Intrinsic asymmetric iontronic-interfaces for giant power generation

Domain: physics
Published: 2025-12-31
Editorial outcome: major_revision

Abstract
Iontronic power source harnesses ion-electron coupling effect for energy conversion, offering great potential in wearable electronics and bioelectronics. However, its limited power density and insufficient current hinder the progress toward commercialization. Here we report an iontronic electricity generator based on intrinsic asymmetric interfaces and controllable energy-release, which reaches a maximum volumetric power density of up to 3680 Wm-3, area power density of 18.4 Wm-2, and peak current of more than 5 A. Cycling power generation is ascribed to reversible electron-coupled ion-oscillation at interface. Synergistically, the intrinsic asymmetric interfaces facilitate ion-electron coupling interaction, and the energy-release gate optimizes the energy conversion pathway, thus ensuring giant power output. The developed generator shows large-scale manufacturability and good flexibility. These exceptional performances in iontronic power source not only offer useful paradigms for wearable electronics, but also indicate a strategy and direction into high-power energy conversion from low-grade environmental source.

Introduction
Iontronics have attracted increasing attention with the ever-growing advancement of human-machine interaction1,2. Unlike conventional electronics that rely on electrons as charge carriers, iontronics integrate electron-ion charge transport and signal exchange at interfaces, enabling diverse functionalities3,4. Such versatility has driven the development of iontronic devices, including transistors5–7, sensors8,9, memristors10,11, and power generators. Among them, iontronic power generator (IPG) enables the conversion of natural energy into electricity, making it essential for self-sustaining devices and bioelectronic applications12–14. IPG can form asymmetric ion/electron interfaces within ion gradient in response to external stimuli such as light, heat and mechanic force, driving ion diffusion and ion-electron interaction across asymmetric interfaces15–18. Thus, the induced asymmetric interfaces serve as the backbone for charge transport and energy conversion in IPGs.

Over the past decade, various strategies have been developed to enhance the responsive asymmetry of interfaces, including designing multiscale hierarchical architectures19,20, engineering heterogeneous device structures21–23, and developing highly sensitive functional materials24. These advancements have significantly improved power-generation performance. Beyond stimulus-induced asymmetric ion-electron interfaces, intrinsic asymmetric ion-electron interfaces naturally exist in biological systems and play a crucial role in efficient bioelectricity generation, as exemplified by heterogeneous charged lipids25,26. In light of this, the direct construction of intrinsic asymmetric iontronic-interfaces (IAIs) provides an alternative approach for achieving artificial high-performance power generation.

We find that a pair of nanostructured materials with different ionizable functional groups and interface polarity in an electrolyte, naturally acquires distinct surface charge and ions at the interfaces. This enables controllable construction of IAIs without the need for external stimuli. Previously, IAIs have been utilized in asymmetric electrochemical supercapacitors or primary volta cell, enhancing energy storage density or enabling disposable power supply27,28. However, IAIs for sustainable and high-power energy generation have yet to be reported. Achieving reversible and efficient ion/electron migration based on simply asymmetric two-electrode configuration, without specific stimulus or pre-charging process, remains a challenge.

Results
Design principle for reversible power generation
Herein, we report a reversible iontronic power generation by adopting IAIs and controllable energy-release gate (Fig. 1). The IAIs are composed of capacitive electrode pairs featured with positive surface charges and considerable intrinsic capacitances (Ci), contributing to sufficiently inherent pre-storage of reversely charged ions at interfaces in a charge-free manner. The energy-release gate is designed with an on-off switch, which can be triggered by various environmental energy sources such as light, heat, or force. Cycling power generation mainly relies on reversible interfacial-ion oscillation, assisted by dissolved oxygen-mediated interfacial redox reaction during on-off switching of energy-release gate. As a result, the asymmetric-electrodes based power generator (AEPG) is capable of chemically driven re-generation and energy storage based on ion-electron coupling effect, enabling the energy conversion from waste low-grade chemical energy into electric output. Importantly, the chemical energy of oxygen and water molecules, a ubiquitous resource in ambient environment, could provide a sustainable energy source for this process. In general, the IAIs facilitate ion-electron coupling interaction, and the energy-release gate optimizes the energy conversion pathway, synergistically ensuring giant electric output. The cycling AEPG can supply an ultra-high peak current and power density of up to 5 A and 3680 Wm−3, the highest value among other sorts of typical IPGs reported to date.

Construction and characterizations of intrinsic asymmetric iontronic-interfaces (IAIs)
In principle, asymmetric material pairs are suitable for the construction of IAIs. The nanostructured MnO2 and titanium carbide (Ti3C2Tx) MXene emerge as representative candidates, attributed to the following advantages: 1) opposite surface charges and surface polarities, 2) engineered nanostructures that enable intrinsic ion pre-storage at interface, 3) solution processability for scalable fabrication.

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicate that nanostructured MnO2 is composed of uniform nanoparticles with size of in range of several hundred nanometers (Fig. 2a and Supplementary Fig. 1). The MXene nanosheets were synthesized by selectively etching method29. The lateral size of MXene nanosheets is 1~3 μm as determined by TEM (Fig. 2b and Supplementary Fig. 2a−c). The selected area electron diffraction (SAED) pattern of MXene nanosheets exhibits hexagonal symmetry, confirming the crystalline nature of hexagonal phase (Supplementary Fig. 2d). X-ray photoelectron spectroscopy (XPS) demonstrates the presence of Mn-OH functional groups on the surface of MnO2 nanoparticles, along with −F/O/OH functional groups on MXene nanosheets (Supplementary Fig. 3). As result, the distinct ionizable functional groups contribute to the differentiation in interfacial polarity and surface charge characteristics between the MnO2 and MXene materials.

The MnO2 nanoparticles and MXene nanosheets demonstrate superior solution processability. Flexible MnO2 film is readily fabricated by blade-coating, and paper-like MXene film is prepared by dip-coating onto an interconnected cellulose scaffold (Fig. 2c and Supplementary Fig. 4). Proton-acid treatment30 can enhance the ambient stability of MXene films by suppressing water and oxygen intercalation (Supplementary Fig. 5). The as-prepared MnO2 and MXene films both exhibit porous nanostructures, which facilitate interfacial interactions and ion transport (Supplementary Fig. 6 and 7).

Furthermore, we analyze the interfacial properties of IAIs. Zeta potential testing indicates that MnO2 and MXene films are positively and negatively charged, respectively, as a result of surface functional group dissociation (Fig. 2d). Kelvin probe force microscopy (KPFM) testing shows surface potential difference between MnO2 (~120 mV) and MXene film (~−285 mV, Fig. 2e and f). The work functions of MnO2 (4.5 eV) and MXene film (4.1 eV) are determined by ultraviolet photoelectron spectroscopy (UPS, Fig. 2g). These results consistently confirm the reverse surface charge characteristic of the two materials, resulting in an intrinsic potential difference. Benefiting from distinct surface charge and porous nanostructures, the interfaces of MnO2 and MXene are capable for spontaneously storing sufficient interfacial ion based on electric double layer (EDL) effect, thereby facilitating natural formation of IAIs. To further quantify the intrinsic ion storage at interface, we introduce a parameter of intrinsic interfacial capacitance (Ci), which can be measured by electrochemical impedance spectroscopy (EIS)31 (see the Methods section for details):

Z'' = 1 / (2πf * Ci) (1)

where f and Z” represents frequency and imaginary part impedance, respectively. The low-frequency response in EIS can reflect the capacitive characteristics of interface, which are related to ion adsorption and accumulation at interface. As shown in Fig. 2h, the Ci of MnO2 and MXene (2×2 cm2) is 62 and 83 mF, respectively, demonstrating substantial ion accumulation at interface. Therefore, the interfaces of MnO2 and MXene demonstrate clear iontronic asymmetry and significant intrinsic storage, validating the available construction of IAIs (Fig. 2i).

Electric output performance of asymmetric-electrodes based power generator (AEPG)
The AEPG device adopts a sandwich structure, consisting of IAIs separated by an ultrathin cellulose membrane and immersed in an aqueous NaCl electrolyte (Supplementary Fig. 8). Due to interfacial asymmetry of IAIs, the intrinsic electrode potential (Eintrinsic) of MnO2 electrode (~0.48 V) versus to Ag/AgCl reference electrode obviously exceeds that of MXene (~0.04 V) at pristine state (Supplementary Fig. 9a). The AEPG unit (2×2 cm2) featured with low internal resistance (~4 Ω), can generate open-circuit voltage (Voc) and short-circuit current (Isc) peak of up to 0.45 V and 30 mA (Fig. 3a and Supplementary Fig. 9b). The AEPG device retains ~46% of its initial current after cycling power generation for 280 h, underscoring its repeated electricity-generating capability (Supplementary Fig. 10). Both interfacial asymmetry and Ci are essential for achieving high-performance electric output. For instance, symmetric electrode pairs exhibit negligible Voc and Isc. The asymmetric MnO2-graphite or MXene-graphite device renders a minimal Isc alongside considerable Voc as result of low Ci of graphite (1.9 μF cm−2, Supplementary Fig. 11). In contrast, MnO2-MXene AEPG offers superior Voc and Isc, outperforming other devices. Diverse potential-asymmetric electrode pairs can be harnessed to construct IAIs, and corresponding AEPGs deliver favorable performance, elucidating the power-generating universality (Supplementary Fig. 12).

The AEPG delivers cyclic electric output without pre-charging from an external electric power. After the completed release of pre-stored energy through prolonged short-circuiting discharge, the AEPG recovers to its initial voltage (~0.45 V) at re-off state, validating its inherent regenerative property (Fig. 3b and Supplementary Fig. 13). Moreover, the AEPG can be discharged in a tunable constant-current manner. Upon discharging to 0 V, the full-discharged AEPG repeatedly recovers its voltage at the re-off state, further affirming re-generating behavior (Fig. 3c and Supplementary Fig. 14).

Relying on an intermittent cyclic power generation mode, the AEPG undergoes cycles of regeneration, energy storage, and periodic energy output during discharge. This mode inspires the design of an environment-triggered energy-release gate, facilitating the device to achieve an adaptive and environmentally compatible intermittent operation. The energy-release gate can be implemented through a stimuli-responsive on/off switch, as illustrated in Supplementary Fig. 15. To verify its effectiveness, we systematically compare the current and electric energy output characteristics of the device with and without the energy-release gate. In the absence of an energy-release gate, the device generates continuous current output upon triggering on-state, but the current rapidly drops from 30 mA to 0.015 mA within ~1 min (Fig. 3d). Correspondingly, the output energy curve exhibits a plateau, with the output electricity energy density approaching a limited value of 16.5 J m−2 (~115 h, Fig. 3e), exhibiting disposable power supply. In contrast, the AEPG with energy-release gate affords intermittent cyclic current signals (Fig. 3f). The output energy density exhibits a linear accumulation with the increasing cycles, reaching up to 543 J m−2 (~115 h, Fig. 3g), which is ~33 times higher than that of device without energy-release gate. The result reveals that energy-release gate is available for optimizing energy conversion pathway and essential to giant electric output. In the lack of an energy-release gate, the generated energy of device is unable for accumulation, leading to continuous but weak current output that is practically unusable. In essence, the energy-release gate enables physicochemical interface modulation, which allows ions to be stored at the interface and then collectively released, thereby optimizing energy conversion pathway. The paradigm of slow harvesting and collective release, provides an alternative route for achieving giant conversion from low-grade energy.

