Synergistic dual anion regulation unlocks giant thermopower and power density in hydrogel

Domain: biology
Published: 2026-03-30
Editorial outcome: major_revision

Abstract
Harvesting low-grade heat from the environment and converting it into electricity holds
the potential to power devices independent of cables or batteries. However, their effectiveness is
limited by weak ion selectivity and insufficient concentration gradients. Here, we introduce the
use of a calix[4]pyrrole as effective anion traps to selectively capture Fe(CN) 4– and Cl− anions,
enabling simultaneous modulation of redox ion distribution and suppression of anion mobility
under a temperature gradient. This strategy combines desolvation-induced entropy gain with
thermodiffusion enhancement arising from the mobility asymmetry between cations and anions.
This leads to a synergistic boost in thermopower to an impressive 8.1 mV K−1, and results in a 20-
fold increase in output power compared to the PVA/Fe(CN) 3–/4– system. Demonstrated through a
proof-of-concept wearable device with 36 unipolar elements, our system generated nearly 3 volts
under ambient conditions. This strategy offers a promising route toward thermoelectric materials
with enhanced thermopower for efficient harvesting low-grade thermal energy.

Introduction
Generating electricity from low-grade heat has been of interest for many decades. Widespread
low-grade heat sources (<100°C) are typically derived from the environment, industrial processes,
the human body heat, and solar heating1,2. However, the efficient transformation of this ubiquitous
but underutilized energy form faces challenges due to the limited efficacy of existing
technologies3-5. Thermoelectric (TE) technology, particularly valued for its ability to convert
thermal energy directly into electrical power, encounters limitations with conventional
semiconductor-based devices, which typically demonstrate low thermopower (in microvolts per
kelvin, µV K−1), alongside issues related to fragility, cost, and complex manufacturing that restrict
their application in flexible and wearable technologies6-11. Thermodiffusion cells (TDCs) and
thermogalvanic cells (TGCs) present a promising pathway for converting low-grade heat directly
into electricity, showcasing enhanced thermopower in millivolts per kelvin (mV K−1) and
providing a scalable solution for energy conversion12-14. TDCs operate on the principle of the Soret
effect, where a temperature gradient induces the thermodiffusion of cations and anions, creating a
polarized voltage difference. Although TDCs exhibit considerable thermopower, the intermittent
nature of their electrical output constrains their practical application. In contrast, TGCs facilitate
the generation of consistent electric power across varying temperature gradients via
electrochemical redox reactions at two electrodes15,16. Nonetheless, the relatively lower
thermopower of TGCs compared to that of TDCs, coupled with the potential for electrolyte
leakage, poses challenges that necessitate further advancements17,18.

Thermopower in thermoelectric materials is closely related to the entropy difference (∆S)
between redox ions and their concentration gradient across a thermal gradient, with efforts
predominantly focused on enhancing ∆S to augment thermopower due to the concentration
difference (∆C) typically being negligible19,20. Strategies to increase ∆S involve altering the
solvation shells of the redox couple or the redox couple's structure itself. For instance, Zhou et al.
enhanced the thermopower of an aqueous Fe(CN) 3−/Fe(CN) 4− electrolyte from 1.4 to 4.2 mV K−1
by adding guanidinium and urea, leveraging ionic bonding to reorganize the solvation shells,
thereby increasing ∆S1. Similarly, Kim et al. found that mixing methanol with water as a solvent
rearranged the solvation shells, boosting the thermopower to 2.9 mV K−113. However, such
methods can diminish the electrolyte's ionic conductivity, potentially impacting power
performance.

Increasing ∆C represents an alternative strategy to enhance thermopower. Li et al. generated a
continuous ∆C of Fe(CN) 3− and Fe(CN) 4− ions through an in-situ induced photocatalytic
process20. Yamada et al.'s created a substantial ∆C of I− / I − at the cold electrode with the selective
encapsulation of I − in α-cyclodextrin21. Zhou et al. further amplified both ∆C and ∆S by inducing
the crystallization of Fe(CN) 4− ions with guanidinium cations, achieving a thermopower of 3.73
mV K−119. Despite these advancements, thermopowers resulting from thermogalvanic effects of
redox couples remain modest compared to those derived from ionic thermodiffusion, highlighting
the critical need for integrated strategies that can synergistically couple and amplify both effects
to achieve substantial gains in thermoelectric performance22-28.

Herein, we introduced a approach using calix[4]pyrrole to develop a quasi-solid-state thermocell
that not only overcomes the electrolyte leakage issue but also significantly enhances thermopower
to 8.1 mV K−1 and power density to 5.33 mW m-2 K-2. The integration of phenylboronic acid-
functionalized calix[4]pyrrole (C4P) within the hydrogel matrix substantially enhances both
thermogalvanic and thermodiffusion effects through precise anion modulation. Acting as an anion-
selective molecular trap, C4P captures Fe(CN) 4⁻ and Cl⁻ through stabilizing hydrogen bonds
within its macrocyclic structure29. This selective host-guest complexation induces desolvation of
Fe(CN) 4⁻, thereby increasing redox entropy (ΔS) and establishing a pronounced concentration
gradient (ΔC) across the temperature gradient. Selective suppression of anion mobility, coupled
with preserved high cation mobility, amplifies the asymmetry of ionic mobility. Together, these
synergistic effects maximize the contributions of both thermogalvanic and thermodiffusion
processes, delivering performance in ionic thermoelectric systems.

Results
Cell Preparation and Thermoelectric Properties
Gel-based thermoelectric cells (TECs) were prepared using polyvinyl alcohol (PVA),
employing sequential freeze-thaw cycles and ion exchange techniques based on the traditional gel
thermoelectric cell design (PVA/Fe(CN) 3−/4−)12. When subjected to a modest temperature gradient
of 10 K, these TECs exhibited two distinct voltage response profiles (Fig. 1b). Unlike in liquid-
based systems, ion thermodiffusion within the gel matrix cannot be neglected, as it significantly
impacts the voltage stabilization time due to charge accumulation asymmetry at the hot and cold
interfaces. The pure PVA/Fe(CN) 3−/4− gel exhibited a thermopower comparable to its aqueous
counterpart (~1.4 mV K⁻¹), indicating a negligible contribution from thermodiffusion (S ), and
td
reached voltage equilibrium within about 10 minutesthe, the shortest time among all tested
samples. In comparison, systems relying solely on the thermomigration of K⁺ and Cl⁻ ions required
longer to stabilize. The introduction of C4P alone significantly boosted thermopower but
prolonged the equilibrium time to nearly 20 minutes, attributed to the reduced mobility of
Fe(CN) 4− ions due to host–guest complexation with C4P. Systematic testing of six TECs
prototypes revealed that the combined incorporation of KCl and C4P into the PVA/Fe(CN) 3−/4−
matrix notably enhanced thermopower from 1.4 mV K⁻¹ to 8.1 mV K⁻¹ (Fig. 1c, top). This
enhancement exceeded the additive effects of KCl or C4P alone and is attributed to two key factors:
(1) the selective complexation of Fe(CN) ⁴⁻ ions by C4P generates a redox ion concentration
gradient and suppresses the redox activity of the Fe(CN) ⁴⁻anion, promoting the Fe(CN) 3− + e⁻ →
Fe(CN) 4− reaction and thus increasing thermopower; and (2) C4P restricts the mobility of anions
(Fe(CN) ⁴⁻ and Cl⁻ anions), thereby increasing the migration asymmetry between anions and
cations and effectively amplifying the thermodiffusion effect. In contrast, KCl alone produced only
modest thermopower enhancement, and the combined effect with Fe(CN) 3–/4– falls short of their
simple sum (Fig. 1c, bottom) because elevated ionic strength accelerates both cation and anion
migration, diminishing the thermodiffusion potential. Thus, selectively impeding anion migration
is essential for fully exploiting thermodiffusion in salt-doped gel systems.

A comparative study was conducted between PVA/KCl/Fe(CN) 3−/4− and
PVA/C4P/KCl/Fe(CN) 3−/4− to further explore the effect of C4P's host-guest interactions with
anions on the TECs performance (Supplementary Figs. 4 and 5). The results revealed that while
C4P’s inclusion slightly influence the thermal or ion conductivities of the cells (Supplementary
Figs. 6 and 17), it did lead to a notably increase in thermopower. This enhancement resulted in
higher short-circuit current density and a substantial increase in the maximum power density
(P ). Specifically, at a thermal gradient of 10 Kelvin, the P for the TECs including C4P
max max
increased from 34.7 mW m−2 to 532.6 mW m−2 (Supplementary Fig. 5A). To decouple and
quantify the individual contributions to the overall thermoelectric response, we first employed an
isothermal binary-cell configuration (Supplementary Fig. 7). In the PVA/C4P/Fe(CN) 3−/4−
system, the thermopower of Fe(CN) 3−/4− redox couple was determined to be 4.5 mV K⁻¹
(Supplementary Fig. 8), with thermogalvanic accounting for 55.6% of the total thermopower
(Fig. 1d), closely matching the directly measured thermopower (4.8 mV K⁻¹). As a complementary
approach, we measured the thermopower of C4P/Fe(CN) 3−/4− in a liquid-phase configuration,
replacing the gel with deionized water under identical ionic composition and conditions
(Supplementary Fig. 9). Here, thermodiffusion is negligible, and the measured value reflects a
30.9% thermogalvanic contribution. Together, the two methods consistently reveal the dual origins
of the enhanced thermopower. Notably, thermodiffusion-derived values from both methods (3.6
and 5.6 mV K⁻¹, respectively) exceed the PVA/C4P/KCl control, due to increased K⁺ mobility and
C4P’s selective suppression of Cl⁻ and Fe(CN) 4− transport, which amplifies mobility asymmetry
and boosts overall thermopower. The operational stability was further tested using a homemade
temperature control device over five thermal cycles, confirming the cells' robust thermal-electrical
conversion efficiency (Fig. 1e).

