Harnessing dual forms of water energy for all-weather high-performance electricity generation using amorphous slurry

Abstract

Harvesting ubiquitous water energy through hydrovoltaic technology offers a promising avenue for clean energy and has attracted significant interest. However, current hydrovoltaic systems are plagued by their reliance on a single form of water, which limits their current density to below 5 μA cm⁻² when humidity deviates from the optimal level. Here we present a dual-mode water-driven electricity generator (DWEG) that utilizes amorphous slurry to harvest energy from both moisture and liquid water through absorption and evaporation modes, respectively. Leveraging the efficient ion diffusion driven by water gradients at high humidity and the hydration free-energy difference at low relative humidity, this design achieves a current density above 144 μA cm⁻² across 5 to 90% relative humidity, and maintains a voltage of 0.7 V for over 420 hours at 90% relative humidity. We demonstrate that DWEG arrays can be readily scaled up to directly power desk lamps for more than five days, or even charge a tablet computer with an aluminum electrode. This work opens a route towards efficient energy harvesting from multiple forms of water energy under all-weather conditions.

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Broader context

Harnessing water energy through hydrovoltaic technology presents a transformative opportunity for sustainable energy generation. Current hydrovoltaic systems, however, are limited by their reliance on a single form of water, restricting their performance under varying humidity conditions. This work introduces a groundbreaking dual-mode water-driven electricity generator (DWEG) using amorphous slurry, inspired by natural seaweed, to efficiently harvest energy from both moisture and liquid water. Unlike traditional hygroscopic films, the amorphous slurry synchronizes structural integrity with water retention, enabling unprecedented performance across a wide range of humidity and temperature conditions. Leveraging the efficient ion diffusion driven by water gradients at high humidity and hydration free-energy difference at low humidity, this design achieves a current density above 144 μA cm⁻² across 5 to 90% relative humidity, and maintains a voltage of 0.7 V for over 420 hours at 90% relative humidity. Scalable through simple screen printing, integrated DWEG arrays power high-demand electronics like tablet computers without external power sources, showcasing their potential for real-world applications. This research not only advances hydrovoltaic technology but also opens new avenues for sustainable energy solutions, with significant implications for future research in micro-energy systems.

1. Introduction

Capturing energy from the water cycle offers a highly promising solution to escalating energy demands, as water absorbs nearly 70% of solar radiation that reaches the Earth's surface.^1,2 Hydrovoltaics, an emerging energy conversion technology,^3–5 can harness energy from ubiquitous water, such as droplets,^6–8 waves,^9,10 and moisture,^11–13 through interactions with functional materials. Especially, the evaporation-driven electricity generation and moisture-driven electricity generation have garnered significant interest owing to their versatility, sustainability, and portability.^14–16 However, evaporation-driven electricity generators require continuous vaporization of liquid water for sustained energy production,^17–19 whereas moisture-driven electricity generators rely on ample surrounding humidity.^20,21 As a result, the electric output of these generators is significantly limited by specific relative humidity (RH) levels, owing to reduced water vaporization at high RH and diminished moisture absorption at low RH. Recent studies have integrated solar energy to enhance water vaporization at high RH,^22–24 and developed heterogeneous films to boost voltage output at lower RH,^25,26 yet the current remained limited to a few micro-amperes or even nano-amperes when the humidity deviates from the optimal level.

In an effort to generate considerable electric output under varying humidity conditions, moisture absorption and water evaporation were integrated into the design, enabling continuous energy harvesting from environmental changes in moisture levels.^27–29 However, evaporation-driven electricity generation only occurs after moisture absorption, as these systems rely on a single form of water, limiting their effectiveness in arid regions. This limitation arises from the challenge of synchronizing the collapse of the hygroscopic film structure with its water retention capacity. In nature, seaweed mud consists of a complex matrix of microbes and organic and inorganic materials, all bound together by extracellular polymeric substances.³⁰ The hydrophilic groups in the organic materials naturally absorb water from ambient moisture, and the amorphous structure allows the mud to maintain its morphology upon absorbing liquid water (Fig. S1 and S2, ESI†), avoiding the structural collapse observed in polyelectrolyte films.^31,32 As a result, the seaweed mud serves as an ideal analogue for designing artificial composites capable of harvesting energy from both liquid water and moisture.