The electrode nanostructure facilitates interfacial ion adsorption owing to its high specific surface area, thus ensuring high current output (Supplementary Fig. 16). The AEPG operates reliably over a wide temperature range (0 to 60 oC, Supplementary Fig. 17) and shows good compatibility with hydrogel electrolyte (Supplementary Fig. 18). The AEPG operates in various electrolytes, with performance differences arising from variations in ion mobility (Supplementary Fig. 19a). The generated voltage varied slightly with the ion concentration, while the current signal exhibited increasing variation with ascending concentration owing to enhanced Ci and ion migration (Supplementary Fig. 19b). On the account of the influence of separator thickness on device resistance, the current output of AEPG was visibly decreased with increasing spacing (Supplementary Fig. 19c and d). Different recovery time has an effect on electric output, because AEPG requires an adequate recovery period to return to its initial state (Supplementary Fig. 20).

Validation of the electricity-generating mechanism
The underlying mechanism of AEPG can be ascribed to reversible ion migration mediated by redox reactions at asymmetric ion/electron coupled interfaces, thereby integrating chemical energy harvesting, interfacial storage, and electrical conversion within a simple two-electrode configuration (Fig. 4a). Specifically, reversible electricity generation in AEPG proceeds through three distinct states: original, discharging, and re-generating. In the original state, MnO₂ and MXene films inherently exhibit opposite surface charges and selectively adsorb counter-ions through functional group ionization, resulting in IAIs formation. Upon triggering gate-on for discharging, interfacial ions are released away from interfaces through the internal circuit. Meanwhile, the electrons flow through external circuit and excess electronic charge accumulates at electrode surfaces. Prior studies have demonstrated that interfacial redox reaction could induce charge transfer to power electricity generation and even drive spontaneous catalysis32–36. On this basis, accumulated electric charge can be transferred by spontaneous interfacial redox reaction during the regeneration process, leading to ion re-adsorption and energy regeneration in AEPG. Through reversible ion/electron coupling, the AEPG achieves cyclic power generation. Unlike air self-charging batteries that rely on bulk ion insertion/extraction37–39, the AEPG operates via interfacial ion migration. In contrast to conventional IPGs with simultaneous energy generation and discharge, the AEPG decouples these processes. The harvested environmental energy is stored then released collectively, contributing to unprecedent performance output (Supplementary Fig. 21).

Above-mentioned mechanism is further supported by experimental and theoretical results related to interfacial ion migration and electron transfer. Electrochemical quartz crystal microbalance (EQCM) monitors trace-level mass change (Δm) through frequency change (Δf), enabling real-time tracking of ionic fluxes at interface (Fig. 4b). Upon discharging, a significant decrease in electrode mass is observed, signifying the expulsion of interfacial ion from interface (Fig. 4c). In the re-generating state, the electrode mass increases and returns to its initial value due to the ion re-migration to interface. The periodic variation in the electrode mass provides strong evidence for the reversible ion migration at interface during cycling power generation. Kinetic Monte Carlo simulation further uncovers reversible ion migration, which is modeled by electrode pairs with opposite charges (Supplementary Fig. 22). Simulated ion distribution at interfaces renders reversible variation during cyclic power generation, coinciding with the experimental results (Supplementary Fig. 23).

Along with interfacial ion-oscillation, the electrode potential exhibits dynamically reversible fluctuations during electricity generation (Fig. 4d and Supplementary Fig. 24). Cyclic voltammogram curves of electrode display a notably rectangular shape within the scanning window corresponding to fluctuated range, devoid of discernible redox peaks, elucidating their capacitive property and reliable electrochemical stability (Supplementary Fig. 25). In-situ Raman spectra illustrate that the characteristic peaks of MnO2 and MXene electrodes remain no discernible variation during cycling electricity generation, demonstrating their stable phase structure characteristics (Fig. 4e and Supplementary Fig. 26). The morphological microstructure and chemical composition of the electrodes display negligible change after energy generation cycles, as verified by SEM and X-ray photoelectron spectroscopy results (Supplementary Fig. 27 and 28).

In the re-generating process, the accumulated interfacial charge could initiate interfacial redox reaction, which plays a critical role in ion re-adsorption and energy regeneration. Interfacial charge transfer consumes dissolved oxygen or yields reactive oxygen intermediates (e.g., hydroxyl radical)34,38,40. To validate this mechanism, dissolved oxygen concentration in the electrolyte is monitored during cycling electricity generation using dissolved oxygen meter (Supplementary Fig. 29a). The concentration of dissolved oxygen decreases obviously after repeated electricity generation, indicating oxygen consumption during re-generating process (Fig. 4f). The consumption amount of oxygen correlates positively with the transferred charge (Supplementary Fig. 29b). When oxygen into the electrolyte is inhibited, the AEPG device fails to recover its voltage, whereas vigorous stirring greatly enhances oxygen mass transport and lead to rapid regeneration (Supplementary Fig. 30a and b). The spontaneity of the interfacial redox reaction is confirmed using a galvanic-like cell configuration, where the observed cell voltage (~0.2 V) indicates that dissolved oxygen-mediated interfacial electron transfer could be thermodynamically favorable (Supplementary Fig. 30c and d). Above results coherently corroborates the significant role of dissolved oxygen in mediating interfacial charge transfer.

EPR spectroscopy is employed to detect hydroxyl radical (·OH) during re-generating process, using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trapping agent40–42. As shown in Fig. 4g, no visible signal is detected on the MXene electrode prior to power generation. In contrast, the quadruplet DMPO-·OH (1:2:2:1) characteristic peaks appears during power generation, evidencing hydroxyl radical formation. Meanwhile, no DMPO-trapped radical signals are detected at the MnO2 electrode either before or after power generation. Therefore, the observed dissolved O2 consumption and •OH formation can verify the presence of the interfacial reaction, which mediates interfacial charge transfer and supplies the driving force for reversible ion migration and energy regeneration.

In the energy conversion process of AEPG, low-graded chemical energy derived from interfacial redox reaction could serve as the energy input. This input is harvested and stored at EDL interfaces as an intermediate state, and ultimately converted into electrical energy. The energy conversion efficiency of APEG is estimated to be about 23% (Supplementary Fig. 31, see the Supplementary Note 1 for details).

Scalable manufacturability and integration of flexible AEPGs
Due to the excellent solution processability of MnO2 nanoparticles and MXene nanosheets, they can be formulated into an ink, enabling scalable and industry-compatible manufacture. By utilizing continuous roll-to-roll coating and dip-coating techniques, the large-scale production of MnO2 and MXene films becomes feasible with low cost, paving the way for practical applications (Supplementary Fig. 32 and 33 and Supplementary Video 1). A roll of electrode materials with a length of up to 4.5 m is displayed in Fig. 5a. AEPGs with different sizes are feasible with ease and exhibits favorable electricity-generating performance (Supplementary Fig. 34). The generated Isc of AEPG increase linearly with the device area, verifying the scaling current output of AEPG. Unprecedently, a large-area AEPG, comparable in size to A4 paper, delivers an Isc of more than 5 A, representing the highest value among other sorts of typical IPGs reported to date (Fig. 5b and d, Supplementary Table 1). By integration in series, the Voc of AEPGs increases proportionally with the number of units, reaching around 6 V with 13 units (Fig. 5c and Supplementary Fig. 35). Previously reported IPGs exhibit low current density and limited performance-scalability, primarily due to the bottleneck in achieving synchronized stimulus-response behavior over large areas, which significantly constrains overall current output43. The complicated processing of device manufacture further hinders its feasibility for large-scale applications44. Strikingly, the AEPG enables a linearly scalable output, attributed to its high current density, scalable manufacturability and innovative working mechanism.

Benefiting from foldable traits of materials, the scalable AEPG device can be further transformed into miniaturized and portable reconfiguration by using stacking strategy, which fully exploit vertical space. A tiny bulk of monolithic device (2 cm × 2 cm × 5 mm) supplies an Isc of ~143 mA, a giant area power density of 18.4 Wm−2, and a volumetric power density of up to 3680 Wm−3 with a load resistance of 5 Ω, prior to that of reported IPGs (Fig. 5e and Supplementary Fig. 36). Additionally, the AEPG is highly flexible and durable under repeated mechanical deformations (Supplementary Fig. 37). Even after bending for 1000 cycles, AEPG still maintains 95% current level (Fig. 5f and Supplementary Video 2), which make them highly suitable for powering wearable and flexible electronics that require high resiliency to various deformations.

Application demonstration for AEPG
As depicted in Fig. 6a, we developed a self-powered smart textile capable of on-demand electricity supply, intelligent luminescence display and real-time environmental sensing. The system integrates AEPGs with circuit design to function as a self-powered power source. The architecture primarily consists of AEPGs for electricity generation, a body-coupled energy-release gate driven by sorts of human motions (e.g., breathing, walking, arm movement), a power manager module for energy storage and circuit boosting, and a microcontroller for signal transmission, all of which can be woven within the fabric (Fig. 6b–d and Supplementary Fig. 38). The electric output of AEPGs is stored in a commercial lithium-ion battery and subsequently converted to a standardized 5 V output through a custom-designed booster circuit, enabling sufficient charging of various wearable electronics, such as smart telephone (Fig. 6e–g and Supplementary Fig. 39).

A flexible fiber-base electroluminescent indicator light is seamlessly integrated into clothing and efficiently powered by the integrated AEPGs. The intelligent luminescence display enhances self-visibility, thereby ensuring safer navigation in low-light conditions (Fig. 6h, Supplementary Fig. 40 and Supplementary Video 3). In addition, an ambient sensor, activated by self-powered supply system, enables real-time detection of atmospheric temperature and relative humidity. The collected data is transmitted to a microcontroller chip, which further relays the information to the textile display (Supplementary Fig. 41a). This real-time monitoring allows users to effortlessly track outdoor climate conditions, enhancing environmental awareness. This on-body interactive system could be particularly beneficial for individuals with conditions such as cerebrovascular disease or peripheral neuritis, who may have impaired sensitivity to environmental temperature and humidity (Supplementary Fig. 41b). By improving environmental perception, the system provides timely feedback and appropriate wear guidance, enhancing user comfort and safety.

