Introduction: The Challenge of Stretchable Moisture-Electric Generators
Wearable and implantable electronic devices require energy sources that are soft, stretchable, and capable of delivering stable, continuous power output. To better meet the demands of continuous output and mechanical flexibility, researchers have conducted in-depth investigations into hydrogel-based moisture-electric generators.
However, a critical issue remains: fully stretchable hydrogel moisture-electric generators (FSHMEGs) suffer from weak interfacial adhesion between functional layers, which leads to low electrical output and fragile mechanical performance under complex deformations. A breakthrough study published in Nano-Micro Letters by Professor Yanhong Tian's team at Harbin Institute of Technology provides a theoretical foundation for overcoming this challenge, successfully fabricating a fully stretchable hydrogel moisture-electric generator.
The Current Benchmark: Weak interface interaction
The critical problem in stretchable hydrogel moisture-electric generators is that weak adhesion at the hydrogel–electrode interface results in inadequate electrical output and poor mechanical stability. To solve this problem, the researchers developed a highly adhesive hydrogel that reinforces the interaction between the functional layers and the electrode, consequently improving the electrical output performance.
The Resolution approach：
The researchers propose an interface engineering strategy that enhances device performance by regulating the interfacial adhesion between functional layers. A highly adhesive hydrogel swollen in a water-glycerol binary solvent is integrated between a liquid metal and a stretchable silver electrode to construct a fully stretchable moisture-electric generator. The introduction of glycerol exposes more hydrogen-bonding functional groups, increasing the effective contact sites between the hydrogel and the electrodes and thereby significantly enhancing interfacial adhesion. The resulting robust and durable hydrogel-electrode interface not only reduces interfacial resistance, ensuring efficient charge transport under strain, but also prevents delamination under large deformation. Moreover, glycerol endows the hydrogel with excellent anti-drying, anti-freezing, and anti-swelling properties, thereby enabling ultra-long-term stable operation of the device.
Adhesion-Enhanced Ion Transport and Mechanical Robustness: Results and Validation
Using both experimental and theoretical approaches, the team demonstrated a stepwise verification of their technology:
- Step 1: Experimental Verification: The team experimentally elucidated the adhesion mechanism of the highly adhesive hydrogel, demonstrating that it exhibits lower interfacial impedance, which facilitates more efficient ion transport.
- Step 2: Theoretical Calculation and Simulation: Through AIMD simulations and DFT calculations, it was verified that the highly adhesive hydrogel–electrode interface enables faster ion migration rates and a lower free energy barrier.
- Step 3: High Electrical Performance and Excellent Mechanical Robustness: The device achieved an output voltage exceeding 0.94 V and a current density of 141 μA cm⁻². Notably, after 1,040 stretching cycles, the device maintained stable operation, and even after 8,000 bending cycles at a bending angle of 180°, its performance degradation remained negligible.
Real-World Impact: Flexible, Stretchable and Stable Energy Supply
By employing an intrinsically adhesive hydrogel as an interfacial layer, this work establishes a stable hydrogel–electrode interface that effectively mitigates interfacial mismatch, thereby paving the way for the following applications:
- Flexible Energy Source: Powering wearable electronic devices.
- Respiratory Monitoring: Enabling non-invasive respiration monitoring.
Conclusion and Future Outlook
This study provides a practical pathway toward high-performance moisture-electric generators, underscoring the importance of an interface-centered design philosophy in soft energy systems and offering a universal strategy for improving interfacial reliability in flexible electronics. This approach opens up new opportunities for the development of durable, self-powered wearable devices capable of operating reliably under complex environmental and mechanical conditions.