Decoupling heat and ion transport with supercapacitor-mediation in cold-source-free thermogalvanic cells

Decoupling heat and ion transport with supercapacitor-mediation in cold-source-free thermogalvanic cells | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Decoupling heat and ion transport with supercapacitor-mediation in cold-source-free thermogalvanic cells Jun zhang, Jili Zheng, xiaotian li, xiqiao Cheng, shiwei zhang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7743745/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Thermogalvanic cells represent a pivotal technology for the direct conversion of low-grade thermal energy into electricity. However, constrained by the strong coupling between heat and ion transport within the redox mediators, conventional approaches rely on introducing a cold source to disrupt this coupling and enhance cell output, making efficient and sustainable operation dependent on an external cold supply. In the absence of forced cooling, the temperature difference (ΔT) and the output current of the cell exhibit a mutual limitation, resulting in a low relative Carnot efficiency (η r < 3%) or low output power density (P max < 0.5 W m − 2 ). Here, we report a cold-source-free thermogalvanic cell that decouples heat and ion transport in the redox medium. This design, for the first time, utilizes supercapacitor-mediated redox reactions within the thermogalvanic cell. It achieves thermal isolation through the spatial separation of the hot and cold electrodes and establishes a high-speed ionic transport highway via the supercapacitor unit. This device, operating without forced cooling with a heat source at 70°C, realizes a temperature difference ΔT > 40 K between the two electrodes and enables unrestricted ion transport. The cell achieves a high output power density of 3.52 W m − 2 and a maximum relative Carnot efficiency of 7.3%, which are the highest reported value without an external cold source and the η r value exceeds the predicted commercialization threshold of 5%. This novel thermogalvanic cell design promises the ultimate utilization and commercialization of low-grade thermal energy. Physical sciences/Energy science and technology/Thermoelectric devices and materials Physical sciences/Energy science and technology/Energy harvesting/Devices for energy harvesting Thermogalvanic cells Decoupled heat and ion transport Supercapacitor-mediated Cold-source-free Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Low-grade thermal energy (< 100 ℃) is widely distributed in industrial waste heat, solar radiation heat, and geothermal sources. Its global dissipation reaches ~ 85 PWh/year, accounting for over 60% of waste heat 1 , 2 . Due to the irreversible thermodynamics of heat and the distributed nature of thermal sources, effectively converting scattered low-grade heat into electricity remains a critical challenge 3 – 5 . Currently, advanced thermoelectric conversion systems such as electronic thermoelectric systems (based on the Seebeck effect) and ionic thermoelectric systems (relying on the thermodiffusion effect and the thermogalvanic effect) can directly convert low-grade heat into electricity. These systems offer advantages including no moving parts, silent operation, and zero greenhouse gas emissions, thereby providing a promising pathway for waste heat utilization 6 – 8 . Conventional electronic thermoelectric systems (e.g., based on Bi 2 Te 3 ) exhibit performance dependent on the material’ s thermoelectric figure of merit, with a Seebeck coefficient (thermopower, Se) of only 100–200 µV K − 1 , coupled with high costs, which pose barriers to market application 9 – 12 . In contrast, ionic thermoelectric systems, such as thermodiffusion cells and thermogalvanic cells (TGCs), have attracted significant attention due to their high thermopower (Se on the order of mV K − 1 ), low cost, and scalability 13 – 15 . Although thermodiffusion cells can achieve a high thermopower of up to 31 mV K − 1 , their intermittent power output characteristics limit industrial-scale applications 16 . In comparison, thermogalvanic cells, which utilize continuous cyclic reactions of redox couples to generate stable and continuous electrical output under temperature differences, offer a more feasible pathway for harnessing near-ambient thermal energy. TGCs primarily utilize liquid-phase redox couples, such as the typical Fe(CN) 6 4− /Fe(CN) 6 3− system, as the reaction medium. Their core performance indicator, the relative Carnot efficiency (η r ), is closely related to the thermal conductivity and ionic conductivity of the liquid redox medium, as expressed by η r ∝ (Se) 2 σ/k, where k represents the effective thermal conductivity and σ denotes the effective ionic conductivity 16 – 18 . A relative Carnot efficiency of approximately 5% is considered the potential threshold for the commercial viability of TGCs in harvesting low-grade heat 1 , 19 . To achieve a high relative Carnot efficiency, it is imperative to reduce the thermal conductivity of the liquid medium while maintaining high ionic conductivity. However, heat and ion transport in liquid redox media exhibit strong coupling, meaning the thermal and ionic conductivities typically increase or decrease simultaneously 19 – 21 , thereby limiting the enhancement of cell efficiency. Consequently, decoupling heat and ion transport within the liquid redox medium is essential. Currently, decoupling heat and ion transport mainly involves two strategies. One strategy introduces an external cold source to disrupt the coupling between heat and ion transport. This is achieved by forcibly increasing the temperature difference (ΔT) between the hot and cold electrodes of the TGC, resulting in a lower effective thermal conductivity of the medium and thus improving the cell's relative Carnot efficiency. However, the requirement for an external cold source constrains its practical applications 20 – 22 . The other strategy involves introducing porous thermal barriers, such as polymer separators, gels, or thermosensitive crystalline additives, between the hot and cold electrodes of the TGC. These materials weaken the coupling between heat and ion transport in the liquid medium and reduce the effective thermal conductivity 1 , 23 , 24 . Nevertheless, although the incorporation of porous insulating materials reduces the effective thermal conductivity of the liquid medium to some extent, it simultaneously increases the ion diffusion resistance, leading to reduced ionic conductivity and ultimately limiting thermal energy conversion. These limitations underscore the urgent need for innovative designs that minimize the effective thermal conductivity while maximizing the effective ionic conductivity of the liquid medium without introducing forced cooling. Spatial separation of the hot and cold electrodes in TGCs presents a promising novel approach to significantly enhance thermal energy utilization by reducing the effective thermal conductivity of the liquid medium to nearly zero. However, it inherently obstructs the transport of redox ions between the electrodes. In contrast, supercapacitor-mediated ion transport offers rapid ion adsorption/desorption kinetics and enables directional charge transfer 25 , 26 . Integrating the spatial separation strategy of TGCs with supercapacitor-mediated ion transport holds great potential for developing a thermoelectric conversion system characterized by extremely low thermal conductivity and high ionic conductivity, thereby achieving decoupled heat and ion transport within the liquid medium. Building upon this concept, we report a TGC that utilizes supercapacitors to decouple heat and ion transport within the redox medium. By employing capacitive storage to mediate the redox reactions of the thermogalvanic cell, the traditional process of ion transport, which is accompanied by heat transfer between the conventional hot and cold electrodes, is transformed into capacitive adsorption and electron transfer occurring between the hot and cold supercapacitors. This innovation decouples the synchronous transport of heat and ions inherent in conventional TGCs (Fig. 1 A), ensuring highly efficient ion transfer between the hot and cold electrodes while simultaneously achieving thermal isolation between them, thereby enhancing thermal energy utilization efficiency. In this device (Fig. 1 B), the hot electrode facilitates the oxidation of Fe(CN) 6 4− to Fe(CN) 6 3− . The generated electrons are transferred to the cold electrode. Simultaneously, positively charged K⁺ ions undergo transmembrane transport and are stored on the surface of the hot supercapacitor, while the positive charge generated by K⁺ adsorption is transferred to the cold supercapacitor 27 . Conversely, at the cold electrode, Fe(CN) 6 3− accepts the electrons transferred from the hot side, reducing to Fe(CN) 6 4− . During this process, positively charged K⁺ ions from the cold supercapacitor side transfer across the membrane to the cold electrode side. The remaining negatively charged Cl⁻ ions are stored on the surface of the cold supercapacitor, which simultaneously accepts the positive charge transferred from the hot supercapacitor to maintain charge balance 24 , 28 , 29 . Leveraging this decoupled heat and ion transport, the supercapacitor-mediated TGC achieves a maximum relative Carnot efficiency of 7.3% without the need for forced cooling. Results Cell Construction and Supercapacitor-Mediation We constructed a supercapacitor-mediated thermogalvanic cell (SC-TGC) system that decouples heat and ion transport (Fig. 1 B; as described in Experimental Section for details). Both terminal cells were filled with a K 4 [Fe(CN) 6 ]/K 3 [Fe(CN) 6 ] mixed electrolyte on the electrode side to serve as the redox ions for the thermogalvanic reaction. A KCl electrolyte was added on the capacitor side to balance the ion diffusion required by the redox reactions on the electrode side, while avoiding the introduction of new cationic species. To validate the concept of the capacitor-mediated thermogalvanic cell, the redox reaction of the K 4 [Fe(CN) 6 ]/K 3 [Fe(CN) 6 ] pair on carbon cloth electrodes and the capacitive characteristics of the activated carbon electrodes were investigated separately by cyclic voltammetry (Fig. 2 A and Fig. S1 ). The distinctive redox peaks in the cyclic voltammograms correspond to the oxidation of Fe(CN) 6 4− to Fe(CN) 6 3− at the hot electrode and the reduction of Fe(CN) 6 