Discussion
In summary, we have developed a facile strategy to achieve giant power generation by integrating naturally asymmetric iontronic-interfaces with a controllable energy-release gate. The asymmetric interfaces facilitate ion-electron coupling interaction, and environment-compatible gate optimizes the energy conversion pathway. Based on reversible interfacial ion migration mediated by interfacial redox reaction, the AEPG delivers an ultrahigh peak current and volumetric power density of up to 5 A and 3680 Wm-3, respectively. Unlike conventional IPGs with simultaneous energy generation and discharge, our AEPG can decouple discharging and re-generating steps and implement “slow harvesting then collective energy-release” paradigm, thus leading to unprecedent performance output. Through continuous solution-coating techniques compatible with industrial production, large area flexible AEPGs can be mass-produced and endure repeated bending for thousands of cycles. The proof-of-concept application demonstration of AEPGs in self-powered smart textiles underscores their practical potential. This work paves the way for interface engineering strategies toward next-generation high-power iontronic power sources.

Methods
Preparation of MXene nanosheets dispersion
MXene dispersion was synthesized through etching method. Typically, 3.2 g of LiF (Sigma Aldrich) was added to 40 mL HCL solution (Sigma Aldrich, 9 mol L−1) under magnetic stirring. 2.0 g of MAX powder (Jilin 11 technology Co., Ltd., 400 mesh) was slowly added to the mixture. Then the solution was stirred at 45°C for 36 h. After reaction, 100 mL of deionized water was added to terminate the reaction. The accordion-like MXene product was washed with deionized water for several cycles by centrifugation (2000 g, 5 min) until the supernatant became neutral. The resulting sediments were dispersed into deionized water, and sonicated for 15 min to accomplish exfoliation. Next, the solution was centrifuged at 1250 g for 30 min to remove the impurities. The purified Ti3C2Tx dispersion was further concentrated by centrifugation (2000 g, 45 min). Finally, the sediments were dispersed into deionized water to obtain 20 mg mL−1 MXene nanosheets dispersion.

Preparation of MnO2 slurry
Polyvinylidenefluoride (PVDF, Mw ~275000, 10 g) was dissolved in 500 mL N-methyl-2-pyrrolidone (NMP, Aladdin) to obtain uniform solution. Then ball-milling MnO2 nanoparticles (1.6 g), Super-P carbon black (SuperP, 0.2 g) and 10 mL PDVF solution were mixed by a planetary mixer at 330 g for 10 min (DAC 330-100 SE, FlackTek SpeedMixer). Finally, the uniform MnO2 slurry was obtained.

Fabrication of AEPG device
The MnO2 film were fabricated by continuous blade-coating. The MnO2 slurry was coated on graphite foil and dried at 90 oC to remove NMP solvent. The MXene electrode were obtained by dipping coating. The cellulose paper (thickness of 0.15 mm) was dipped into 20 mg mL−1 MXene dispersion and dried at 60 oC. The as-prepared Mxene membrane is soaked into 0.1 M HCl for 10 min and washed by deionized water. Proton-acid treatment can remove extrinsic intercalants and enhance interlayer interactions, thereby improving the ambient stability of MXene by limiting the intercalation of H2O and O2 in the open air. Next, the as-prepared MnO2 and MXene films, and cellulose separator were stacked in a sandwich-type configuration with electrolyte addition (0.2 mol L−1 NaCl aqueous solution).

Electric measurements
The performance of electricity generation testing was carried out on a Keithley 2612B (Keithley Instruments, Cleveland, OH.). The circuit parameter for recording Voc was set current to 0 nA. The circuit parameter of testing Isc was set voltage of 0 V. It should be noted that, for large-area AEPG devices, the device resistance is very small, and the resistance of measurement leads becomes non-negligible. In this case, the measured current signal corresponds to that under a finite load due to voltage division between the internal and lead resistance. Accordingly, the actual Isc was obtained by correcting the measured values with consideration of the voltage division. The SW-520D, KSD9700, XH-M131, MKA50202 on/off switches served as gate, which could be induced by mechanic force, heat, light, and magnetism stimulus, respectively. The electrode potential and cyclic voltammogram curve were tested on a CHI 760D electrochemical workstation (CH Instruments, Inc) by using a three-electrode electrochemical system. The investigated electrode, Pt foil, and saturated Ag/AgCl electrode was working electrode, counter electrode, and referenced electrode, respectively. The Ci was measured by electrochemical impedance (EIS) spectra. In the EIS test, the initial potential, frequency range and alternating current amplitude was set to Voc, 0.1 Hz−100 kHz and 5 mV, respectively.

In situ EQCM test
EQCM test was carried out by the use of the CHI440C (CH Instruments, Inc). The electrode material of MnO2 or Mxene was coated onto quartz crystal served as investigated electrode. The EQCM test allows for simultaneous recording of both Voc and Δf of the quartz crystal. The EQCM cell was placed on a vibration-isolated probe station to minimize mechanical disturbances and enclosed within a metal shielding box to eliminate electromagnetic interference.

Experiments on human participants
All experiments were approval by the Institutional Review Board of Tsinghua University (approval no. 20220227). All human participants gave written and informed consent before participation in the studies.

Characterization
Scanning electron microscope (SEM) were conducted by using a Sirion-200 field-emission scanning electron microscope (FEI Corporation, USA). Transmission electron microscope (TEM) were carried out on JEM-100Plus (JEOL, Japan). X-ray diffraction (XRD) patterns were taken on a Bruker AXS D2 PHASER diffractometer with Cu Kα radiation source (Bruker Corporation, Germany). X-ray photoelectron spectra (XPS) were obtained on an ESCALAB 250 photoelectron spectrometer (Thermo Fisher) with an Al Kα source. In situ Raman spectra were measured on a LabRAM HR Evolution Raman microscope with a 532 nm laser (HORIBA Jobin Yvon, France).

Kinetic Monte Carlo simulation
The kinetic Monte Carlo simulation was conducted by using N-Fold Way (NFW) algorithm. The rate of a diffusional hop was written as:
r = D0 exp(-ΔE / kBT) (2)
where ΔE, D0, kB and T refer to energy change induced by hop, frequency factor, Boltzmann constant, and temperature, respectively. The total energy of our coarse grain model was written as:
Etot = α Σ a,b=ions or electrodes (Z a Z b / d ab) + Σ b K b (Z b - Z ref)2 (3)
where α is denoted as a scaling factor, the former term is used to describe the interaction between ions. Za is the charge quantity of the ath ions or electrodes (1e or −1e for ions and ±3e or ±1e for electrodes). The d ensures that the coulomb attraction is sufficiently weak to be broken by kinetic energy (kBT). The dc and α were assumed 1 μm and 0.01 eV∙μm e−2 in the coarse grain model. Due to the differing Fermi levels of electrode pairs, electrons may transfer between electrode pairs, potentially disrupting charge neutrality at each electrode at gate-on state. Harmonic energy term (i.e., the second term) was employed to depict the physics wherein electrons transfer between two electrodes to minimize energy. The energy penalty arising from deviation from charge neutrality would hinder further electron transfer in the final stage. Eventually, the entire system reaches an equilibrium state. The second term, Kb is pre-factor (2 eV e−2), and Zref is a constant and equals to the average charge quantity of electrodes sites.