A multidimensional performance-cost analysis was conducted to benchmark our approach
against reported ionic thermoelectric strategies (Fig. 1F). In this comparison, the cost evaluation
excluded common matrix and electrolyte components (PVA, Fe(CN) 3–/4–, and KCl) and
considered only the materials responsible for enhancing thermoelectric performance. To ensure
fair comparison, only literature reports employing carbon-based electrodes were included to
eliminate electrode-dependent effects. The results demonstrate that our dual-anion regulation
approach achieves a significantly higher thermoelectric enhancement than existing strategies,
highlighting both the efficacy and practical potential of our molecular-level design. Additionally,
we performed control tests using Au@Cu and Pt electrodes to assess the influence of electrode
materials on thermoelectric performance (Supplementary Figs. 41–50). Although Au@Cu
electrodes exhibited higher apparent thermopower than carbon paper, subsequent analyses
revealed that this enhancement primarily originated from corrosion-induced parasitic reactions. In
contrast, both carbon and Pt electrodes delivered stable and intrinsic values, underscoring the
importance of electrode selection for the reliable evaluation of ionic thermoelectric materials.

Mechanism of the TEC
A working principle for the synergistic dual anion regulation enhanced thermopower of the
system was proposed, as shown in Fig. 2a. Central to this design is the introduction of selective
host–guest interactions between C4P and Fe(CN) 4⁻/Cl⁻, which act as a molecular gating
mechanism for both ionic mobility and redox thermodynamics. Multiple lines of evidence
confirmed that C4P preferentially binds Fe(CN) 4⁻ over Fe(CN) 3⁻, including NMR
(Supplementary Figs. 12, 13), UV–vis spectroscopy (Fig. 2b, Supplementary Figs. 18 and 19),
XRD (Supplementary Fig. 20) and XPS (Supplementary Figs. 21 and 22). When 1 equiv. of
Fe(CN) 4⁻ was added to the C4P solution, a slight chemical shift change was observed. In contrast,
no significant chemical shift change was noted for C4P/Fe(CN) 3⁻ (Supplementary Fig. 12).
Additionally, UV-visible spectroscopy showed significant red shifts in the absorption peaks of
Fe(CN) 4⁻ after C4P addition, while no obvious adsorption peaks shift of Fe(CN) 3- (Fig. 2b). XPS
analysis showed an obvious binding energy increasement of Fe(CN) 4⁻ after C4P addition, while
no binding energy change observed in Fe(CN) 3⁻ (Supplementary Fig. 21). This selective anion
recognition breaks the symmetry of the redox pair and enables asymmetric molecular-level control
across the thermocells. By selectively immobilizing Fe(CN) 4− and Cl⁻ via host–guest
complexation, C4P effectively reduces the thermal mobility of these anions under a temperature
gradient while allowing K⁺ to migrate freely (Supplementary Figs. 12, 13). Cyclic voltammetry
(CV) measurements confirmed a substantial decrease in overall ionic mobility after C4P addition
(Supplementary Fig. 15). Molecular dynamics (MD) simulations further disentangle the individual
contributions, revealing that C4P strongly suppresses Fe(CN) 4− and Cl⁻ transport, with Cl⁻
mobility reduced by 91.3% (Fig. 2c, Supplementary Fig. 16). This pronounced asymmetry in ionic
diffusivity amplifies the cation–anion mobility difference, thereby enhancing thermopower under
the applied thermal gradient.

Beyond anions transport regulation, entropy modulation introduced by host–guest complexation
plays a pivotal role in boosting the thermogalvanic component of the thermopower (Figs. 2d and
2e, Supplementary Figs. 24 and 25). At the cold end, C4P selectively binds Fe(CN) 4−, disrupting
its hydration shell and releasing multiple structured water molecules into the bulk phase
(Supplementary Figs. 31-34). This desolvation event dramatically increases the local entropy
associated with Fe(CN) 4−, as confirmed by ITC thermograms and MD-derived entropy changes
(Fig. 2f, Supplementary Fig. 23). The resulting entropy gain increases the value of ΔS in the
thermopower relation S = ΔS / nF. The complexation step steepens the entropy difference between
redox states, thus boosting thermopower. Meanwhile, CV measurements revealed diminished
redox currents upon C4P binding, indicating suppressed electrochemical activity due to effective
concentration reduction of the free Fe(CN) 4− species (Supplementary Figs. 14 and 26). More
importantly, this entropy modulation is temperature-responsive (Supplementary Fig. 28). At the
hot end, elevated thermal energy weakens the C4P–Fe(CN) 4− as evidenced by a declining
association constant (K ) with increasing temperature (Supplementary Fig. 27). This thermal
as
weakening promotes complex dissociation, followed by rehydration of Fe(CN) 4−, effectively
reversing the entropy gain achieved through desolvation at the cold end. This reversible entropy-
switching mechanism enables a dynamic response to the applied thermal gradient: entropy is
increased at the cold end through binding and desolvation, and decreased at the hot end through
dissociation and rehydration (Supplementary Movie 1 and 2). Such a cyclical entropy change
across the device mimics an entropy pump, which is highly favorable for enhancing the net
thermogalvanic voltage.

Taken together, the entropy modulation effect, achieved through supramolecular desolvation
and reversible binding, acts in concert with ion mobility regulation to deliver a dual-boosting
strategy. This mechanism establishes C4P not just as a passive additive, but as an active
thermodynamic regulator, capable of elevating ionic thermopower beyond conventional limits.

Working modes of the gel TECs
The discharge behavior of the TEC with dual effects differs significantly from traditional
thermogalvanic and thermodiffusion cells (Fig. 3A). Thermogalvanic cells operate continuously,
generating electrons through oxidation and reduction of ion pairs at the cold and hot electrodes,
respectively. In contrast, thermodiffusion cells function capacitive-like, featuring non-Faradaic
discharge currents. To illustrate these differences, we examined three representative thermoelectric
cells (Fig. 3B). The power output profile of the PVA/Fe(CN) 3-/4- based thermogalvanic cell
stabilizes rapidly upon connection to an external circuit, maintaining relatively constant energy
output despite a gradual and inevitable power reduction over prolonged discharge periods. On the
contrary, the PVA/KCl-based thermodiffusion cell exhibited a rapid and continuous decline in
power output, approaching zero after approximately 5 min (Fig. 3B). This rapid decrease occurred
due to internal charge equilibration, requiring the system voltage to be periodically re-established
under open-circuit conditions with a maintained temperature gradient. This behavior arises
because the external circuit resistance (100 Ω) is substantially lower than the cell’s internal
resistance (~3 kΩ). When the external load resistance was increased to 5 kΩ, the discharge rate
slowed, but the power still steadily diminished, approaching zero within approximately 1 hour
(Supplementary Fig. 29). These results clearly high light that purely thermodiffusion-driven cells,
although capable of generating high initial peak power, are not sustainable for long-term
continuous power delivery. As a result, the dual-effect TEC, incorporating both thermodiffusion
and thermogalvanic effects, did not achieve immediate equilibrium upon connection to an external
circuit (Fig. 3C). Instead, the voltage gradually decreased over extended discharge times.
However, unlike purely diffusion-driven cells, this dual-effect TEC maintained a relatively stable
and sustained power output due to the continuous conversion of ion pairs within the cell. As a
result, it effectively avoided the rapid energy depletion typical of pure thermodiffusion systems.
Comparative analysis of power densities clearly demonstrate that the dual-effect TEC achieves
long-term stability comparable to a conventional thermogalvanic cell, with significant additional
contributions from the thermodiffusion effect. Consequently, the integrated system yields a
remarkable 20-fold increase in energy density during a 1-hour discharge period compared to the
baseline PVA/ Fe(CN) 3-/4- system (Fig. 3B). Extending the discharge duration to five hours
(Supplementary Figs. 51–53) further confirms the superior stability of the dual-effect TEC system,
which delivers an energy density approximately twelve times higher than that of the baseline.
The detailed workflow is illustrated in Fig. 3C, the device operates through three sequential stages:
thermovoltage establishment under a temperature gradient, controlled discharge through an
external load, and short-circuit resetting to equilibrate internal charges.

Adjusting the external circuit load demonstrated that the TEC reaches a maximum energy
density of 912.6 J m⁻² at an optimized load of 100 Ω (Figs. 3d and 3e). Over a continuous
operational period of seven days, the TEC maintained approximately 90% of its initial
thermopower, while its energy density retention was 54.5% (Figs. 3f and Supplementary Fig. 30).
The observed performance decline after prolonged use can be primarily attributed to partial
dehydration processes within the gel structure. Therefore, future studies should prioritize
developing advanced encapsulation techniques and optimized storage conditions to further
enhance the long-term stability and reliability of gel-based thermoelectric devices.

Application Performance of gel TECs
The mechanical performance of TECs is crucial for their practical application32-34. To evaluate
the impact of C4P on mechanical properties, we varied C4P concentrations while keeping KCl and
Fe(CN) 3-/4- levels constant. As anticipated, the incorporation of C4P significantly enhanced the
tensile properties of the gel TEC. This enhancement stems from strong hydrogen bonding between
the abundant –BOH groups in C4P and –OH groups along the PVA backbone, which promotes
increased cross-linking within the gel matrix (Supplementary Fig. 35). As a result, the tensile
strength of the gel increased nearly threefold, reaching 406 kPa, while elongation doubled to 410%.
The improved mechanical strength enables the gel to lift weights up to 5 kg and retain over 80%
of its stress capacity after 100 cycles at 100% tensile strain (Supplementary Fig. 36).

