Reduced self-discharge of supercapacitors using piezoelectric-material-based composite hydrogel electrolytes

Supercapacitors based on hydrogel electrolytes have attracted widespread attention owing to their unique properties. However, their practical application in long-term energy storage is severely constrained by self-discharge behavior, which leads to rapid energy loss. Here we propose a piezoelectric effect to suppress self-discharge in supercapacitors by embedding piezoelectric Pb 0.988 (Zr 0.52 Ti 0.48 ) 0.976 Nb 0.024 O 3 (PZT) nanoparticles into hydrogel electrolyte, generating a persistent local electric field that modulates ion diffusion. Self-discharge tests show that, compared with the blank hydrogel electrolyte, the supercapacitor with PZT composite hydrogel electrolyte delivers an OC V retention that is 101.8% higher (1.11 vs 0.55 V) and a 69.7% lower leakage current (1.90 vs 6.27 μA). Mechanistic analysis indicates that the reduced self-discharge can be attributed to the structure of the reverse diode formed by the piezoelectric enhanced local electric field and the improvement of the electrode/electrolyte interface. Therefore, the self-discharge process attributed to diffusion-controlled faradaic reactions can be suppressed. Furthermore, the universality of this approach was validated using multi-walled carbon nanotubes (MWCNT), activated carbon (AC), and MXene as electrode materials, confirming its broad applicability in diverse supercapacitor systems.