Here we propose a dual-mode water-driven electricity generator (DWEG) that utilizes amorphous slurry as an analogue of seaweed mud encapsulated within a resin matrix. The synthetic slurry, which includes cellulose nanocrystals (CNCs), poly(vinyl alcohol), and a water–glycerol binary solvent system, enables the DWEG to harness energy from moisture through the water gradient at high RH and from liquid water based on the hydration free energy difference at low RH (Fig. 1). Benefitting from abundant mobile ions produced by CNCs and strong water retention ability in the water–glycerol solvent, a DWEG unit produces a sustained voltage of 0.7 V for over 420 hours at 90% RH, especially with a high current density ranging from 30 to 621 μA cm⁻² across broad temperature and RH levels. Notably, the DWEG can be readily integrated to directly power commercial portable electronics, such as desk lamps and tablets.

Fig. 1 Design of the DWEG. Schematic showing the imitative prototype, structure of the DWEG, and working mechanism. Emulating the amorphous structure and energy-harvesting properties of seaweed mud, the amorphous slurry integrates porous silver and carbon tape electrodes, enabling the efficient capture of energy from both liquid water and ambient moisture through switching absorption and evaporation processes. The electricity generated by the DWEG is driven by a water gradient mechanism during moisture absorption and is primarily influenced by the hydration free energy mechanism during water evaporation.

2. Results and discussion

2.1. Design and fabrication of the DWEG

By mimicking the amorphous structure and energy-harvesting properties of seaweed mud, we developed an amorphous slurry, integrated with silver and carbon tape electrodes, to create a DWEG (Fig. S1–S3, ESI†). Distinguished from traditional hygroscopic films, this pioneering amorphous slurry endows the DWEG with great anti-freezing properties, moldability, and liquid water tolerance (Fig. 2a). Specifically, the amorphous slurry is a solid–liquid hybrid system composed of cellulose nanocrystals (CNCs), poly(vinyl alcohol) (PVA), and a glycerol–water binary solvent (Fig. 2b). The uniformly dispersed solid component CNC nanoparticles, derived from natural cotton, contain abundant ionic functional groups, i.e., –SO₃H, which are crucial for dissociating mobile ions upon interaction with water, mimicking the role of organic matter in seaweed mud (Fig. S4 and S5, ESI†). The zeta potential result in Fig. 2c reveals CNC's dominant role in endowing the DWEG with favorable ion dissociation ability. The non-ionic polyhydroxy PVA provides necessary viscosity by forming hydrogen bonding with the CNC hydroxyl groups,³³ while the water retention capacity of glycerol ensures system's adaptability in low-humidity environments. Furthermore, glycerol's interaction with CNCs and PVA facilitates ion transport at high RH (Fig. S6, ESI†). Notably, the interactions between different components remain purely physical, as no new chemical bonds are observed in the FTIR spectra (Fig. S5b, ESI†). Fig. 2d and Fig. S7 (ESI†) show that the glycerol–water solvent plays a key role in improving the anti-freezing and anti-drying properties of the amorphous slurry. Structurally, the fusiform CNC nanoparticles form a mutually stacked network, bound by PVA via hydrogen bonding, creating a porous framework that provides efficient pathways for water and H⁺ ion transport (Fig. S8, ESI†).