3− to Fe(CN) 6 4− at the cold electrode 29 . The nearly rectangular cyclic voltammogram of the capacitor in the KCl electrolyte indicates its electrical energy storage characteristics 26 . To further demonstrate the system design, the concentration changes of Fe(CN) 6 4− and Fe(CN) 6 3− in the electrode-side electrolyte, and of K + and Cl − in the capacitor-side electrolyte, were measured during the heating process (Fig. 2 B and C). When the hot cell was heated under open-circuit conditions, the concentrations of Fe(CN) 6 4− and Fe(CN) 6 3− on the electrode side remained largely unchanged. During the subsequent 180-minute discharge phase, the concentration of Fe(CN) 6 4− decreased from 0.3 to approximately 0.1 mol L − 1 (volume V = 2 mL), while the concentration of Fe(CN) 6 3− increased from 0.1 to approximately 0.3 mol L − 1 . The cold cell exhibited opposite concentration changes for Fe(CN) 6 4− and Fe(CN) 6 3− on its electrode side (Fig. S2). In the cold-end capacitor-side electrolyte, the K + concentration decreased by 0.4 mmol after the discharge phase, resulting from the diffusion of K + to the electrode side driven by the cold-end electrode reaction. Simultaneously, the Cl⁻ concentration also decreased by 0.4 mmol, which was attributed to the adsorption of Cl − onto the capacitor. In the hot-end capacitor-side electrolyte, the concentrations of K + and Cl − remained essentially constant, primarily because the amount of K + adsorbed on the capacitor was compensated by the K + diffusing from the electrode side to the capacitor side. Further measurement of the ions adsorbed on the post-reaction capacitors revealed that the adsorption quantities of both Cl − and K + on the cold and hot capacitors were approximately 0.6 mmol each (Fig. 2 D and E). This value aligns with the amount of K + diffusion caused by the Fe(CN) 6 4− /Fe(CN) 6 3− conversion on the electrode side. These results confirm that the redox reactions at the cold/hot electrodes induce the directional diffusion of cations, leading to the equivalent adsorption of anions and cations on the capacitors, thereby demonstrating the mediation of the traditional thermogalvanic redox reactions by the supercapacitors. Furthermore, the cyclic voltammetry (CV) curves of Fe(CN) 6 4− and Fe(CN) 6 3− at different scan rates (Fig. 2 F and Fig. S3) showed that the plot of the redox peak currents against ω 1/2 is highly symmetric about the x-axis. This indicates that the redox reaction possesses good reversibility 30 , which enables the potential for reverse operation of the system by switching the hot and cold ends. Supercapacitor-Assisted Electrodes We evaluated the capacitive and ion adsorption characteristics of the supercapacitor-assisted electrodes. Fig. S4a and Fig. S5 show scanning electron microscopy (SEM) images of the activated carbon powder, revealing a porous structure rich in micropores 31 . Brunauer-Emmett-Teller (BET) analysis of the porosity of the carbon powder (Fig. S4b) indicated a pore size distribution predominantly within the range of 0.4 to 0.8 nm 32 . The charge storage capacity of the capacitive electrodes was assessed via galvanostatic charge-discharge (GCD) tests (Fig. S4c), conducted within a potential window of 0.15 to 0.75 V vs. Ag/AgCl. These tests were performed within the aqueous stability window to simulate the operational conditions of the supercapacitor. The specific capacitance calculated from the GCD curves (Fig. S4d) was greater than 120 F g − 1 at current densities significantly lower than 0.5 A g − 1 , which is relevant to the operating current of the SC-TGC. GCD tests performed at different temperatures (Fig. S6) showed that rising temperature significantly increased the specific capacitance, which is beneficial for electron storage 33 . Cyclic voltammetry (CV) tests were conducted on the carbon powder before and after ion adsorption (Fig. 2 G). The enlarged CV curve after adsorption suggests the occurrence of ion adsorption within the porous carbon material. Energy-dispersive X-ray spectroscopy (EDS) analysis of the electrodes before and after adsorption (Fig. S8 and S10) indicated the presence of adsorbed K + on the hot-end carbon surface and adsorbed Cl − on the cold-end carbon surface. X-ray photoelectron spectroscopy (XPS) analysis before and after the reaction (Fig. 2 H and I) further confirmed these findings: the appearance of a K 2p peak on the hot-end carbon and a Cl 2p peak on the cold-end carbon after adsorption verified that K + adsorption occurred on the hot-end capacitor surface, while Cl − adsorption occurred on the cold-end capacitor surface following the discharge process. Furthermore, the stability of the ion adsorption/desorption on the capacitor-assisted electrodes was tested (Fig. S8f). GCD cycling tests over five consecutive cycles showed no degradation in capacitance, demonstrating the excellent reversibility and repeatability of the ion adsorption/desorption process mediated by the supercapacitors. Validation of the Working Mode To further validate the SC-TGC system, we proposed a continuous operational mode involving alternating the hot and cold ends, which primarily consists of four stages: 1) Temperature increase at the hot end and voltage establishment; 2) System discharge; 3) Temperature increase at the cold end and reverse voltage establishment; 4) System reverse discharge, awaiting the next cycle. Figure 3 A illustrates the redox couple reactions, cation/anion diffusion, and adsorption/desorption processes during these four stages. In the first stage, the thermogalvanic effect of the Fe(CN) 6 4− /Fe(CN) 6 3− couple establishes an electric field between the hot and cold electrodes. In the second stage, when an external load is applied, electrons flow from the hot electrode to the cold electrode, while K + and Cl − are adsorbed onto the hot-end and cold-end capacitors, respectively, reducing the internal electrostatic field and voltage. In the third stage, the thermogalvanic effect generates a reverse electric field. In the final stage, the external load is reapplied, Fe(CN) 6 4− and Fe(CN) 6 3− are consumed and converted, and the adsorbed K + and Cl − are desorbed from the capacitor surfaces. After the temperature difference is removed, the concentrations of Fe(CN) 6 4− / Fe(CN) 6 3− and K + /Cl − are re-established through diffusion within the electrolyte, restoring the concentration distribution to that of the first stage. The open-circuit voltage, short-circuit current, and Fe(CN) 6 4− / Fe(CN) 6 3− concentrations were measured for these four distinct stages (Fig. 3 B and 3 C). During the first open-circuit stage, the cell voltage increased to approximately 200 mV, while the concentrations of Fe(CN) 6 4− and Fe(CN) 6 3− remained largely unchanged. In the second short-circuit discharge stage, the current decreased from 8 mA to 0.1 mA. Concurrently, the concentration of Fe(CN) 6 4− in the hot cell decreased from 0.32 to 0.08 mol L⁻¹, whereas the concentration of Fe(CN) 6 3− increased from 0.08 to 0.32 mol L⁻¹. In the third reverse temperature-increasing stage, the cell voltage rose to -200 mV, and the internal concentrations of Fe(CN) 6 4− and Fe(CN) 6 3− remained stable. In the fourth reverse discharge stage, the current initially increased to -8 mA and then decreased to -0.1 mA. During this stage, the concentration of Fe(CN) 6 4− in the cold cell increased again to 0.32 mol L⁻¹, while the concentration of Fe(CN) 6 3− decreased to 0.08 mol L⁻¹. Through these four stages, a stable cycling of the Fe(CN) 6 4− / Fe(CN) 6 3− couple within the cell was successfully achieved. Figure 3 D illustrates the operating voltage and current curves of the SC-TGC under an external load. When connected to a 50 Ω resistor for 60 minutes, the cell voltage decreased from an initial open-circuit voltage of 200 mV to 20 mV, and the current dropped to 0.6 mA. Upon removal of the heat source from the hot-end cell, both the voltage and current eventually decayed to zero. Furthermore, we evaluated the stability of the electrical energy output of the SC-TGC (Fig. 3 E). The voltage and current in the first cycle were significantly lower than those in subsequent cycles (Fig. S15). This is attributed to the fact that after completing the first reaction cycle, the concentration of either Fe(CN) 6 4− or Fe(CN) 6 3− inside the cell exceeded its initial concentration of 0.3 mol L⁻¹ (Figs. S16, S17). The higher concentration led to an increase in the output voltage. Over the subsequent five cycles, the output voltage and current remained essentially constant. Additional long-term cycling stability tests performed on the Fe(CN) 6 4− / Fe(CN) 6 3− electrolyte (Fig. S18) showed that after 2000 cyclic voltammetry scans, the performance degradation was stabilized within 2%, indicating excellent stability of the cell. In addition, the output power during the forward and reverse discharge processes within the same cycle was measured (Fig. 3 F). The maximum power density was maintained at 0.45 W m − 2 for both directions, confirming the reliability of the SC-TGC system operating with alternating hot and cold ends. Cell Performance and the Mechanism of Heat-Ion Transport Decoupling We evaluated the thermoelectric performance of the conventional TGC and the SC-TGC separately. The hot-end temperature was varied between 25 and 70°C, and the corresponding open-circuit voltage was measured (Fig. 4 A). As the hot-end temperature increased from 25 to 70°C, the open-circuit voltage of the SC-TGC correspondingly rose from 70 to 202 mV, which is significantly higher than that of the TGC, which remained at approximately 5 mV. This substantial enhancement is primarily attributed to the fact that the temperature difference between the hot and cold cells of the SC-TGC increased from 2 to 48 K as the hot-end temperature rose from 25 to 70°C. In contrast, the temperature difference between the hot and cold electrodes of the TGC remained around 3 K. This significantly larger temperature gradient drastically boosted the voltage output. Owing to this highly efficient voltage generation, the Se coefficient of the SC-TGC reached 4.49 mV K − 1 at 70°C, representing a 280% increase compared to the Se value of 1.6 mV K − 1 for the TGC (Fig. 4 C). Concurrently, at a hot-end temperature of 70°C and under an external load of 50 Ω, the short-circuit current of the SC-TGC was also markedly higher than that of the TGC (Fig. 4 B). Subsequently, the energy density was evaluated under