In the kinetic Monte Carlo simulations, the charge numbers of electrode pairs change based on 1 + exp(P * f * t / tsc) * P f (Nf - Ni), where Pf is the final electron recovery proportion, ts is the simulation time and tsc is the characteristic time, and Nf and Ni are the final and initial charge numbers of electrodes, respectively. The distribution evolution of ions is mainly focused.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this review, the authors report an ionictronic electricity generator based on intrinsic asymmetric interfaces and controllable energy-release, which exhibits high performance. This work indicate a new strategy for high-power energy conversion from low-grade environmental source. It is suggested that the paper can be reconsidered after major modifications.\n1. “The lateral size of the MXene nanosheets is 1~3 μm”. It's hard to be illustrated from the TEM.\n2. Please describe how the degree of ion accumulation at interface is reflected by electrochemical impedance spectroscopy.\n3. How is the mechanism of self-charging in this work different from that of recent air self-charging batteries.\n4. It is recommended to add the testing and application of the AEPG in hydrogel electrolyte systems.\n5. It is recommended that the author carefully review the article and polish the language to make the article language more refined.", "reviewer_2": "The manuscript presents the development of an asymmetric electrochemical power generator (AEPG) that functions through interfacial redox-mediated self-charging and discharging processes. The device demonstrates intermittent, cyclic electrical output enabled by a distinctive gate-switching mechanism and leverages reversible ion migration alongside interfacial charge transfer. This concept is both interesting and holds promise for advancing low-grade energy harvesting technologies. However, there are some fundamental and technical aspects that could benefit from further clarification and additional data prior to publication.\nBelow are several comments and suggestions that the authors may find helpful for strengthening their revised manuscript.\n1. The authors present an interesting working principle for the AEPG, describing it as “self-charging and ion oscillation based on interfacial electrochemical reactions.” However, providing more quantitative thermodynamic and kinetic analyses would greatly enhance understanding. In particular, clearer evidence from an energy conservation perspective supporting the claim that the interfacial reaction between MnO₂ and MXene acts as a spontaneously sustainable driving force would strengthen the argument. Additionally, including an evaluation of the energy conversion efficiency from the interfacial reaction to the electrical output would offer a more reliable assessment of the proposed mechanism’s feasibility.\n- For instance, while the spontaneity of redox reactions (such as MnO₂ with dissolved oxygen) is qualitatively described, incorporating quantitative data—such as ΔG values, reaction kinetics, and electrochemical potential diagrams—would further substantiate the claims.\n2. The term “self-charging” might be open to interpretation, potentially suggesting perpetual motion or conflicts with energy conservation principles. Since the manuscript lacks a quantitative assessment of the energy input from dissolved oxygen, the current wording might give the impression of operation without any external energy source, which may require a more cautious phrasing.\n3. To provide a more comprehensive evaluation, it would be helpful to include comparisons in Fig. 3a with other heterogeneous electrode pairs that exhibit similar interfacial potential differences. This could enrich the analysis of electrical output characteristics.\n4. The comparison between devices with and without the \"energy-release gate\" is quite insightful. To further strengthen the manuscript, it would be helpful to provide a clearer explanation of whether this gate acts primarily as a passive component controlling discharge conditions or if it involves an active mechanism contributing to energy conversion. Additionally, clarifying whether the gate functions at the circuit design level or as a physicochemical interface modulation element would enhance the reader’s understanding and the overall impact of the work.\n5. The observation that Raman peaks remain unchanged after long-term cycling is encouraging; however, additional evidence would help to more comprehensively assess electrochemical degradation. Incorporating more quantitative analyses, such as XPS, SEM, and TEM, to investigate changes in chemical composition and interface structure would provide stronger support for the material stability claims.\n6. The claim that dissolved oxygen acts as an electron acceptor is intriguing, but it would benefit from additional experimental support. Measurements such as pH variation, dissolved oxygen concentration in the electrolyte, and ORR kinetics could help to strengthen the evidence for this mechanism.", "reviewer_3": "In this manuscript, the authors report an ionictronic electricity generator based on intrinsic asymmetric interfaces and controllable energy-release, which has been tested with figure-of-merit numbers among the highest values in related field. In my opinion, the topic is urgent and the manuscript is well prepared. Therefore, I would give opportunity for publication, however, major revision is needed before final acceptance.\n1) The key concern is regarding the using of MXene as the fundamental material. It is known that MXene tends to be oxidized in the open air for long time of exposure, so how to solve the reliability issue of the developed device.\n2) What is the purpose of the choose of nanoparticle MnO2, please explain the the difference between the nanosizing and non-nanosizing.\n3) It is also known that MnO₂ undergoes significant volume expansion during the electrochemical process due to valence state changes of Mn. Therefore, it is necessary to clarify why such volume expansion does not occur during the self-charging process.\n4) In Figure 4c, there the obvious fluctuations in the curves, please explain the reasons.\n5) It is advisable to upload some videos of the application side to showcase its practical application effects, like Figure S23.", "reviewer_4": "This work describes ionic power sources based on reversible electron-coupled ion-oscillation with intrinsic asymmetric interfaces. The performance itself looks high, but the authors could not adequately explain the underlying mechanism of the redox reaction at the electrode interface, particularly the role of hydroxyl radicals, and how it contributes to the self-charging process. This is critical. In addition, it is unclear whether this system is generating energy or simply functioning as a continuously discharging capacitor. Overall, I am not positive for the publication of this work at this stage. The detailed comments are as follows:\n- The authors claims that interfacial redox reactions induce ion re-adsorption (i.e., self-charging). However, the underlying mechanism of the redox reaction is not sufficiently explained. Solid–liquid electrification of this kind is often triggered by external stimuli such as contact, temperature, or pressure. Therefore, the authors should more clearly analyze how the redox reaction is initiated and quantify the electron transfer energy barrier to substantiate the self-charging mechanism.\n- The device operational mechanism seems to be considerably affected by ambient moisture. Thus, it is crucial to assess its effectiveness under different humidity levels.\n- While the AEPG system undergoes a self-charging process, the specific role of the redox reactions remains unclear. The asymmetric potential and oppositely charged surfaces of the two electrodes can naturally form an electric double layer (EDL). The system may be able to re-establish the EDL after discharge without requiring a redox reaction. I wonder which part of the system necessitates the redox process. If redox reactions are essential for ion adsorption, a comparative analysis between redox-mediated and non-redox systems should be provided. In addition, cyclic voltammetry (CV) data supporting the redox process would be necessary to validate the presence and role of the reaction.\n- The operating mechanism of the system relies on the spontaneous formation of EDLs at the electrolyte–electrode interface, enabled by the asymmetric nature of the electrodes. During discharge, electricity is generated through ion–electron coupling. However, due to limitations in maintaining continuous energy generation, the system appears to function more like a capacitor (as also shown in the CV curves), rather than as an energy-harvesting device that continuously discharges via an external switch. Therefore, the author should clarify why the AEPG can be categorized as an energy-generating system in contrast to conventional systems, as shown in Figure 5d.\n- Furthermore, due to the energy-release gate mechanism, which repeatedly discharges stored energy, residual ion accumulation appears to occur during repeated charging–discharging cycles, as shown in Figure 3f. This may lead to performance degradation. I wonder whether there are effective strategies to mitigate this issue.\n- Additionally, as Figure 3f shows a continuous decrease in short-circuit current (Isc), I am curious about the long-term stability of this system and how it performs over extended periods.\n- This system operates through repeated charging and discharging cycles to generate energy. To maximize output energy, it may be necessary to determine the optimal durations for both charging and discharging phases."}, "author_response": "To make it clear, we have used blue fonts for our replies, and highlighted fonts for revision. A tracked version of the revised manuscript has also been uploaded to the submission web site.\nReviewer #1 (Remarks to the Author):\nIn this review, the authors report an ionictronic electricity generator based on intrinsic asymmetric\ninterfaces and controllable energy-release, which exhibits high performance. This work indicates a\nnew strategy for high-power energy conversion from low-grade environmental source. It is suggested\nthat the paper can be reconsidered after major modifications.\nReply: We sincerely appreciate the referee for the positive comments and constructive suggestions for\nimproving our manuscript. We have conducted additional experiments and added more discussions in\nthe revised manuscript. Corresponding revisions and explanations are summarized as below.\n1. “The lateral size of the MXene nanosheets is 1~3 μm”. It's hard to be illustrated from the TEM.\nReply: We have supplemented additional TEM characterization to support evaluation of lateral\ndimensions. The results consistently support the lateral size of MXene nanosheets predominantly\nranges from 1 to 3 m (Figure R1). Related data has been added in the revised manuscript (Page 6 and\n7).\nFigure R1. TEM images of the MXene nanosheets.\n2. Please describe how the degree of ion accumulation at interface is reflected by electrochemical\nimpedance spectroscopy.\nReply: The low-frequency response in electrochemical impedance spectroscopy (EIS) can reflect the\ncapacitive characteristics at the electrode/electrolyte interface, which are closely related to ion\nadsorption and accumulation at interface. Specifically, the intrinsic electric double layer (EDL) at the\ninterface exhibits a nearly capacitive impedance response under small-amplitude alternating current\n(AC) perturbation, which reflects the degree of interfacial-ion accumulation. By extracting the low-\nfrequency imaginary part of the impedance (Z′′) and combining it with the frequency (f), the intrinsic\ninterfacial capacitance (C ) can be calculated as:\ni\n1 1\n(cid:3398)𝑍(cid:4593)(cid:4593) (cid:3404) (cid:3400)\n𝐶 2𝜋𝑓\n(cid:3036)\nAccordingly, C could be determined in this work. A considerable C generally corresponds to a\ni i\nsufficient ion adsorption, quantitatively indicating substantial ion accumulation at the interface. This\nanalytical method has been widely adopted in previous studies (Nat. Commun. 2014, 5, 3317; J. Phys.\nChem. C 2024, 128, 3674−3674；J. Phys. Chem. C 2008, 112, 74867495). For instance, Vera et al.\nemployed EIS technique to quantify interfacial capacitance, underscoring correlation between\ncapacitance and ion adsorption at interfaces (J. Phys. Chem. C 2008, 112, 74867495).\nFurthermore, the calculated C of MnO₂ and MXene (2  2 cm2) were calculated to be 62 and 83 mF,\ni\nrespectively, substantially surpassing that of commercial graphite (7.6 F) by more than four orders\nof magnitude, thereby ensuring sufficient interfacial-ion adsorption and facilitating power generation\nprocess. As suggested, relevant discussion has been added to the revised manuscript (Page 8).