Boosted thermopower in aqueous thermocells through additives-induced ionic regulation for low-grade heat harvesting

Yijie Mu; Kedi Li; Kaiyu Mu; Yung-Kang Peng; Shien Ping Feng

doi:10.20517/energymater.2025.34

Boosted thermopower in aqueous thermocells through additives-induced ionic regulation for low-grade heat harvesting

Yijie Mu, Kedi Li, Kaiyu Mu, Yung-Kang Peng, Shien Ping Feng^*

^*Corresponding author for this work

Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review

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Abstract

Aqueous thermocells are promising techniques for the conversion of low-grade waste heat into electricity. However, current improvement strategies are mainly focused on single redox ions and sacrifice the electrical conductivity due to concentrated molecular additives. Herein, we report a chemical additives-regulated thermocell that introduced two ionic additives, guanidine hydrochloride and cysteamine hydrochloride, into 0.4 M ferri/ferrocyanide {[Fe(CN)₆]^3-/4-} electrolyte to simultaneously exert the selective crystallization effect on [Fe(CN)₆]^4- and the chemical regulation effect for [Fe(CN)₆]^3-, synergistically inducing concentration gradients of both redox ions between two electrodes, thereby improving the thermoelectric performance. Our thermocell obtained a high thermopower of 4.34 mV K^-1 with comparable electrical conductivity and a Carnot-relative efficiency of 5.50% with minimal amounts of the two additives, showing adaptability to various cell orientations and thus different practical scenarios. A record-high thermopower of 9.06 mV K^-1 and a Carnot-relative efficiency of 12.65% were achieved by adopting optimized concentrations of two additives under cold-over-hot orientation. A 20-unit module was developed to directly power various electronics, demonstrating its feasibility for low-grade heat harvesting. © The Author(s) 2025

Original language	English
Article number	500119
Journal	Energy Materials
Volume	5
DOIs	https://doi.org/10.20517/energymater.2025.34
Publication status	Published - 12 Jun 2025

Funding

This work was supported by financial support from the General Research Fund (17203520, 17207422) and Collaborative Research Fund (C7082-21G, C6016-22G) from the Research Grants Council of the Hong Kong Special Administrative Region and the Startup Grant of the City University of Hong Kong

Research Keywords

Thermocells
guanidine hydrochloride
cysteamine hydrochloride
chemical regulation

Publisher's Copyright Statement

This full text is made available under CC-BY 4.0. https://creativecommons.org/licenses/by/4.0/

RGC Funding Information

RGC-funded

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10.20517/energymater.2025.34

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1 Finished
3 Active

CRF-ExtU-Lead: High-performance Ionic Thermoelectric Hydrogel for Multifunctional Smart Skin and Body Heat Harvesting
Huang, B. (Main Project Coordinator [External]) & FENG, S. P. (Principal Investigator / Project Coordinator)
1/04/23 → …
Project: Research
GRF: Development of Ionic-thermoelectric Material and Device for Converting Low-grade Heat to Electricity
FENG, S. P. (Principal Investigator / Project Coordinator)
1/09/22 → …
Project: Research
CRF-ExtU-Lead: Active Fluid for Enhanced Thermal Transport and Energy Harvesting
Tang, J. (Main Project Coordinator [External]) & FENG, S. P. (Principal Investigator / Project Coordinator)
1/06/22 → …
Project: Research

Cite this

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title = "Boosted thermopower in aqueous thermocells through additives-induced ionic regulation for low-grade heat harvesting",

abstract = "Aqueous thermocells are promising techniques for the conversion of low-grade waste heat into electricity. However, current improvement strategies are mainly focused on single redox ions and sacrifice the electrical conductivity due to concentrated molecular additives. Herein, we report a chemical additives-regulated thermocell that introduced two ionic additives, guanidine hydrochloride and cysteamine hydrochloride, into 0.4 M ferri/ferrocyanide {[Fe(CN)6]3-/4-} electrolyte to simultaneously exert the selective crystallization effect on [Fe(CN)6]4- and the chemical regulation effect for [Fe(CN)6]3-, synergistically inducing concentration gradients of both redox ions between two electrodes, thereby improving the thermoelectric performance. Our thermocell obtained a high thermopower of 4.34 mV K-1 with comparable electrical conductivity and a Carnot-relative efficiency of 5.50% with minimal amounts of the two additives, showing adaptability to various cell orientations and thus different practical scenarios. A record-high thermopower of 9.06 mV K-1 and a Carnot-relative efficiency of 12.65% were achieved by adopting optimized concentrations of two additives under cold-over-hot orientation. A 20-unit module was developed to directly power various electronics, demonstrating its feasibility for low-grade heat harvesting. {\textcopyright} The Author(s) 2025",

