A Low-Cost Self-Pumping Membraneless Thermally Regenerative Flow Battery for Small-Scale Waste Heat Recovery

The all-aqueous thermally regenerative battery has the advantages of high open-circuit voltage, high power density, and high Coulombic efficiency, providing a promising way for low-temperature waste heat recovery. In this study, a passive membraneless thermally regenerative flow battery driven by capillary force and gravity is proposed to reduce the cost of construction and operation. The feasibility of power generation and the influence of key parameters (height difference, support electrolyte concentration, etc.) on the battery performance are studied. The results showed that a laminar flow induced by a fiber-based microfluidic reactor could effectively separate the catholytes and anolytes, and the battery could achieve long-term power production and obtain a maximum power density of 15.2 mW cm–2. The performance of the battery first increased and then decreased with the inlet height, and the optimal height was 3 mm. This is mainly due to the fact that the inlet height affects the flow rate of the electrolyte, which affects the mass transfer and laminar flow effect in the porous electrode. Within a certain range, as the concentration of the supporting electrolyte increases, the conductivity of the electrolyte is significantly improved, although the flow rate decreases to a certain extent due to the increase in viscosity, resulting in a further improvement in the battery performance. Through the above optimization, the maximum power density of the battery obtained in this study is 24.9 mW cm–2, and the maximum theoretical thermal efficiency can reach 1.26% (the relative Carnot efficiency can reach 10.6%).