Sensitivity is a crucial parameter for flexible pressure sensors and electronic skins. While introducing microstructures (e.g., micro-pyramids) can effectively improve the sensitivity, it in turn leads to a limited pressure-response range due to the poor structural compressibility. Here, we report a strategy of engineering intrafillable microstructures that can significantly boost the sensitivity while simultaneously broadening the pressure responding range. Such intrafillable microstructures feature undercuts and grooves that accommodate deformed surface microstructures, effectively enhancing the structural compressibility and the pressure-response range. The intrafillable iontronic sensor exhibits an unprecedentedly high sensitivity (Smin > 220 kPa−1) over a broad pressure regime (0.08 Pa-360 kPa), and an ultrahigh pressure resolution (18 Pa or 0.0056%) over the full pressure range, together with remarkable mechanical stability. The intrafillable structure is a general design expected to be applied to other types of sensors to achieve a broader pressure-response range and a higher sensitivity.

Flexible electronic skins (e-skins) with high sensitivity and broad-range pressure sensing are highly desired in artificial intelligence, and humanmachine interaction. Capacitive-type e-skins have a simple configuration, but the change in dimensions of the dielectric layer is often quite limited, although introducing surface microstructures might improve the sensitivity in some extent. Moreover, such surface structures typically require costly microfabrication methods to fabricate. Here, a low-cost microstructured ionic gel (MIG) with uniform cone-like surface microstructures for highperformance capacitive e-skins is reported. The MIG film is templated from a Calathea zebrine leaf using soft lithography, and sandwiched by two flexible electrodes. The device exhibits a low limit of detection down to 0.1 Pa, a ultrahigh sensitivity of 54.31 kPa −1 in the low pressure regime (<0.5 kPa), and the sensitivity keeps larger than 1 kPa −1 over a broad-range pressure from 0.1 Pa to 115 kPa. Electric double layers (EDL) form on both the top and bottom interfaces, and the area of EDL of the rough interface increases as the cones are compressed. Such ionic skins with biomimetic gel templated Calathea zebrine leaf allow for sensitive tactile sensing in the applications of human-machine interaction.

Electronic skins (e-skins) are devices that can respond to mechanical stimuli and enable robots to perceive their surroundings. A great challenge for existing e-skins is that they may easily fail under extreme mechanical conditions due to their multilayered architecture with mechanical mismatch and weak adhesion between the interlayers. Here we report a flexible pressure sensor with tough interfaces enabled by two strategies: quasi-homogeneous composition that ensures mechanical match of interlayers, and interlinked microconed interface that results in a high interfacial toughness of 390 J·m−2. The tough interface endows the sensor with exceptional signal stability determined by performing 100,000 cycles of rubbing, and fixing the sensor on a car tread and driving 2.6 km on an asphalt road. The topological interlinks can be further extended to soft robot-sensor integration, enabling a seamless interface between the sensor and robot for highly stable sensing performance during manipulation tasks under complicated mechanical conditions.

Flexible pressure sensors that have high sensitivity, high linearity, and a wide pressure-response range are highly desired in applications of robotic sensation and human health monitoring. The challenge comes from the incompressibility of soft materials and the stiffening of microstructures in the device interfaces that lead to gradually saturated response. Therefore, the signal is nonlinear and pressure-response range is limited. Here, we show an iontronic flexible pressure sensor that can achieve high sensitivity (49.1 kPa–1), linear response (R 2 > 0.995) over a broad pressure range (up to 485 kPa) enabled by graded interlocks of an array of hemispheres with fine pillars in the ionic layer. The high linearity comes from the fact that the pillar deformation can compensate for the effect of structural stiffening. The response-relaxation time of the sensor is <5 ms, allowing the device to detect vibration signals with frequencies up to 200 Hz. Our sensor has been used to recognize objects with different weights based on machine learning during the gripper grasping tasks. This work provides a strategy to make flexible pressure sensors that have combined performances of high sensitivity, high linearity, and wide pressure-response range.

Electrodermal devices that capture the physiological response of skin are crucial for monitoring vital signals, but they often require convoluted layered designs with either electronic or ionic active materials relying on complicated synthesis procedures, encapsulation, and packaging techniques. Here, we report that the ionic transport in living systems can provide a simple mode of iontronic sensing and bypass the need of artificial ionic materials. A simple skin-electrode mechanosensing structure (SEMS) is constructed, exhibiting high pressure-resolution and spatial-resolution, being capable of feeling touch and detecting weak physiological signals such as fingertip pulse under different skin humidity. Our mechanical analysis reveals the critical role of instability in high-aspect-ratio microstructures on sensing. We further demonstrate pressure mapping with millimeter-spatial-resolution using a fully textile SEMS-based glove. The simplicity and reliability of SEMS hold great promise of diverse healthcare applications, such as pulse detection and recovering the sensory capability in patients with tactile dysfunction.

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The removal of toxic dyes and insoluble oil from wastewater is a hot topic in both academic and industrial fields. Herein, we report a cationic absorbent poly­(epichlorohydrin)–ethylenediamine hydrogel (PEE-Gel) via a simple one-step copolymerization and it can be successfully used for the removal of toxic dyes and insoluble oil from wastewater. The adsorption toward anionic dyes shows high efficiency and high selectivity at a wide pH range (from 2 to 12). The adsorption capacity at low equilibrium concentration (10 mg L–1) is as high as 1411.4 mg g–1 which is very close to the maximum adsorption capacity (1540.19 mg g–1). The adsorption of dye molecules onto PEE-Gel is very steady and can be difficult to be regenerated. The PEE-Gel with full dye adsorption (PEE-Gel-Dye) shows superoleophobicity under water, and PEE-Gel-Dye can be reused to separate toluene-in-water emulsion with high efficiency and durability. These results suggest that PEE-Gel is a promising and competitive candidate for water purification.

The development of high-efficiency catalysts for hydrogen evolution via water splitting has been an effective strategy to solve the energy environmental problems and energy crisis. The abundant-reserving transition metals and their phosphides are becoming attractive Pt alternatives for hydrogen evolution reaction (HER). Herein, a crystalline/amorphous Co/CoP film was facilely prepared on nickel foam (NF) by a one-step electrodeposition technique at room temperature, named Co/CoP-NF. The as-prepared Co/CoP-NF electrocatalyst exhibits excellent electrocatalytic activity for HER, on par with Pt/C, showing a low overpotential of 35 mV at a current density of 10 mA·cm and small Tafel slope of 71 mV·dec in 1.0 M NaOH solution. More importantly, the Co/CoP-NF catalyst presents good long-term durability at an overpotential of 60 mV. Moreover, the influence of the electrodeposition parameters on the catalytic performance of the catalyst was discussed. This study offers an effective strategy to develop a non-noble-metal HER catalyst for industrial production of hydrogen.