Fig. 2 Preparation and properties of the amorphous slurry. (a) Comparison of the amorphous slurry and traditional films in terms of anti-freezing properties, moldability, modularity, and liquid water tolerance. (b) Schematic illustration of the amorphous slurry composed of CNCs, PVA, and a glycerol–water binary solvent system. (c) Zeta potential of hybrid systems with different components. (d) The amorphous slurry shows no cracking after 10 hours of water evaporation at 5% RH and remains unfrozen after 10 hours of exposure at −7 °C. (e) Photograph of the amorphous slurry filled into a 3D-printed mold characterized “DUT”. (f) Moisture absorption and water evaporation kinetics for the DWEG at 90% RH and after adding water at 5% RH, respectively. (g) Absorption and evaporation cycles at 90% and 5% RH. (h) Electrochemical impedance spectroscopy of the DWEG at 95% and 5% RH. The inset shows the corresponding equivalent circuit, where R_s, R_ct, and CPE_dl are the Ohmic resistance, charge transport resistance, and constant phase element (CPE), respectively. The ion conductivity is determined as σ = L/(R × S), with σ, L, S, and R being the ionic conductivity, the thickness of the DWEG, the electrode area, and the ion diffusing resistance, respectively.

The amorphous slurry can be readily printed into different shapes and filled into various matrixes, such as “DUT”, demonstrating its exceptional plasticity (Fig. 2e). In an environment with 90% RH, the slurry's abundant hydrophilic groups enable it to spontaneously absorb moisture, increasing its mass by 150% (Fig. 2f). This phenomenon could also be observed under other RH conditions (Fig. S9, ESI†). Meanwhile, the slurry retains its stable structure after the addition of liquid water (Fig. S10, ESI†) and then evaporates liquid water to 32% of its weight at 5% RH. Fig. 2g demonstrates the slurry's remarkable stability in cyclically absorbing and evaporating water molecules under dynamic environmental conditions. Furthermore, leveraging the glycerol–water solvent and abundant ionic functional groups, the slurry exhibits strong ion transport capabilities, with an ionic conductivity of 0.21 μS cm⁻¹ at 95% RH and 6.05 μS cm⁻¹ at 5% RH (Fig. 2h). These properties form the essential foundation for the DWEG to efficiently harvest energy from both moisture and liquid water, ensuring high electric output under all weather conditions.

2.2. Electrical output performance of the DWEG

To evaluate the electrical output performance under various RH conditions, we first measure the open-circuit voltage V_oc and short-circuit current density J_sc of a 0.3 cm × 0.3 cm DWEG unit during moisture absorption. Prior to testing, the DWEG was stored in a controlled environment at ∼35% RH and 25 °C. As shown in Fig. 3a, the DWEG spontaneously absorbed moisture, generating a stable V_oc of 0.54 V at 50% RH, which gradually increased to ∼0.7 V at 90% RH. Notably, this output could sustain for over 420 h (Fig. 3b), representing a more than two-fold improvement over the results from previous hydrovoltaic generators under similar conditions^{20,27,31,34–40} (Table S1, ESI†). The DWEG shows excellent cyclic stability, retaining ∼88% of the initial performance after 110 autonomous charge–discharge cycles and >90% after 10 water adsorption–dehydration cycles (Fig. S11 and S12, ESI†). Meanwhile, the J_sc was significantly increased from 147 μA cm⁻² at 50% RH to 258 μA cm⁻² at 90% RH, owing to the enhanced moisture adsorption and ion dissociation (Fig. S9a and S13, ESI†). Moreover, the DWEG delivered a maximum power density of 32 μW cm⁻² when the load resistance matched the internal resistance (7 kΩ), marking one of the highest among other hydrovoltaic generators (Fig. 3c and Table S2, ESI†).^{11,16,25,30,35,37,39–46}

Fig. 3 Electric output performance of the DWEG. (a) V_oc and J_sc in response to RH variation in the moisture adsorption process. (b) V_oc curve of the DWEG at 90% RH and 25 °C. (c) Output performance of the DWEG with different load resistances at 90% RH and 25 °C. (d) V_oc and J_sc in response to RH variation in the evaporation process. (e) The curve of J_sc before and after adding a droplet at RH below 30%. (f) The DWEG can produce a J_sc above 147 μA cm⁻² in a wide range of RH (5 – 90%). (g) Comparison of J_sc between the DWEG and previous hydrovoltaic generators at all RH. (h) J_sc in response to temperature variation at 5% RH and 90% RH. (i) J_sc of the DWEG in a wide range of RH (5–90%) and temperatures (−7 to 65 °C).

