Heterogeneous MXene/PS-b-P2VP Nanofluidic Membranes with Controllable Ion Transport for Osmotic Energy Conversion

Membrane-based osmotic power harvesting is a strategy for sustainable power generation. 2D nanofluids with high ion conductivity and selectivity are emerging candidates for osmotic energy conversion. However, the ion diffusion under nanoconfinement is hindered by homogeneous 2D membranes with monotonic charge regulation and severe concentration polarization, which results in an undesirable power conversion performance. Here, an asymmetric nanochannel membrane with a two-layered structure is reported, in which the angstrom-scale channels of 2D transition metal carbides/nitrides (MXenes) act as a screening layer for controlling ion transport, and the nanoscale pores of the block copolymer (BCP) are the pH-responsive arrays with an ordered nanovoid structure. The heterogeneous nanofluidic device exhibits an asymmetric charge distribution and enlarged 1D BCP porosity under acidic and alkaline conditions, respectively; this improves the gradient-driven ion diffusion, allowing a high-performance osmotic energy conversion with a power density of up to 6.74 W m⁻² by mixing artificial river water and seawater. Experiments and theoretical simulations indicate that the tunable asymmetric heterostructure contributes to impairing the concentration polarization and enhancing the ion flux. This efficient osmotic energy generator can advance the fundamental understanding of the MXene-based heterogeneous nanofluidic devices as a paradigm for membrane-based energy conversion technologies.     

In Situ Growth of Imine-Bridged Anion-Selective COF/AAO Membrane for Ion Current Rectification and Nanofluidic Osmotic Energy Conversion

Facing the energy crisis, using the salinity gradient between seawater and freshwater for osmotic energy conversion is a direct way to obtain energy. So far, most nanofluidic membranes utilized for osmotic energy generation are cation-selective. Given that both anion- and cation-selective membranes have the identical importance for energy conversion devices, it is of great significance to develop anion-selective membranes. Herein, an anion-selective membrane is synthesized by in situ growth of imine-bridged covalent organic framework (COF) on ordered anodic aluminum oxide (AAO) at room temperature. The imine groups and residual amino groups of COF can combine with protons in neutral solution, enabling the COF positively charged and efficiently transport of anions. Particularly, due to the asymmetry in the charge and structure of COF/AAO, the as-prepared membrane exhibits excellent ionic current rectification property, which can inhibit ion concentration polarization effectively and possess high ion selectivity and permeability. Using the present COF/AAO membrane, salinity gradient energy can be successfully harvested from solutions with high salt content, and the output power density reached 17.95W m⁻² under a 500-fold salinity gradient. The study provides a new avenue for construction and application of anion-selective membranes in the smart ion transport and efficient energy conversion.     

Paper-Mill Waste Reinforced Nanofluidic Membrane as High-Performance Osmotic Energy Generators

Nanofluidic membranes consisting of 2D materials and polymers are considered promising candidates for harvesting osmotic energy from river estuaries owing to their unique ion channels. However, micron-scale polymer chains agglomerate in the nanochannels, resulting in steric hindrance and affection ion transport. Herein, a nanofluidic membrane is designed from MXene and xylan nanoparticles that are derived from paper-mill waste. The demonstrated membrane reinforced by paper-mill waste has the characteristics of green, low-cost, and outstanding performance in mechanical properties and surface-charge-governed ionic transport. The MXene/carboxmethyl xylan (CMX) membrane demonstrates a high surface charge (ζ-potential of −44.3 mV) and 12 times higher strength (284.96 MPa) than the pristine MXene membrane. The resulting membrane shows intriguing features of high surface charge, high ion selectivity, and reduced steric hindrance, enabling it high osmotic energy generation performance. A potential of the nanofluidic membrane is ≈109 mV, the corresponding current of up to 2.73 µA, and the output power density of 14.52 mW m⁻² are obtained under a 1000-fold salt concentration gradient. As the electrolyte pH increases, the power density reaches 56.54 mW m⁻². This works demonstrate that CMX nanoparticles can effectively enhance the properties of the nanofluidic membrane and provide a promising strategy to design high-performance nanofluidic devices.     