To showcase the practical application of TECs in real-world scenarios, three distinct integrated
thermoelectric devices were developed, particularly focusing on wearable technology where touch
and breathing represent common thermal interactions (Fig. 4a). For respiration monitoring, three
elongated strips of TEC gels, each measuring 1 × 3 × 0.5 cm, were affixed onto the surface of a
mouthpiece, and connected in series (Fig. 4b). This configuration allows for the detection of
breathing; as the wearer exhales, a temperature differential is established across the top and bottom
surfaces of the gel, resulting in an observable increase in voltage. Conversely, during inhalation,
the gel's surface temperature drops swiftly, leading to a rapid decrease in voltage. Additionally,
we integrated three block-shaped thermoelectric gels, each measuring 1 × 1 × 1 cm, in series to
create an interactive human-computer interface. This assembly was designed to interface with a
smartphone via a Bluetooth-enabled sensing module (Fig. 4c and Supplementary Movie 3). By
applying pressure to different numbers of thermo-gel blocks, voltage signals of varying intensities
are generated. This capability allows for nuanced human-computer interactions, where the
intensity and pattern of touch can be translated into specific commands or inputs, showcasing the
versatility and potential of TECs in creating responsive, self-powered wearable technologies (Fig.
4d). Moreover, the thermoelectric gel is well suited for on-body applications, enabling real-time
body-temperature monitoring (Fig. 4e). When attached to an artificial arm, the gel produces a
stable baseline voltage under normal body temperature (~37 °C). Upon simulating a fever
condition (~39 °C), the increased thermal gradient leads to a clear voltage rise, sufficient to trigger
an LED alarm. The reversible and repeatable response confirms reliable signal transduction under
cyclic thermal stimuli, highlighting the potential of this soft thermoelectric system for continuous,
on-body health monitoring applications.

To demonstrate the scalability and applicability of TECs, a 10 cm × 10 cm mold within nine gel
units were arranged and internally connected in series to amplify power output, aiming to energize
the device efficiently (Supplementary Fig. 37). By strategically configuring four such power
generation modules in a stepped series connection, a peak voltage of 2.9 V was realized, facilitated
by a temperature differential of approximately 10 Kelvin (Fig. 4f and Supplementary Fig. 38). This
configuration allows the thermoelectric cell array to directly power both a temperature/humidity
meter and LEDs without any external power source (Fig. 4g). Furthermore, by harvesting waste
heat rather than dissipating it, integration of the TEC with a radiative cooling film contributes to
enhanced building cooling performance (Supplementary Fig. 54). Together, these results
demonstrate the scalability and versatile application potential of the TEC platform.

Methods
General information
One-dimensional nuclear magnetic resonance (NMR) spectra were recorded on a Bruker
AVANCE-400 spectrometer. Chemical shifts are quoted in ppm relative to TMS, which was used
as an internal reference. Ultraviolet-visible (UV-vis) spectra were obtained using a UV-2600
spectrophotometer. Cyclic voltammetry (CV) measurements were performed on an
electrochemical workstation (CHI760) scanning from - 1 V to + 1 V at 100 mV/s. Scanning
electron microscope (SEM) images and energy dispersive X-ray spectra (EDX) were acquired on
a scanning electron microscope (TESCAN MIRA LMS) equipped with an EDX spectrometer.
Microscopic images of the electrode sheets were acquired by a polarizing microscope (Olympus
GX71). X-ray photoelectron spectroscopy (XPS) was performed using a Kratos spectrometer
(Thermo Scientific ESCALAB 250Xi) equipped with a monochromatic Al Kα source. X-ray
diffraction (XRD) (Bruker D8 Advance) was used to assess the crystal structure of the synthesized
samples using Cu Kα 5 (λ=1.5406 Å) radiation. The thermal conductivity (κ) of the samples was
measured by a thermal conductivity meter (Hot Disk TPS 2500S). The electrical conductivity of
the samples was obtained from the slope of the current-voltage curve from a Keithley 2450 source
meter. The thermodynamic data for the complexation process were measured using an isothermal
titration micro calorimeter (Malvern PEAQ ITC).

Synthesis of the C4P
C4P was prepared according to the previous reported method (Supplementary Fig 1)37.
Specifically, 8.2 g (0.05 mol) of 4-acetylphenylboronic acid, 3.5 mL (0.05 mol) of pyrrole and 3.3
mL (0.05 mol) of methanesulfonic acid were dissolved in methanol (500 mL) and reacted under
internal nitrogen atmosphere at room temperature for 5 h. After that, the reaction was neutralized
with NH OH and passed through a short silica gel precolumn. The volatiles were removed using
4
a rotary evaporator and the crude product was recrystallized from acetic acid (30-50 mL) to give
the desired product (5.7 g, 53.6% yield). 1H NMR (400 MHz, dimethyl sulfoxide-d6): δ(ppm) 9.64
(4H), 7.90 (8H), 7.66(8H), 6.94 (8H), 5.88 (8H), 1.8 (12H) (Supplementary Fig 2).

Preparation of PVA-based thermoelectric gel cells (TECs)
The preparation process of TEC is shown in Supplementary Fig 3. Specifically, a certain amount
of KCl and C4P (this step is omitted for PVA/Fe(CN) 3-/4-) were added to 10 mL of deionized
water, followed by dissolution of KCl and dispersion of C4P using 100 W ultrasonication.
Subsequently, 1 g (10 wt%) of PVA powder was added to the solution, and the mixture was stirred
at 90°C until PVA was completely dissolved (magnetic stirrer at 500 rpm). The solution was then
poured into silica gel molds while still warm and frozen at -20°C for 12 h. After removal from the
molds, the gels were left at room temperature (~25°C) for 6 h. This freezing-thawing cycle was
repeated twice more (three cycles in total) to form a PVA gel38-41. Finally, the obtained gels were
placed in aqueous solutions of different concentrations of Fe(CN) 3-/4- (25 °C, 12 h) to obtain TECs
through solvent exchange (Supplementary Figs. 10 and 11).

Fabrication of TECs
To eliminate concerns related to electrode corrosion, hydrophilic carbon paper (CP, model
CPM16) supplied by Shanghai TANJI Corporation was employed as the electrode material. The
hydrophilic surface treatment significantly enhanced wettability without notably affecting
electrical conductivity, as confirmed by contact angle and conductivity measurements
(Supplementary Figs. 27, 39 and 40). The thermoelectric gel (TEC) was sandwiched between two
sheets of carbon paper and then encapsulated using polyimide (PI) tape, forming a CP | TEC | CP
structured device. This configuration was used for all subsequent thermoelectric performance
measurements.

