# High-Performance Cu-Based Liquid Thermocells Enabled by Thermosensitive Crystallization and Etched Carbon Cloth Electrode

## TL;DR

Researchers improved thermocells using a copper-based system and etched carbon cloth, achieving higher efficiency in converting low-grade heat into electricity.

## Contribution

A novel Cu+/Cu2+ redox couple with thermosensitive crystallization and etched carbon cloth electrodes is introduced for high-performance thermocells.

## Key findings

- Thermopower increased from 1.47 to 2.93 mV K⁻¹ using the Cu+/Cu2+ redox couple.
- Etched carbon cloth electrodes improved current density and electroactive surface area.
- A normalized power density of 3.97 mW m⁻² K⁻² was achieved with the optimized system.

## Abstract

A novel Cu+/Cu2+ redox couple was introduced to enable a thermosensitive crystallization process, significantly enhancing thermopower from 1.47 to 2.93 mV K‒1.A readily fabricated etched carbon cloth electrode offered an enlarged electroactive surface area, demonstrating superior current density through improved kinetics.The optimized Cu+/Cu2+ system, achieved through synergistic enhancements in thermodynamic and kinetic performance, delivered an outstanding normalized power density Pmax (ΔT)‒2 of 3.97 mW m‒2 K‒2.

A novel Cu+/Cu2+ redox couple was introduced to enable a thermosensitive crystallization process, significantly enhancing thermopower from 1.47 to 2.93 mV K‒1.

A readily fabricated etched carbon cloth electrode offered an enlarged electroactive surface area, demonstrating superior current density through improved kinetics.

The optimized Cu+/Cu2+ system, achieved through synergistic enhancements in thermodynamic and kinetic performance, delivered an outstanding normalized power density Pmax (ΔT)‒2 of 3.97 mW m‒2 K‒2.

The online version contains supplementary material available at 10.1007/s40820-025-01977-w.

Thermocells are garnering increasing attention as a promising thermoelectric technology for harvesting low-grade heat. However, their performance is often limited by the scarcity of high-performance redox couples that possess both high thermopower and rapid redox kinetics. This work addresses this challenge by leveraging our recently developed copper (I/II) (Cu+/Cu2+) redox couple. We significantly enhance the performance of Cu-based liquid thermocells by integrating a thermosensitive crystallization process with etched carbon cloth electrodes, achieving synergistic improvements in thermodynamic and kinetic performance. The thermosensitive crystallization process establishes a persistent Cu2+ concentration gradient, boosting the thermopower from 1.47 to 2.93 mV K−1. Moreover, the etched carbon cloth electrodes provide a larger electroactive surface area and demonstrate a higher current density. Consequently, the optimized Cu+/Cu2+ system achieved an exceptional normalized power density Pmax (ΔT)−2 of 3.97 mW m‒2 K−2. A thermocell module comprised of 20 cells directly power various electronic devices at a temperature difference of 40 K. This work successfully exhibits potential of Cu+/Cu2+ redox couple in thermoelectric conversion and introduces a valuable redox couple for high-performance thermocells.

The online version contains supplementary material available at 10.1007/s40820-025-01977-w.