Biomimetic Aerogel for Moisture-Induced Energy Harvesting and Self-Powered Electronic Skin

Moisture–electric generator (MEG)-based blue energy is widely studied. There is still a significant challenge in improving the power of the MEGs system and expanding its application in self-powered electronic skin. Inspired by the structure of ferns, a biomimetic moisture–electric aerogel is designed to collect energy. Polyvinyl alcohol dendritic colloids act as “roots” and “stems” to provide support and channels to transport water molecules. Meanwhile, “leaf-like” graphene oxide sheets generate electricity through direct interaction with water. Besides, based on the above biomimetic structure, this work further enhances the output performance of MEGs by increasing the specific surface area (120.4 m² g⁻¹) and introducing an ultra-high ion density gradient (from −35 to +37 mV). Meanwhile, due to the excellent water absorption, the MEGs show good salt resistance and cyclic stability. By constructing unique biomimetic structures, ultra-high ion density gradient, and regulating environmental conditions, a high-performance MEG is obtained, including ultra-high open-circuit voltage (1.9 V) and short-circuit current (82.5 µA), the industry-leading power density among MEGs with continuous output is reported in the literature (22.55 µW cm⁻²). Besides, the MEGs can accurately respond to environmental and pressure changes, showing its application potential in self-powered electronic skin.     

A Biomimetic Transpiration Textile for Highly Efficient Personal Drying and Cooling

Efficient sweat release and heat dissipation are required for functional textiles that improve comfort and productivity while being worn in daily life. However, the porous structure of textiles exhibits an opposite effect on water transport and heat transfer capacities, leading to a longstanding bottleneck for the design of multifunctional drying and cooling textiles. Here, a biomimetic transpiration textile based on the hierarchical and interconnected network of vascular plants is demonstrated for highly efficient personal drying and cooling. The transpiration-inspired design offers a textile with distinct advantages, including a desired one-way water transport index (1072%), rapid water evaporation rate (0.36 g h⁻¹), and outstanding through-plane (0.182 W m⁻¹ K⁻¹) and in-plane (1.137 W m⁻¹ K⁻¹) thermal conductivities. Moreover, based on the optimized performance, plausible mechanisms are proposed and calculated to provide insight into the water transport and heat transfer within the hierarchical and interconnected network, which provide promising benefits to the development of multifunctional drying and cooling textiles. Overall, the successful synthesis of this biomimetic transpiration textile provides a comfortable microclimate to the human body, thus satisfying the growing demand for better health, productivity, and sustainability.     

High-Strength,Thin PBO Nanofiber Membrane with Long-Term Stability for Osmotic Energy Conversion

Ion-selective membrane embedded in a reverse electrodialysis system can achieve the conversion of osmotic energy into electricity. However, the ingenious design and development of pure polymer membranes that simultaneously satisfy excellent mechanical strength, long-term stability, high power density, and increased testing area is a crucial challenge. Here, high-strength, thin PBO nanofiber membranes (PBONM) with 3D nanofluidic channels and a thickness of 0.81 µm are prepared via a simple vacuum-assisted filtration technology. The thin PBONM exhibits excellent mechanical properties: stress of 235.8 MPa and modulus of 16.96 GPa, outperforming the state-of-the-art nanofluidic membranes. The obtained PBONM reveals surface-charge-governed ion transport behavior and high ion selectivity of 0.88 at a 50-fold concentration gradient. The PBO membrane-based generator delivers a power density of 7.7 and 40.2 W m⁻² at 50-fold and 500-fold concentration gradient. Importantly, this PBONM presents excellent stability in response to different external environments including various saline solutions, pH, and temperature. In addition, the maximum power density of PBONM reaches up to 5.9 W m⁻² under an increased testing area of 0.79 mm², exceeding other membrane-based generators with comparable testing areas. This work paves the way for constructing high-strength fiber nanofluidic membranes for highly efficient osmotic energy conversion.     