TECs performance characterization
The thermal power of the prepared TECs was measured using a homemade instrument. A flat
heating table served as the heat source at the hot end, while an alumin (Al) plate with internal water
circulation channels was mounted at the cold end to maintain a constant temperature through water
circulation42,43. Unless otherwise specified, the TECs used for the tests had dimensions of 1 × 1 ×
1 cm, with a spacing of 1 cm between the hot and cold ends. The CP electrodes were 1.5 × 1.5 cm
strips, making contact with the gel in a square area of approximately 1 × 1 cm. Temperature was
measured in real time by a type K thermocouple affixed to the Al plate, thereby allowing precise
control of the temperature difference between the two ends of the TECs during the test. For
cooling, the temperature at the hot end was rapidly reduced by activating the water circulation on
the Al plate at the hot end. Voltage-time and current-voltage curves were obtained using Keithley
2450 and UNIT-61E instruments. The power-voltage curves were then calculated from the
corresponding current and voltage values. A near-saturation state was defined when the measured
voltage variation rate was less than 0.1 mV min-1.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Harvesting low-grade heat from the environment and converting it into electricity holds the potential to power devices independent of cables or batteries. However, their effectiveness is limited by weak ion selectivity and insufficient concentration gradients. In this nice manuscript, the authors introduce the use of a novel calix[4]pyrrole as effective anion traps to selectively capture Fe(CN)64– and Cl− anions, enabling simultaneous modulation of redox ion distribution and suppression of anion mobility under a temperature gradient. This strategy combines desolvation-induced entropy gain with thermodiffusion enhancement arising from the mobility asymmetry between cations and anions. This leads to a synergistic boost in thermopower to an impressive 8.1 mV K−1, and results in a 20-fold increase in output power compared to the PVA/Fe(CN)63–/4– system. Demonstrated through a proof-of-concept wearable device with 36 unipolar elements, the reported system generated nearly 3 volts under ambient conditions. This approach is promising for the design of high-thermopower thermoelectric materials and the low-grade heat energy harvesting. This well-written manuscript, with good novelty and scientific value, can be published as it is.", "reviewer_2": "The authors reported a thermoelectric hydrogel that combines thermogalvanic effect and ion diffusion to realize an enhancement in thermoelectric output performance by using a calix[4]pyrrole as a anion trap. However, the similar synergistic enhancement mechanisms can be seen in the previously published articles. This is not new. In addition, the combination of thermogalvanic effect and thermodiffusion is also common in this thermoelectric gel field. Moreover, the improvement in thermopower is not impressive enough. The basic thermopower of PVA-Fe(CN)6.4/3- gels is usually ~2 mV/K, many researchers show the thermopower can be elevated 2-3 folds via similar modulation of ion distribution or diffusion. In a word, I did not find evident novelty in this work.\nSome concerns are given below, which you should well address.\n1. The authors should systematically compare the different modulation mechanisms in ion distribution and diffusion, in order to propose the superior effective routine.\n2. How did the authors calculate the different contributions in thermopower (Figure 1d)? Is the computational process reasonable?\n3. What is the condition in the MD simulations presented in Figure 2? How did the simulated results agree with the experimental data?\n4. How did the PVA chin play a role in this thermoelectric output? Will the introduced C4P and other ions interact with chins?\n5. How did the measurement platform operate in these thermoelectric experiments? The operation mechanism is very important for reliability and accuracy of the results.\n6. The demonstrations are too crude and thin. Could the authors do some novel and remarkable application presentions?\n7. Water vapors and other VOCs exist in the expired gas. Did the author consider these influences in the mask experiment?\n8. One array has 9 thermocells, so four arrays should be 36 thermocell units. By using so many cells in series to power small electronics, what is the meaning?\n9. In the supporting information, I find some minor errors. Besides, the SI file is in tracking revision mode, so there are some highlighted contents.", "reviewer_3": "The manuscript reports a compelling and technically innovative strategy for enhancing ionic thermoelectric performance through synergistic dual-anion regulation in quasi–solid-state thermocells. By integrating phenylboronic acid–functionalized calix[4]pyrrole (C4P) into PVA-based hydrogels, the authors achieve simultaneous modulation of anion transport and redox ion distribution, leading to a record-high thermopower of 8.1 mV K⁻¹ and a power density of 5.33 mW m⁻² K⁻² . The study combines molecular-level host–guest interactions, entropy modulation, and ion mobility asymmetry to deliver a mechanistically rich explanation for the observed performance improvements. Moreover, the authors demonstrate promising wearable and scalable thermoelectric applications, including respiration sensing and powering small devices. Overall, the work is scientifically sound, well contextualized within the existing literature, and represents a significant advancement for the field of low-grade heat harvesting, aligning well with the standards of Nature Communications.\nHowever, several minor issues require clarification (listed below) before the manuscript can be fully recommended for publication.\n• The fonts of the figure size are a bit small which is not ideal for reading\n• The cost analysis should be improved giving more details about the calculations\n• The three stages of figure 3C should be explained in the text\n• All the results showed in the manuscript are basically at 10 K temperature gradient. However, Figure S52 showed power outputs at several temperatures (which is not mentioned in text). Figure S5B shows values until 20 K of temperature gradients. I am wondering if the authors have explored the limits of operation of this device. If so indicate the optimum temperature gradient to maximize the power"}, "author_response": "We made the following corrections in response to the referees’ comments.\nReviewer #1 (Remarks to the Author):\nHarvesting low-grade heat from the environment and converting it into electricity holds\nthe potential to power devices independent of cables or batteries. However, their\neffectiveness is limited by weak ion selectivity and insufficient concentration gradients.\nIn this nice manuscript, the authors introduce the use of a novel calix[4]pyrrole as\neffective anion traps to selectively capture Fe(CN) 4– and Cl− anions, enabling\n6\nsimultaneous modulation of redox ion distribution and suppression of anion mobility\nunder a temperature gradient. This strategy combines desolvation-induced entropy gain\nwith thermodiffusion enhancement arising from the mobility asymmetry between\ncations and anions. This leads to a synergistic boost in thermopower to an impressive\n8.1 mV K−1, and results in a 20-fold increase in output power compared to the\nPVA/Fe(CN) 3–/4– system. Demonstrated through a proof-of-concept wearable device\n6\nwith 36 unipolar elements, the reported system generated nearly 3 volts under ambient\nconditions. This approach is promising for the design of high-thermopower\nthermoelectric materials and the low-grade heat energy harvesting. This well-written\nmanuscript, with good novelty and scientific value, can be published as it is.\nResponse：We sincerely thank the Reviewer #1 for the highly positive assessment and\nfor recognizing the novelty, scientific value, and potential impact of our work. We\ngreatly appreciate the Reviewer’s support and encouragement.\nReviewer #2 (Remarks to the Author):\nThe authors reported a thermoelectric hydrogel that combines thermogalvanic effect\nand ion diffusion to realize an enhancement in thermoelectric output performance by\nusing a calix[4]pyrrole as a anion trap. However, the similar synergistic enhancement\nmechanisms can be seen in the previously published articles. This is not new. In addition,\nthe combination of thermogalvanic effect and thermodiffusion is also common in this\nthermoelectric gel field. Moreover, the improvement in thermopower is not impressive\nenough. The basic thermopower of PVA-Fe(CN) 4/3- gels is usually ~2 mV/K, many\n6\nresearchers show the thermopower can be elevated 2-3 folds via similar modulation of\nion distribution or diffusion. In a word, I did not find evident novelty in this work.\nSome concerns are given below, which you should well address.\nResponse: We thank the Reviewer #2 for the thoughtful critique. We believe that the\nconcerns arise from two key misunderstandings: 1. misinterpretation of the novelty of\nour strategy, and 2. misjudgment of the reported thermopower due to electrode-related\nartifacts in the literature. Below, we clarify these two misunderstandings:\n(a) On the novelty of the strategy\nWhile ion trapping and thermodiffusion enhancement have indeed been reported, our\nwork introduces a fundamentally different and previously unreported strategy:\nsimultaneous and selective regulation anions to realize both thermodiffusion and\nthermogalvanic processes using a single supramolecular receptor. In prior studies, ion-\ntrap strategies have almost exclusively been applied to pure thermodiffusion systems,\nwhere trapping slows one ionic species to increase mobility asymmetry (eScience, 2023,\n3, 100169). In contrast, thermogalvanic systems impose far stricter requirements,\nbecause any additive must selectively distinguish redox-active ions, modulate redox\nentropy, and remain reversible under a thermal gradient. Achieving simultaneous\ncontrol over thermodiffusion and redox entropy using a single molecular motif is highly\nnontrivial and, to our knowledge, has not been previously reported. Importantly, as\nshown in Fig. 1C and Fig. S46, simply combining thermodiffusion and thermogalvanic\neffects does not automatically lead to performance enhancement. Without selective\nanion regulation, the two effects cannot be additively coupled. This point has also been\noverlooked by previous researchers in the field. This overlooked limitation is a key\nconceptual insight of our work. Finally, our study provides a new strategy and research\ndirection, guiding future work on synergistic enhancement and ion-specific recognition\nmaterials. This is undoubtedly innovative.\n(b) On the thermoelectric performance\nWe thank the reviewer for raising this important point regarding thermoelectric\nperformance benchmarking. We would like to clarify that the performance reported in\nthis study is both competitive and rigorously validated under artifact-free conditions.