\n3. How is the mechanism of self-charging in this work different from that of recent air self-charging\nbatteries.\nReply: Thanks for your good point. The recently proposed “air self-charging batteries” represent an\nemerging energy conversion technology (Nat. Commun. 2020, 11, 2199; Angew. Chem. Int. Ed. 2024,\n63, e202411845; Adv. Mater. 2024, 36, 2308042). The self-charging mechanism in our work is\nfundamentally different from that of air self-charging batteries, as summarized in Table R1. Air self-\ncharging batteries typically rely on ion insertion/extraction within electrode material (i.e., bulk-\nphase effect), along with its variation on bulk phase and valance state. Unlikely, AEPG mainly relies\non reversible intrinsic-ion migration at electrode/electrolyte interfaces (i.e., interfacial effect),\nwithout bulk structural or chemical valence change of electrode material. To systematically elaborate\nthe mechanism difference between AEPG and air self-charging battery, their working principles are\ndiscussed below:\nTable R1. Comparison between air self-charging battery and AEPG.\nAir self-charging batteries can supply electricity based on ion insertion/extraction within bulk-\nphase material. For example, Zhang et al. developed chemically self-charging aqueous zinc-ion\nbatteries based on CaV O ·3H O (CaVO) electrode (Nat. Commun. 2020, 11, 2199). During discharge\n6 16 2\nprocess, Zn²⁺ ions are inserted into CaVO electrode, leading to reduction of the vanadium (V) oxidation\nstate. In the self-charging process, the discharged CaZn VO electrode spontaneously undergoes\n3.6\nreduction with dissolved oxygen (Figure R2). Meanwhile, the Zn2+ ions are extracted from CaZn VO\n3.6\nand the oxidation state of V makes reversible recovery. The entire process involves reversible Zn2+ ion\ninsertion/extraction within the bulk-phase structure, accompanied by significant variation on oxidation\nstate and phase structure.\nFigure R2. Schematic illustration of working mechanism of self-charging aqueous zinc-ion batteries\n(Nat. Commun. 2020, 11, 2199).\nAEPG in our work exert power generation ascribed to reversible ion adsorption and desorption at\nmaterial interfaces (Figure R3). During discharge process, interfacial ions are released away from\ninterfaces, leading to electric output. In the self-charging process, accumulated electrons could be\ntransferred via spontaneous redox reaction with dissolved oxygen, resulting in ion re-adsorption and\nenergy regeneration. Such reversible processes mainly occur at the interfaces and maintain phase-\nstructure and valence state of electrode material.\nFigure R3. Schematic illustration of working mechanism of AEPG.\nIn summary, the self-charging behavior of AEPG devices arises from the reversible migration of\ninterfacial ions, whereas that of conventional batteries relies on the reversible insertion and extraction\nof ions within the bulk phase. These two fundamentally different self-charging mechanisms and device\narchitectures highlight the diversity and potential of emerging energy conversion strategies. Related\ndiscussion has been added in revised manuscript (Page 11) and highlighted.\n4. It is recommended to add the testing and application of the AEPG in hydrogel electrolyte systems.\nReply: Thanks for your insightful comment. Peering your suggestion, we have investigated the power-\ngenerating performance of AEPGs using polyacrylamide (PAM) hydrogel and polyacrylamide-\npolydiallyl dimethyl ammonium chloride (PAM-PDDA) double-network hydrogel as the electrolytes\n(Figure R4ac). The hydrogel was formed through photo-initiated polymerization in NaCl solution,\nwhich enabled ionic confinement within polymer matrix and facilitated ionic conductivity. And such\nhydrogels exhibit remarkable flexibility. The AEPG can generate a voltage of 0.43 V and current of\n29 mA in the PAM hydrogel electrolyte system, with a slight increase to 0.45 V and 35 mA in the\nPAM-PDDA hydrogel (Figure R4d and e). These results demonstrate its good compatibility and\nadaptability of the AEPG in hydrogel electrolyte, illuminating its potential application for self-powered\nsoft micropower source and portable electronics.\nRelated discussion has been added in revised manuscript (Page 11) and highlighted; related data has\nbeen added in Supplementary Information (Page 14).\nFigure R4. (a, b) Photographs of PAM and PAM-PDDA hydrogels. (c) Chemical structure of the\nhydrogels. (d) Voltage and current output of AEPGs based on PAM and PAM-PDDA hydrogels. (e)\nCurrent-time curves of AEPG based on PAM-PDDA hydrogel.\n5. It is recommended that the author carefully review the article and polish the language to make the\narticle language more refined.\nReply: Thanks for your valuable suggestion. We have carefully polished the language throughout the\nmain text to ensure a more refined presentation. Related revisions have been highlighted in the revised\nmanuscript.\nReviewer #2 (Remarks to the Author):\nThe manuscript presents the development of an asymmetric electrochemical power generator (AEPG)\nthat functions through interfacial redox-mediated self-charging and discharging processes. The device\ndemonstrates intermittent, cyclic electrical output enabled by a distinctive gate-switching mechanism\nand leverages reversible ion migration alongside interfacial charge transfer. This concept is both\ninteresting and holds promise for advancing low-grade energy harvesting technologies. However, there\nare some fundamental and technical aspects that could benefit from further clarification and additional\ndata prior to publication.\nReply: We sincerely appreciate the referee for the positive comments and constructive suggestions for\nimproving our manuscript. We have conducted additional experiments and added more discussions in\nthe revised manuscript. Corresponding revisions and explanations are summarized as below.\nBelow are several comments and suggestions that the authors may find helpful for strengthening their\nrevised manuscript.\n1. The authors present an interesting working principle for the AEPG, describing it as “self-charging\nand ion oscillation based on interfacial electrochemical reactions.” However, providing more\nquantitative thermodynamic and kinetic analyses would greatly enhance understanding. In particular,\nclearer evidence from an energy conservation perspective supporting the claim that the interfacial\nreaction between MnO₂ and MXene acts as a spontaneously sustainable driving force would strengthen\nthe argument. Additionally, including an evaluation of the energy conversion efficiency from the\ninterfacial reaction to the electrical output would offer a more reliable assessment of the proposed\nmechanism’s feasibility.\n- For instance, while the spontaneity of redox reactions (such as MnO₂ with dissolved oxygen) is\nqualitatively described, incorporating quantitative data—such as ΔG values, reaction kinetics, and\nelectrochemical potential diagrams—would further substantiate the claims.\n6. The claim that dissolved oxygen acts as an electron acceptor is intriguing, but it would benefit from\nadditional experimental support. Measurements such as pH variation, dissolved oxygen concentration\nin the electrolyte, and ORR kinetics could help to strengthen the evidence for this mechanism.\nReply: We thank the reviewer for the questions about energy conversion and microscopic mechanism.\nAs questions 1 and 6 are closely related, herein we address them together.\nFigure R1. (a) Schematic illustration of the configuration for dissolved oxygen measurement. (b)\nTime-dependent dissolved oxygen concentration during cycling electricity generation. (c) Correlation\nbetween oxygen consumption and transferred charge during electricity generation.\n1. The significance of dissolved oxygen\nWe propose that accumulated electrons are spontaneously transferred via interfacial redox reaction\nwith dissolved oxygen (i.e., electron acceptor), which thus acts as fundamental driving force for the\nrepeatable electricity generation. To validate this presumption, we have supplemented a series of\nexperiments result as suggested. First, dissolved oxygen concentration in the electrolyte was\nmonitored during cycling electricity generation using dissolved oxygen meter (JPSJ-605F, Figure\nR1a). It is noted that dissolved oxygen concentration is measured in a specifically sealed system to\nprevent oxygen replenishment from the ambient air. Before cycling power generation, the dissolved\noxygen concentration exhibited slight fluctuations and remained nearly constant value. After repeated\npower generation, the dissolved oxygen concentration decreased obviously, indicating oxygen\nconsumption during power generation (Figure R1b). Moreover, the amount of oxygen consumption\ncorrelates positively with the transferred charge (Figure R1c), further confirming the role of dissolved\noxygen in facilitating interfacial charge transfer.\nSecond, when oxygen dissolution into the electrolyte was inhibited, the AEPG device failed to\nrecover its voltage (Figure R2a), whereas vigorous stirring greatly enhanced oxygen mass transport\nkinetics and enabled rapid regeneration (Figure R2b), underscoring the kinetic importance of oxygen\navailability in the cycling electricity generation (Nat. Commun. 2024, 15, 8302). Third, the\nspontaneity of the interfacial redox reaction was confirmed using a galvanic-like cell configuration\n(Figure R2c). In this system, a cell voltage of 0.2 V was observed. According to the relationship\nbetween thermodynamic function and cell voltage (G = nFE), the Gibbs free energy change is less\nthan zero in this case, suggesting that dissolved oxygen-mediated interfacial electron transfer could be\nthermodynamically favorable, thereby supporting the energy conservation perspective. Above all,\nthese results demonstrate that the cycling electricity generation of AEPG is primarily driven by\ninterfacial ion migration coupled with O₂ redox reactions (Figure R2d). Dissolved oxygen, acting as\nan electron acceptor, spontaneously extracts the accumulated electrons and sustains repeatable power\ngeneration.\nFigure R2. (a) Voltage recovery of AEPG with different concertation of dissolved oxygen in\nelectrolyte. (b) Voltage recovery of AEPG with various solution stirring speed. (c) Photograph of the\ndesigned galvanic-like cell. (d) Schematic illustration of transfer pathway of accumulated electron.\n2. Energy conversion analysis\nThe O -mediated spontaneous redox reaction is regarded as the basic driving force for electricity\n2\ngeneration. The chemical energy stored in oxygen molecules, an abundant resource in ambient\nenvironment, can be converted into electricity energy through redox reaction (Nat. Energy 2020, 5,\n422; Nat. Commun. 2020, 11, 2199; J. Am. Chem. Soc. 2021, 143, 15369−15377; Adv. Mater. 2024,\n36, 2308042). In the energy conversion process of AEPG, low-graded chemical energy derived from\ninterfacial redox reaction could serve as the energy input. This input is harvested and stored at EDL\ninterfaces as an intermediate state, and ultimately converted into electrical energy. This working\nparadigm“slow harvesting and collective release” provide an alternative route for giant conversion\nfrom low-grade energy.\n3. Energy conversion efficiency\nWe have calculated energy conversion efficiency in the electricity generation process. In the per-\ncycle of power generation, the maximal energy input of dissolved oxygen-mediated redox could be\nestimated as:\n∆𝐺 (cid:3404) (cid:3398)𝑛𝐹𝐸 (cid:3404) (cid:3398)𝑄𝐸\n(cid:3036)(cid:3041)\n𝑄 (cid:3404) (cid:3505)𝐼𝑑𝑡\nwhere n, F, E, I, Q, and t represents amount of substance of electron, Faraday constant, voltage, current,\ntransfer charge and time, respectively. The measured voltage of interfacial redox reaction is about 0.2\nV. The transferred charge Q in per-cycle of electricity-generating process is essentially equal to the\ntotal charge during the discharge process and can be calculated by integrating the current-time curve.\nThe transfer charge Q is about 28.7 mC (Figure R3b). The energy input was evaluated from one\nelectrode interface. By assuming that both electrodes contribute equally, the total energy input is\nreasonably estimated to be ~11.6 mJ at 298 K. The electrical energy output of AEPG for per-cycle\ngeneration can be calculated by integration of current-time curve:\n𝑊 (cid:3404) (cid:3505)𝑈(cid:4666)𝑡(cid:4667)𝐼(cid:4666)𝑡(cid:4667)𝑑(cid:4666)𝑡(cid:4667) (cid:3404) (cid:3505)𝐼(cid:2870)(cid:4666)𝑡(cid:4667)𝑅𝑑(cid:4666)𝑡(cid:4667)\n(cid:3042)(cid:3048)(cid:3047)\nwhere U and R is the generated voltage and resistance, respectively. As result, the calculated electricity\nenergy is about 2.7 mJ (298 K, Figure R3c). Accordingly, the energy conversion efficiency (W /G )\nout in\nis estimated to be about 23 % at 298 K.