A Molecularly Engineered Zwitterionic Hydrogel with Strengthened Anti-Polyelectrolyte Effect: from High-Rate Solar Desalination to Efficient Electricity Generation

Polyzwitterionic hydrogel is an emerging material for solar-driven water evaporation in saline environment due to its special anti-polyelectrolyte effect, which is a promising approach to co-generation of freshwater and electricity. However, the molecular impact on anti-polyelectrolyte effect remains unclear, let alone to optimize the zwitterionic structure to promote water evaporation efficiency in high-salinity brine. Herein, a molecularly engineered zwitterionic hydrogel is developed and the incorporated phenyl-methylene-imidazole motif greatly enhances the salt binding ability and strengthens anti-polyelectrolyte effect, leading to boosted hydration, improved salt tolerance, ultra-low evaporation enthalpy (almost half of traditional zwitterionic gel), and durable anti-microbial ability in brine. Besides, gradient solar-thermal network is penetrated to optimize water transport channel and heat confinement. The gel exhibits excellent evaporation rate of 3.17 kg m⁻² h⁻¹ in seawater, which is 1.6 times of that in water and such high efficiency could be maintained during 8 h continuous desalination, demonstrating outstanding salt tolerance. The high flux of ion stream can generate considerable voltage (321.3 mV) simultaneously. This work will bring new insights to the understanding of anti-polyelectrolyte effect at molecular level and promote materials design for saline water evaporation.     

Highly Efficient Osmotic Energy Harvesting in Charged Boron-Nitride-Nanopore Membranes

Recent studies of the high energy-conversion efficiency of the nanofluidic platform have revealed the enormous potential for efficient exploitation of electrokinetic phenomena in nanoporous membranes for clean-energy harvesting from salinity gradients. Here, nanofluidic reverse electrodialysis (NF-RED) consisting of vertically aligned boron-nitride-nanopore (VA-BNNP) membranes is presented, which can efficiently harness osmotic power. The power density of the VA-BNNP reaches up to 105 W m⁻², which is several orders of magnitude higher than in other nanopores with similar pore sizes, leading to 165 mW m⁻² of net power density (i.e., power per membrane area). Low-pressure chemical vapor deposition technology is employed to uniformly deposit a thin BN layer within 1D anodized alumina pores to prepare a macroscopic VA-BNNP membrane with a high nanopore density, ≈10⁸ pores cm⁻². These membranes can resolve fundamental questions regarding the ion mobility, liquid transport, and power generation in highly charged nanopores. It is shown that the transference number in the VA-BNNP is almost constant over the entire salt concentration range, which is different from other nanopore systems. Moreover, it is also demonstrated that the BN deposition on the nanopore channels can significantly enhance the diffusio-osmosis velocity by two orders of magnitude at a high salinity gradient, resulting in a huge increase in power density.     

Ni-based Plasmonic/Magnetic Nanostructures as Efficient Light Absorbers for Steam Generation

Solar steam generation technologies have gained increasing attention due to their great potential for clean water generation with low energy consumption. The rational design of a light absorber that can maximize solar energy utilization is therefore of great importance. Here, the synthesis of Ni@C@SiO₂ core–shell nanoparticles as promising light absorbers for steam generation by taking advantage of the plasmonic excitation of Ni nanoparticles, the broadband absorption of carbon, and the protective function and hydrophilic property of silica is reported. The nanoparticle-based evaporator shows an excellent photothermal efficiency of 91.2%, with an evaporation rate of 1.67 kg m⁻² h⁻¹. The performance can be further enhanced by incorporating the nanoparticles into a polyvinyl alcohol hydrogel to make a composite film. In addition, utilizing the magnetic property of the core–shell particles allows the creation of surface texture in the film by applying an external magnetic field, which helps increase surface roughness and further boost the evaporation rate to as high as 2.25 kg m⁻² h⁻¹.     

Lignin-Derived Ionic Conducting Membranes for Low-Grade Thermal Energy Harvesting

Wood-based ionic conductive membranes have emerged as a new paradigm for low-grade thermal energy harvesting applications due to their unique andtailorable structures. Herein, a lignin-derivedionic conducting membrane with hierarchical aligned channels is synthesized viaa double network crosslinking approach. Their excellent thermal stability andsuperior swelling ratio allow their optimization as low-grade heat recovery technologies. Several vertically aligned nanoscaleconfinements are found in the synthesized membranes, contributing towardenhanced ionic diffusion. Among all the combinations, the membrane comprising69.2 wt.% of lignin and infiltrated with 0.5 m KOH exhibits anexceptional ionic figure of merit (ZTi) of 0.25, relatively higher ionic conductivity(51.5 mS cm^‒1), lower thermal conductivity(0.195 W m^‒1·K), and a remarkable ionic Seebeck coefficientof 5.71 mV K^‒1 under the application of an axialtemperature gradient. A numerical model is also utilized to evaluate theveracity of experimental observations and to gain a better understanding of thefundamental mechanisms involved in attaining such values. These results displaythe potential of lignin-basedmembranes for future thermal energy harvesting applications and are a new facetin thermoelectric energy conversion which is certain to pave the way forfurther investigations on sustainable ionic conductive membranes.     