\nSpecifically, the present work achieves a thermopower of approximately 3 mV K⁻¹\noriginating from the thermogalvanic (redox) contribution, and a total thermopower of\n8.1 mV K⁻¹, which places this system among the leading gel-based ionic thermoelectric\nmaterials reported to date. As discussed in detail in the main text and Supporting\nInformation, a critical issue but often overlooked issue in the current literature is the\nuse of non-inert metal electrodes, such as copper, gold@copper or aluminum, in\nFe(CN)₆³⁻/⁴⁻-based thermoelectric systems. These electrodes are prone to corrosion or\nparasitic redox reactions in Fe(CN)₆³⁻/⁴⁻ systems, which can introduce additional\nelectrochemical potentials and thereby artificially inflate the measured thermovoltage,\nleading to an overestimation of thermopower (Figs. S46–S49, Table S2). This concern\nwas also a key point of discussion through multiple rounds of review in our previous\nScience submission. For example, in our initial experiments using gold@copper\nelectrodes, we observed an apparent thermopower as high as 12.4 mV K⁻¹; however,\nthe reviewers immediately raised concerns regarding electrode stability, noting that\neven gold electrodes can undergo corrosion in Fe(CN)₆³⁻/⁴⁻ electrolytes. Indeed, in\nrecent years, many studies in this field have reported large thermopower values while\nemploying similar metal electrodes, which has likely contributed to a widespread\noverestimation of achievable thermopower in ionic thermoelectric systems. Consistent\nwith this view, we observed substantial discrepancies in reported thermopower values\nfor identical thermoelectric systems when different electrodes were used (Adv. Mater.\n2023, 35, 2300696; Adv. Energy Mater. 2024, 14, 2303358), further supporting the\nconclusion that electrode effects play a dominant and often overlooked role. To address\nthis issue rigorously, we systematically re-evaluated several representative\nenhancement strategies under carbon-based inert electrodes (Fig. S46). Under these\nstandardized conditions, the thermopower values reported for many existing strategies\ndecreased markedly, whereas our dual-ion regulation strategy retained a thermopower\nof 8.1 mV K⁻¹, demonstrating its intrinsic effectiveness.\nIt should also be clarified that, in most studies, the benchmark PVA/Fe(CN)₆³⁻/⁴⁻ gel\nthermoelectric system exhibits a thermopower of approximately 1.4 mV K⁻¹,\ncomparable to that of aqueous systems (Angew. Chem. Int. Ed. 2016, 55, 12050; Adv.\nMater. 2023, 35, 2300696). This behavior arises because PVA contains only hydroxyl\ngroups, which interact very weakly with Fe(CN)₆³⁻/⁴⁻ ions. We confirmed this weak\ninteraction by infrared spectroscopy (Fig. R2), which is precisely why PVA was\nselected as the gel matrix, to provide a chemically inert baseline that allows the\nenhancement effect of C4P to be clearly isolated. As summarized in Table S2, without\nintroducing additional regulation mechanisms, the thermopower of gel-based\nthermoelectric cells consistently remains below 2 mV K⁻¹, further highlighting the\nsignificance of the enhancement achieved in this work.\nIn summary, this study introduces a new supramolecular strategy for specific ion\nregulation using a macrocyclic host, and achieves a thermopower of 8.1 mV K⁻¹ under\nrigorously controlled, artifact-free conditions. We believe this represents a meaningful\nadvance in both mechanistic understanding and performance benchmarking in the field\nof ionic thermoelectrics, and we hope that the above clarification resolves the\nreviewer’s concerns.\nBelow are our specific responses to the comments raised by the reviewer #2.\nComment 1. The authors should systematically compare the different modulation\nmechanisms in ion distribution and diffusion, in order to propose the superior effective\nroutine.\nResponse：We thank the reviewer #2 for this valuable suggestion. In fact, a systematic\ncomparison of different ion-regulation strategies has already been carried out and is\npresented in Fig. 1F, Fig. S22, and Tables S1–S2 in the original manuscript. In these\nanalyses, we benchmarked our dual-ion regulation strategy against several\nrepresentative and widely adopted modulation mechanisms reported in the field,\nincluding multi-component solvent regulation (e.g., propylene glycol, PG),\ncrystallization-induced concentration gradients (e.g., guanidinium chloride, GdmCl),\nion solvation regulation (e.g., betaine and agar-based systems). Importantly, to\nminimize variability arising from electrode effects and ensure a fair comparison, we\nonly included literature reports employing inert carbon-based electrodes, or we re-\nmeasured representative systems under identical carbon-electrode conditions. This\npoint is critical, as non-inert metal electrodes have been shown to artificially inflate\nthermopower values in Fe(CN)₆³⁻/⁴⁻ systems.\nFigure R1. Comparison of this study with other reported works (Fig. 1F).\nTable S1. Comprehensive TEC performance comparison\nP /(∆T)2 1/κ\nmax\nS σ\ne\nMatrix (mW/K2·m2 （m·K/W 1/cost Ref.\n(mV/K) (S/m)\n）\n)\nPVA/C4P/KCl This\n8.1 5.33 3.25 2.78 8.33\n/FeCN3-/4- work\nGelatin/Betaine\n2.2 0.48 3.5 N/A 4.27 (48)\n/FeCN3−/4−\nCellulose/GdmC\nl 3.42 2.8 2.52 N/A 0.54 (49)\n/LiCl/FeCN3−/4−\nCellulose/PG\n2.3 0.35 5.27 1.21 6.67 (45)\n/FeCN3−/4−\nPVA/Agar\n1.5 0.4 0.66 N/A 5 (17)\n/FeCN3−/4−\n⁎ We calculate the cost in CNY Yuan. In the cost analysis, only the materials directly\nresponsible for performance enhancement, such as C4P in this work, were considered.\nThe loading of each additive was taken from the optimal composition reported in the\ncorresponding literature and normalized to the amount required to prepare 10 g of gel.\nAll costs were calculated based on the listed prices from the Energy Chemical Platform.\nTable S2. Comparison of the thermopower (S ), P /(ΔT)2 and σ of this work with\ne max\nthose reported for TECs in the literature. Detailed comparison conditions and\ncorresponding references are provided in Table S2 of the Supporting Information.\nRedox S\ne\nP\nmax\n/(∆T)2 σ\nMatrix\nElectrode\ncouple （mV/K） (mW/K2·m2) (S/m)\nPVA/C4P/KCl Carbon FeCN3-/4- 8.1 5.33 3.25\nOv-WO /Polyacrylic\nacid/Sv-ZIS\nPVA/GdmCl Cu FeCN3-/4- 6.5 1.96 6\nH O Carbon FeCN3-/4- 2.9 0.64 15\nH O Carbon FeCN3-/4- 1.43 0.01 N/A\nPVA/Agar Carbon FeCN3-/4- 1.5 0.4 0.66\nH O Carbon FeCN3-/4- 1.42 1.9 N/A\nPolyacrylamide/GdmCl Pt FeCN3-/4- 4.4 1.78 10.2\nPolyacrylic Carbon\nFeCN3-/4- 1.3 0.033 N/A\nacid/cellulose\nPVA/gelation Carbon FeCN3-/4- 2.02 0.1 1\nPVA Cu FeCN3-/4- 1.5 0.22 6.3\nH O Carbon FeCN3-/4- 1.4 0.5 N/A\nH O Carbon FeCN3-/4- 4.2 1.1 24\nGelatin/KCl Au@Cu FeCN3-/4- 17 8.9 N/A\nGelatin/KCl Au@Cu FeCN3-/4- 24.7 9.6 N/A\nPoly\nAl\n(N,N-\nFeCN3-/4- 32.4 25.84 3.7\ndimethylacrylamide)/\n([EMIM][DCA]\nAs summarized in Fig. R1 (adapted from Fig. 1F) and Tables S1–S2 (Supporting\ninformation), our dual-ion regulation strategy consistently delivers higher thermopower\nand normalized power density than these established approaches under comparable and\nartifact-free conditions. These results demonstrate that selectively coupling anion\ntrapping, redox entropy amplification, and controlled thermodiffusion provides a more\neffective and generalizable route for enhancing gel-based ionic thermoelectrics.\nComment 2. How did the authors calculate the different contributions in thermopower\n(Figure 1d)? Is the computational process reasonable?\nResponse：We thank the reviewer for raising this important and technically nuanced\nquestion. Disentangling the thermogalvanic and thermodiffusion contributions in ionic\nthermoelectric systems, particularly in quasi-solid-state gels, remains a nontrivial\nchallenge, and careful methodological justification is therefore essential. In Fig. 1d, we\nestimated the relative contributions using a dual-reference strategy, combining two\nexperimentally accessible benchmarks to avoid overinterpretation from any single\nmethod.\nFirst, we employed the three-electrode isothermal reference method, which has\nbeen widely used in the field to evaluate the thermogalvanic contribution under\ncontrolled electrochemical conditions (Science 2020, 368, 1091–1098). In this\napproach, the redox entropy contribution is extracted by suppressing macroscopic\nthermal gradients while maintaining electrochemical equilibrium, allowing estimation\nof the thermogalvanic Seebeck component associated with the Fe(CN)₆³⁻/⁴⁻ redox\ncouple. This method provides a well-established upper-bound estimate for the\nthermogalvanic contribution.\nHowever, we acknowledge that in gel-based systems, ion confinement, interfacial\npolarization, and finite ion mobility can lead to partial coupling between redox reactions\nand thermodiffusive ion transport. As a result, the three-electrode method may still\noverestimate the pure thermogalvanic contribution when directly applied to gel\nelectrolytes.\nTo address this limitation, we introduced a second, independent reference by\nmeasuring the thermopower of the liquid-phase Fe(CN)₆³⁻/⁴⁻ electrolyte, where\nthermodiffusion effects are negligible and ion transport is dominated by fast diffusion.\nThis liquid-phase value therefore provides a conservative and physically grounded\nestimate of the intrinsic thermogalvanic contribution of the redox couple.\nBy jointly comparing these two reference measurements, the three-electrode\nisothermal value and the liquid-phase thermopower, we constrained the plausible range\nof the thermogalvanic contribution in the gel system. The remaining enhancement\nobserved in the gel-based devices was therefore reasonably attributed to\nthermodiffusion-related effects, including ion mobility asymmetry and concentration\ngradient formation.\nWe emphasize that this analysis does not claim complete quantitative decoupling\nof thermogalvanic and thermodiffusion effects, which remains an open challenge in\nionic thermoelectrics. Instead, our approach provides a physically consistent and\nconservative estimation framework, sufficient to support the qualitative and semi-\nquantitative conclusions drawn in Fig. 1d.\nComment 3. What is the condition in the MD simulations presented in Figure 2? How\ndid the simulated results agree with the experimental data?\nResponse：We thank the reviewer for this important question and apologize for any\nlack of clarity in the original presentation. The simulations shown in Figure 2 were\ndesigned to provide microscopic insight into the host–guest interaction between C4P\nand Fe(CN)₆⁴⁻, rather than to yield direct quantitative predictions of thermoelectric\nparameters. As clarified in the revised manuscript and Supporting Information, the\nsimulations were therefore used to analyze qualitative trends, including binding\npreference, solvation structure perturbation, and ion confinement behavior, that are\ndifficult to access experimentally.\nMethod of simulation calculation Specifically, the calculations were performed using\ndensity functional theory (DFT) as implemented in the Vienna Ab initio Simulation\nPackage (VASP). The exchange–correlation interactions were described using the\ngeneralized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE)\nfunctional, and Grimme’s DFT-D3 correction was applied to account for dispersion\ninteractions, which are essential for accurately describing supramolecular host–guest\nbinding. The projector augmented-wave (PAW) method was used to treat core–valence\ninteractions, with a plane-wave energy cutoff of 500 eV. Structural relaxations were\nperformed until the Hellmann–Feynman forces were smaller than 0.02 eV Å⁻¹, and total\nenergy convergence reached 10⁻⁵ eV. A Γ-centered 10 × 10 × 10 k-point grid was\nemployed.