Iron (II/III) perchlorate electrolytes for electrochemically harvesting low-grade thermal energy

Abstract

Remarkable advances have recently been made in the thermocell array with series or parallel interconnection, however, the output power from the thermocell array is mainly limited by the electrolyte performance of an n-type element. In this work, we investigate iron (II/III) perchlorate electrolytes as a new n-type electrolyte and compared with the ferric/ferrous cyanide electrolyte at its introduction with platinum as the electrodes, which has been the benchmark for thermocells. In comparison, the perchlorate electrolyte (Fe 2+ /Fe 3+ ) exhibits a high temperature coefficient of redox potential of +1.76 mV/K, which is complementary to the cyanide electrolyte (Fe(CN) 6 3− /Fe(CN) 6 4− ) with the temperature coefficient of −1.42 mV/K. The power factor and figure of merit for the electrolyte are higher by 28% and 40%, respectively, than those for the cyanide electrolyte. In terms of device performance, the thermocell using the perchlorate electrolyte provides a power density of 687 mW/m 2 that is 45% higher compared to the same device but with the cyanide electrolyte for a small temperature difference of 20 °C. The advent of this high performance n-type electrolyte could open up new ways to achieve substantial advances in p-n thermocells as in p-n thermoelectrics, which has steered the way to the possibility of practical use of thermoelectrics.

Minimal DNA Electron Transfer Catalysts Switched by a Chaotropic Ion

“…Perchlorate and other weakly coordinating anions are ubiquitous in lithium-ion battery electrolytes at molar concentrations, similar to those used in this work. [34][35][36] This underscores the utility of our device in the harsher environments associated with semiconductors. As a period in which hybrid nanoelectronics perform computing tasks will likely be required as the transition from MOSFET-based electronics to next-generation technologies occurs, devices capable of functioning in such environments will be critical.…”

High seebeck coefficient in middle-temperature thermocell with deep eutectic solvent

“…Similar to the S e for solid-state thermoelectrical technologies, the S e of thermocells is defined as the potential difference generated across a cell with a temperature gradient. In liquid-based systems, such a temperature dependence is also related to the redox reaction entropy of a given redox couple, yielding the following relationship: where ΔE is the open-circuit potential, ΔT is the temperature difference, ΔS is the partial molar entropy difference of the redox species (redox reaction entropy), n is the number of electrons in the reaction, and F is the Faraday constant 4 , 5 . S e is one of the key parameters that determines the figure-of-merit of a thermocell, ZT = S e Tσ/κ , where σ is the electrical (or ionic) conductivity of the electrolyte, κ is the thermal conductivity, and T is the absolute temperature.…”

Experimental investigation of a U-tube thermocell under various Fe(CN)63−/4− concentration

“…Therefore, it is critical to identify the proper electrolyte solution with a high Seebeck coefficient. The commonly used redox couples in aqueous solutions are Fe(CN)6 3-/4- [32,33] and Fe 2+/3+ [38,39]. The Seebeck coefficients of these are opposite so that they can be designed as p-n type just like a solid thermoelectric generator [40].…”