We then investigated the electric output of the DWEG dependent on water evaporation when exposed to an environment below 35% RH. As shown in Fig. 3d, the V_oc increased from 0.4 V to 0.76 V as RH decreased, while the J_sc was constrained below 67 μA cm⁻², owing to the limited water content in the amorphous slurry. To enhance the J_sc at a low RH, a 15-μL water droplet was added to the 0.3 cm × 0.3 cm DWEG unit. Fig. 3e shows that the J_sc rapidly peaked after adding a 15-μL water droplet, owing to the accelerated H⁺ ion diffusion driven by droplet penetration. Subsequently, as the droplet gradually distributes uniformly throughout the material, the H⁺ ion diffusion rate decreases, causing the current density to decrease and then stabilize at a value determined by the evaporation rate. At this stage, the elevated water content within the material relative to its initial state leads to enhanced evaporation, thereby maintaining a significantly higher current density. Moreover, this process can be reliably repeated through periodic 15-μL droplet additions (Fig. S14, ESI†). This result indicated that the DWEG successfully harvested energy from liquid water to achieve enhanced current output at low RH. As a result, the DWEG could produce a J_sc above 144 μA cm⁻² across a wide RH range from 5% to 90% RH by efficiently harvesting energy from moisture at high RH and liquid water at low RH (Fig. 3f). This performance stands in striking contrast to previous hydrovoltaic generators, which produced current only in micro-ampere or nano-ampere levels when conditions deviate from their desired RH levels (Fig. 3g and Table S3, ESI†).^{11,25,29,40,45,47}

Temperature is another essential factor to characterize the environmental adaptability of the DWEG. As shown in Fig. 3h, as the temperature increased to 65 °C, the J_sc rose to 621 μA cm⁻² at 90% RH and 482 μA cm⁻² at 5% RH, owing to the accelerated H⁺ ion diffusion at a higher temperature. Moreover, the DWEG remained functional even at low temperatures, e.g., −7 °C, due to glycerol's anti-freezing properties, yielding a J_sc of 80 μA cm⁻² at 90% RH and 101 μA cm⁻² at 5% RH. Notably, systematic assessments of the environmental adaptability showed that the DWEG produced a considerable J_sc ranging from 30 to 621 μA cm⁻² across a broad temperature range from −7 to 65 °C and relative humidity levels from 5% to 90% (Fig. 3i), covering most of the environmental scenarios on the Earth.

2.3. Work mechanism of the DWEG

To understand how the DWEG harvests energy from dual forms of water under all weather conditions, we first explored the moisture absorption process. When exposed to a high humidity environment, the moisture travels through porous top to reach the sealed bottom, spontaneously establishing a vertical water gradient within the amorphous slurry. The peak intensity of the O–H stretching absorption peaks at 3755.73–3338.24 cm⁻¹ is strongly associated with water absorption, indicating a stronger moisture capturing ability of the DWEG (Fig. 4a). The measured moisture absorption ratio, W_a, defined as the weight of adsorbed moisture divided by the total film weight, was inversely proportional to the amorphous slurry thickness d (Fig. 4b). For example, at 65% RH, W_a is about 30% for amorphous slurry less than 0.1 mm thick and gradually decreased to about 16% for a 1 mm thickness one. This result confirmed the formation of a vertical water gradient within the amorphous slurry, with a W_a of ∼30% at the top (W_a-top) and that of ∼2% at the bottom (W_a-bottom) at 65% RH. Then, the difference in the moisture absorption ratio, ΔW_a = W_a-top − W_a-bottom, increases with RH and correlates positively with the open-circuit voltage V_oc (Fig. 4c). Moreover, when ΔW_a is eliminated by sealing both sides, the voltage drops to nearly zero (Fig. S15, ESI†). This occurs because the increased water gradient helps create an improved ion concentration gradient within the amorphous slurry by facilitating H⁺ ion dissociation and diffusion (Fig. S16, ESI†). This coupling relationship between the water gradient and the ion concentration gradient was confirmed by the color change of an acid indicator. As shown in Fig. S17 (ESI†), as the moisture absorption ratio increased, the acid indicator attached to the thin layer of the amorphous slurry changed from yellow to red, signalling a rise in ion concentration.