different external loads ranging from 5 to 200 Ω. Figure 4 E presents the energy density (E 60 min) calculated by integrating the power output curves over a 60-minute discharge period. The SC-TGC achieved its highest E₆₀min of 3.23 kJ m − 2 at an external load of 50 Ω, a value substantially greater than that delivered by the TGC. In the study of Fe(CN) 6 4− / Fe(CN) 6 3− concentration changes presented in Fig. 3 C, we observed that the concentration of either Fe(CN) 6 4− or Fe(CN) 6 3− was not fully converted to its extreme value of 0.4 mol L − 1 during the thermally driven process, thereby limiting the power output. This limitation is primarily attributed to the finite capacitance of the supercapacitor, where its restricted surface ion adsorption capacity prevented the complete conversion of Fe(CN) 6 4− or Fe(CN) 6 3− . To further enhance the electrical output of the SC-TGC, we proposed using supercapacitor-assisted electrodes fabricated from Ti 3 C 2 , which exhibits a higher specific capacitance. Capacitance performance tests of the Ti 3 C 2 electrode (Fig. S20) revealed a specific capacitance of up to 280 F g − 1 at a discharge current of 0.5 A g − 1 , which is 2.3 times higher than that of commercial activated carbon powder. Figure 4 F displays the electrical output characteristics of the SC-TGC employing Ti 3 C 2 -based supercapacitor-assisted electrodes. This configuration achieved a notably high output voltage of 0.61 V and a power density of 3.52 W m − 2 , significantly surpassing the performance of the traditional TGC. Furthermore, the thermal energy conversion efficiency is a critical metric for evaluating thermoelectric devices. Benefiting from the decoupling of heat and ion transport, the SC-TGC demonstrates both high power density and a maximized thermal energy utilization rate, achieving a relative Carnot efficiency of 7.3%. Additionally, we compared the output power and relative Carnot efficiency of our fabricated SC-TGC with those of previously reported cold-source-free devices (Fig. 4 G). The output power of the SC-TGC reaches the highest value among the reported systems, and its relative Carnot efficiency markedly exceeds the conversion efficiencies of other optimized TGCs documented in the literature 1 , 4 , 34 – 40 , even surpassing the predicted commercialization threshold (approximately 5%). The ultimate thermal energy utilization efficiency of the SC-TGC is primarily attributed to the decoupling of heat and ion transport within the system, for which the underlying mechanism is proposed (Fig. 5 ). Owing to the spatial thermal isolation between the cold and hot cells in the SC-TGC, the temperature difference between the two cells reached an extreme value of 48 K when the hot cell was maintained at 70°C, significantly exceeding the 3.1 K difference observed in the traditional TGC (Fig. 5 B). To further clarify how the thermally isolated supercapacitor-assisted electrodes affect ion transport resistance in the SC-TGC, we examined multiple processes inside the cold and hot cells, such as ion reactions, diffusion, and adsorption/desorption. Figure 5 C illustrates the resistance distribution contributed by different processes, such as Fe(CN) 6 4− / Fe(CN) 6 3− diffusion and reaction, K + /Cl − diffusion and adsorption/desorption, and electron transfer, in both the SC-TGC and the TGC. Figure 5 D provides a quantitative numerical comparison of the respective ion reaction and transport rates in the two systems. In the SC-TGC, the diffusion rates of Fe(CN) 6 4− / Fe(CN) 6 3− , the diffusion and adsorption/desorption rates of K + /Cl − , and the transmembrane transport rate of K + all exceed the reaction rate of Fe(CN) 6 4− / Fe(CN) 6 3− . This indicates that the thermoelectric output of the SC-TGC is primarily limited by the reaction kinetics of Fe(CN) 6 4− / Fe(CN) 6 3− at the electrode surface, rather than by ion transport limitations. Furthermore, in the traditional TGC (Fig. 5 D), the thermoelectric conversion performance is also determined by the reaction rate of Fe(CN) 6 4− / Fe(CN) 6 3− . However, due to the spatial separation of Fe(CN) 6 4− and Fe(CN) 6 3− between the hot and cold cells in the SC-TGC, a higher concentration gradient is established, resulting in a reaction rate that is orders of magnitude higher than that in the TGC. These results demonstrate that the SC-TGC achieves an extreme reduction in thermal conductivity while maintaining high ionic conductivity (Fig. S23) 1 , 39 , 41 – 43 , thereby decoupling the traditionally coupled heat and ion transport. This enables the ultimate utilization of thermal energy from the heat source. Thermogalvanic Cell Stacks We designed an SC-TGC stack by connecting seven individual cells in series to demonstrate its scalability. Figure 6 A presents the exploded view of a single SC-TGC unit and the assembly structure of the stack. Figure 6 B illustrates the interconnection scheme between different cell units using a three-cell group as an example. It is important to note that the capacitor sides of cells within the same group are interconnected, while the electrode sides are connected in a head-to-tail fashion between different groups. Fig. S25 shows a photograph of the fabricated SC-TGC stack. During operation under alternating heating at 70°C (Fig. 6 C), the stack achieved maximum open-circuit voltages of 2.32 V during forward discharge and − 2.28 V during reverse discharge (Figs. 6 D and F). The maximum power output reached 4.5 mW (Fig. 6 E). Owing to the substantial voltage and power output delivered by the SC-TGC stack, it successfully illuminated the miniature bulb (Fig. 6 G and H). Discussion In this study, we decoupled heat and ion transport in redox-mediated thermogalvanic systems, achieving a capacitor-mediated thermogalvanic cell (SC-TGC) capable of high power output and ultimate thermal energy utilization. In contrast to conventional TGCs where heat and ion transport are coupled, we developed a unique device architecture mediated by supercapacitors. This design utilizes supercapacitor-assisted electrodes to mediate the redox reactions of the thermogalvanic cell, enabling spatial separation of the hot and cold electrodes for thermal isolation while maintaining unrestricted ion transport. This approach achieves extremely low thermal conductivity while preserving high ionic conductivity, thereby significantly enhancing thermal energy utilization efficiency. Furthermore, since Fe(CN) 6 4− and Fe(CN) 6 3− are spatially separated and stored within individual cells, the concentration gradient of the redox mediators is increased, resulting in a higher thermopower. Consequently, the SC-TGC generated a thermopower of 4.49 mV K − 1 and an E₆₀min energy density of 3.23 kJ m − 2 without requiring an external cold source. Moreover, by optimizing the specific capacitance of the supercapacitor-assisted electrodes, the SC-TGC achieved a power density of 3.52 W m − 2 and a relative Carnot efficiency of 7.3%, significantly outperforming previously reported TGC systems. These results demonstrate that the SC-TGC provides an effective strategy for ultimate low-grade thermal energy utilization without a cold source. Our approach can be extended to other thermal energy harvesting systems, including thermally regenerative electrochemical cycles, by replacing the current supercapacitor-assisted electrodes with alternative pseudocapacitive materials or n-type redox couples. Methods Materials Potassium chloride (KCl, 99.99% metals basis), potassium ferricyanide (> 99.9%, K 3 Fe(CN) 6 ), potassium Ferrocyanide trihydrate (> 99.0%, K 4 Fe(CN) 6 ·3H 2 O), PTFE (60%), ethanol (C 2 H 6 O, HPLC grade, ≥ 99.8%) were purchased from Shanghai McLean Biochemical Technology Co., LTD. Titanium mesh (200 mesh) was purchased from Merck KGaA, Darmstadt, Germany. Supercapacitor activated carbon powder was purchased from Jiangsu Xianfeng nanomaterials Technology Co., LTD. Cation exchange membrane (MC3470) was purchased from Beijing Ander membrane separation Technology Engineering Co., LTD. All chemical reagents used in this work were of analytical grade without the requirement for further purification before use. The solution was freshly prepared for all experiments. Preparation of Supercapacitor-Assisted Electrode and SC-TGC Preparation and electrochemical tests of the active carbon (AC) relay electrode. The AC was mixed with a binder (polytetrafluoroethylene, PTFE) in a mass ratio of 9:1 in ethanol to form a slurry that was then rolled into a film. The AC electrode was obtained by pressing the film (3*3 cm 2 ) onto the Ti-mesh at the pressure of 10 MP. When preparing the Ti 3 C 2 T x -MXene-based electrode as the supercapacitor-assisted component, the same procedure was followed, simply replacing the active carbon with Ti 3 C 2 T x powder. The main body of the reaction device is made of acrylic. The volume of the device is 30*30*10 mm, and the size of the ion-exchange membrane is 40*40*0.1 mm. The various parts of the reaction device are connected by bolts. Characterization and measurements The microstructure and morphology of the catalysts were characterized using field emission scanning electron microscopy (SEM; JSM-7001F, Japan). X-ray photoelectron spectroscopy (XPS) spectra were obtained with an ESCALAB 250XI spectrometer (Thermo Fisher Scientific). Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) In this section, the inductively coupled plasma optical emission spectrometer model Agilent720ES is adopted to test the concentration of K + ions in the system, and Ion Chromatography (IC) is used to test the Cl − ions. The concentration of anions (Cl − ) in the system was tested using an ion chromatograph of model DIONEX AQUION RFIC (Thermo Fisher). The REDOX properties and reversibility of potassium ferricyanide and potassium ferrocyanide were scanned by linear voltammetry using the electrochemical workstation of Shanghai Chenhua. Carbon cloth electrode as the working electrode, with Pt wire and Ag/AgCl electrodes serving as the counter electrode and reference electrode, respectively. The electrolyte was a 0.2 M FeCN 3−/4− solution. The open-circuit voltage, short-circuit current during the device reaction process and the photocurrent in the photocatalytic reaction were recorded with an Agilent data acquisition instrument. The collection frequency is 5 seconds per time. Calculation of the thermal energy conversion efficiency (η) and the Carnot-relative efficiency (η r ) The thermal energy conversion efficiency ( η ) of a TEG device is defined as the ratio of the maximum output work ( W max ) from the device to the heat input work ( W heat ): η = W max / W heat =∫ UIdt/cm∆T The Camot-relative efficiency (η r ) could be calculated as follows: η r = η/(∆T/T hot ) U is the external circuit voltage, I is the current, c is the specific heat capacity, m is the mass of the redox pair, and T hot represents the hot-end temperature. Declarations Competing interests The authors declare no competing interests. Author contributions J.Z. conceived the idea and designed the research. J.L.Z., X.T.L., X.Q.C., S.W.Z., and X.Y.Z. performed the synthesis, structural characterisations and electrochemical tests. J.Z. analysed and discussed the experimental results and wrote the manuscript. M.D. discussed the results and commented on the manuscript. Acknowledgments This work was supported by the Project for the Joint Funds of the Technology Research and Development Program of Henan Province (No. 225200810100), Program for Science & Technology Innovation Talents in Universities of Henan Province (No. 24HASTIT024), Interdisciplinary Innovative Research Group Project of Henan Province (No. 232300421005) and the Doctorate Foundation of Zhengzhou University of Light Industry (No. 2025BSJJ052). References Yu B et al (2020) Thermosensitive crystallization–boosted liquid thermocells for low-grade heat harvesting. Science 370:342–346 Qian X, Ma Z, Huang Q, Jiang H, Yang R (2024) Thermodynamics of ionic thermoelectrics for low-grade heat harvesting. 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Adv Mater 25:6602–6606 Wang Y et al (2023) In situ photocatalytically enhanced thermogalvanic cells for electricity and hydrogen production. Science 381:291–296 Kim K, Hwang S, Lee H (2020) Unravelling ionic speciation and hydration structure of Fe(III/II) redox couples for thermoelectrochemical cells. Electrochim Acta 335:135651 Kim K, Kang J, Lee H (2021) Hybrid thermoelectrochemical and concentration cells for harvesting low-grade waste heat. Chem Eng J 426:131797 Additional Declarations There is NO Competing Interest. Supplementary Files Driveasinglelightbulb.mp4 Drive a single light bulb Drivemultiplelightbulbs.mp4 Drive multiple light bulbs SupplementaryInformation.docx Supplementary Information Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7743745","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":548406593,"identity":"c9894cdc-56e2-4723-9817-b452bb3cb513","order_by":0,"name":"Jun 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20:18:06","extension":"html","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":106601,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/5a05aac7655b5eb1ee167708.html"},{"id":97192467,"identity":"5d64df14-baa0-4d1a-b6bd-e376ca131ffb","added_by":"auto","created_at":"2025-12-01 20:18:05","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":313092,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Schematic illustration comparing a traditional thermogalvanic cell (TGC) and (B) a supercapacitor-mediated TGC (SC-TGC).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/f937368540f7d6c48823fbcf.png"},{"id":97249388,"identity":"7146fb01-f1d3-42bc-88b5-f97504881b39","added_by":"auto","created_at":"2025-12-02 13:12:25","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":518065,"visible":true,"origin":"","legend":"\u003cp\u003e(A) The redox reaction of the K\u003csub\u003e4\u003c/sub\u003e[Fe(CN)\u003csub\u003e6\u003c/sub\u003e]/K\u003csub\u003e3\u003c/sub\u003e[Fe(CN)\u003csub\u003e6\u003c/sub\u003e] pair and the capacitive characteristics of the active carbon electrodes. (B) Concentration changes of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4-\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e in the SC-TGC during operation. (C) Changes in the concentrations of K⁺ and Cl\u003csup\u003e-\u003c/sup\u003e ions in the solutions adjacent to the hot-end and cold-end capacitors before and after the reaction in the SC-TGC. (D and E) Galvanostatic charge-discharge (GCD) curves after capacitive adsorption and the corresponding calculated surface ion adsorption quantities. (F) Relationship between the peak current (for Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4-\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e) and the square root of the scan rate (ω\u003csup\u003e1/2\u003c/sup\u003e) obtained from cyclic voltammetry measurements at different scan rates. (G) Cyclic voltammetry (CV) curves of the activated carbon powder before and after the reaction. (H) X-ray photoelectron spectroscopy (XPS) spectra of K\u003csup\u003e+\u003c/sup\u003e on the hot-end activated carbon powder before and after the reaction. (I) XPS spectra of Cl\u003csup\u003e-\u003c/sup\u003e on the cold-end activated carbon powder before and after the reaction.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/73d9d3cdfad4a32aa774dea3.png"},{"id":97249207,"identity":"35b0f46b-1683-4cac-bac0-a5cad84adcde","added_by":"auto","created_at":"2025-12-02 13:11:16","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":540670,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Schematic diagram illustrating the four-stage reaction mechanism of the SC-TGC system. (B) Voltage and current variations of the system across the four stages over two operational cycles. (C) Concentration changes of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4-\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e during the two key stages of the system. (D) Output voltage and current variations under an external 50 Ω load. (E) Voltage and current profiles during the system's cycling test. (F) Comparison of the power density output between the second and fourth stages of the system.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/657b6690c350fbc9df4d52b3.png"},{"id":97249454,"identity":"9e820254-b8ee-4e86-8264-9c763bcc69f8","added_by":"auto","created_at":"2025-12-02 13:12:39","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":470063,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Comparison of the open-circuit voltage variation versus hot-end temperature between a traditional TGC and the SC-TGC. (B) Comparison of current output under a 50 Ω external load. (C) Comparison of the Se coefficient. (D) Variation of the SC-TGC's output voltage under different external loads. (E) Comparison of energy density. (F) Comparison of power density. (G) Comparison of power density and relative Carnot efficiency among similar reported systems.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/9cfd34490ae55a872d02c346.png"},{"id":97192478,"identity":"1088e462-1bea-4ade-b252-36a49a367a11","added_by":"auto","created_at":"2025-12-01 20:18:05","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":379125,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Schematic diagram illustrating the internal ion diffusion and reaction processes within the SC-TGC. (B) Comparison of the temperature difference between the hot and cold electrodes in the SC-TGC and the traditional TGC. (C) Schematic illustration of the distribution of resistances contributed by different processes in the SC-TGC and the TGC. (D) Quantitative numerical analysis of the respective ion reaction and transport rates in the SC-TGC and the TGC.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/613942668bbb676ea9c512ec.png"},{"id":97250493,"identity":"417e473e-c771-417d-abbf-d39fdcd8ba2e","added_by":"auto","created_at":"2025-12-02 13:14:36","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":636123,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Exploded view of a single SC-TGC unit. (B) Schematic diagram of the stack assembly. (C) Temperature variation profile during stack operation. (D) Voltage and current output of the stack during operation. (E) Power density output of the stack. (F) Measured voltage of the stack under load. (G and H) The stack powers a light-emitting diode (LED) bulb.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/48dc177b780280e1d4aaa542.png"},{"id":98623416,"identity":"ca159ace-e5af-41d1-b981-232c7c7c2126","added_by":"auto","created_at":"2025-12-19 17:06:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3573069,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/efa06c10-ead7-4631-98c2-fd272fda1377.pdf"},{"id":97192470,"identity":"aebb9093-566f-4bb7-b718-62df749a04f0","added_by":"auto","created_at":"2025-12-01 20:18:05","extension":"mp4","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":791402,"visible":true,"origin":"","legend":"Drive a single light bulb","description":"","filename":"Driveasinglelightbulb.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/f29be24b39fb75cc9c12deb6.mp4"},{"id":97192474,"identity":"a368a80e-bc48-497f-a9b4-99849e189d1a","added_by":"auto","created_at":"2025-12-01 20:18:05","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":588067,"visible":true,"origin":"","legend":"Drive multiple light bulbs","description":"","filename":"Drivemultiplelightbulbs.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/98c8518b33e7804407f9d41c.mp4"},{"id":97192492,"identity":"70951854-d8a9-457a-9ea6-f4e681546d9e","added_by":"auto","created_at":"2025-12-01 20:18:06","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":31061790,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7743745/v1/4727aea174e9c6951e6ff359.