Simultaneous power generation and cooling using semiconductor-sensitized thermal cells

This manuscript reports a semiconductor-sensitized thermal cell (STC) that converts ambient heat into electrical power while simultaneously reducing its own temperature under isothermal conditions. Using a printable semiconductor–electrolyte architecture, we fabricate $4,\mathrm{cm} \times 4,\mathrm{cm}$ devices that generate up to approximately $0.2,\mathrm{mW}$ at temperatures of $40$–$55,^\circ\mathrm{C}$. During continuous discharge, the STC exhibits a transient temperature decrease followed by thermal equilibration with the environment. In contrast, periodic on–off discharge produces sustained cooling of approximately $1,^\circ\mathrm{C}$ relative to a non-discharging reference. Notably, parallel integration of four STCs yields a nonlinear enhancement of cooling (approximately $5,^\circ\mathrm{C}$) without a corresponding increase in electrical output. The observed behavior can be understood within a macroscopic energy-balance framework, in which time modulation of electrochemical heat consumption prevents the establishment of thermal steady state. These results demonstrate sustained isothermal cooling induced by heat-to-electricity conversion at practical device scales, and highlight semiconductor-sensitized thermal cells as a platform for coupled energy harvesting and thermal management.

💡 Research Summary

This paper presents a groundbreaking study on Semiconductor-Sensitized Thermal Cells (STCs), a novel class of devices capable of simultaneously converting ambient heat into electrical power and lowering their own temperature under isothermal conditions. The researchers fabricated large-area (4 cm x 4 cm), printable devices using semiconductor pastes and a PEG600-based Cu(I)/Cu(II) electrolyte. A single STC generated up to approximately 0.2 mW of electrical power at temperatures between 40–55°C.

The core investigation focused on the thermal behavior of the STCs during operation. Under continuous discharge through an external load, a single device exhibited a transient cooling effect, with its temperature dropping by about 0.8°C relative to a non-discharging reference cell before eventually thermally equilibrating with the environment. This was explained by a macroscopic energy-balance model where the heat consumed by the electrochemical discharge process (q_out) initially exceeds the environmental heat influx (q_in).

The key breakthrough was achieved through periodic on-off discharge cycling. By modulating the electrical load in cycles (e.g., 120 seconds on, 120 seconds off), the researchers demonstrated sustained cooling of approximately 1°C. This persistent effect occurs because the periodic operation prevents the system from reaching a thermal steady state; the time-averaged heat consumption <q_out> remains greater than the time-averaged heat influx <q_in>.

A striking and non-intuitive finding emerged from integrating four STCs in parallel. While the total electrical power output remained nearly unchanged from that of a single cell (due to the fixed external load), the cooling magnitude was dramatically enhanced to about 5°C. This nonlinear scaling suggests that the cooling performance is not directly tied to the electrical output but is instead governed by the total extent of ionic reconfiguration and associated entropy changes at the electrode-electrolyte interface during redox reactions. This implies the involvement of mechanisms like electrochemical entropy changes or ionic Peltier effects.

The study positions STCs as a dual-function platform for coupled energy harvesting and thermal management, contrasting with previous micro-scale isothermal generators that offered only negligible thermal signatures. The work successfully demonstrates that heat-to-electricity conversion can be engineered to produce measurable and sustainable cooling at practical device scales. The authors envision future applications in passive cooling for high-power electronics, distributed thermal energy harvesting in buildings, and reduction of urban cooling loads, marking a significant step towards thermal-energy-positive systems.