\nWe emphasize that, although the reviewer refers to “MD simulations,” the\ncalculations in Fig. 2 are static DFT-based structural and electronic analyses, rather\nthan time-evolved classical molecular dynamics. Their purpose is therefore not to\nreproduce macroscopic transport coefficients or thermopower values, but rather to\nelucidate relative binding tendencies, electronic redistribution, and confinement effects\ninduced by C4P complexation. Consistent with this scope, the simulated results show\nthat Fe(CN)₆⁴⁻ exhibits stronger binding and more pronounced electronic interaction\nwith C4P than Fe(CN)₆³⁻, in agreement with our ¹H NMR, UV–vis, XPS, and\nelectrochemical measurements. In particular, the simulations support the\nexperimentally observed preferential complexation of Fe(CN)₆⁴⁻, which underpins both\nthe redox entropy amplification and the temperature-dependent concentration gradient\ndiscussed in the main text. Thus, while direct numerical agreement with experimental\nthermopower values is neither expected nor claimed, the simulations provide a\nmechanistically consistent microscopic rationale that corroborates the experimental\ntrends.\nComment 4. How did the PVA chin play a role in this thermoelectric output? Will the\nintroduced C4P and other ions interact with chins?\nResponse：We thank the reviewer for this insightful question and are pleased to clarify\nthe role of the PVA matrix in our thermoelectric system. In the present study, PVA\nprimarily serves as a mechanically robust and chemically inert gel matrix, rather than\nan active contributor to thermoelectric output. Compared with a purely liquid\nelectrolyte, the introduction of the PVA network reduces overall ionic conductivity,\nwhich is a prerequisite for the emergence of a measurable thermodiffusion effect in\nquasi-solid-state systems. Importantly, PVA itself does not participate in or enhance the\nthermogalvanic (redox-driven) contribution. This point is supported by both\nspectroscopic and electrochemical evidence. As shown in Figure R2, UV–vis spectra\nreveal no discernible interaction between PVA and the Fe(CN)₆³⁻/⁴⁻ redox couple,\nindicating that PVA does not alter the electronic structure or coordination environment\nof the redox ions. Consistently, electrochemical measurements demonstrate that the\nthermogalvanic thermopower of the PVA/Fe(CN)₆³⁻/⁴⁻ gel (~1.4 mV K⁻¹) closely\nmatches that of the corresponding aqueous system, confirming that PVA does not affect\nthe intrinsic redox entropy contribution. Moreover, the thermodiffusion contribution in\nthe PVA-only gel remains relatively small, especially when compared with many\npreviously reported gel systems exhibiting thermopower values exceeding 20 mV K⁻¹,\nfurther underscoring the passive role of PVA in ion selectivity and transport modulation.\nRegarding interactions with the introduced functional components, PVA does not show\nstrong direct interactions with Fe(CN)₆³⁻/⁴⁻ or K⁺/Cl⁻ ions.\nFigure R2. UV-Vis spectrum of PVA/FeCN3-/4-.\nHowever, PVA does interact with C4P through a separate and well-defined\nmechanism. As discussed in the manuscript section on mechanical properties, C4P\ncontains boronic acid functionalities that can form dynamic boronic ester bonds with\nthe hydroxyl groups of PVA chains. This interaction serves to reinforce the polymer\nnetwork and improve mechanical robustness, rather than to directly influence ion\ntransport or redox thermodynamics. The formation of these boronic ester linkages is\nevidenced by the characteristic vibrational features observed in the FTIR spectra shown\nin Figure R3. Taken together, these results demonstrate that PVA acts as an electrically\nneutral, mechanically supportive scaffold that enables gel formation and suppresses\nexcessive ion mobility, while the enhanced thermoelectric performance originates\npredominantly from the molecular-level ion regulation introduced by C4P, rather than\nfrom the polymer matrix itself.\nFigure R3. Infrared spectrum of PVA/C4P\nComment 5. How did the measurement platform operate in these thermoelectric\nexperiments? The operation mechanism is very important for reliability and accuracy\nof the results.\nResponse：We thank the reviewer for raising this important point regarding the\nexperimental platform and operational protocol. Ensuring reliable, reproducible, and\nartifact-free thermoelectric measurements was a central consideration in the design of\nour testing system. The measurement platform and testing procedures are described in\ndetail in the Methods section, and the overall operation protocol follows established\nstandards widely adopted in authoritative studies on ionic thermoelectrics and\nthermogalvanic cells (Science 2020, 368, 1091–1098; Science 2023, 381, 291–296).\nImportantly, we implemented a more stringent equilibrium criterion (<0.1 mV/min)\nthan commonly used to further enhance measurement reliability.\nBriefly, the thermoelectric performance of the TECs was evaluated using a custom-\nbuilt steady-state thermal–electrical testing platform. A flat electrical heating stage was\nused to impose a controlled temperature at the hot side, while a water-cooled aluminum\n(Al) plate with internal circulation channels served as the cold side, enabling precise\nand stable temperature control. Unless otherwise stated, TEC samples with dimensions\nof 1 × 1 × 1 cm³ and a fixed hot–cold spacing of 1 cm were used to ensure consistent\nthermal gradients across all measurements. Hydrophilic carbon paper (CP) electrodes\n(1.5 × 1.5 cm²) were employed to contact the gel over an effective area of approximately\n1 × 1 cm², minimizing contact resistance while avoiding metal-related electrochemical\nartifacts. The temperature difference (ΔT) was monitored in real time using a Type-K\nthermocouple affixed directly to the Al plate, allowing accurate feedback control of the\nthermal gradient during both heating and cooling processes. Rapid cooling was\nachieved by activating the water circulation system, ensuring reproducible thermal\ncycling. Electrical signals were recorded using a Keithley 2450 source meter in\nconjunction with a UNIT-61E multimeter, enabling high-resolution acquisition of\nvoltage–time (V–t) and current–voltage (I–V) characteristics. Output power was\ncalculated from the measured current and voltage values under defined external loads.\nTo ensure that all reported thermopower values correspond to a true steady state rather\nthan transient polarization or capacitive effects, we adopted a strict equilibrium\ncriterion, defining a near-saturation state only when the voltage drift rate was less than\n0.1 mV min⁻¹. This threshold is more rigorous than that used in many prior reports and\nensures that the measured thermoelectric output reflects a stable balance between ion\ntransport, redox reactions, and thermal driving forces.\nOverall, this carefully controlled platform and conservative equilibrium definition\nprovide a robust operational framework, ensuring that the reported thermoelectric\nperformance is accurate, reproducible, and free from transient or measurement-induced\nartifacts.\nComment 6. The demonstrations are too crude and thin. Could the authors do some\nnovel and remarkable application presentions?\nResponse：We thank the reviewer for this constructive suggestion regarding the\napplication demonstrations. We agree that compelling application scenarios are\nimportant for illustrating the practical relevance of emerging thermoelectric concepts.\nThe primary objective of this work is to introduce and validate a fundamentally new\nperformance-enhancement strategy for gel-based ionic thermoelectric cells based on\ndual-ion regulation through supramolecular host–guest interactions. Accordingly, the\napplication demonstrations in the original manuscript were intentionally designed as\nproof-of-concept validations, focusing on the two intrinsic and most widely accepted\nfunctions of thermoelectric devices: temperature sensing and self-powered energy\ngeneration. These demonstrations were chosen to directly reflect the core operating\nprinciples of the device and to allow clear comparison with existing literature, where\nreported applications are similarly centered on thermal sensing and low-grade heat\nharvesting.\nNevertheless, we appreciate the reviewer’s perspective that more vivid application\nscenarios could further strengthen the manuscript. In response, we have expanded the\napplication section by adding a new, more scenario-oriented demonstration, namely a\nbody-temperature monitoring and early-warning system, as shown in Figure R4. In this\nexperiment, the thermoelectric gel was conformally attached to a simulated human arm,\nwith a heating plate used to reproduce normal body temperature conditions. The output\nvoltage was continuously monitored over an extended period. At a defined time point,\nthe simulated “body temperature” was deliberately increased to mimic a fever event.\nThis temperature change was successfully detected via signal transmission, which\nsubsequently triggered an early-warning response (LED activation), completing a\nclosed-loop sensing-and-alert function. This demonstration highlights the potential of\nour system for continuous, wearable, and self-powered health monitoring. In addition,\nwe note that a wireless signal transmission demonstration using a Bluetooth module\nwas already included in our application tests, enabling remote signal readout without\nexternal power input. Taken together, these demonstrations go beyond static\nmeasurements and showcase the feasibility of real-time sensing, signal processing, and\nactuation, rather than serving as purely illustrative examples.\nFigure R4. Body temperature detection\nFinally, we would like to emphasize that our group is actively exploring more\nadvanced and unconventional application scenarios for ionic thermoelectrics, including\nmulti-parameter sensing and integrated soft electronic systems. However, these\ndirections often involve additional mechanisms and device architectures, which are\nbeyond the scope of a single mechanistic study and are therefore being developed as\nseparate works. We fully share the reviewer’s view that the application landscape of\nionic thermoelectrics should continue to expand beyond temperature recognition alone,\nand we hope that the present study can serve as a solid materials and mechanism\nfoundation for such future developments.\nWe thank the reviewer again for this valuable suggestion, which has helped us\nfurther strengthen the application relevance of the manuscript.\nComment 7. Water vapors and other VOCs exist in the expired gas. Did the author\nconsider these influences in the mask experiment?\nResponse：We thank the reviewer for raising this important question regarding potential\ninterference from water vapor and volatile organic compounds (VOCs) in the breath-\ndetection experiment. In our experimental configuration, the thermoelectric gel was\nattached to the outer surface of the mask and fully encapsulated, effectively isolating it\nfrom direct contact with exhaled gas. Under these conditions, trace amounts of water\nvapor and VOCs present in expired breath are unlikely to directly interact with the gel\nor electrodes. Importantly, the output signal of the device is fundamentally governed by\nthe temperature gradient induced by breathing, rather than by chemical adsorption or\nhumidity-driven effects.\nTo further substantiate this point, we performed an additional control experiment to\nexplicitly evaluate the influence of ambient humidity. Specifically, the encapsulated\nthermoelectric gel was placed in a sealed container with an initial relative humidity of\n38% RH, while both electrodes were positioned on the same plane to ensure a negligible\ntemperature gradient. The open-circuit voltage was continuously monitored. The\nhumidity inside the container was then increased to 97% RH using a saturated copper\nsulfate solution, and the voltage response was recorded.