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Decoupling heat and ion transport with supercapacitor-mediation in cold-source-free thermogalvanic cells","fulltext":[{"header":"Introduction","content":"\u003cp\u003eLow-grade thermal energy (\u0026lt;\u0026thinsp;100 ℃) is widely distributed in industrial waste heat, solar radiation heat, and geothermal sources. Its global dissipation reaches\u0026thinsp;~\u0026thinsp;85 PWh/year, accounting for over 60% of waste heat\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Due to the irreversible thermodynamics of heat and the distributed nature of thermal sources, effectively converting scattered low-grade heat into electricity remains a critical challenge\u003csup\u003e\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Currently, advanced thermoelectric conversion systems such as electronic thermoelectric systems (based on the Seebeck effect) and ionic thermoelectric systems (relying on the thermodiffusion effect and the thermogalvanic effect) can directly convert low-grade heat into electricity. These systems offer advantages including no moving parts, silent operation, and zero greenhouse gas emissions, thereby providing a promising pathway for waste heat utilization\u003csup\u003e\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Conventional electronic thermoelectric systems (e.g., based on Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e) exhibit performance dependent on the material\u0026rsquo; s thermoelectric figure of merit, with a Seebeck coefficient (thermopower, Se) of only 100\u0026ndash;200 \u0026micro;V K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, coupled with high costs, which pose barriers to market application\u003csup\u003e\u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. In contrast, ionic thermoelectric systems, such as thermodiffusion cells and thermogalvanic cells (TGCs), have attracted significant attention due to their high thermopower (Se on the order of mV K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), low cost, and scalability\u003csup\u003e\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. Although thermodiffusion cells can achieve a high thermopower of up to 31 mV K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, their intermittent power output characteristics limit industrial-scale applications\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. In comparison, thermogalvanic cells, which utilize continuous cyclic reactions of redox couples to generate stable and continuous electrical output under temperature differences, offer a more feasible pathway for harnessing near-ambient thermal energy.\u003c/p\u003e\u003cp\u003eTGCs primarily utilize liquid-phase redox couples, such as the typical Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e system, as the reaction medium. Their core performance indicator, the relative Carnot efficiency (η\u003csub\u003er\u003c/sub\u003e), is closely related to the thermal conductivity and ionic conductivity of the liquid redox medium, as expressed by η\u003csub\u003er\u003c/sub\u003e \u0026prop; (Se)\u003csup\u003e2\u003c/sup\u003eσ/k, where k represents the effective thermal conductivity and σ denotes the effective ionic conductivity\u003csup\u003e\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. A relative Carnot efficiency of approximately 5% is considered the potential threshold for the commercial viability of TGCs in harvesting low-grade heat\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. To achieve a high relative Carnot efficiency, it is imperative to reduce the thermal conductivity of the liquid medium while maintaining high ionic conductivity. However, heat and ion transport in liquid redox media exhibit strong coupling, meaning the thermal and ionic conductivities typically increase or decrease simultaneously\u003csup\u003e\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, thereby limiting the enhancement of cell efficiency. Consequently, decoupling heat and ion transport within the liquid redox medium is essential. Currently, decoupling heat and ion transport mainly involves two strategies. One strategy introduces an external cold source to disrupt the coupling between heat and ion transport. This is achieved by forcibly increasing the temperature difference (ΔT) between the hot and cold electrodes of the TGC, resulting in a lower effective thermal conductivity of the medium and thus improving the cell's relative Carnot efficiency. However, the requirement for an external cold source constrains its practical applications\u003csup\u003e\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. The other strategy involves introducing porous thermal barriers, such as polymer separators, gels, or thermosensitive crystalline additives, between the hot and cold electrodes of the TGC. These materials weaken the coupling between heat and ion transport in the liquid medium and reduce the effective thermal conductivity\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Nevertheless, although the incorporation of porous insulating materials reduces the effective thermal conductivity of the liquid medium to some extent, it simultaneously increases the ion diffusion resistance, leading to reduced ionic conductivity and ultimately limiting thermal energy conversion. These limitations underscore the urgent need for innovative designs that minimize the effective thermal conductivity while maximizing the effective ionic conductivity of the liquid medium without introducing forced cooling.\u003c/p\u003e\u003cp\u003eSpatial separation of the hot and cold electrodes in TGCs presents a promising novel approach to significantly enhance thermal energy utilization by reducing the effective thermal conductivity of the liquid medium to nearly zero. However, it inherently obstructs the transport of redox ions between the electrodes. In contrast, supercapacitor-mediated ion transport offers rapid ion adsorption/desorption kinetics and enables directional charge transfer\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. Integrating the spatial separation strategy of TGCs with supercapacitor-mediated ion transport holds great potential for developing a thermoelectric conversion system characterized by extremely low thermal conductivity and high ionic conductivity, thereby achieving decoupled heat and ion transport within the liquid medium. Building upon this concept, we report a TGC that utilizes supercapacitors to decouple heat and ion transport within the redox medium. By employing capacitive storage to mediate the redox reactions of the thermogalvanic cell, the traditional process of ion transport, which is accompanied by heat transfer between the conventional hot and cold electrodes, is transformed into capacitive adsorption and electron transfer occurring between the hot and cold supercapacitors. This innovation decouples the synchronous transport of heat and ions inherent in conventional TGCs (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA), ensuring highly efficient ion transfer between the hot and cold electrodes while simultaneously achieving thermal isolation between them, thereby enhancing thermal energy utilization efficiency. In this device (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB), the hot electrode facilitates the oxidation of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e to Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e. The generated electrons are transferred to the cold electrode. Simultaneously, positively charged K⁺ ions undergo transmembrane transport and are stored on the surface of the hot supercapacitor, while the positive charge generated by K⁺ adsorption is transferred to the cold supercapacitor\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. Conversely, at the cold electrode, Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e accepts the electrons transferred from the hot side, reducing to Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e. During this process, positively charged K⁺ ions from the cold supercapacitor side transfer across the membrane to the cold electrode side. The remaining negatively charged Cl⁻ ions are stored on the surface of the cold supercapacitor, which simultaneously accepts the positive charge transferred from the hot supercapacitor to maintain charge balance\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. Leveraging this decoupled heat and ion transport, the supercapacitor-mediated TGC achieves a maximum relative Carnot efficiency of 7.3% without the need for forced cooling.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eCell Construction and Supercapacitor-Mediation\u003c/h2\u003e\u003cp\u003eWe constructed a supercapacitor-mediated thermogalvanic cell (SC-TGC) system that decouples heat and ion transport (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB; as described in Experimental Section for details). Both terminal cells were filled with a K\u003csub\u003e4\u003c/sub\u003e[Fe(CN)\u003csub\u003e6\u003c/sub\u003e]/K\u003csub\u003e3\u003c/sub\u003e[Fe(CN)\u003csub\u003e6\u003c/sub\u003e] mixed electrolyte on the electrode side to serve as the redox ions for the thermogalvanic reaction. A KCl electrolyte was added on the capacitor side to balance the ion diffusion required by the redox reactions on the electrode side, while avoiding the introduction of new cationic species. To validate the concept of the capacitor-mediated thermogalvanic cell, the redox reaction of the K\u003csub\u003e4\u003c/sub\u003e[Fe(CN)\u003csub\u003e6\u003c/sub\u003e]/K\u003csub\u003e3\u003c/sub\u003e[Fe(CN)\u003csub\u003e6\u003c/sub\u003e] pair on carbon cloth electrodes and the capacitive characteristics of the activated carbon electrodes were investigated separately by cyclic voltammetry (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA and Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). The distinctive redox peaks in the cyclic voltammograms correspond to the oxidation of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e to Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e at the hot electrode and the reduction of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e to Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e at the cold electrode\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. The nearly rectangular cyclic voltammogram of the capacitor in the KCl electrolyte indicates its electrical energy storage characteristics\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. To further demonstrate the system design, the concentration changes of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e in the electrode-side electrolyte, and of K\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e in the capacitor-side electrolyte, were measured during the heating process (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB and C). When the hot cell was heated under open-circuit conditions, the concentrations of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e on the electrode side remained largely unchanged. During the subsequent 180-minute discharge phase, the concentration of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e decreased from 0.3 to approximately 0.1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (volume V\u0026thinsp;=\u0026thinsp;2 mL), while the concentration of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e increased from 0.1 to approximately 0.3 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The cold cell exhibited opposite concentration changes for Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e on its electrode side (Fig. S2). In the cold-end capacitor-side electrolyte, the K\u003csup\u003e+\u003c/sup\u003e concentration decreased by 0.4 mmol after the discharge phase, resulting from the diffusion of K\u003csup\u003e+\u003c/sup\u003e to the electrode side driven by the cold-end electrode reaction. Simultaneously, the Cl⁻ concentration also decreased by 0.4 mmol, which was attributed to the adsorption of Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e onto the capacitor. In the hot-end capacitor-side electrolyte, the concentrations of K\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e remained essentially constant, primarily because the amount of K\u003csup\u003e+\u003c/sup\u003e adsorbed on the capacitor was compensated by the K\u003csup\u003e+\u003c/sup\u003e diffusing from the electrode side to the capacitor side. Further measurement of the ions adsorbed on the post-reaction capacitors revealed that the adsorption quantities of both Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e and K\u003csup\u003e+\u003c/sup\u003e on the cold and hot capacitors were approximately 0.6 mmol each (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD and E). This value aligns with the amount of K\u003csup\u003e+\u003c/sup\u003e diffusion caused by the Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e conversion on the electrode side. These results confirm that the redox reactions at the cold/hot electrodes induce the directional diffusion of cations, leading to the equivalent adsorption of anions and cations on the capacitors, thereby demonstrating the mediation of the traditional thermogalvanic redox reactions by the supercapacitors. Furthermore, the cyclic voltammetry (CV) curves of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e at different scan rates (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF and Fig. S3) showed that the plot of the redox peak currents against ω\u003csup\u003e1/2\u003c/sup\u003e is highly symmetric about the x-axis. This indicates that the redox reaction possesses good reversibility\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e, which enables the potential for reverse operation of the system by switching the hot and cold ends.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eSupercapacitor-Assisted Electrodes\u003c/h3\u003e\n\u003cp\u003eWe evaluated the capacitive and ion adsorption characteristics of the supercapacitor-assisted electrodes. Fig. S4a and Fig. S5 show scanning electron microscopy (SEM) images of the activated carbon powder, revealing a porous structure rich in micropores\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Brunauer-Emmett-Teller (BET) analysis of the porosity of the carbon powder (Fig. S4b) indicated a pore size distribution predominantly within the range of 0.4 to 0.8 nm\u003csup\u003e32\u003c/sup\u003e. The charge storage capacity of the capacitive electrodes was assessed via galvanostatic charge-discharge (GCD) tests (Fig. S4c), conducted within a potential window of 0.15 to 0.75 V vs. Ag/AgCl. These tests were performed within the aqueous stability window to simulate the operational conditions of the supercapacitor. The specific capacitance calculated from the GCD curves (Fig. S4d) was greater than 120 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at current densities significantly lower than 0.5 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is relevant to the operating current of the SC-TGC. GCD tests performed at different temperatures (Fig. S6) showed that rising temperature significantly increased the specific capacitance, which is beneficial for electron storage\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. Cyclic voltammetry (CV) tests were conducted on the carbon powder before and after ion adsorption (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eG). The enlarged CV curve after adsorption suggests the occurrence of ion adsorption within the porous carbon material. Energy-dispersive X-ray spectroscopy (EDS) analysis of the electrodes before and after adsorption (Fig. S8 and S10) indicated the presence of adsorbed K\u003csup\u003e+\u003c/sup\u003e on the hot-end carbon surface and adsorbed Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e on the cold-end carbon surface. X-ray photoelectron spectroscopy (XPS) analysis before and after the reaction (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eH and I) further confirmed these findings: the appearance of a K 2p peak on the hot-end carbon and a Cl 2p peak on the cold-end carbon after adsorption verified that K\u003csup\u003e+\u003c/sup\u003e adsorption occurred on the hot-end capacitor surface, while Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e adsorption occurred on the cold-end capacitor surface following the discharge process. Furthermore, the stability of the ion adsorption/desorption on the capacitor-assisted electrodes was tested (Fig. S8f). GCD cycling tests over five consecutive cycles showed no degradation in capacitance, demonstrating the excellent reversibility and repeatability of the ion adsorption/desorption process mediated by the supercapacitors.\u003c/p\u003e\n\u003ch3\u003eValidation of the Working Mode\u003c/h3\u003e\n\u003cp\u003e\u003c/p\u003e\u003cp\u003eTo further validate the SC-TGC system, we proposed a continuous operational mode involving alternating the hot and cold ends, which primarily consists of four stages: 1) Temperature increase at the hot end and voltage establishment; 2) System discharge; 3) Temperature increase at the cold end and reverse voltage establishment; 4) System reverse discharge, awaiting the next cycle. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA illustrates the redox couple reactions, cation/anion diffusion, and adsorption/desorption processes during these four stages. In the first stage, the thermogalvanic effect of the Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e couple establishes an electric field between the hot and cold electrodes. In the second stage, when an external load is applied, electrons flow from the hot electrode to the cold electrode, while K\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e are adsorbed onto the hot-end and cold-end capacitors, respectively, reducing the internal electrostatic field and voltage. In the third stage, the thermogalvanic effect generates a reverse electric field. In the final stage, the external load is reapplied, Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e are consumed and converted, and the adsorbed K\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e are desorbed from the capacitor surfaces. After the temperature difference is removed, the concentrations of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e and K\u003csup\u003e+\u003c/sup\u003e/Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e are re-established through diffusion within the electrolyte, restoring the concentration distribution to that of the first stage. The open-circuit voltage, short-circuit current, and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e concentrations were measured for these four distinct stages (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC). During the first open-circuit stage, the cell voltage increased to approximately 200 mV, while the concentrations of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e remained largely unchanged. In the second short-circuit discharge stage, the current decreased from 8 mA to 0.1 mA. Concurrently, the concentration of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e in the hot cell decreased from 0.32 to 0.08 mol L⁻\u0026sup1;, whereas the concentration of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e increased from 0.08 to 0.32 mol L⁻\u0026sup1;. In the third reverse temperature-increasing stage, the cell voltage rose to -200 mV, and the internal concentrations of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e remained stable. In the fourth reverse discharge stage, the current initially increased to -8 mA and then decreased to -0.1 mA. During this stage, the concentration of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e in the cold cell increased again to 0.32 mol L⁻\u0026sup1;, while the concentration of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e decreased to 0.08 mol L⁻\u0026sup1;. Through these four stages, a stable cycling of the Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e couple within the cell was successfully achieved.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD illustrates the operating voltage and current curves of the SC-TGC under an external load. When connected to a 50 Ω resistor for 60 minutes, the cell voltage decreased from an initial open-circuit voltage of 200 mV to 20 mV, and the current dropped to 0.6 mA. Upon removal of the heat source from the hot-end cell, both the voltage and current eventually decayed to zero. Furthermore, we evaluated the stability of the electrical energy output of the SC-TGC (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE). The voltage and current in the first cycle were significantly lower than those in subsequent cycles (Fig. S15). This is attributed to the fact that after completing the first reaction cycle, the concentration of either Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e or Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e inside the cell exceeded its initial concentration of 0.3 mol L⁻\u0026sup1; (Figs. S16, S17). The higher concentration led to an increase in the output voltage. Over the subsequent five cycles, the output voltage and current remained essentially constant. Additional long-term cycling stability tests performed on the Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e electrolyte (Fig. S18) showed that after 2000 cyclic voltammetry scans, the performance degradation was stabilized within 2%, indicating excellent stability of the cell. In addition, the output power during the forward and reverse discharge processes within the same cycle was measured (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF). The maximum power density was maintained at 0.45 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for both directions, confirming the reliability of the SC-TGC system operating with alternating hot and cold ends.