\nFigure R3. (a) The current-time profile for per-cycle of electricity generation. (b) Accumulated charge\nfor per-cycle of electricity generation. (c) The electricity energy of AEPG for per-cycle power\ngeneration.\nIn conclusion, dissolved oxygen acting as an electron acceptor, spontaneously extracts the\naccumulated electrons and sustains repeatable power generation. Energy input source comes from\nchemical energy of dissolved oxygen molecules. Through EDL energy as an intermediation, input\nenergy is ultimately converted into electricity energy. The energy conversion efficiency of AEPG is\ncalculated to be about 23%. Thus, our work provides an alternative route for giant conversion from\nlow-grade energy.\nAs suggested, more experimental results and theoretical discussions have added in the revised\nmanuscript carefully. Related demonstration about energy source and underlying mechanism have\nbeen added to the revised manuscript (Page 1114 and Supplementary Information Page 2225) and\nhighlighted.\n2. The term “self-charging” might be open to interpretation, potentially suggesting perpetual motion\nor conflicts with energy conservation principles. Since the manuscript lacks a quantitative assessment\nof the energy input from dissolved oxygen, the current wording might give the impression of operation\nwithout any external energy source, which may require a more cautious phrasing.\nReply: We agree with this insightful point. To precisely elaborate our design concepts and avoid\npotential misinterpretation, the term “self-charging” has been removed throughout the manuscript.\nAlternatively, the AEPG device is now referred to as an “electricity generator” in the revised version.\nAs discussed in the response to Comment 1, the energy conversion process has been analyzed and\nquantitatively evaluated in accordance with energy conservation principle.\n3. To provide a more comprehensive evaluation, it would be helpful to include comparisons in Fig. 3a\nwith other heterogeneous electrode pairs that exhibit similar interfacial potential differences. This\ncould enrich the analysis of electrical output characteristics.\nReply: Thanks for your valuable comment. As suggested, we have evaluated the output performance\nof AEPG with sorts of diverse heterogeneous electrode pairs, including MnO -MoS , MnO -WC,\n2 2 2\nMnO -Active carbon (AC), RuO -WC, RuO -AC, RuO -MXene, Pt-MXene, Pt-WC, Pt-MoS .\n2 2 2 2 2\nRemarkably, all AEPGs based on different heterogeneous electrode pairs (2 2 cm2) are capable of\ndelivering electric output (Figure R4a). The high V can approach 0.54 V, and I is up to 32 mA for\noc sc\nPt-WC AEPG (Figure R4b). Thus, diverse potential-asymmetric electrode pairs can be applied to\nconstruct different types of AEPGs in principle, exhibiting unprecedent universality of AEPGs without\nmaterial restriction.\nRelated discussion has been added in the revised manuscript (Page 8). We have added Figure R4 to\nSupplementary Fig. 12 (Supplementary Information, Page 10).\nFigure R4. (a) Voltage and current output of AEPGs with different electrode pairs. (b)Voltage-time\nand current-time profiles of Pt-WC AEPG during power generation.\n4. The comparison between devices with and without the \"energy-release gate\" is quite insightful. To\nfurther strengthen the manuscript, it would be helpful to provide a clearer explanation of whether this\ngate acts primarily as a passive component controlling discharge conditions or if it involves an active\nmechanism contributing to energy conversion. Additionally, clarifying whether the gate functions at\nthe circuit design level or as a physicochemical interface modulation element would enhance the\nreader’s understanding and the overall impact of the work.\nReply: Thanks for your valuable and insightful suggestion, which has greatly inspired our thinking\nregarding the underlying significance of “energy-release” gate. The “gate” superficially appears to\ncontrol discharge condition. In essence, at the macroscopic conversion perspective, gate can allow\ncontrolled energy release, achieving desirable power, energy and efficiency output. Thus, it could\ncontribute to optimizing energy conversion pathway and improving conversion efficiency via “slow\nharvesting then collective energy-release” paradigm. At the microscopic mechanism level, the gate\nfunctions as a physicochemical interface modulation element, enabling controllable ion-storage and\nion-release at interface based on ion-electron coupling, which leads to unprecedent performance output.\nThe significance of gate is further elucidated in detail:\nFigure R5. (a) Energy-conversion pathway with and without energy-gate. (b) Comparison of current\noutput with and without energy-gate. (c) Comparison of electricity output with and without energy-\ngate.\n1) Energy-conversion pathway optimization\nIn the energy conversion process, low-graded chemical energy—originating from interfacial redox\nreaction—is regarded as the energy input, which could be ultimately converted into electricity power.\nThe designed gate decouples the electricity-harvesting and electricity-release processes, allowing the\nharvesting chemical energy to be stored as EDL energy as transition and collectively released as giant\nelectricity energy (Figure R5a). For this reason, we metaphorically refer to the gate as “energy-release\ngate”. In contrast, without the gate, this intermediate storage step is bypassed, and the input energy is\ndirectly and continuously converted into electricity in real time. However, the instantaneous electric\noutput under such conditions is extremely low (Figure R5b), which is insufficient for practical\napplications. In principle, the presence or absence of a gate has no influence on the energy input itself,\nbut the gate effectively optimizes energy conversion pathway (Figure R5c).\nFigure R6. Comparison of electric energy density output of AEPG with and without gate.\nAs displayed in Figure R6, the device without gate exhibits a plateau in the output energy curve,\nwith a limited energy density of 16.5 J m⁻² (~115 h). In contrast, the AEPG with gate achieves a linearly\naccumulating energy density of 543 J m⁻² (~115 h), about 33 times that of device without a gate.\nFurthermore, we analyzed the output electrical energy under identical energy input. Assuming the\nAEPG with a gate generate current I for t period, whereas device without gate delivers current I\n1 1 2\nwithin t period. Based on above analysis, we can assume I  I and t  t . For identical energy input,\n2 1 2 1 2\nthe transferred charge (Q) at interface could be regarded as equal:\nQ = I  t = I  t\n1 1 2 2\nAnd the device with or without gate generates electricity represents W and W , respectively, which\n1 2\ncould be calculated by:\n(cid:3047)(cid:3117)\n𝑊 (cid:3404) (cid:3505) 𝐼 (cid:3400)𝐼 (cid:3400)𝑅 𝑑𝑡\n(cid:2869) (cid:2869) (cid:2869)\n(cid:2868)\n(cid:3047)(cid:3118)\n𝑊 (cid:3404) (cid:3505) 𝐼 (cid:3400)𝐼 (cid:3400)𝑅 𝑑𝑡\n(cid:2870) (cid:2870) (cid:2870)\n(cid:2868)\nwhere R is resistance. Due to I  I , the generated electricity of AEPG with gate will surpass that of\n1 2\ndevice without gate (W  W ). Therefore, energy-release gate is available for optimizing energy\n1 2\nconversion pathway and essential to sustainable giant electric output.\n2) Physicochemical interface modulation\nAt the microscopic level, in the absence of a gate, dissolved oxygen–mediated interfacial reactions\ndrive ion transport but preclude substantial ion accumulation at the interface, thereby preventing\nutilization of the intrinsic interfacial capacitance. In contrast, the presence of gate enables ion\naccumulation at the interface, enabling to store EDL energy, which is collectively released and\nconverted into electrical energy. Consequently, gate provides effective interfacial modulation and\ncontributes to energy conversion.\nAbove all, the “energy-release gate” achieves physicochemical interface modulation, allowing\nions to be stored at the interface and then collectively released, thereby optimizing energy\nconversion and allowing efficient utilization of low-grade chemical energy. Related discussions\nhave been added to the revised manuscript (Page 10).\n5. The observation that Raman peaks remain unchanged after long-term cycling is encouraging;\nhowever, additional evidence would help to more comprehensively assess electrochemical degradation.\nIncorporating more quantitative analyses, such as XPS, SEM, and TEM, to investigate changes in\nchemical composition and interface structure would provide stronger support for the material stability\nclaims.\nReply: Thanks for your valuable comments. According to your suggestion, we have supplemented\nmore quantitative analyses (XPS, SEM, and TEM) of electrode pairs (MnO and MXene) before and\n2\nafter cycling electricity generation. The morphological microstructure of electrode pairs displays\nnegligible change after power generation, as verified by SEM and TEM results (Figure R7). Moreover,\nhigh-resolution XPS spectra show negligible shift in Mn 2p (MnO ) and Ti 2p (MXene) peaks after\n2\npower generation (Figure R8), demonstrating stability of chemical composition for electrode pairs.\nCoinciding with the in-situ Raman, above results can provide stronger support for the material stability.\nAnd the material stability also strengthens proposed working mechanism of AEPG.\nAs suggested, related discussions have been added to the revised manuscript (Page 13) and the\nSupplementary Information (Page 21).\nFigure R7. SEM images of MnO₂ before (a) and after (b) cycling electricity generation. (c, d) SEM\nimages of MXene before (c) and after (d) electricity generation. (e, f) TEM images of MnO₂ before (e)\nand after (f) electricity generation. (g, h) TEM images of MXene before (g) and after (h) electricity\ngeneration.\nFigure R8. (a) Comparison of XPS spectra of Mn 2p (MnO electrode) before and after power\n2\ngeneration. (b) XPS spectra of Ti 2p (MXene electrode) before and after power generation.\nReviewer #3 (Remarks to the Author):\nIn this manuscript, the authors report an ionictronic electricity generator based on intrinsic asymmetric\ninterfaces and controllable energy-release, which has been tested with figure-of-merit numbers among\nthe highest values in related field. In my opinion, the topic is urgent and the manuscript is well prepared.\nTherefore, I would give opportunity for publication, however, major revision is needed before final\nacceptance.\nReply: We sincerely appreciate the referee for the positive comments and constructive suggestions for\nimproving our manuscript. We have conducted additional experiments and added more discussions in\nthe revised manuscript. Corresponding revisions and explanations are summarized as below.\n1) The key concern is regarding the using of MXene as the fundamental material. It is known that\nMXene tends to be oxidized in the open air for long time of exposure, so how to solve the reliability\nissue of the developed device.\nReply: Thank you for your valuable comment. We fully agree that the environmental stability of\nMXene is a key concern for its practical application in energy conversion. In our work, we sought to\naddress this issue by adopting a proton acid treatment, as reported in the literature (Adv. Funct. Mater.\n2020, 30, 1906996), to remove extrinsic intercalants and enhance interlayer interactions, thereby\nimproving the ambient stability of MXene by limiting the intercalation of H O and O in the open air.\n2 2\nAs shown in Figure R1, the treated MXene retained its original color and morphological characteristics\nafter immersion in deionized water for 31 days, whereas the untreated MXene film suffered from\noxidation under the same conditions. These results confirm the improved environmental stability of\nthe proton-treated MXene.\nFigure R1. Photographs of untreated MXene (a) and treated MXene (b) immersed in deionized water\nfor different durations.\nImportantly, the MXene electrode maintains its microstructure and chemical composition during\ncyclic electricity generation, as verified by SEM, Raman and XPS analyses. No obvious morphological\nchanges were observed in the SEM images before and after power generation (Figure R2a and b),\nindicating its structural stability. In-situ Raman spectra illustrate that the characteristic peaks of MXene\nelectrode remain no discernible variation during cycling electricity generation (Figure R2c), indicating\nchemical stability of MXene. In addition, XPS analysis reveals that the Ti 2p peaks of MXene exhibit\nnegligible shifts after the cycles of energy generation (Figure R2d). As a result, such stability ensures\nthe reliable power-generating performance of device.\nFigure R2. SEM images of treated MXene before (a) and after (b) electricity generation. (c) Contour-\ntype in situ Raman spectra of treated MXene films during cycling electricity generation. (d) XPS\nspectra of Ti 2p (MXene electrode) before and after power generation.