\nAs shown in Figure R5, the change in ambient humidity had a negligible effect on\nthe output voltage, confirming that external water vapor does not significantly influence\nthe device response when encapsulation is employed. In contrast, during the breath-\ndetection experiment, the observed voltage variation was approximately 20 mV, which\nis orders of magnitude larger than the humidity-induced fluctuation observed in the\ncontrol test. This clearly indicates that the signal variation in the mask experiment\noriginates predominantly from breath-induced temperature changes, rather than from\nwater vapor effects.\nFigure R5. Effect of humidity on gel devices.\nRegarding VOC interference, direct experimental quantification was not performed\ndue to instrumental limitations. However, it is well established that the concentration\nof VOCs in normal human breath is extremely low (ACS Sens. 2023, 8, 1328–1338),\nseveral orders of magnitude lower than that of water vapor. Combined with the mask\nfiltration, device encapsulation, and indirect exposure configuration, the potential\ninfluence of VOCs on the thermoelectric output can be reasonably considered\nnegligible.\nTaken together, both control experiments and literature evidence confirm that the\nmask-based breath-detection signal is dominated by thermal effects, and is not\nmeasurably perturbed by humidity or VOCs under the tested conditions.\nComment 8. One array has 9 thermocells, so four arrays should be 36 thermocell units.\nBy using so many cells in series to power small electronics, what is the meaning?\nResponse ： We thank the reviewer for this thoughtful question regarding the\nsignificance of multi-cell integration. In thermoelectric research, both ionic and\nelectronic, the integration of multiple thermocell units in series is a fundamental and\nunavoidable step toward practical voltage output and device-level power supply. Single\nthermoelectric units typically generate millivolt-level voltages under realistic\ntemperature gradients; therefore, series integration is the standard strategy to reach\nvoltages compatible with electronics. Our demonstration follows this well-established\nprinciple and is intended to illustrate scalability and practical voltage upconversion,\nrather than to suggest that a single unit is sufficient for direct powering. Admittedly,\ndue to laboratory-scale fabrication and manual assembly, the demonstrated 36-unit\narray is relatively large in footprint. However, this does not reflect a fundamental\nlimitation of the material system. On the contrary, miniaturized and high-density\nintegration of thermoelectric units has been widely reported and represents an active\nresearch direction in the field. For example, arrays containing 101 units (Adv. Sci. 2023,\n10, 2300253), 144 units (Nat. Commun. 2015, 6, 8356), and even larger-scale\nintegrations (Nat. Electron. 2022, 5, 333–347) have been successfully demonstrated.\nImportantly, the number of units used in our work is not excessive by field standards.\nRather, it highlights a key advantage of our system: owing to the high intrinsic\nthermopower (8.1 mV K⁻¹) achieved in each unit, a relatively small number of cells (36\nunits) is sufficient to generate an output voltage of approximately 3 V under a modest\ntemperature gradient (~10 K). In contrast, many previously reported systems require\neither substantially larger temperature gradients or significantly more units to reach\ncomparable voltages. Therefore, the 36-unit demonstration serves two purposes: 1. to\nvalidate that the high thermopower achieved at the single-cell level can be linearly\ntranslated to device-scale voltage output, and 2. to illustrate the practical feasibility and\nefficiency of our dual-ion regulation strategy for powering low-power electronics under\nnear-ambient conditions. We believe this demonstration meaningfully supports the\npotential of the proposed material system for future scalable thermoelectric applications.\nComment 9. In the supporting information, I find some minor errors. Besides, the SI\nfile is in tracking revision mode, so there are some highlighted contents.\nResponse：We thank the reviewer for carefully noting these issues and sincerely\napologize for the oversight. We have now thoroughly reviewed the entire Supporting\nInformation, corrected all minor errors, and removed all tracked changes and\nhighlighted content. The revised Supporting Information has been carefully checked to\nensure clarity, consistency, and a clean final presentation.\nReviewer #3 (Remarks to the Author):\nThe manuscript reports a compelling and technically innovative strategy for enhancing\nionic thermoelectric performance through synergistic dual-anion regulation in quasi–\nsolid-state thermocells. By integrating phenylboronic acid–functionalized\ncalix[4]pyrrole (C4P) into PVA-based hydrogels, the authors achieve simultaneous\nmodulation of anion transport and redox ion distribution, leading to a record-high\nthermopower of 8.1 mV K⁻¹ and a power density of 5.33 mW m⁻² K⁻² . The study\ncombines molecular-level host–guest interactions, entropy modulation, and ion\nmobility asymmetry to deliver a mechanistically rich explanation for the observed\nperformance improvements. Moreover, the authors demonstrate promising wearable\nand scalable thermoelectric applications, including respiration sensing and powering\nsmall devices. Overall, the work is scientifically sound, well contextualized within the\nexisting literature, and represents a significant advancement for the field of low-grade\nheat harvesting, aligning well with the standards of Nature Communications.\nHowever, several minor issues require clarification (listed below) before the manuscript\ncan be fully recommended for publication.\nResponse：We sincerely thank the reviewer #3 for the positive evaluation of our work\nand for recognizing its technical innovation, mechanistic depth, and potential impact\non the field of ionic thermoelectrics. We have carefully addressed all the minor issues\nand requests for clarification raised by the reviewer and revised the manuscript\naccordingly. Detailed, point-by-point responses to each comment are provided below.\nComment 1. The fonts of the figure size are a bit small which is not ideal for reading\nResponse：We thank the reviewer for this helpful suggestion and apologize for any\ninconvenience caused by the small font size in the figures. All figures have now been\ncarefully revised, and the font sizes have been uniformly increased to improve clarity\nand readability throughout the manuscript.\nComment 2. The cost analysis should be improved giving more details about the\ncalculations\nResponse：We thank the reviewer for this constructive suggestion and apologize for\nthe lack of clarity in the initial presentation. We have now revised the cost analysis\nsection to provide a more detailed and transparent description of the calculation\nmethodology. Specifically, the cost analysis considers only the materials directly\nresponsible for thermoelectric performance enhancement (e.g., C4P in this work), while\nexcluding the gel matrix and common electrolyte components to enable fair comparison\nacross different systems. For each strategy, the additive loading was taken from the\noptimal concentration reported in the corresponding literature, normalized to the\namount required to prepare 10 g of gel. The material costs were calculated using list\nprices obtained from the Energy Chemical Platform.\nComment 3. The three stages of figure 3C should be explained in the text\nResponse：We thank the reviewer for this helpful suggestion. We have now added a\ndetailed explanation of the three operational stages shown in Fig. 3C to the main text\nto improve clarity. Briefly, as shown in Fig. 3C, the device operates through three\nsequential stages: thermovoltage establishment under a temperature gradient,\ncontrolled discharge through an external load, and short-circuit resetting to equilibrate\ninternal charges.\nComment 4. All the results showed in the manuscript are basically at 10 K temperature\ngradient. However, Figure S52 showed power outputs at several temperatures (which\nis not mentioned in text). Figure S5B shows values until 20 K of temperature gradients.\nI am wondering if the authors have explored the limits of operation of this device. If so\nindicate the optimum temperature gradient to maximize the power\nResponse：We thank the reviewer for this important question regarding the operational\ntemperature range of the device. As shown in Fig. S5, the thermoelectric performance\nof the system does not monotonically increase with temperature gradient; instead, a\ngradual decline in thermopower is observed at higher ΔT. This behavior primarily\noriginates from the suppression of the thermodiffusion contribution at elevated\ntemperature gradients, a phenomenon that has also been reported in pure\nthermodiffusion-based systems (Adv. Mater. 2024, 36, 2402386; Adv. Mater. 2025, 37,\ne10199), where optimal performance is typically achieved under relatively small\ntemperature differences. To explicitly address the temperature–performance\nrelationship and the operational limits of our device, we have added additional data at\ndifferent temperature gradients (Fig. R6). These results show that the thermopower\nremains relatively stable at ~8.1 mV K⁻¹ when the temperature gradient is below 15 K.\nUpon further increasing ΔT, the thermodiffusion effect becomes increasingly\ncompressed, leading to a progressive decay in overall thermopower. Based on these\nresults, the optimal operating temperature gradient for maximizing power output lies in\nthe range of approximately 5–15 K. Importantly, this range closely matches temperature\ndifferences commonly encountered in practical low-grade heat sources, further\nsupporting the applicability of our system for real-world thermal energy harvesting.\nFigure R6. Thermopower variation of the thermoelectric gel under different\ntemperature differences"}, {"round": 2, "reviewer_comments": {"reviewer_1": "This revised manuscript can be published as it is now.", "reviewer_2": "The key point of this manuscript is the strategy the combine desolvation-induced entropy gain with thermodiffusion enhancement arising from the mobility asymmetry. This is reason why the thermopower increases. I think the authors should discuss the operating principle more deeply and enhance the application demonstrations to emphasize the difference and novelty of this work.\n1. In Fig. 4e, how did the gel TEC activate the alarm LED? Did the gel TEC power the LED directly? I do not find any information or details in the manuscript or supporting information?\n2. In Fig. 4c, could the authors show the details on how to conduct the human-computer interaction?\n3. There are 3 operating stages of the gel TEC. In practice, how did the gel cell output power? Could the cell operate continuously? Or, the cell only work for a short time and then re-build voltage?\n4. How did the author compare the power density of different gel systems? The indexed power density is the maximal value at the certain conditions? Is there a general standard?\n5. As we know some gels have intrinsic thermoelectric property, I suggest the authors should give a consideration on this point.\n6. Could the authors carry out some more advanced or important demonstrations to show the application potential?", "reviewer_3": "The authors provided reasonables responses to my concerns. The manuscript can be published"}, "author_response": "We made the following corrections in response to the referees’ comments.\nReviewer #1 (Remarks to the Author):\nThis revised manuscript can be published as it is now.\nResponse：We sincerely thank Reviewer #1 for the positive evaluation and approval of\nour revised manuscript.