First Decade of Interfacial Iontronic Sensing: From Droplet Sensors to Artificial Skins

Abstract

Over the past decade, a brand‐new pressure‐ and tactile‐sensing modality, known as iontronic sensing has emerged, utilizing the supercapacitive nature of the electrical double layer (EDL) that occurs at the electrolytic–electronic interface, leading to ultrahigh device sensitivity, high noise immunity, high resolution, high spatial definition, optical transparency, and responses to both static and dynamic stimuli, in addition to thin and flexible device architectures. Together, it offers unique combination of enabling features to tackle the grand challenges in pressure‐ and tactile‐sensing applications, in particular, with recent interest and rapid progress in the development of robotic intelligence, electronic skin, wearable health as well as the internet‐of‐things, from both academic and industrial communities. A historical perspective of the iontronic sensing discovery, an overview of the fundamental working mechanism along with its device architectures, a survey of the unique material aspects and structural designs dedicated, and finally, a discussion of the newly enabled applications, technical challenges, and future outlooks are provided for this promising sensing modality with implementations. The state‐of‐the‐art developments of the iontronic sensing technology in its first decade are summarized, potentially providing a technical roadmap for the next wave of innovations and breakthroughs in this field.

Skin-like mechanoresponsive self-healing ionic elastomer from supramolecular zwitterionic network

“…5h ). As shown, the fabricated sensor could operate over a wide pressure range with a sensitivity of 200 MPa −1 in the low-pressure range (<0.5 kPa), and 22.9 and 3.5 MPa −1 in the high-pressure range, typical for iontronic sensors 50 . Upon loading a pressure of 0.36 kPa, the response time appeared to be very short within 700 ms (Fig.…”

“…5g , the pressure sensor has a sandwich-like structure consisting of two elastic conductive fabrics as electrodes and PAA/betaine elastomer as the iontronic layer. When a normal force is applied to the sensor, the electrical double layer capacitance at the elastic electrolytic–electronic interface will correspondingly change 50 . We evaluated pressure sensitivity, response time, and repeatability to characterize the performance of PAA/betaine elastomer-based iontronic sensor.…”

Highly Sensitive Pseudocapacitive Iontronic Pressure Sensor with Broad Sensing Range

“…Kim et al developed the top floating electrode for iontronic PPS with greatly enhanced sensitivity [ 20 ]. Additionally, recently introducing the remarkable interfacial capacitance for PPS by electrical double layer (EDL) effect is also an effective strategy [ 24 ]. For example, Pan et al introduced the iontronic PPS based on the EDL capacitive materials [ 21 , 25 , 26 ], such as graphene [ 20 ], silver [ 21 ], and Au [ 23 ].…”

Ionogel-based flexible stress and strain sensors

“…They are different from traditional flexible electrostatic capacitive sensors mentioned in the above section. Interfacial iontronic sensors mainly utilize the supercapacitive nature of the electrical double layer (EDL) that occurs at the electrolytic-electronic interface [77]. The EDL capacitance of the sensor is dependent on the interfacial contact area between the ionogel layer and the counter electrode.…”

“…Similarly, GF of capacitive and interfacial iontronic IFSS is the ratio of the fitted ΔC/C 0 to stress (Figure 6(e)). Iontronic pressure sensors emerged in the last decade have much larger sensitivity than traditional capacitive sensors, and have become a promising pressure sensing solution [77]. It is worth noting that GF may not be a constant in the whole working range.…”