Development of a membrane-less microfluidic thermally regenerative ammonia-based battery towards small-scale low-grade thermal energy recovery*

Developing low-cost and simple thermally regenerative ammonia-based batteries is a promising method to harvest low-grade waste heat. This paper proposes a membrane-less microfluidic thermally regenerative ammonia-based battery (M-TRAB) for harvesting low-grade waste heat. A liquid-liquid interface is developed by flowing colaminar streams of anolyte and catholyte in a microchannel. It can replace the anion exchange membrane for separating reactants. A M-TRAB with a flow rate of 1500 mu L min-1 obtains the maximum power density of 27 W m- 2. The stable output voltage is generated with different flow rates, and the maximum theoretical thermal energy efficiency can reach 1.3% (the relative Carnot efficiency is 14.9%). And the influences of the microchannel length and NH3 concentration on the performance are investigated. Moreover, based on the lower density of anolyte than catholyte, a novel upward-anode structure forms a clearer interface, and almost non-existent ammonia-crossover occurs, especially in a tapered channel. And a maximum power density of 54.8 W m- 2 is obtained. It indicates that the low-cost MTRAB is a potential choice for assistant cooling in small systems.