4. Experimental Section

Materials: Poly (methylmethacrylate (PMMA, 98.5%), Polydimethylsiloxane (PDMS, 85%), Trichloromethane (CHCl₃, 99%), Poly vinylidene fluoride-hexafluoro propylene (PVDF-HFP, 99%), 1-ethyl-3-methylimidazolium dicyanamide (EMIM[DCA], 99%). Taro leaf (Produced in Yuxi City, Yunnan Province), Sand paper. All chemicals were of analytical purity and used directly without any processing, except for taro leaves and sandpaper that have been cleaned.
Preparation of PDMS electrodes: PDMS electrodes were prepared by plant template method combined with electron beam deposition (Figure S1). The PMMA particles are mixed with trichloromethane at a mass ratio of 8:100 and stirred until completely dissolved, and then the prepared PMMA solution was applied dropwise to the surface of fresh taro leaves then heating at 60 ℃ for 1 h. The PMMA film was peeled off from the leaf as a PMMA template with the opposite structure of the taro. Next, the PDMS precursor solution was mixed with the curing agent (10:1) and smeared onto the above PMMA template then heating at 60 ℃ for 2 h. Then, the PDMS film was peeled off from the PMMA template to obtain the PDMS film with taro leaf papillary microstructure (PM-PDMS), and the PMMA template was cleaned and dried naturally for recycling and reusing. Finally, the microstructured gold electrode (with the Au film thickness of 250 nm) was prepared by electron beam evaporation, which was denoted as PM-PDMS / Au.
Preparation of ionogel dielectric layers: Ionogel with different roughness were prepared by sandpaper reverse mold (Figure S3). After completely dissolving 0.2 g PVDF-HFP in 2.5 ml acetone solution, 0.2 ml, 0.4 ml, 0.6 ml, and 0.8 ml EMIM[DCA] ionic liquids were added to the same four PVDF-HFP solutions, respectively, which were recorded as EMIM[DCA]-8 wt%, EMIM[DCA]-16 wt%, EMIM[DCA]-24 wt%, and EMIM[DCA]-32 wt%, and stirred vigorously to ensure the uniform mixing of ionic liquid and PVDF-HFP. Then a little of the above-configured mixed solution was applied onto the sandpaper with different roughness, heating at 60 °C for 2 h to obtain ionogel film possessing rough surface. Furthermore, a slide of smooth ionogel film was selected as a substrate for contrastive analysis.
Assembly of flexible ion pressure sensor: The flexible ion pressure sensor was designed as sandwich-like structure where the PM-PDMS / Au film acts as the upper and lower electrodes and the ionogel was employed as the dielectric layer film, and the copper wire was used as a test electrode. Further, the electrical double layer capacitive ion pressure sensor can be encapsulated with PI film (Figure 1).
Characterization and measurements: SEM morphological and elemental characterization of PDMS and PVDF films was performed by the Phenom Pro X. Characterization of the mechanical properties of PDMS films and ionogel was exerted using a universal material testing machine (UTM 4000, Shenzhen Suns Co. Ltd, China). By controlling the stepper motor to provide different pressures, the performance of the capacitive pressure sensor at low frequencies is tested with the Victor 4091C precision LCR meter, and the capacitive sensing performance at high frequencies is measured by Keithley 4200 SCS semiconductor parameter tester. Electrochemical workstation (CHI-660e, Shanghai Chenhua Co. Ltd, China) was employed to test the electrochemical impedance spectra and cyclic voltammetric curves of all the samples. The ionic conductivity of the ionogel can be calculated from obtained electrochemical impedance spectroscopy data. Thermal conductivity monitoring of ionogel was measured by Hot Disk TPS 2500 S thermal conductivity meter; The thermoelectric performance of ionogel was characterized by the customized thermoelectric test system (refer to the published work).[58]