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Artificial nanofluidic channels that achieve light-driven ion transport in biological systems based on photoelectric effect have attracted significant attention for signal transduction and light energy conversion. However, the light-responsive performance is limited by the charge separation efficiency on the surface of the channels. Herein, we introduce semiconductor p–n junctions into nanofluidic channels to enhance their light-driven ion transport. The p–n junction is formed by an n-type titanium dioxide (TiO2) nanoparticles layer on an electrochemically fabricated p-type polypyrrole (PPy) membrane. The light-induced charge separation at p–n junctions increases the surface charge density of the positively charged PPy membrane. Consequently, the light-driven ion current through the nanofluidic channels is enhanced from 79.6 to 111.9 nA by 40.6% when compared with a single-component p-type PPy membrane. The proof-of-concept demonstration of enhanced light-driven ion transport by semiconductor p–n junctions provides a route toward high-performance light-responsive nanofluidic channels, which demonstrates potential applications for light-controlled mass transport, signal transduction, and energy conversion. [ABSTRACT FROM AUTHOR]

Ion transport plays an important role in various biological processes because of the ability of ions to move rapidly in biological ion channel‐confined spaces. For example, rapid proton transport in ATPases is attributed to confined channel spaces and conjugated sites. According to molecular dynamics simulations, the confined spaces and conjugated sites in nanochannels can enhance ion transport. Herein, it is demonstrated that the ATPase‐like structures of sulfonic acid‐modified covalent organic framework nanochannels, which promote the formation of highly ordered and continuous water molecular chains and confined spaces, can support ion (H+, Li+, Na+, and K+) transport rates that are an order of magnitude higher than those of bulk water. The ion transport rates in the nanochannel are superior to those in other artificial channels. Moreover, the selectivity of cations in the nanochannel is evaluated using the diffusion potential with a concentration gradient. The simulations and experimental results demonstrate that confined spaces and conjugated sites are crucial for efficient ion transport in nanochannels modified by sulfonic acid groups as cation conductor materials. [ABSTRACT FROM AUTHOR]

The conversion of osmotic energy and low-grade heat into electricity provides new solutions to the looming energy crisis. The cooperative utilization of these two kinds of renewable energy sources might enhance the power generation density. Herein, we demonstrate heat and osmosis cooperatively driven power generation in 2D hybrid nanofluidic channels composed of montmorillonite and graphene oxide nanosheets. The hybrid nanochannels exhibit enhanced mechanical strength, cation selectivity and ion flux when compared with single-component nanochannels. With the cooperation of osmosis (artificial sea/river water) and heat (50 °C gradient), the hybrid nanochannels output a high power density of ∼10.29 W m−2, which is improved by 96% when compared with the power density under a single osmotic gradient. The cooperation effect can be ascribed to the enhanced ion permeation from high to low concentrations by judiciously engineering the direction of the heat gradient, which is subsequently supported by theoretical simulations. Our work demonstrates the potentiality to maximize power generation by cooperatively harvesting multiple renewable energies. [ABSTRACT FROM AUTHOR]

The integration of two-dimensional (2D) nanochannels with differing properties presents a promising avenue for mimicking ion transport processes in biological systems. In this study, a bioinspired Janus nanochannel membrane (BJNM) is developed by incorporating intercalated montmorillonite (MMT) and graphene oxide (GO) nanosheets. The asymmetric characteristics in chemical composition, structure, and charge distribution confer the BJNM with the ability to rectify ion transport, as evidenced by nonlinear current-voltage relationships. Through optimization of the electrolyte solution and applied voltage range, a notable rectification ratio of 40.9 is achieved. The underlying mechanism of ion rectification is explored through numerical simulations, highlighting the significance of 2D heterojunctions. These findings provide valuable insights for the design of nanofluidic systems tailored for precise ion transport, biosensing applications, and energy conversion processes. [Display omitted] • Bioinspired two-dimensional nanochannel membranes with Janus heterostructures were fabricated. • The highly rectified ion transport was achieved due to the multiple asymmetries of the membrane. • A remarkable rectification ratio of 40.9 was obtained through the optimization of external factors. • The ion transport mechanism was validated by experimental measurements and theoretical simulations. [ABSTRACT FROM AUTHOR]