Neuron-Inspired Self-Powered Hydrogels with Excellent Adhesion,Recyclability and Dual-Mode Output for Multifunctional Ionic Skin

Hydrogels are promising materials for electronic skin due to their flexibility and modifiability. Reported hydrogel electronic skins can recognize stimulations and output signals, but the single output signal and the requirement of external power source limit their further applications. In this study, inspired by the neuron system, the self-powered neuron system-like hydrogels based on gelatin, water/glycerin and ionic liquid modified metal organic frameworks (MOFs) are prepared. The optimized hydrogel exhibits excellent adhesion (40 kPa), stretchability (0%–100%), water retention (>92% at 0% relative humidity (RH) atmosphere), ionic conductivity (>10⁻³ S m⁻¹) and stability (>30 days). Besides, the neuron system-like hydrogels are highly sensitive to pressure (0—10 N) and humidity (0%–75% RH) with dual-modal output, without external power source. Finally, the optimized hydrogel ionic skin is applied in human motion detection, energy harvesting, and low humidity sensing. This study provides a preliminary exploration of self-powered ionic skin for multi-application scenarios.     

A Bionic-Gill 3D Hydrogel Evaporator with Multidirectional Crossflow Salt Mitigation and Aquaculture Applications

In recent years, interfacial solar-driven steam generation has gained huge attention as a sustainable and energy-efficient technology. However, salt scaling on and inside the evaporator structure induced by insufficient ion distribution control will lower the evaporation performance and hinder the stability and durability of evaporators. Herein, inspired by the highly efficient salt-expelling property of the gill filaments of large yellow croaker, a bionic-gill 3D hydrogel evaporator is proposed with fabulous multidirectional ion migration controllability. A 3D structure composed of arrayed beaded hollow columns with beaded hollow holes inspired by gill filaments ensuring longitudinal ion backflow and the peristome-mimetic arrayed grooves of microcavities ensuring lateral ion advection is designed and constructed to achieve fabulous multidirectional crossflow salt ion migration, which ensures high evaporation performance for pure water (an evaporation rate of 2.53 kg m⁻² h⁻¹ with an energy efficiency of 99.3%) as well as for high salinity brine (2.11 kg m⁻² h⁻¹ for 25.0 wt.% NaCl solution), with no salt crystallizing after long-term use. Furthermore, the 3D hydrogel evaporator has excellent chemical stability, mechanical properties, folding-irrelevant evaporation performance, and portability so that it can be used for the preliminary desalination of breeding wastewater through the proposed self-circulation koi aquaculture system.     

Phase-Separated Polyzwitterionic Hydrogels with Tunable Sponge-Like Structures for Stable Solar Steam Generation

Solar steam generation (SSG) through hydrogel-based evaporators has shown great promise for freshwater production. However, developing hydrogel-based evaporators with stable SSG performance in high-salinity brines remains challenging. Herein, phase-separated polyzwitterionic hydrogel-based evaporators are presented with sponge-like structures comprising interconnected pores for stable SSG performance, which are fabricated by photopolymerization of sulfobetaine methacrylate (SBMA) in water-dimethyl sulfoxide (DMSO) mixed solvents. It is shown that driven by competitive adsorption, the structures of the resulting poly(sulfobetaine methacrylate) (PSBMA) hydrogels can be readily tuned by the volume ratio of DMSO to achieve phase separation. The optimized phase-separated PSBMA hydrogels, combining the unique anti-polyelectrolyte effects of polyzwitterionic hydrogels, demonstrate a rapid water transport capability in brines. After introducing photothermal polypyrrole particles on the surface of the phase-separated PSBMA hydrogel evaporators, a stable water evaporation rate of ≈2.024 kg m⁻² h⁻¹ and high solar-to-vapor efficiency of ≈97.5% in a 3.5 wt.% brine are obtained under simulated solar light irradiation (1.0 kW m⁻²). Surprisingly, the evaporation rates remain stable even under high-intensity solar irradiation (2.0 kW m⁻²). It is anticipated that the polyzwitterionic hydrogel evaporators with sponge-like porous structures will contribute to developing SSG technology for high-salinity seawater applications.     