\u003c/p\u003e\n\u003ch3\u003eCell Performance and the Mechanism of Heat-Ion Transport Decoupling\u003c/h3\u003e\n\u003cp\u003eWe evaluated the thermoelectric performance of the conventional TGC and the SC-TGC separately. The hot-end temperature was varied between 25 and 70\u0026deg;C, and the corresponding open-circuit voltage was measured (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). As the hot-end temperature increased from 25 to 70\u0026deg;C, the open-circuit voltage of the SC-TGC correspondingly rose from 70 to 202 mV, which is significantly higher than that of the TGC, which remained at approximately 5 mV. This substantial enhancement is primarily attributed to the fact that the temperature difference between the hot and cold cells of the SC-TGC increased from 2 to 48 K as the hot-end temperature rose from 25 to 70\u0026deg;C. In contrast, the temperature difference between the hot and cold electrodes of the TGC remained around 3 K. This significantly larger temperature gradient drastically boosted the voltage output. Owing to this highly efficient voltage generation, the Se coefficient of the SC-TGC reached 4.49 mV K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 70\u0026deg;C, representing a 280% increase compared to the Se value of 1.6 mV K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for the TGC (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). Concurrently, at a hot-end temperature of 70\u0026deg;C and under an external load of 50 Ω, the short-circuit current of the SC-TGC was also markedly higher than that of the TGC (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). Subsequently, the energy density was evaluated under different external loads ranging from 5 to 200 Ω. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eE presents the energy density (E\u003csub\u003e60\u003c/sub\u003emin) calculated by integrating the power output curves over a 60-minute discharge period. The SC-TGC achieved its highest E₆₀min of 3.23 kJ m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at an external load of 50 Ω, a value substantially greater than that delivered by the TGC.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn the study of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e concentration changes presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC, we observed that the concentration of either Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e or Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e was not fully converted to its extreme value of 0.4 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e during the thermally driven process, thereby limiting the power output. This limitation is primarily attributed to the finite capacitance of the supercapacitor, where its restricted surface ion adsorption capacity prevented the complete conversion of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e or Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e. To further enhance the electrical output of the SC-TGC, we proposed using supercapacitor-assisted electrodes fabricated from Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e, which exhibits a higher specific capacitance. Capacitance performance tests of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e electrode (Fig. S20) revealed a specific capacitance of up to 280 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a discharge current of 0.5 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is 2.3 times higher than that of commercial activated carbon powder. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eF displays the electrical output characteristics of the SC-TGC employing Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e-based supercapacitor-assisted electrodes. This configuration achieved a notably high output voltage of 0.61 V and a power density of 3.52 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, significantly surpassing the performance of the traditional TGC. Furthermore, the thermal energy conversion efficiency is a critical metric for evaluating thermoelectric devices. Benefiting from the decoupling of heat and ion transport, the SC-TGC demonstrates both high power density and a maximized thermal energy utilization rate, achieving a relative Carnot efficiency of 7.3%. Additionally, we compared the output power and relative Carnot efficiency of our fabricated SC-TGC with those of previously reported cold-source-free devices (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eG). The output power of the SC-TGC reaches the highest value among the reported systems, and its relative Carnot efficiency markedly exceeds the conversion efficiencies of other optimized TGCs documented in the literature\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan additionalcitationids=\"CR35 CR36 CR37 CR38 CR39\" citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e, even surpassing the predicted commercialization threshold (approximately 5%).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe ultimate thermal energy utilization efficiency of the SC-TGC is primarily attributed to the decoupling of heat and ion transport within the system, for which the underlying mechanism is proposed (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Owing to the spatial thermal isolation between the cold and hot cells in the SC-TGC, the temperature difference between the two cells reached an extreme value of 48 K when the hot cell was maintained at 70\u0026deg;C, significantly exceeding the 3.1 K difference observed in the traditional TGC (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB). To further clarify how the thermally isolated supercapacitor-assisted electrodes affect ion transport resistance in the SC-TGC, we examined multiple processes inside the cold and hot cells, such as ion reactions, diffusion, and adsorption/desorption. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC illustrates the resistance distribution contributed by different processes, such as Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e diffusion and reaction, K\u003csup\u003e+\u003c/sup\u003e/Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e diffusion and adsorption/desorption, and electron transfer, in both the SC-TGC and the TGC. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD provides a quantitative numerical comparison of the respective ion reaction and transport rates in the two systems. In the SC-TGC, the diffusion rates of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e, the diffusion and adsorption/desorption rates of K\u003csup\u003e+\u003c/sup\u003e/Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, and the transmembrane transport rate of K\u003csup\u003e+\u003c/sup\u003e all exceed the reaction rate of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e. This indicates that the thermoelectric output of the SC-TGC is primarily limited by the reaction kinetics of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e at the electrode surface, rather than by ion transport limitations. Furthermore, in the traditional TGC (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD), the thermoelectric conversion performance is also determined by the reaction rate of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e/ Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e. However, due to the spatial separation of Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e between the hot and cold cells in the SC-TGC, a higher concentration gradient is established, resulting in a reaction rate that is orders of magnitude higher than that in the TGC. These results demonstrate that the SC-TGC achieves an extreme reduction in thermal conductivity while maintaining high ionic conductivity (Fig. S23)\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan additionalcitationids=\"CR42\" citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e, thereby decoupling the traditionally coupled heat and ion transport. This enables the ultimate utilization of thermal energy from the heat source.\u003c/p\u003e\n\u003ch3\u003eThermogalvanic Cell Stacks\u003c/h3\u003e\n\u003cp\u003eWe designed an SC-TGC stack by connecting seven individual cells in series to demonstrate its scalability. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA presents the exploded view of a single SC-TGC unit and the assembly structure of the stack. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB illustrates the interconnection scheme between different cell units using a three-cell group as an example. It is important to note that the capacitor sides of cells within the same group are interconnected, while the electrode sides are connected in a head-to-tail fashion between different groups. Fig. S25 shows a photograph of the fabricated SC-TGC stack. During operation under alternating heating at 70\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC), the stack achieved maximum open-circuit voltages of 2.32 V during forward discharge and \u0026minus;\u0026thinsp;2.28 V during reverse discharge (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eD and F). The maximum power output reached 4.5 mW (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eE). Owing to the substantial voltage and power output delivered by the SC-TGC stack, it successfully illuminated the miniature bulb (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eG and H).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, we decoupled heat and ion transport in redox-mediated thermogalvanic systems, achieving a capacitor-mediated thermogalvanic cell (SC-TGC) capable of high power output and ultimate thermal energy utilization. In contrast to conventional TGCs where heat and ion transport are coupled, we developed a unique device architecture mediated by supercapacitors. This design utilizes supercapacitor-assisted electrodes to mediate the redox reactions of the thermogalvanic cell, enabling spatial separation of the hot and cold electrodes for thermal isolation while maintaining unrestricted ion transport. This approach achieves extremely low thermal conductivity while preserving high ionic conductivity, thereby significantly enhancing thermal energy utilization efficiency. Furthermore, since Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e and Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e are spatially separated and stored within individual cells, the concentration gradient of the redox mediators is increased, resulting in a higher thermopower. Consequently, the SC-TGC generated a thermopower of 4.49 mV K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and an E₆₀min energy density of 3.23 kJ m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e without requiring an external cold source. Moreover, by optimizing the specific capacitance of the supercapacitor-assisted electrodes, the SC-TGC achieved a power density of 3.52 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and a relative Carnot efficiency of 7.3%, significantly outperforming previously reported TGC systems. These results demonstrate that the SC-TGC provides an effective strategy for ultimate low-grade thermal energy utilization without a cold source. Our approach can be extended to other thermal energy harvesting systems, including thermally regenerative electrochemical cycles, by replacing the current supercapacitor-assisted electrodes with alternative pseudocapacitive materials or n-type redox couples.