\nReviewer #2 (Remarks to the Author):\nThe key point of this manuscript is the strategy the combine desolvation-induced\nentropy gain with thermodiffusion enhancement arising from the mobility asymmetry.\nThis is reason why the thermopower increases. I think the authors should discuss the\noperating principle more deeply and enhance the application demonstrations to\nemphasize the difference and novelty of this work.\n1. In Fig. 4e, how did the gel TEC activate the alarm LED? Did the gel TEC power the\nLED directly? I do not find any information or details in the manuscript or supporting\ninformation?\nResponse：We apologize for the confusion caused by the oversimplified description in\nthe original manuscript. In the actual setup, the series-connected TEC array directly\npowers the LED without any external circuitry. The assembled device delivers an output\nvoltage of nearly 3 V, which is sufficient to drive the LED when connected directly\nacross its anode and cathode.\nTo clarify this point and avoid misunderstanding, we have revised the corresponding\ntext in the manuscript as follows: “This configuration allows the thermoelectric cell\narray to directly power both a temperature/humidity meter and LEDs without any\nexternal power source (Fig. 4g).”\n2. In Fig. 4c, could the authors show the details on how to conduct the human-computer\ninteraction?\nResponse：We thank the reviewer for this helpful suggestion. To clarify the human–\ncomputer interaction process, we have added a detailed description of the interactive\ndemonstration in the Supporting Information. Briefly, three TEC units connected in\nseries serve as a self-powered voltage source and are directly interfaced with an Arduino\ndevelopment board. The generated voltage under a temperature gradient is continuously\nmonitored by custom firmware, which classifies the signal into three discrete levels\ncorresponding to predefined text commands. These encoded signals are then wirelessly\ntransmitted to a smartphone via an HC-05 Bluetooth module.\nThe following description has been added to the Supporting Information:\nInteractive Signal Encoding and Wireless Transmission. To demonstrate the practical\napplicability of the TEC array as a self-powered signal source, an interactive\ncommunication system was constructed. Three TEC units were connected in series and\ninterfaced with an Arduino Uno board, where the open-circuit voltage generated under\na temperature gradient served as the input signal. Custom firmware continuously\nmonitored the voltage and classified it into three discrete levels, each corresponding to\na predefined text message, which was then wirelessly transmitted to a smartphone via\nan HC-05 Bluetooth module.\n3. There are 3 operating stages of the gel TEC. In practice, how did the gel cell output\npower? Could the cell operate continuously? Or, the cell only work for a short time and\nthen re-build voltage?\nResponse：We thank the reviewer for this insightful question regarding the practical\noperating mode of the gel TEC.\nIn practice, the TEC operates through three sequential stages to achieve stable and\nefficient power output. First, a temperature gradient is applied under open-circuit\nconditions to allow the device to “charge,” during which thermodiffusion and\nthermogalvanic processes establish a steady-state voltage. Once this equilibrium is\nreached, an external load is connected and the device begins to discharge, delivering\nelectrical power. During discharge, the initial output gradually decreases as the energy\nstored through thermal diffusion is released, after which the power stabilizes at a\nrelatively constant plateau dominated by the continuous thermogalvanic redox\nreactions. Finally, after discharge, briefly short-circuiting the electrodes restores\ninternal charge balance and enables the next operating cycle.\nTo evaluate the sustainability of the output, we performed extended discharge tests\n(Figs. S51–S53). As shown in Fig. S51, the TEC continuously discharged through a 100\nΩ load for 5 h while maintaining stable power generation, delivering a total energy\ndensity approximately 12 times higher than that of the baseline thermogalvanic system.\nTo the best of our knowledge, this represents one of the longest continuous-output\ndemonstrations reported for gel-based ionic thermoelectrics.\nFig.R1. (Fig. S51) Comparison of energy output variation between two types of gel-\nbased thermogalvanic cells during discharge across a 100 Ω load under a 10 K\ntemperature difference for 5 h. The PVA/C4P/KCl/Fe(CN)₆³⁻/⁴⁻ thermocell maintains\nmarkedly higher output power than the PVA/Fe(CN)₆³⁻/⁴⁻ system throughout the\ndischarge period. Over 5 h, its total energy output is approximately twelve times greater,\ndemonstrating the enhanced stability and sustained energy conversion efficiency\nachieved through dual-anion regulation.\nMoreover, even the purely thermogalvanic control device exhibits gradual power\ndecay during prolonged discharge (Fig. S52), indicating that completely continuous and\nperfectly stable output remains a general challenge for ionic thermoelectric systems.\nThese results highlight both the practical working mode of our device and the improved\nstability enabled by the dual-anion regulation strategy.\nFig. R2. (Fig. S52) Enlarged view of the PVA/Fe(CN)₆³⁻/⁴⁻ cell from Fig. S48. Notably,\neven the purely thermogalvanic system exhibits inevitable power decay during\nprolonged discharge.\n4. How did the author compare the power density of different gel systems? The indexed\npower density is the maximal value at the certain conditions? Is there a general standard?\nResponse： We thank the reviewer for this insightful question regarding the comparison\nmethodology for power density across different gel systems. The maximum power\ndensity (P ) was calculated using the standard formula 𝑃 =\n𝑉𝑜𝑐𝐼𝑠𝑐\n, where V is\nmax 𝑚𝑎𝑥 oc\n4\nthe open-circuit voltage and I is the short-circuit current density. This approach is\nsc\nwidely adopted in thermoelectric studies to estimate the theoretical peak (instantaneous)\noutput under matched-load conditions and serves as a common benchmark for reporting\ndevice performance.\nFor purely thermogalvanic systems, where the output remains relatively stable over\ntime, using P for comparison is generally reasonable, although it may slightly\nmax\noverestimate the practically deliverable power. However, for systems that involve\nsignificant thermodiffusion or capacitive-like effects, the initial current can be\ntransiently large due to rapid ion redistribution. This leads to a high apparent P that\nmax\ndecays quickly and cannot be sustained. In such cases, relying solely on peak power\nmay be misleading and does not accurately reflect real usable energy output.\nTherefore, in addition to P , we evaluated the time-dependent power profile P(t) and\nmax\ncalculated the total delivered energy by integrating power over time:\n𝑡\n𝐸 = ∫ 𝑃(𝑡)𝑑𝑡\nmeaningful metric, as it captures both output magnitude and stability. This integration-\nbased evaluation is commonly used in electrochemical and energy storage research to\nquantify usable energy delivery. Accordingly, our manuscript reports both peak power\ndensity and energy density to ensure fair and comprehensive comparison among\ndifferent ionic thermoelectric systems.\n5. As we know some gels have intrinsic thermoelectric property, I suggest the authors\nshould give a consideration on this point.\nResponse： We sincerely thank the reviewer for this valuable suggestion. We fully\nagree that the intrinsic thermoelectric properties of polymer matrices should be\ncarefully considered. In this work, PVA was deliberately selected as the gel matrix to\nminimize any background thermoelectric contribution. Owing to its simple chemical\nstructure, which contains only neutral hydroxyl groups and no charged or redox-active\nfunctionalities, pure PVA hydrogels exhibit negligible thermoelectric output in our\nmeasurements, with thermopower values close to zero. This ensures that the observed\nvoltage signals originate predominantly from the Fe(CN)₆³⁻/⁴⁻ redox couple and the\nC4P-mediated ion regulation, rather than from the polymer itself.\nAdditionally, prior to each measurement, the device was short-circuited under zero\ntemperature gradient for a sufficient period to eliminate any residual internal potential\nand fully equilibrate the system. This procedure further ensures the accuracy and\nreliability of the recorded thermoelectric performance.\n6. Could the authors carry out some more advanced or important demonstrations to\nshow the application potential?\nResponse： We thank the reviewer for this insightful suggestion. As noted in our\nresponse in Round 1, practical demonstrations of ionic thermoelectric cells remain\nlimited in the current literature and most studies focus primarily on the fundamental\nthermal-voltage response under a temperature gradient.\nIn contrast, our work emphasizes thermal energy utilization, enabled by the relatively\nhigh-power output of our thermocells. Building on complementary expertise within our\ngroup, we have therefore designed an integrated system that combines ionic\nthermoelectric conversion with radiative cooling for enhanced building cooling\nperformance. In this configuration, the thermocell actively dissipates additional thermal\nenergy, while the radiative cooler provides passive heat rejection, resulting in\nsynergistic cooling enhancement. To the best of our knowledge, such a strategy—\nleveraging thermoelectric devices not for power generation but as active thermal loads\nfor cooling—has rarely been explored, particularly in the context of passive daytime\nradiative cooling. While this section presents only a proof-of-concept demonstration of\nthe core functionality, we are actively expanding this direction into a comprehensive\nstudy. We hope this initial effort offers a fresh application perspective for the\ncommunity.\nAs illustrated in Fig. R3, we constructed a scaled-down building model using an acrylic\nchamber illuminated by a solar simulator at 1 sun (1000 W/m2). The internal air\ntemperature was monitored via a thermocouple. Four configurations were compared: (i)\nbare chamber (control), (ii) chamber topped with a radiative cooling (RC) film\ncomposed of cellulose nanofiber (CNF) and TiO powder, (iii) RC film with pure PVA\n2\nhydrogel, and (iv) RC film integrated with the TEC. Notably, the chamber covered with\nRC/TEC exhibited the lowest interior temperature. Compared to the RC/PVA hydrogel\nreference, the TEC integration further reduced the internal temperature by 2.6 °C,\ndemonstrating that the thermoelectric conversion actively enhances cooling. Relative\nto the bare chamber, the total cooling effect reached 18.1 °C, highlighting the\nsynergistic performance of the hybrid system.\nRelevant descriptions and experimental details have been added to both the main text\nand the SI.\nFig. R3 (Fig. S54). TEC for building thermal management. (A) Schematic illustration\nof the scaled model integrating the TEC with a radiative cooling film for active–passive\nhybrid heat dissipation. (B) Comparison of interior temperature evolution under\ndifferent configurations, demonstrating enhanced cooling performance of the RC/TEC\nsystem.\nReviewer #3 (Remarks to the Author):\nThe authors provided reasonables responses to my concerns. The manuscript can be\npublished\nResponse： We sincerely thank you for your positive evaluation and acceptance of our\nmanuscript. We greatly appreciate your recognition of our work."}, {"round": 3, "reviewer_comments": {"reviewer_2": "This paper can be considered of acceptance."}, "author_response": ""}]

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