The simulation of the ion pumping against a proton gradient energized by light in photosynthesis is of significant importance for the energy conversion in a non‐biological environment. Herein, we report light‐powered ion pumping in a polystyrene sulfonate anion (PSS) doped polypyrrole (PPy) conducting polymer membrane (PSS‐PPy) with a symmetric geometry. This PSS‐PPy conducting polymer membrane exhibits a cationic selectivity and a light‐responsive surface‐charge‐governed ion transport attributed to the negatively charged PSS groups. An asymmetric visible irradiation on one side of the PSS‐PPy membrane induces a built‐in electric field across the membrane due to the intrinsic photoelectronic property of PPy, which drives the cationic transport against the concentration gradient, demonstrating an ion‐pumping effect. This work is a prototype that uses a geometry‐symmetric conducting polymer membrane as a light‐powered artificial ion pump for active ion transport, which exhibits potential applications in nanofluidic energy conversion. [ABSTRACT FROM AUTHOR]

Biomimetic nanochannels are desirable materials for high‐efficiency utilization of osmotic energy. However, the current power generation performance is limited by the low ion selectivity and ion flux. Here, novel nanochannels with double‐network structure based on cellulose nanofibers intercalated with carbon nanotubes are demonstrated. The relatively high cationic selectivity and ion flux are obtained due to the enlarged charge polarity and space for ion transport in the double‐network nanochannel, which is favorable for the osmotic power conversion. To the best of the authors' knowledge, the power density under 50‐fold NaCl (4.67 W m−2) outperforms most state‐of‐the‐art nanochannel membranes with the same test conditions. By applying the concentration gradient between artificial (50‐fold KCl) and real seawater/river water, a high power density of 5.53 and 6.51 W m−2 can be achieved respectively, which exceeds the standard output of the ion‐selective membrane for commercialization. The design of the biomimetic double‐network nanochannels provides a new platform for controllable ion transport and high‐performance power generation. [ABSTRACT FROM AUTHOR]

The design of an electrode surface is critical to the oxygen evolution reaction (OER) during electrochemical water splitting since the catalytic activity depends strongly on surface characteristics, such as the coating uniformity of the catalysts, electrolyte wetting, and the gas‐bubble release ability. Here, nonprecious‐metal electrocatalysts (MnO nanowires) are electrochemically deposited on the surface of a porous gold microgrid. The discontinuous solid–liquid contact lines, which are formed by the microgrids during the liquid‐phase electrochemical reaction, generate MnO nanowires with high coating uniformity. The micro/nanostructure of the electrode induces a superhydrophilic surface, which facilitates the wetting of the alkaline electrolyte and increases the electrochemical active surface area. Simultaneously, the underwater superaerophobicity of the electrode promotes the release of the oxygen products, thus reducing the occupation of the catalytic sites by the gas bubbles. The synergistic effect of electrolyte wetting and gas release ensures that this superhydrophilic/superaerophobic electrode exhibits a current density of 10 mA cm−2 for the OER at an overpotential of 530 mV in 0.1 m KOH, placing the catalyst among the best MnO catalysts for OER. This work avails a new basis for synergistically optimizing the synthesis methods (electrolyte wetting and gas‐bubble release) toward high‐performance OER electrodes. [ABSTRACT FROM AUTHOR]

