A High Performance All-Aqueous Thermally Regenerative Ammonia Battery

Abstract

Terrawatt-hours of low-grade (t < 150 °C) waste heat are lost to the environment each year through inefficiencies in manufacturing, power generation, and waste management processes. Though several methods have been proposed to capture and convert this unused resource into electricity, most have exhibited low power densities (0.5-12 W m-2, normalized to membrane area) which has been a major roadblock to harnessing this energy stream. Recently, thermally regenerative ammonia batteries (TRABs) have overcome this limitation by producing power densities greater than 100 W m-2. However, the most promising TRABs still exhibit poor coulombic efficiencies, are susceptible to dendrite formation, and have low energy storage densities. To overcome these limitations, we show via Cu(I, II)-based half-reactions that it is possible to design an all-aqueous TRAB chemistry with distinct advantages over the conventional TRABs. To prove the utility of this approach, we used a rotating disc electrode (RDE) to quantify fundamental performance parameters of the new Cu(I, II)-based TRAB, including equilibrium potentials, limiting current densities and rate constants of the half-reactions at each electrode. Cell coulombic efficiency, power density, and energy storage densities were quantified using a conventional zero-gap flow battery system. Single cell tests achieved power densities up to 350 W m-2 (normalized to membrane area) with cell coulombic efficiencies greater than 90%, and energy densities four times larger than conventional TRABs.