Fig. 4 Working mechanism of the DWEG. (a) FTIR spectrum tracking once the amorphous slurry is exposed in the specific environment (60% RH) versus time. (b) W_a in the amorphous slurry is plotted against thickness d at 65%, 80%, and 90% RH. (c) The ΔW_a and V_oc of the DWEG at different RH in the moisture absorption process. (d) Voltage signals generated by the DWEG in response to the water-molecule exchange direction at four different unsealed interfaces. The insets are schematic illustrations of the absorption (solid line) and evaporation (dashed line) at four different unsealed interfaces. (e) The KPFM detecting potential change of the slurry's bottom surface at ∼20% RH. The scan range is 2 μm × 2 μm. (f) W_e in the amorphous slurry is plotted against thickness d at 5%, 15%, and 30% RH. (g) Stimulated proton hydration free energy with different numbers of water molecules. The inset is the model of the protonated water cluster with different numbers of water molecules. (h) Schematic of electricity generation induced by proton hydration free energy driven proton diffusion.

We then examined the diffusion behavior of H⁺ ions in the DWEG during water evaporation, following the uniform infiltration of the added water into the amorphous slurry. Common wisdom holds that water molecules primarily move from bottom to top, driven by evaporation at the exposed top surface, a process believed to facilitate the upward H⁺ ions diffusion.^28,48 However, Fig. 4d shows that the voltage signal polarity during water evaporation aligned with those observed during moisture absorption. Since voltage polarity consistently aligns with the internal ion diffusion direction,^11,27 this indicates counterintuitive top-to-bottom H⁺ ion movement opposing water molecule flow. Besides, the bottom-side potential, measured via a Kelvin probe force microscope (KPEM), increased from ∼320 mV to ∼550 mV with extended drying time (Fig. 4e), which also confirmed the downward ion diffusion. This abnormal ion diffusion direction was further elaborated by applying an alternating bias voltage. Specifically, when the direction of applied external bias voltage is the same as the direction of intrinsic ion flow, the output current is enhanced, and vice versa.^16,25 As shown in Fig. S18 (ESI†), when applying a +1.0 V bias voltage, i.e., the top-down bias voltage, the current of the DWEG was enhanced to ∼6 μA, and conversely, the current was reduced to 0.6 μA, further confirming the top-to-bottom proton movement.

To reveal the driving force behind this abnormal proton diffusion, we examined the hydration free energy of the proton in the DWEG. The hydration free energy of protons refers to the energy released when protons form protonated water clusters with surrounding water molecules through hydrogen bonding, a process largely influenced by water content.^49–51 Specifically, the lower the water content, the greater the tendency for protons to form smaller protonated water clusters, and conversely, higher water content leads to the formation of larger clusters. Fig. 4f demonstrates that water evaporation from the top surface led to reduced water content compared to the sealed bottom surface. As a result, the protonated water clusters at the top surface shrank into smaller sizes than those at the bottom. Meanwhile, the hydration free energy for different cluster sizes was determined utilizing density functional theory (DFT) simulation (Note S1, ESI†). As shown in Fig. 4g, the hydration free energy for a small cluster with a single water molecule was −249.5 kcal mol⁻¹, which decreased to −268.9 kcal mol⁻¹ when containing four water molecules. These results indicated that a hydration free energy difference was established within the DWEG, which drove the protons downward as they naturally sought to form configurations with lower energy (Fig. 4h). Notably, although the reduction of water content at the top surface also tended to establish a bottom-to-top ion concentration difference to drive proton upward diffusion, sufficient water retention could continuously trigger ion dissociation to mitigate this concentration difference. This phenomenon was confirmed by the acid indicator that did not appear change color after 10-hour operation at 25% RH (Fig. S19, ESI†). Consequently, the hydration free energy difference acts as the dominant driving force, directing proton downward diffusion to achieve energy harvesting from liquid water during the evaporation process.