The characteristics of electrolyte wetting and gas release are of vital importance for the electrocatalytic activity of a hydrogen evolution electrode (HEE). Herein, we reported a strategy to synergistically optimize the electrolyte wetting and gas release of a HEE to enhance its electrocatalytic activity. In our work, Pt nanosheets arrays were electrochemically deposited on a conductive substrate of Au microgrid to form a HEE. The micropores of Au grids induced discontinuous solid/liquid two‐phase contact lines in microscale, which facilitated the wetting of proton‐contained electrolyte. Simultaneously, the superaerophobicity of HEE promoted the release of hydrogen gas products. The joint improvement on electrolyte wetting and gas release enhanced the current density of hydrogen evolution reaction at a high overpotential by ∼300 % when compared with Pt nanosheets arrays on a flat Au substrate. [ABSTRACT FROM AUTHOR]

Nanofluidic diodes mimicking biological ion channels are emerging as desirable materials for controllable ion transport in artificial nanochannels due to their rectification properties. However, the precise control of the chemical composition, geometric structure, surface charges and subsequent rectification of nanofluidic diodes is still challenging. Herein, bottom-up self-assembly is used to fabricate nanofluidic diodes with building blocks of an alumina nanoporous membrane and ion-selective polystyrene opals. Through changing the sphere sizes of opals, the surface charges of opals and the assembly sequence of the building blocks, the chemical composition, geometric structure and surface charges of nanofluidic diodes are tailored on demand, which results in precise control of the rectification. The ion rectification of these assembled diodes is theoretically investigated by a model calculation based on Poisson–Nernst–Planck equations. The bottom-up assembled diodes are applied in conversion of osmotic energy into electricity, which demonstrates a high conversion performance. [ABSTRACT FROM AUTHOR]

The harvest of osmotic energy based on two-dimensional (2D) nanochannel membranes has been attracting wide attentions for addressing the energy issues. Here, we report the nanoscale modulation of interlayer space in 2D nanochannel membranes based on montmorillonite (MMT) for osmotic energy conversion. Cationic surfactants with different alkyl chain lengths are intercalated between MMT nanosheets to regulate the interlayer spacing of 1.74 and 2.49 nm, thus achieving the modulation of ion flux through the nanoclay membranes. A high power density of ∼4.13 W/m2 can be attained in 300-fold concentration gradient. The mechanism of the influence of nanochannel sizes on osmotic energy conversion performance is investigated by experiments and theoretical simulations. Realizing the nanoscale modulation of interlayer space in 2D nanochannels provides new insights for designing nanofluidic membranes toward clean energy harvesting. [Display omitted] • Two-dimensional nanochannel membranes were fabricated based on nanoclay. • The nanoscale modulation of interlayer space was achieved. • The membranes were integrated as osmotic power generators. • The energy conversion was investigated by experiments complemented with theoretical simulations. [ABSTRACT FROM AUTHOR]

The controllable ion transport in the photoreceptors of rod cells is essentially important for the light detection and information transduction in visual systems. Herein, inspired by the photochromism‐regulated ion transport in rod cells with stacking structure, layered ion channels have been developed with a visual photochromic function induced by the alternate irradiation with visible and UV light. The layered structure is formed by stacking spiropyran‐modified montmorillonite 2D nanosheets on the surface of an alumina nanoporous membrane. The visual photochromism resulting from the photoisomerization of spiropyran chromophores reversibly regulates the ion transport through layered ion channels. Furthermore, the cooperation of photochromism and pH value achieves multiple switchable states of layered ion channels for the controllable ion transport mimicking the biological process of the visual cycle. The ion transport properties of these states are explained quantitatively by a theoretical calculation based on the Poisson and Nernst–Plank (PNP) equations. [ABSTRACT FROM AUTHOR]

Inspired by the formation mechanism of a biological membrane potential, we described the generation of an artificial membrane potential through redox-regulating anion distribution on the two sides of a polypyrrole film. The polarity of the membrane potential could be regulated by the redox reaction. [ABSTRACT FROM AUTHOR]

Inspired by the bifunctional utilization of light energy and a proton gradient in photosynthesis, we proposed conceptually an energy-harvesting device that is capable of converting light and a salinity gradient into electricity simultaneously. Our bioinspired concept provided a potential opportunity to harvest multiple renewable energies and maximize the overall power output. [ABSTRACT FROM AUTHOR]

