(307c) Elevated Temperature Performance of the All-Aqueous Copper Thermally Regenerative Battery

Increasing the energy efficiencies of thermal energy conversion processes is a potential method for reducing greenhouse gas emissions. Many different electrochemical technologies provide new opportunities for converting energy in low-grade heat streams into grid-scale power and energy, but improvements are required for commercialization of such technologies. The thermally regenerative ammonia battery (TRAB) is a leading technology in this area because it combines the mature, established technologies of distillation and redox flow batteries to utilize low-grade heat and produce electrical energy. The first TRAB chemistry to use fully-aqueous electrolyte components was recently developed using Cu(I, II) complexation with bromide and ammonia to stabilize each copper oxidation state and create a potential difference between the two electrolytes (referred to as the Cu_aq-TRAB). The Cu_aq-TRAB was shown to have high power density and energy efficiency at room temperature compared to other large-scale low-grade heat technologies. In this work, we constructed a full-cell model of the Cu_aq-TRAB in COMSOL Multiphysics informed by and validated against experimental half- and full-cell data at elevated temperatures (up to 75 °C). Using this model, a sensitivity analysis was completed to determine the contributions of key variables to Cu_aq-TRAB polarization and discharge curves at multiple operating temperatures. It was determined that membrane conductivity was the dominant loss in the Cu_aq-TRAB, with power and energy density being strongly sensitive to ohmic losses when compared to mass transport and kinetic losses. The methodology presented provides a technology evaluation framework that can be applied to many other flow batteries and technologies suitable for utilizing low-grade heat.