In terms of energy conversion, both absorption and evaporation processes are thermodynamically driven by minimization of Gibbs free energy resulting from interfacial vapor pressure differences, ultimately generating electricity. During absorption, when the environmental vapor pressure exceeds the equilibrium vapor pressure of the slurry, water vapor spontaneously adsorbs onto the interface to form liquid water. A portion of the released latent heat from the exothermic phase transition promotes H⁺ ion diffusion through an established ion concentration difference,³⁸ converting thermal energy into electrical energy. In contrast, evaporation occurs when the ambient vapor pressure is lower than the saturated vapor pressure of water retained inside the material, involving an endothermic process.⁵² Here, absorbed thermal energy is partially converted into electrical energy via H⁺ ion diffusion driven by the hydration free energy difference.

2.4. Functionality integration and applications

The integration of the DWEG units is essential for scaling up energy output to meet the demands of practical applications. Here we employed a screen-printing method for large-scale integration of DWEG units (Fig. 5a). Specifically, the amorphous slurry was spread into 3D-printed molds containing hundreds of hexagonal units, after which the corresponding electrodes were attached to the top and bottom of the mold, achieving parallel scalable integration. These arrays were then affixed to acrylic sheets and inserted into prefabricated slots, allowing for further integration either in series, by connecting the units end-to-end, or in parallel, by connecting them head-to-head, to generate customized electrical output. For example, a 3D-printed mold measuring 2.0 cm × 7.0 cm produced a V_oc of approximately 0.6 V and a current of about 260 μA under laboratory conditions (25 °C, 50% ± 5% RH) when assembled with a carbon tape electrode and an Ag electrode (Fig. S20, ESI†). Fig. 5b and Fig. S21 (ESI†) show that connecting 70 such molds in series or 80 such molds in parallel, the voltage and current were linearly scaled up to 42 V and 18.5 mA, respectively.

Fig. 5 Scalable integration of the DWEG. (a) Schematic showing the scale integration of DWEG arrays in series and parallel via screen printing. (b) V_oc and I_sc of integrated DWEG arrays with dimensions of 2.0 cm × 7.0 cm. (c) A calculator was continuously driven by six serial DWEG arrays with dimensions of 2.0 cm × 7.0 cm. (d) A table lamp was continuously driven by twelve serial DWEG arrays. (e) A tablet computer being directly charged by nine DWEG arrays with dimensions of 16 cm × 16 cm.

Notably, the integrated DWEG arrays could continuously power various commercial electronic devices, such as calculators and table lamps for more than five days, as demonstrated in Fig. 5c and d, and Movie S1 (ESI†). This distinguishes it from previous hydrovoltaic generators that could only power devices for a few hours.^41,53 Notably, the lamp brightness could be readily restored to its original level by adding water droplets into these arrays (Fig. S22, ESI†), a process that greatly enhanced the potential of DWEG arrays as a sustainable energy source. Moreover, the current output of DWEG arrays could be further enhanced by integrating Al and Ag electrodes, making them suitable for high-power electronic devices. This was because the Al electrode could react with H⁺ ions from the amorphous slurry, facilitating faster charge transfer to increase the output current (Fig. S23, ESI†). For example, a 2.0 cm × 7.0 cm DWEG array produced an enhanced current of 0.65 mA, which scaled up to 24 mA when 40 such arrays were connected in parallel (Fig. S24, ESI†). With this high current output, we pioneeringly employed nine integrated DWEG arrays to achieve direct smartphone charging with a measurable 2% battery increase (Movie S2, ESI†). Remarkably, the arrays could also initiate charging for higher-power tablet computers without capacitors (Fig. 5e and Movie S3, ESI†). These results represent a critical proof of concept for direct charging without capacitors—a key advancement over previous work.