High Performance Anion Exchange Membranes with Confined Sub-2-nm Ion Channel

As a key component of low-cost anion exchange membrane fuel cells (AEMFCs), anion exchange membranes (AEMs) are far from commercial application, because of dissatisfactory alkaline stability and conductivity. Herein, a new insight is proposed to prepare high performance AEMs by constructing of confined ion channel. With an intermediate oligomer produced before the main copolymerization, novel poly(vinyl-carbazolyl aryl piperidinium) AEMs with confined sub-2-nm ion channel are successfully prepared. The unique sub-2-nm ion channel enable membranes ultrahigh hydroxide conductivity of 261.6 mS cm⁻¹, and the state-of-the-art chemical stability over 5000 h. Moreover, the AEMs also exhibit good mechanical stability with lower water uptake and dimensional swelling. Based on the as-prepared AEMs and ionomer, fuel cells exhibit outstanding peak power density of 1.8 and 0.2 W cm⁻² with Pt-based catalysts and completely non-precious metal catalysts, respectively.     

Degenerately Doped Semi-Crystalline Polymers for High Performance Thermoelectrics

Thermoelectric (TE) energy conversion in conjugated polymers is considered a promising approach for low-energy harvesting and self-powered temperature sensing. To enhance the TE performance, it is necessary to understand the relationship between the Seebeck coefficient (α) and electrical conductivity (σ). Typical doped polymers exhibit α–σ relationship that is distinct from that of inorganic materials due to their large structural and energetic disorder, which prevents them from achieving the maximum TE power factor (PF = α²σ). Here, an ideal α–σ relationship in the Kang–Snyder model following a transport parameter s  = 1 is demonstrated with two degenerately doped semi-crystalline polymers, poly[(4,4′-(bis(hexyldecylsulfanyl)methylene)cyclopenta[2,1-b:3,4-b′]dithiophene)-alt-(benzo[c][1,2,5]thiadiazole)] (PCPDTSBT) and poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDT2FBT) using a sequential doping method. The results allow the realization of the PFs reaching theoretic maxima (i.e., 112.01  µ W m⁻¹ K⁻² for PPDT2FBT and 49.80  µ W m⁻¹ K⁻² for PCPDTSBT) and close to metallic behavior in heavily doped films. Additionally, it is shown that the PF maxima appear when the doping state switches from non-degenerate to degenerate. Strategies towards an optimal α–σ relationship enable optimization of the PF and provide an understanding of the charge transport of doped polymers.     

Highly Salt-Resistant 3D Hydrogel Evaporator for Continuous Solar Desalination via Localized Crystallization

The emerging solar desalination by interfacial evaporation shows great potential for alleviating the global freshwater crisis. However, salt deposition on the whole evaporation surface during steam generation leads to a deterioration in the evaporation rate and long-term stability. Herein, it is demonstrated that a hydrogel-based 3D structure can serve as an efficient and stable solar evaporator by salt localized crystallization for high-salinity brine desalination. Under the function of micron-grade brine transport management and edge-preferential crystallization promoted by this novel design, this 3D hydrogel evaporator exhibits a superior salt-resistant property without salt deposition on the photothermal surface even in 20 wt% brine for continuous 24-h illumination. Moreover, by virtue of the synergistic effect of the promising 3D structure and excellent water transport of hydrogel, the proposed evaporator possesses an excellent evaporation performance achieving 2.07 kg m⁻² h⁻¹ on average in a high-salinity brine (from 10 to 25 wt% NaCl) under 1 sun irradiation, among the best values reported in the literature. With stable and efficient evaporation performance out of high-salinity brine, this design holds great potential for its applications in sustainable solar desalination.     