keywords = "Thermocells, guanidine hydrochloride, cysteamine hydrochloride, chemical regulation",

author = "Yijie Mu and Kedi Li and Kaiyu Mu and Yung-Kang Peng and Feng, {Shien Ping}",

year = "2025",

month = jun,

day = "12",

doi = "10.20517/energymater.2025.34",

language = "English",

volume = "5",

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TY - JOUR

T1 - Boosted thermopower in aqueous thermocells through additives-induced ionic regulation for low-grade heat harvesting

AU - Mu, Yijie

AU - Li, Kedi

AU - Mu, Kaiyu

AU - Peng, Yung-Kang

AU - Feng, Shien Ping

PY - 2025/6/12

Y1 - 2025/6/12

N2 - Aqueous thermocells are promising techniques for the conversion of low-grade waste heat into electricity. However, current improvement strategies are mainly focused on single redox ions and sacrifice the electrical conductivity due to concentrated molecular additives. Herein, we report a chemical additives-regulated thermocell that introduced two ionic additives, guanidine hydrochloride and cysteamine hydrochloride, into 0.4 M ferri/ferrocyanide {[Fe(CN)6]3-/4-} electrolyte to simultaneously exert the selective crystallization effect on [Fe(CN)6]4- and the chemical regulation effect for [Fe(CN)6]3-, synergistically inducing concentration gradients of both redox ions between two electrodes, thereby improving the thermoelectric performance. Our thermocell obtained a high thermopower of 4.34 mV K-1 with comparable electrical conductivity and a Carnot-relative efficiency of 5.50% with minimal amounts of the two additives, showing adaptability to various cell orientations and thus different practical scenarios. A record-high thermopower of 9.06 mV K-1 and a Carnot-relative efficiency of 12.65% were achieved by adopting optimized concentrations of two additives under cold-over-hot orientation. A 20-unit module was developed to directly power various electronics, demonstrating its feasibility for low-grade heat harvesting. © The Author(s) 2025

AB - Aqueous thermocells are promising techniques for the conversion of low-grade waste heat into electricity. However, current improvement strategies are mainly focused on single redox ions and sacrifice the electrical conductivity due to concentrated molecular additives. Herein, we report a chemical additives-regulated thermocell that introduced two ionic additives, guanidine hydrochloride and cysteamine hydrochloride, into 0.4 M ferri/ferrocyanide {[Fe(CN)6]3-/4-} electrolyte to simultaneously exert the selective crystallization effect on [Fe(CN)6]4- and the chemical regulation effect for [Fe(CN)6]3-, synergistically inducing concentration gradients of both redox ions between two electrodes, thereby improving the thermoelectric performance. Our thermocell obtained a high thermopower of 4.34 mV K-1 with comparable electrical conductivity and a Carnot-relative efficiency of 5.50% with minimal amounts of the two additives, showing adaptability to various cell orientations and thus different practical scenarios. A record-high thermopower of 9.06 mV K-1 and a Carnot-relative efficiency of 12.65% were achieved by adopting optimized concentrations of two additives under cold-over-hot orientation. A 20-unit module was developed to directly power various electronics, demonstrating its feasibility for low-grade heat harvesting. © The Author(s) 2025

KW - Thermocells

KW - guanidine hydrochloride

KW - cysteamine hydrochloride

KW - chemical regulation

U2 - 10.20517/energymater.2025.34

DO - 10.20517/energymater.2025.34

M3 - RGC 21 - Publication in refereed journal

SN - 2770-5900

VL - 5

JO - Energy Materials

JF - Energy Materials

M1 - 500119

ER -

Boosted thermopower in aqueous thermocells through additives-induced ionic regulation for low-grade heat harvesting

Abstract

Funding

Research Keywords

Publisher's Copyright Statement

RGC Funding Information

Access Output

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Permanent Link

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Projects

CRF-ExtU-Lead: High-performance Ionic Thermoelectric Hydrogel for Multifunctional Smart Skin and Body Heat Harvesting

GRF: Development of Ionic-thermoelectric Material and Device for Converting Low-grade Heat to Electricity

CRF-ExtU-Lead: Active Fluid for Enhanced Thermal Transport and Energy Harvesting

Cite this