3. Conclusions

In summary, we have developed a DWEG by imitating the amorphous structure and energy-harvesting properties of the seaweed mud. Leveraging the efficient ion diffusion driven by ion concentration differences at high RH and ion hydration energy gradients at low RH, the DWEG is capable of high-performance electricity generation from both moisture and liquid water through absorption and evaporation modes, respectively. As a result, a single DWEG unit can generate a current density ranging from 30 to 621 μA cm⁻² across a broad temperature range of −7 to 65 °C and a RH of 5 to 95%, demonstrating adaptability to various weather conditions. The DWEG can be efficiently scaled up through screen printing to achieve a voltage and current of 42 V and 18.5 mA, respectively, making it capable of powering devices such as desk lamps for over five days and even charging a tablet computer when integrated with an Al electrode. This work promises new design strategies for the harvesting and conversion of multiple energy sources in water circulation, fostering the advancement of high-performance, all-weather power sources.

4. Experimental section

4.1. Materials

CNC solution was obtained by hydrolyzing cotton with concentrated sulfuric acid as reported previously.⁵⁴ Glycerol with a purity of 99% and PVA with an alcoholysis degree of 95.5–96.5 mol% and a viscosity of 24.0–30.0 mPa s were purchased from Aladdin Co., Ltd. Double-sided conductive carbon tape (no. 7321) was purchased from Nisshin EM Co., Ltd.

4.2. Preparation of the DWEG

First, a PVA solution of 10 wt% was prepared by dissolving PVA in deionized water at 95 °C. The CNC solution was then uniformly mixed with PVA solution and glycerol, and the mixture was concentrated through stirring and heating to obtain the amorphous slurry with a CNC/PVA/glycerol mass ratio of 3 : 1 : 2. The prepared amorphous slurry was stored in a drying cabinet at 25 °C and 35% RH. Finally, the amorphous slurry was placed into a prefabricated 3D-printed mold and sandwiched between a silver electrode with array holes and a conductive carbon tape to obtain the DWEG.

4.3. Characterization

Voltage and current measurements were conducted using a CHI 660E electrochemical workstation in the voltage range of 0–10 V. For measurements outside this range, a Keithley DMM6500 (Keithley Instruments) was used. The experiment was conducted in an environmental chamber (DHTHM-50-40-P-ES) with precisely controlled temperature and relative humidity. To avoid static charge interference, an insulation pad was placed to prevent the sample from contacting the metal surface. ATR-FTIR spectra were obtained using a Nicolet iS50 spectrometer. The microstructure and elemental composition of the DWEG were analyzed with a scanning electron microscope (SU5000 HITACHI) equipped with an energy dispersive X-ray spectroscope (EDS), and a transmission electron microscope (JEM-2100F) provided transmission images.

Author contributions

Y. L. and W. G. conceived the project. Y. L. and Y. S. supervised the project. W. G., Y. L., and Q. W. designed the project. W. G., Q. W., W. L., W. X., and C. L. performed the experiments. W. G., Q. W., Y. L., Y. S., K. Z., X. L., and H. S. analyzed the data. All the authors contributed to manuscript writing and editing.

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

We acknowledge the financial support from the National Key R&D Program of China (2022YFB4602401), the National Natural Science Foundation of China (52475294 and 52075071), the State Key Laboratory of High-performance Precision Manufacturing (ZY202404), and the Fundamental Research Funds for the Central Universities (DUT24YG133). Y. S. acknowledges support from the Canada Research Chairs Program.

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Footnotes

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5ee01315a

‡ These authors contributed equally to this work.

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