Stimuli-Responsive Delivery of Ions through Layered Materials-Based Triangular Nanofluidic Device.

The elegance and accuracy of biological ion channels inspire the fabrication of artificial devices with similar properties. Here, we report the fabrication of iontronic devices capable of delivering ions at the nanomolar (nmol) level of accuracy. The triangular nanofluidic device prepared with reconstructed vanadium pentoxide (VO) membranes of thickness 45 ± 5.5 µm can continuously deliver K+, Na+, and Ca2+ ions at the rate of 0.44 ± 0.24, 0.35 ± 0.06, and 0.03 nmol/min, respectively. The ionic flow rate can be further tuned by modulating the membrane thickness and salt concentration at the source reservoir. The triangular VO device can also deliver ions in minuscule doses (∼132 ± 9.7 nmol) by electrothermally heating (33 °C) with a nichrome wire (NW) or applying light of specific intensities. The simplicity of the fabrication process of reconstructed layered material-based nanofluidic devices allows the design of complicated iontronic devices such as the three-terminal-Ni-VO (3T-Ni-VO) devices.

Application of lamellar nickel hydroxide membrane as a tunable platform for ionic thermoelectric studies.

The recent trend in thermoelectric literature suggests that ionic thermoelectric (i-TE) materials are ideal for directly converting low-grade waste heat into electricity. Here, we developed a unique platform for i-TE studies by stacking two-dimensional sheets of ß-Ni(OH)2 prepared by a bottom-up method. The lamellar membrane of ß-Ni(OH)2 (Ni-M) itself does not display significant thermovoltages, but when doped with mobile anion-generating species (like aminopropyl functionalized magnesium phyllosilicate or organic halide salts), it exhibits significant negative Seebeck coefficient (up to -13.7 ± 0.2 mV K-1). Similarly, upon doping with cation-generating species like poly(4-styrene sulfonic acid) (PSS), it displays positive Seebeck coefficient values (up to +12 ± 1.9 mV K-1). The positive and negative i-TE materials prepared by doping Ni-M are assembled into ionic thermopiles capable of generating thermovoltages up to 1 V, at ΔT = 12 K. The Ni-M-based nanofluidic systems demonstrated an additional path of electricity harvesting by connecting colder zones of the positive and negative i-TE materials with other ion conducting membranes. In contrast to organic polymer-based i-TE systems, the Ni-M based system exhibited consistent performance despite being exposed to high temperatures (∼200 °C, 5 minutes).