Photosynthesis involves two opposite directions of proton flux across the photosynthetic membrane through embedded proton pumps and proton channels, which provides a biological prototype for designing new photovoltaic systems with alternating current (AC) generation. Here, Pt nanoparticles (Pt NPs) unilaterally covered TiO 2 nanoporous membrane, owing to similar characteristics with natural photosynthetic membrane, is employed to construct a photoelectrochemical cell with AC output through the combination with electron donor and acceptor. Ultraviolet light (UV) irradiation induces protons consumption and generation respectively in the two parts of solution across the membrane via asymmetric photochemical reactions. The resulting concentration gradient of HCl powers the generation of a forward photocurrent. Turning UV illumination off causes a reversed transmembrane HCl concentration gradient mainly because hydrogen atoms adsorbed on Pt NPs are oxidized to be protons, which leads to a reversal in the direction of the current. Upon illumination periodically switching on and off, a continuous and steady AC is generated from the photoelectrochemical cell. Moreover, the waveform of AC is adjustable, and a stable square-wave signal can be obtained by optimizing light on/off frequency and proton source concentration in this system. [ABSTRACT FROM AUTHOR]

The action potential across biological membranes formed by osmotic gradient induced by external conditions plays a key role in the signal transmission of life processes, which can inspire researchers to develop artificial osmotic power generation device with multi-stimuli controllable power output. Herein, an adaptive 2D nanochannel membrane is fabricated by stacking of montmorillonite nanosheets co-modified with a laboratory synthesized cationic surfactant containing spiropyran species and a commercially cationic surfactant of dioctadecyldimethylammonium bromide. Similar to biological action potentials, the osmotic power generation of 2D nanochannel membranes can be regulated by external multiple stimuli such as light, pH and temperature based on the adaptive ion selectivity and ion flux of nanofluidic channels relying on the surface charges of spiropyran species and the phase state of surfactants. Impressively, the control of temperature rising to 60 °C significantly boosted the maximum power density of 2D nanochannel membrane from ∼0.81 W/m2 to be ∼7.12 W/m2 by 8.8 times at a gradient of artificial sea water and river water resulting from the enhanced ion flux by phase transition of surfactants, which is the highest value among those of clay-based nanochannel membranes and ion exchange membranes. Our results implies that the development of adaptive 2D nanochannel membranes is a new strategy for improving the power output of osmotic energy conversion devices. [Display omitted] • An adaptive two-dimensional nanochannel membrane is fabricated. • The membrane was integrated into an osmotic power harvesting system. • The system demonstrated multi-stimuli controllable power output performance. • The system performed a high power density of ∼7.12 W/m2 at 60 °C. [ABSTRACT FROM AUTHOR]

The harvesting of the energy stored in the salinity gradient between seawater and river water by a membrane‐scale nanofluidic diode for sustainable generation of electricity is attracting significant attention in recent years. However, the performance of previously reported nanofluidic diodes is sensitive to the pH conditions, which restricts their potential applications in wider fields with variable pH values. Herein, a pH‐resistant membrane‐scale nanofluidic diode with a high ion rectification ratio of ≈85 that demonstrates a stable ion rectification property over a wider pH range from 4 to 10 is reported. This pH‐resistant ion rectification is explained quantitatively by a theoretical calculation based on the Poisson and Nernst–Plank equations. The nanofluidic diode membrane is integrated into a power generation device to harvest the energy stored in the salinity gradient. By mixing the simulated seawater (0.5 m KCl) and river water (0.01 m KCl) through the membrane, the device outputs an impressive power density of 3.15 W m−2 and demonstrates high stability over a wider pH range. The membrane‐scale nanofluidic diode provides a pH‐resistant platform to control the ion transport and to convert the salinity gradient into electric energy. [ABSTRACT FROM AUTHOR]