, which signals the beginning of performance degradation. The results demonstrate that decoupled Cu/Zn-TRABs with double and triple-membrane designs improve the energy density by 45–50%, mainly due to the delay of the transition region. The power density of the decoupled Cu/Zn-TRABs is reduced at high currents, but with concentration optimization or elevated temperatures, it is able to be promoted significantly. With an energy density of 1034 W h m⁻³ obtained by a decoupled Cu/Zn-TRAB with double-IEM (ion exchange membrane) design, a thermoelectric conversion efficiency of 1.86% (15.6% relative to the Carnot efficiency) is achieved at a condenser temperature of 16 °C.

Thermally-regenerative ammonia-based flow battery (TR-AFB) is considered to be an efficient way to harvest low-grade waste heat, but its performace such as power density and voltage are still need to improve. In this paper, an isothermal three-dimension (3-D) numerical model for TR-AFB has been proposed in order to optimize its performance. Firstly, the concentration distribution of species in the flow channel of TR-AFB and effects of different flow forms on power production are described. The results indicate that dead zones are found in the initial experimental flow channel, which greatly affect the performance of the battery. Therefore, in order to improve the performance, flow channels of TR-AFB have been optimized using silicon rubber sheet channel and copper electrode flow channel. According to the optimization results, it is found that the maximum power density of the battery can be increased by about 33% (12.1 W m⁻²), while the pump power consumption only increase by 2.13 × 10⁻² W m⁻². By comparing the performance of batteries with different flow channels, the general laws of designing flow channel are summarized. That is to minimize the flow dead zones, increase the reaction areas and reduce the distance between electrodes within the allowable range.

The Organic Rankine Cycle (ORC) is regarded as a suitable way to recover waste heat from gaseous fuel internal combustion engines. As waste heat recovery systems (WHRS) have always been designed based on rated working conditions, while engines often work under part-load conditions, it is quite significant to analyze the part-load performance and corresponding operation strategy of ORC systems. This paper presents a dynamic model of ORC with a medium cycle used for a large gaseous fuel engine and analyzes the effect of adjustable parameters on the system performance, giving effective control directions under various conditions. The results indicate that the intermediary fluid mass flow rate has nearly no effect on the output power and thermal efficiency of the ORC, while the mass flow rate of working fluid has a great effect on them. In order to get a better system performance under different working conditions, the system should be operated with the working fluid mass flow rate as large as possible, but with a slight degree of superheating. Then, with the control of constant superheat degree at the end of the heating process, the performance of the combined system that consists of ORC and the engine at steady state under seven typical working conditions is also analyzed. The results indicate that the energy-saving effect of WHRS becomes worse and worse as the working condition decreases. Especially at 40% working condition the WHRS nearly has no energy-saving effect anymore.