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003eMaterials\u003c/h2\u003e\u003cp\u003ePotassium chloride (KCl, 99.99% metals basis), potassium ferricyanide (\u0026gt;\u0026thinsp;99.9%, K\u003csub\u003e3\u003c/sub\u003eFe(CN)\u003csub\u003e6\u003c/sub\u003e), potassium Ferrocyanide trihydrate (\u0026gt;\u0026thinsp;99.0%, K\u003csub\u003e4\u003c/sub\u003eFe(CN)\u003csub\u003e6\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO), PTFE (60%), ethanol (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eO, HPLC grade, \u0026ge;\u0026thinsp;99.8%) were purchased from Shanghai McLean Biochemical Technology Co., LTD. Titanium mesh (200 mesh) was purchased from Merck KGaA, Darmstadt, Germany. Supercapacitor activated carbon powder was purchased from Jiangsu Xianfeng nanomaterials Technology Co., LTD. Cation exchange membrane (MC3470) was purchased from Beijing Ander membrane separation Technology Engineering Co., LTD. All chemical reagents used in this work were of analytical grade without the requirement for further purification before use. The solution was freshly prepared for all experiments.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003ePreparation of Supercapacitor-Assisted Electrode and SC-TGC\u003c/h2\u003e\u003cp\u003ePreparation and electrochemical tests of the active carbon (AC) relay electrode. The AC was mixed with a binder (polytetrafluoroethylene, PTFE) in a mass ratio of 9:1 in ethanol to form a slurry that was then rolled into a film. The AC electrode was obtained by pressing the film (3*3 cm\u003csup\u003e2\u003c/sup\u003e) onto the Ti-mesh at the pressure of 10 MP. When preparing the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003ex\u003c/sub\u003e-MXene-based electrode as the supercapacitor-assisted component, the same procedure was followed, simply replacing the active carbon with Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003ex\u003c/sub\u003e powder. The main body of the reaction device is made of acrylic. The volume of the device is 30*30*10 mm, and the size of the ion-exchange membrane is 40*40*0.1 mm. The various parts of the reaction device are connected by bolts.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eCharacterization and measurements\u003c/h2\u003e\u003cp\u003eThe microstructure and morphology of the catalysts were characterized using field emission scanning electron microscopy (SEM; JSM-7001F, Japan). X-ray photoelectron spectroscopy (XPS) spectra were obtained with an ESCALAB 250XI spectrometer (Thermo Fisher Scientific). Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) In this section, the inductively coupled plasma optical emission spectrometer model Agilent720ES is adopted to test the concentration of K\u003csup\u003e+\u003c/sup\u003e ions in the system, and Ion Chromatography (IC) is used to test the Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e ions. The concentration of anions (Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e) in the system was tested using an ion chromatograph of model DIONEX AQUION RFIC (Thermo Fisher). The REDOX properties and reversibility of potassium ferricyanide and potassium ferrocyanide were scanned by linear voltammetry using the electrochemical workstation of Shanghai Chenhua. Carbon cloth electrode as the working electrode, with Pt wire and Ag/AgCl electrodes serving as the counter electrode and reference electrode, respectively. The electrolyte was a 0.2 M FeCN\u003csup\u003e3\u0026minus;/4\u0026minus;\u003c/sup\u003e solution. The open-circuit voltage, short-circuit current during the device reaction process and the photocurrent in the photocatalytic reaction were recorded with an Agilent data acquisition instrument. The collection frequency is 5 seconds per time.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eCalculation of the thermal energy conversion efficiency (η) and the Carnot-relative efficiency (η\u003csub\u003er\u003c/sub\u003e)\u003c/h2\u003e\u003cp\u003eThe thermal energy conversion efficiency (\u003cem\u003eη\u003c/em\u003e) of a TEG device is defined as the ratio of the maximum output work (\u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e) from the device to the heat input work (\u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003eheat\u003c/em\u003e\u003c/sub\u003e):\u003c/p\u003e\u003cp\u003e\u003cem\u003eη\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e/\u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003eheat\u003c/em\u003e\u003c/sub\u003e=\u0026int;\u003cem\u003eUIdt/cm∆T\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThe Camot-relative efficiency (η\u003csub\u003er\u003c/sub\u003e) could be calculated as follows:\u003c/p\u003e\u003cp\u003e\u003cem\u003eη\u003c/em\u003e\u003csub\u003e\u003cem\u003er\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eη/(∆T/T\u003c/em\u003e\u003csub\u003e\u003cem\u003ehot\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eU\u003c/em\u003e is the external circuit voltage, \u003cem\u003eI\u003c/em\u003e is the current, \u003cem\u003ec\u003c/em\u003e is the specific heat capacity, \u003cem\u003em\u003c/em\u003e is the mass of the redox pair, and \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003ehot\u003c/em\u003e\u003c/sub\u003e represents the hot-end temperature.\u003c/p\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eCompeting interests\u003c/h2\u003e\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e\u003cp\u003eJ.Z. conceived the idea and designed the research. J.L.Z., X.T.L., X.Q.C., S.W.Z., and X.Y.Z. performed the synthesis, structural characterisations and electrochemical tests. J.Z. analysed and discussed the experimental results and wrote the manuscript. M.D. discussed the results and commented on the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eThis work was supported by the Project for the Joint Funds of the Technology Research and Development Program of Henan Province (No. 225200810100), Program for Science \u0026amp; Technology Innovation Talents in Universities of Henan Province (No. 24HASTIT024), Interdisciplinary Innovative Research Group Project of Henan Province (No. 232300421005) and the Doctorate Foundation of Zhengzhou University of Light Industry (No. 2025BSJJ052).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eYu B et al (2020) Thermosensitive crystallization\u0026ndash;boosted liquid thermocells for low-grade heat harvesting. 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Chem Eng J 426:131797\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Thermogalvanic cells, Decoupled heat and ion transport, Supercapacitor-mediated, Cold-source-free","lastPublishedDoi":"10.21203/rs.3.rs-7743745/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7743745/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThermogalvanic cells represent a pivotal technology for the direct conversion of low-grade thermal energy into electricity. However, constrained by the strong coupling between heat and ion transport within the redox mediators, conventional approaches rely on introducing a cold source to disrupt this coupling and enhance cell output, making efficient and sustainable operation dependent on an external cold supply. In the absence of forced cooling, the temperature difference (ΔT) and the output current of the cell exhibit a mutual limitation, resulting in a low relative Carnot efficiency (η\u003csub\u003er\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;3%) or low output power density (P\u003csub\u003emax\u003c/sub\u003e \u0026lt; 0.5 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e). Here, we report a cold-source-free thermogalvanic cell that decouples heat and ion transport in the redox medium. This design, for the first time, utilizes supercapacitor-mediated redox reactions within the thermogalvanic cell. It achieves thermal isolation through the spatial separation of the hot and cold electrodes and establishes a high-speed ionic transport highway via the supercapacitor unit. This device, operating without forced cooling with a heat source at 70\u0026deg;C, realizes a temperature difference ΔT\u0026thinsp;\u0026gt;\u0026thinsp;40 K between the two electrodes and enables unrestricted ion transport. The cell achieves a high output power density of 3.52 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and a maximum relative Carnot efficiency of 7.3%, which are the highest reported value without an external cold source and the η\u003csub\u003er\u003c/sub\u003e value exceeds the predicted commercialization threshold of 5%. This novel thermogalvanic cell design promises the ultimate utilization and commercialization of low-grade thermal energy.\u003c/p\u003e","manuscriptTitle":"Decoupling heat and ion transport with supercapacitor-mediation in cold-source-free thermogalvanic cells","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-01 20:18:01","doi":"10.21203/rs.3.rs-7743745/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"10ea88d5-142e-4566-a319-1b020655a373","owner":[],"postedDate":"December 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":58354307,"name":"Physical sciences/Energy science and technology/Thermoelectric devices and materials"},{"id":58354308,"name":"Physical sciences/Energy science and technology/Energy harvesting/Devices for energy harvesting"}],"tags":[],"updatedAt":"2025-12-18T02:46:05+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-01 20:18:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7743745","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7743745","identity":"rs-7743745","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}