Aramid Nanofiber Membranes for Energy Harvesting from Proton Gradients

Harvesting osmotic energy from industrial wastewater is an often-overlooked source of electricity that can be used as a part of the comprehensive distributed energy systems. However, this concept requires, a new generation of inexpensive ion-selective membranes that must withstand harsh chemical conditions with both high/low pH, have high temperature resilience, display exceptional mechanical properties, and support high ionic conductance. Here, aramid nanofibers (ANFs) based membranes with high chemical/thermal stability, mechanical strength, toughness, and surface charge density make them capable of high-performance osmotic energy harvesting from pH gradients generated upon wastewater dilution. ANF membranes produce an averaged output power density of 17.3 W m^?2 for more than 240 h at pH 0. Taking advantage of the high temperature resilience of aramid, the output power density is increased further to 77 W m^?2 at 70 °C, typical for industrial wastewater. Such output power performance is 10× better compared to the current state-of-the-art membranes being augmented by Kevlar-like environmental robustness of ANF membranes. The improved efficiency of energy harvesting is ascribed to the high proton selectivity of ANFs. Retaining high output power density for large membrane area and fluoride-free synthesis of ANFs from recyclable material opens the door for scalable wastewater energy harvesting.     

Photovoltaic performance of Organic Photovoltaics for indoor energy harvester

Wireless sensor network becomes widespread into home and offices to keep them comfort and save the energy. The battery-less wireless sensor nodes need the high performance indoor solar cells for stable and sustainable operation. Organic Photovoltaics (OPV) has great indoor photovoltaic performance because ultra-thin organic layer has strong absorption against the UV–visible spectrum that is good spectral matching with indoor lightings. In this study, OPV module has 8 cells in series and same size as the conventional amorphous silicon solar cells (a-Si) for indoor light harvesting. OPV and a-Si are measured their photovoltaic performance under the fluorescent light and demonstrated for energy harvester of wireless sensor network. The output power of OPV and a-Si is 43.4 μW cm⁻² and 28.5 μW cm⁻² at fluorescent light 1000lux respectively. The data transmission rate of the wireless sensor node driven by OPV is 30–40% improved under the dim light condition compared to a-Si.     

Laterally Heterogeneous 2D Layered Materials as an Artificial Light‐Harvesting Proton Pump

Heterogeneous structures in nacre‐mimetic 2D layered materials generate novel transport phenomena in angstrom range, and thus provide new possibilities for innovative applications for sustainable energy, a clean environment, and human healthcare. In the two orthogonal transport directions, either vertical or horizontal, heterostructures in horizontal direction have never been reported before. Here, a 2D‐material‐based laterally heterogeneous membrane is fabricated via an unconventional dual‐flow filtration method. Negatively and positively charged graphene oxide multilayers are laterally patterned and interconnected in a planar configuration. Upon visible light illumination on the bipolar nanofluidic heterojunction, protons are able to move uphill against their concentration gradient, functioning as a light‐harvesting proton pump. A maximum proton concentration gradient of about 5.4 pH units mm^?2 membrane area can be established at a transport rate up to 14.8 mol h^?1 m^?2. The transport mechanism can be understood as a light‐triggered asymmetric polarization in surface potential and the consequent change in proton capacity in separate parts. The implementation of photonic–ionic conversion with abiotic materials provides a full‐solid‐state solution for bionic vision and artificial photosynthesis. There is plenty of room to expect the laterally heterogeneous membranes for new functions and better performance in the abundant family of liquid processable colloidal 2D materials.     

Highly improved thermoelectric performances of PEDOT:PSS/SWCNT composites by solvent treatment

Composites of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and single-wall carbon nanotube (SWCNT) were prepared by mixing aqueous dispersions of PEDOT:PSS and SWCNT at different weight ratios. By being soaked with DMSO for 2 min at room temperature, the PEDOT:PSS/SWCNT composite with an optimized SWCNT weight ratio of 74 wt% exhibited a high electric conductivity of 3800 S cm⁻¹ and a reasonable Seebeck coefficient of 28 μV K⁻¹, leading to a promising power factor of 300 μW m⁻¹ K⁻² and a hopeful ZT value of 0.13. Possible reasons for the highly improved properties are carefully discussed.