\nIn addition, it is worth emphasizing that the MnO -MXene asymmetric electrode pair was employed\n2\nas a representative model to conceptually validate electricity generation mechanism. Owing to the\ninherent universality of AEPG concept, considerable electric output has also been achieved using\nalternative, more stable electrode materials (e.g., nanostructured Pt and active carbon, Figure R3).\nUndoubtedly, electrode stability is a critical factor that governs device durability and cycling\nperformance. Therefore, our future efforts will focus on the rational design of electrode materials that\nconcurrently achieve high performance, long-term stability, and device-level applicability—an\nessential step toward the practical deployment of AEPG devices.\nAs suggested, related discussions have been added to the revised manuscript (Page 6 and 20) and\nthe Supplementary Information (Page 6).\nFigure R3. Voltage and current output of AEPGs with different electrode pairs.\n2) What is the purpose of the choose of nanoparticle MnO , please explain the difference between the\n2\nnanosizing and non-nanosizing.\nReply: The nanostructure of MnO plays a critical role in enhancing intrinsic-ion adsorption at\n2\ninterfaces due to its high specific surface area, which significantly contributes to improved current\noutput. Peering your suggestion, we have added a comparative analysis between nanosizing and non-\nnanosizing MnO . SEM images show that nanosizing MnO consists of uniform nanoparticles (~\n2 2\nhundreds of nanometers, Figure R4b), while the non-sizing MnO exhibits micrometer-scale structure\n2\n(Figure R4a). Furthermore, BET analysis reveals that nanosizing MnO possesses a higher specific\n2\nsurface area (65.1 m2 g1) compared to non-nanosizing counterpart (15.9 m2 g1), confirming its\nsuperior interfacial-ion adsorption capability (Figure R4c). Expectedly, the device based on nanosizing\nMnO achieves a higher current output (30 mA) compared to its nanosizing counterpart (10 mA, Figure\nhigh electric output attributed to increased specific surface area and interfacial ion adsorption.\nAs suggested, related discussions have been added to the revised manuscript (Page 10) and the\nSupplementary Information (Page 13).\nFigure R4. (a, b) SEM images of non-nanosizing and nanosizing MnO . (c) Specific surface area non-\n2\nnanosizing and nanosizing MnO and the correspondingcurrent output. (d) Current-time curves of\n2\n3) It is also known that MnO₂ undergoes significant volume expansion during the electrochemical\nprocess due to valence state changes of Mn. Therefore, it is necessary to clarify why such volume\nexpansion does not occur during the self-charging process.\nReply: We sincerely thank the reviewer for the point. While this perspective aligns with the\nconventional electrochemical behavior of MnO , it does not directly pertain to the AEPG device in our\n2\nwork, whose working mechanism is fundamentally different, as detailed below.\nIn typical electrochemical process, MnO usually undergoes bulk phase transitions and valence state\n2\nchange of Mn element under an externally applied bias, resulting in significant volume expansion.\nHowever, unlike conventional processes, the working principle of AEPG device mainly relies on\nreversible ion migration at the electrode-electrolyte interfaces without involving bulk structural change.\nAs a result, there could be no volume expansion or valence state change during the self-charging\nprocess.\nTo validate this point, we conducted structural and compositional analyses of the MnO₂ electrode\nbefore and after electricity generation. As shown in Figure R5a and b, the microstructure of MnO2\nshows negligible change after power generation. Moreover, XPS spectra show no noticeable shift in\nMn 2p peaks, indicating stable Mn valence state during electricity generation (Figure R5c).\nAbove all, the cycling power generation of AEPG mainly relies on reversible interfacial-ion\nmigration, which involves in interfacial effect rather than bulk-phase process, thus effectively avoiding\nthe bulk volume expansion.\nRelated discussion has been added in revised manuscript (Page 13) and highlighted; related data has\nbeen added in Supplementary Information (Page 21).\nFigure R5. SEM images of MnO₂ before (a) and after (b) cycling electricity generation. (c) XPS\nspectra of Mn 2p (MnO ) before and after power generation.\n2\n4) In Figure 4c, there the obvious fluctuations in the curves, please explain the reasons.\nReply: Thanks for your valuable comment. The mentioned fluctuations in Figure 4c can be attributed\nto the inherently high sensitivity of electrochemical quartz crystal microbalance (EQCM) technique.\nOwing to this sensitivity, EQCM is capable of detecting mass variations on the nanogram level.\nFigure R6. (a) Working principle of EQCM measurement. (b) Schematic illustration of the in-situ\nEQCM testing configuration.\nIn principle, EQCM enables real-time tracking the mass change of electrode, providing insights into\nion migration at interfaces during power generation (Figure R6a). The Sauerbrey equation is applied\nto convert the frequency shift (f) into mass change: f = Cm, where C is the sensitivity factor\nf f\nof crystal (C = 0.056 Hz ng1 cm2) and m is the change in mass of the coating material per unit area\nf\n(Nat. Mater. 2009, 8, 872875). To ensure reliable mass-frequency correlation, the quartz crystal is\nintentionally loaded with a minimal amount of material. Excessive mass loaded on the crystal electrode\ncauses the loss of resonance and reduce the sensitivity of the measurement. Although high sensitivity\nof EQCM make it sensitive to interfacial ion diffusion, it also renders the system highly susceptible\nto environmental disturbances, such as mechanical vibrations and electromagnetic interference. To\nminimize these effects, we constructed a built-in apparatus for EQCM testing as displayed in Figure\nR6b. The EQCM cell was placed on a vibration-isolated probe station to minimize mechanical\ndisturbances and enclosed within a metal shielding box to eliminate electromagnetic interference.\nNevertheless, it is difficult to eliminate all external perturbations entirely, thus, minor\nfluctuations and noise in the curves are sometimes inevitable. Importantly, the periodic variation\nof curves provides strong evidence for the reversible ion migration at interface during cycling power\ngeneration (Figure 4c in the main text), which is the key focus of our work.\nAs suggested, we have added related discussions have been added to the revised manuscript (Page\n21) and highlighted.\n5) It is advisable to upload some videos of the application side to showcase its practical application\neffects, like Figure S23.\nReply: Thanks for your helpful suggestion. We have supplemented application demonstrations of\nscalable manufacturability and practical application scenarios (Figure R7). As suggested,\ncorresponding videos have been uploaded in the Supplementary Video S2 and S4 to further showcase\nits applicability.\nFigure R7. (a) Photograph of continuous fabrication of electricity-generating film by roll-to-roll\ncoating. (b) Application demonstration of self-powered smart clothing for intelligent display and\nenvironmental perception.\nReviewer #4 (Remarks to the Author):\nThis work describes ionic power sources based on reversible electron-coupled ion-oscillation with\nintrinsic asymmetric interfaces. The performance itself looks high, but the authors could not adequately\nexplain the underlying mechanism of the redox reaction at the electrode interface, particularly the role\nof hydroxyl radicals, and how it contributes to the self-charging process. This is critical. In addition, it\nis unclear whether this system is generating energy or simply functioning as a continuously discharging\ncapacitor. Overall, I am not positive for the publication of this work at this stage. The detailed\ncomments are as follows:\nReply: We sincerely appreciate the referee’s helpful and constructive comments for further improving\nour manuscript. Accordingly, we have conducted additional experiments and added more discussions\nfor underlying mechanism and electricity-generating characteristic. Corresponding revisions and\nexplanations are summarized as below.\n- The authors claims that interfacial redox reactions induce ion re-adsorption (i.e., self-charging).\nHowever, the underlying mechanism of the redox reaction is not sufficiently explained. Solid–liquid\nelectrification of this kind is often triggered by external stimuli such as contact, temperature, or\npressure. Therefore, the authors should more clearly analyze how the redox reaction is initiated and\nquantify the electron transfer energy barrier to substantiate the self-charging mechanism.\n- While the AEPG system undergoes a self-charging process, the specific role of the redox reactions\nremains unclear. The asymmetric potential and oppositely charged surfaces of the two electrodes can\nnaturally form an electric double layer (EDL). The system may be able to re-establish the EDL after\ndischarge without requiring a redox reaction. I wonder which part of the system necessitates the redox\nprocess. If redox reactions are essential for ion adsorption, a comparative analysis between redox-\nmediated and non-redox systems should be provided. In addition, cyclic voltammetry (CV) data\nsupporting the redox process would be necessary to validate the presence and role of the reaction.\nReply: We are grateful for the reviewers’ insightful comments. Given that Comments 1 and 3 both\nrelate on the necessity and mechanism of the interfacial redox process, we respond to them together\nbelow.\nOur central point is that interfacial redox provides the electron-transfer pathway required to\nregenerate the intrinsic electric double layer (EDL), thereby enabling self-charging (Figure R1). In\nthe initial state, counter-ions are intrinsically adsorbed at the interfaces of asymmetric electrode pairs.\nAt gate-on state (i.e., discharging), these ions desorb; electrons flow through the external circuit and\nexcess electronic charge accumulates at electrode surfaces. In the absence of interfacial redox\nreaction, accumulated charge electrostatically hinders ion re-adsorption, so the original EDL\ncannot re-establish at open-circuit state—even with asymmetric electrodes. Experimentally, EQCM\nevidences reversible ion-migration at interface, alongside cycling performance and no electrode\ndegradation. In this case, there is certainly driving force for transferring accumulated electrons\nto ensuring reversible ion-migration.\nFigure R1. Comparison of the electron-ion coupling process at interfaces between the absence and\npresence of interfacial redox reaction, demonstrating the necessity of interfacial redox reaction for\nEDL and energy regeneration.\nFigure R2. (a) Schematic illustration of interfacial electron transfer mediated by dissolved oxygen in\npreviously reported work (Nat. Commun. 2022, 13, 130). (b) Summary of the redox reaction\nmechanisms induced by electrostatic charges at interfaces. Interfacial electrostatic charges can supply\nelectrons, electric fields, and radicals that are essential for initiating chemical reactions, as reported in\nprevious study (Adv. Colloid Interface Sci. 2025, 339, 103436).\nRecent studies have reported that dissolved-oxygen/water-mediated interfacial charge\ntransfer can power electricity generation and even drive spontaneous catalysis (Chem. Soc. Rev.\n2024, 53, 43494373; Nat. Commun. 2025, 16, 1692; Proc. Natl. Acad. Sci. 2019，116，1929419298;\nNat. Energy 2023, 8, 11371144). In such process, interfacial electron transfer consumes dissolved\noxygen or yields reactive oxygen intermediates (e.g., hydroxyl radicals), as schematically illustrated\nin Figure R2 (Nat. Commun. 2022, 13, 130; Adv. Colloid Interface Sci. 2025, 339, 103436). Inspired\nby these works, we attribute the regeneration step in the AEPG to a similar interfacial reaction that\nremoves the accumulated electronic charge. As shown in Figure R1, when the gate is on state,\ninterfacial ions desorb and electrons accumulate on the electrode surface. The stored interfacial charge\nthen initiates redox reaction. Dissolved oxygen and hydroxide ion can serve as electron acceptor and\ndonor, respectively. The redox-mediated charge transfer facilitates ion re-adsorption and EDL\nreconstruction. Therefore, ion reconstruction and energy regeneration necessitates this interfacial\nreaction, which serves as the driving force and external energy input for self-charging process.\nFigure R3. (a) Schematic illustration of the configuration for dissolved oxygen measurement. (b)\nTime-dependent dissolved oxygen concentration. (c) Correlation between oxygen consumption and\ntransferred charge during electricity generation.