Bto nanoparticles

The fabrication process of the triboelectric layers is schematically illustrated in Figure S21, Supporting Information. Briefly, a PDMS precursor and a curing agent (Sylgard 184, Dow Corning, US) were mixed in a 10:1 weight ratio, followed by degassing the PDMS solution in a vacuum desiccator to remove any trapped air bubbles. The PDMS solution was then poured onto a micropatterned mold, spread evenly using spin‐coating at 1000 rpm for 30 s, and cured at 80 °C for 3 h. Subsequently, a single‐sided micropatterned PDMS film (height of 5 µm, diameter of 10 µm, and pitch of 12 µm) was obtained by peeling it off the mold, which was used as a one‐layer triboelectric nanogenerator (1‐TENG). For the fabrication of bifacial PDMS micropatterns, the single‐sided micropatterned PDMS film was placed onto the PDMS that has been spin‐coated on another mold but yet cured. After aligning the PDMS layers, the curing and demolding processes were conducted to obtain bifacial PDMS micropatterns as a tribo‐positive friction layer.
To synthesize FBP with bifacial micropatterns as a tribo‐negative friction layer, BTO nanoparticles (average diameter of ≈200 nm, US Research Nanomaterials, Inc., US) were dispersed in ethanol at different concentrations (0, 1, 5, and 10 wt%) through sonication for 30 min. The BTO‐ethanol dispersion was then mixed with the PDMS base using a planetary centrifugal mixer (ARE‐310, THINKY, US) at 2000 rpm for 15 min and degassed at 2200 rpm for 5 min. The BTO/PDMS base solution was stirred overnight at 100 °C to evaporate ethanol solvent and mixed with a curing agent with a weight ratio of 10:1, followed by the aforementioned curing and demolding processes. For the FOTS coating on the bifacial BTO/PDMS micropatterns, the bifacial surfaces were treated with O₂ plasma using a plasma cleaner (Tergeo, PIE Scientific LLC, US) to form hydrophilic functional groups on the surfaces. Then, the bifacial micropatterns were coated with FOTS using a self‐assembled monolayer (SAM) coater (AVC‐150, SORONA, South Korea).

First, acetic acid (Daejung Inc., Busan, Korea) was used to adjust the pH of an ethanol–water mixed solution (95:5 (v/v), Daejung Inc.) to 3–5. Thereafter, TOS (1 mL, Sigma-Aldrich, St. Louis, MO, USA) was added to the combination solution and hydrolyzed for 1 h at 25 °C. Subsequently, BTO nanoparticles (0.5 g, average diameter: 100 nm, US Research Nanomaterials Inc., Houston, TX, USA) were added, and the mixture was manually agitated for 3 h at 60 °C to enable TOS to adhere to the BTO surface. Thereafter, the mixture was centrifuged for 10 min at 8000 rpm to remove any unreacted silane reagent and rinsed several times with ethanol. Finally, the collected TOS-BTO nanoparticles were placed in a vacuum oven at 60 °C for 24 h to eliminate any residual solvent.

The PVDF polymer used in this experiment was a semicrystalline PVDF (pellet, Sigma-Aldrich) which has a number average molecular weight of ~275,000. Dimethylformamide (DMF) and acetone solvent were purchased from Sigma-Aldrich. BTO nanoparticles (average diameter of 200 nm) were purchased from US Research Nanomaterials Inc. PZT micropowders (50–100 μm, APC 850) were purchased from APC Inc.