CO₂-responsive liquid–solid triboelectric nanogenerator based on reversible interfacial charge-state switching

This study demonstrates, for the first time, a CO₂-responsive liquid–solid triboelectric nanogenerator (L-S TENG) whose electrical output can be reversibly switched through protonation caused by CO₂ purging. To achieve CO₂ responsivity while maintaining efficient triboelectric performance, a multilayered dielectric structure was designed, consisting of an electrospun poly(vinylidene fluoride) (PVDF) base membrane, a thin polydimethylsiloxane (PDMS) interfacial coating, and a poly(methyl methacrylate-co-2-(diethylamino)ethyl methacrylate) (PMD) top layer. The top PMD layer serves as the CO₂-responsive layer, where tertiary amine groups undergo protonation/deprotonation through CO₂ and N₂ purging. After N₂ purging, the device produced a stable open-circuit voltage of ∼15 V, whereas CO₂ purging suppressed the output to nearly zero. This switching behavior arises from reversible change in the surface charge state, which directly affects the induced charge density on the spreading droplet, thereby modulating the triboelectric output. In situ FT-IR and XPS analyses confirmed the transition between protonated and neutral amine states, and Kelvin probe force microscopy (KPFM) revealed the corresponding increase in surface work function upon CO₂ adsorption. The clear and reversible chemical switching demonstrated here indicates the potential of integrating stimuli-responsive surface chemistry into triboelectric interfaces, providing an important step toward future gas-interactive and adaptively tunable L–S TENG systems.