\nFigure R4. (a) Schematic of DMPO trapping hydroxyl radical for EPR measurement. (b) EPR spectra\nof electrode pair with/without power generation. (c) EPR spectra of electrode pair with/without power\ngeneration.\nFurthermore, we have supplemented a series of experimental results to validate our presumption.\nFirst, dissolved oxygen concentration in the electrolyte was monitored during cycling electricity\ngeneration using dissolved oxygen meter (JPSJ-605F, Figure R3a). It is noted that dissolved oxygen\nconcentration is measured in a specifically sealed system to prevent oxygen replenishment from the\nambient air. Before cycling power generation, the dissolved oxygen concentration exhibited slight\nfluctuations and remained nearly constant value. After repeated power generation, the dissolved\noxygen concentration decreased obviously, indicating oxygen consumption during power generation\n(Figure R3b). Moreover, the amount of oxygen consumption correlates positively with the transferred\ncharge (Figure R3c), further confirming the role of dissolved oxygen in facilitating interfacial charge\ntransfer. Second, using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a highly efficient spin-trapping\nagent in electrolyte (Nat. Commun. 2022, 13, 130; Nat. Commun. 2024, 15, 8367), we applied electron\nparamagnetic resonance spectroscopy (EPR, JEOL JES-FA 200) to track hydroxyl radical (OH)\nduring electricity generation (Figure R4a). Note that, for measurement convenience, MnO₂ and MXene\nwere separated into two electrolyte compartments linked by a salt bridge. As shown in Figure R4b,\nthere is no visible peak was measured on the MXene electrode before power generation. In contrast,\nthe quadruplet DMPO-OH (1:2:2:1) characteristic peaks were yielded on the MXene electrode during\npower generation, evidencing the formation of hydroxyl radical. By comparison, no DMPO-trapped\nradical signals were detected at the MnO electrode either before or after power generation. The\n2\naccumulated interfacial charge (e- or h+) can be transferred via proposed redox reaction, and\ncorrespondingly we can observe either dissolved oxygen consumption (at the electron-accumulating\nMnO interface) or hydroxyl radical production (at the hole-accumulating MXene interface).\nof the designed galvanic-like cell.\nThird, when oxygen dissolution into the electrolyte was inhibited, this “non-redox system” failed\nto recover its initial voltage (Figure R5a), underscoring the importance of redox availability in the\ncycling electricity generation. Fourth, the spontaneity of the interfacial redox reaction was\nconfirmed using a galvanic-like cell configuration (Figure R5b). In this system, a cell voltage of 0.2 V\nwas observed. According to the relationship between thermodynamic function and cell voltage (G =\nnFE), the Gibbs free energy change is less than zero in this case, suggesting that dissolved oxygen-\nmediated interfacial electron transfer could be thermodynamically favorable.\nFigure R6. Cyclic voltammogram curves of MnO (a) and MXene film (b) in a three-electrode\n2\nelectrochemical system. Platinum foil and Ag/AgCl electrode is used as counter and reference\nelectrodes, respectively. And the scan rate is 5 mV s1.\nCyclic voltammetry (CV) primarily delineates the electrochemical stability window and bias-driven\nfaradaic behavior. It is not diagnostic for interfacial reaction and charge transfer at open-circuit state.\nOn the other hand, CV curves of electrode display a notably rectangular shape within the scanning\nwindow corresponding to fluctuated range (Figure R6), devoid of discernible redox peaks, elucidating\nreliable stability of electrode material, in accordance with proposed mechanism.\nIn summary, the observed dissolved O consumption and •OH formation verify the presence of the\n2\ninterfacial reaction. This reaction serves as the pathway for interfacial charge transfer, which is\nnecessary for reversible ion re-adsorption, and thereby provides the driving force and chemical-energy\ninput for ion reconstruction and energy regeneration.\nAs suggested, more experimental results discussions on energy conversion have added in the revised\nmanuscript carefully (Page 1114, Supplementary Information Page 2025) and highlighted.\n- The device operational mechanism seems to be considerably affected by ambient moisture. Thus, it\nis crucial to assess its effectiveness under different humidity levels.\nReply: Thanks for the comments. According to the proposed mechanism, the device operation is not\nexpected to be affected by environmental humidity, since the electrode interfaces are already immersed\ninto electrolyte solution and electricity generation mainly relies on reversible ion migration coupled\nwith redox reaction at interface. In addition, we have evaluated the device performance at different\nrelative humidity. As shown in Figure R7, electric output remained unchanged as humidity increased\nfrom 30% to 70%, indicating the negligible influence of ambient humidity.\nFigure R7. The voltage (a) and current (b) of AEPG under different relative humidity.\n-The operating mechanism of the system relies on the spontaneous formation of EDLs at the\nelectrolyte–electrode interface, enabled by the asymmetric nature of the electrodes. During discharge,\nelectricity is generated through ion–electron coupling. However, due to limitations in maintaining\ncontinuous energy generation, the system appears to function more like a capacitor (as also shown in\nthe CV curves), rather than as an energy-harvesting device that continuously discharges via an external\nswitch. Therefore, the author should clarify why the AEPG can be categorized as an energy-generating\nsystem in contrast to conventional systems, as shown in Figure 5d.\nReply: Thanks for your comment. AEPG device is an energy-generating system that integrates\nchemical energy harvesting, interfacial storage, and electrical conversion, rather than a conventional\ncapacitor. To make distinction clear, we systematically compare working principles, performance\nparadigm, and energy conversion of the two systems.\n Conventional supercapacitor for energy storage: A supercapacitor must be pre-charged by an\nexternal electric power (Figure R8a). The applied bias injects electronic charge into electrode and\ndrives counter-ion adsorption, storing energy as ionic potential energy in the EDL. Upon discharge,\nthis stored energy is converted back into electrical output. Thus, energy conversion follows a pathway\nwhere electrical energy is transiently stored in the EDL before being released as electric output.\nWithout prior charging, a supercapacitor cannot supply power.\nFigure R8. Comparison of working principle, performance paradigm, and energy-conversion pathway\nbetween AEPG and supercapacitor.\n AEPG for electricity generation via chemical self-charging: The AEPG device delivers cyclic\nelectric output without pre-charging from an external electrical power, and hence can be categorized\nas an electricity-generating system (Figure R8b). Its self-charging/discharge processes rely on\nreversible interfacial-ion migration assisted by interfacial redox reaction, which serves as the driving\nforce for cycling power generation. The energy conversion of AEPG follows a pathway where\nchemical energy is transiently stored in the EDL before being released as electric output. Although an\nintermediate storage step is involved, the stored energy originates from interfacial redox rather than\nfrom externally supplied electrical input. Notably, the AEPG is not a single-use device. Owing to\nasymmetric interfaces, a small amount of ionic-potential energy is present at the outset. According to\nequivalent circuit model, this initial energy is estimated about 7.1 J m-2 (𝐸 (cid:3404)\n(cid:2887)(cid:3400)(cid:3022)(cid:3118)\n, C and U are intrinsic\n(cid:2870)\ninterfacial capacitance and voltage). The output energy density exhibits a linear accumulation with the\nincreasing cycles, reaching up to 543 J m2 (~115 h, Fig. 3g in main text), substantially exceeding\ninitial energy. This demonstrates net energy generation from interfacial chemistry, not mere release of\npre-stored energy.\nIn short, the AEPG device operates in a chemically self-charging mode that supports cyclic output.\nBy contrast, a capacitor merely stores externally pre-charged electrical energy and subsequently\nreleases it; thus, the two systems are fundamentally distinct. Related discussions have been added to\nthe revised manuscript (Page 10) and highlighted.\n- Furthermore, due to the energy-release gate mechanism, which repeatedly discharges stored energy,\nresidual ion accumulation appears to occur during repeated charging–discharging cycles, as shown in\nFigure 3f. This may lead to performance degradation. I wonder whether there are effective strategies\nto mitigate this issue.\nReply: Thanks for your comment. The performance degradation can be mainly attributed to the\nintrinsically limited kinetics of dissolved oxygen-mediated interfacial electron transfer, which hinders\nion re-adsorption and the full recovery of intrinsic interface during repeated self-charging/discharging\ncycles. Thus, efficient oxygen mass transfer could significantly promote interface recovery and\naccelerate re-generation process, for instance, by increasing temperature, stirring, or optimizing the\npore structure of materials (Figure R9). Alternatively, introducing suitable and efficient charge capture\nagents to substitute oxygen molecules could further facilitate electrons transfer, thereby improving\nrecovery process.\nRelated discussions have been added to the revised manuscript (Page 14) and the Supplementary\nInformation (Page 23).\nFigure R9. Voltage recovery of AEPG with various solution stirring speed.\n- Additionally, as Figure 3f shows a continuous decrease in short-circuit current (I ), I am curious\nsc\nabout the long-term stability of this system and how it performs over extended periods.\nReply: Thanks for your good comment. Following your suggestion, we have supplemented extended\nlong-term current-time curve, as shown in Figure R10a. The AEPG device retains ~46% of its initial\ncurrent after cycling power generation for 280 h, underscoring its repeated electricity-generating\ncapability. In addition, to further validate the ultra-long-term reliability of this electricity generation,\nour group has conducted cycling tests on the derivative AEPG (MnO -MoS ) for more than 8 months.\n2 2\nIts current retention is about 50% after tens of thousands of cycles lasting over 8 months (Figure R10b),\nreflecting remarkable durability.\nRelated discussions have been added to the revised manuscript (Page 8) and the Supplementary\nInformation (Page 9).\nFigure R10. (a) Current output of MnO -MXene AEPG during long-term power generation. (b) A\n2\ncontinuous recording of current density of MnO -MoS AEPG over more than 8 months of electricity\n2 2\ngeneration.\n- This system operates through repeated charging and discharging cycles to generate energy. To\nmaximize output energy, it may be necessary to determine the optimal durations for both charging and\ndischarging phases.\nReply: Thanks for your valuable comment. The AEPG device can decouple energy-harvesting and\ndischarging processes through the energy-release gate, where the “gate-off” state corresponds to\nenergy-harvesting and the “gate-on” state to discharging, thereby enabling repeated energy-harvesting\nand discharging cycles. We examined the effect of different on/off time ratios on electric output, with\nthe gate-on time set at 1s. As shown in Figure R11, the current output increases with recovery time\nand saturates after 20 min. This suggests that AEPG requires an adequate recovery duration to allow\nenergy re-harvesting following discharging. Insufficient recovery leads to reduced performance,\nwhereas prolonged gate-off time beyond 20 min yields no obvious improvement. Accordingly, an\noperation condition of 1s gate-on and 20 min gate-off was adopted in this work.\nRelated discussions have been added to the revised manuscript (Page 11) and the Supplementary\nInformation (Page 16).\nFigure R11. The plot of current output with different recovery time. The on-time and off-time is 1 s\nand recovery time, respectively."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The author has revised the comments, so it is recommended to accept.", "reviewer_3": "I accept the revised version.", "reviewer_4": "The authors carefully addressed all concerns made by the reviewers, so the revised version is ready to be published as is."}, "author_response": "Reply: Thank you very much for your positive comments on our manuscript.\nReply: We sincerely appreciate the referee for the positive comments.\nReply: Thank you very much for your positive comments on our manuscript."}]

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