The invention of hydroelectric nanogenerators (HENGs) is a breakthrough technology for green electricity generation. However, the underlying mechanisms driving energy conversion remain largely unknown, impeding the development of HENGs with high energy densities. Here, we develop a new Multiphysics model involving Darcy's law, phase transfer in porous media, and current modules to reveal the mechanisms of electricity generation in HENGs. This is the first model to simulate evaporation as a streaming potential variable with the Robin-type boundary condition that overcomes the shortcomings of Neumann- and Dirichlet-type boundary conditions. Including the streaming potential and electric double layer (EDL) effects, the simulation can be based on actual water flow conditions, which is more convincing and lays a microscopic foundation for future research and exploration into the mechanism of hydroelectric electricity generation. The new model reveals that the concentrations of salt solutions significantly impact the output power density of HENGs by affecting the solution conductivity in the stern layer, while relative humidity has a minimal impact. This model along with experimental validation offers a robust method to improve the electrical output of HENGs.@en

Improving the kinetic performance of thick electrodes is key to enhancing lithium extraction from salt lakes. Nano-melamine foam (MF), known for its unique porous structure, is ideal for building a three-dimensional (3D) conductive network, thereby boosting electrode kinetics. In our study, we developed a thick electrode (20 mg·g−1) with a 3D-conductive network by in-situ growing LiFePO4 (LFP) onto a nanoscale MF substrate. This electrode exhibited superior kinetic performance and a high lithium adsorption capacity in brine, achieving up to 32.8 mg·g−1 in just 10 min. Remarkably, even in simulated brine with a high Mg2+/Li+ ratio, it maintained an average coulomb efficiency of 62 %, significantly lowering the Mg2+/Li+ ratio from 65.6 to 0.47. It also showed exceptional stability in actual brine, maintaining an average coulomb efficiency of about 56.6 %. Our development of this high conductivity, thick electrode provides new insights into efficient lithium extraction methods.@en

Hydroelectric nanogenerators (HENGs) utilize the synergy between conductive nanomaterials and hydrodynamic flow to generate electricity, but their applications are limited by low output power density. Here, a high-performance HENG is developed by employing single-layer MXene (SMX) nanosheets on wool cloth. The SMX-based HENGs exhibit a maximum energy density of 0.683 mW cm−2, a current of 1.994 mA, and a voltage of 0.687 V, sufficient to power small wearable electronics. Moreover, the hydrophilicity of the HENGs is maintained due to the addition oxidized ketjen black nanoparticles to the SMX matrix. This is attributed to the functional groups (e.g., –COOH and –OH) on OKB, which are important for efficient ion transport and maintaining a high steady-state power density. Important insights into energy generation for the development of high-efficiency HENGs for practical applications have been gained from numerical simulation using COMSOL multiphysics.@en

Enhancing the kinetic performance of thick electrodes is essential for improving the efficiency of lithium extraction processes. Biochar, known for its affordability and unique three-dimensional (3D) structure, is utilized across various applications. In this study, we developed a biochar-based, 3D-conductive network thick electrode (∼20 mg cm−2) by in-situ deposition of LiFePO4 (LFP) onto watermelon peel biomass (WB). Utilizing Density Functional Theory (DFT) calculations complemented by experimental data, we confirmed that this The thick electrode exhibits outstanding kinetic properties and a high capacity for lithium intercalation in brines, even in environments where the Magnesia-lithium ratios are significantly high. The electrode showed an impressive intercalation capacity of 30.67 mg g−1 within 10 min in a pure lithium solution. It also maintained high intercalation performance (31.17 mg g−1) in simulated brines with high Magnesia-lithium ratios. Moreover, in actual brine, it demonstrated a significant extraction capacity (23.87 mg g−1), effectively lowering the Magnesia-lithium ratio from 65 to 0.50. This breakthrough in high-conductivity thick electrode design offers new perspectives for lithium extraction technologies.@en

Despite the high energy density of lithium-rich manganese-based (LR) cathode materials, the practical implementation in batteries has been impeded by the intrinsic issues regarding cycling. Herein, a coherent interface modification strategy is proposed. The LR materials are coated with a lattice-matched Li3BO3 (LBO) layer at the interface. The coating applied to the electrode has two impacts. (1) It reduces interfacial side reactions between the electrode materials and electrolyte, thereby improving structural stability. (2) It mitigates stress between solid particles, which enhances the cycling stability (83% after 500 cycles at 2C) of LR. Furthermore, the LBO coating promotes the development of a spinel-like structure on the electrode materials surface, eliminating unstable oxygen, increasing oxygen vacancy (Ov), consequently enhancing the initial Coulombic efficiency (ICE, 92.18%), and alleviating particle breakage (Young’s moduli of LR@S@LBO is 3.26 ± 1.6 GPa) after optimization. Theoretical calculations show that Ov and spinel can improve the diffusion of Li+ and the structural stability of LR materials. This work shows great potential for the rational design of high-energy-density electrode materials.@en

Ion transport within saturated porous media is an intricate process in which efficient ion delivery is desired in many engineering problems. However, controlling the behavior of ion transport proves challenging, as ion transport is influenced by a variety of driving mechanisms, which requires a systematic understanding. Herein, we study a coupled advection–diffusion–electromigration system for controlled ion transport within porous media using the scaling analysis. Using the Lattice–Boltzmann–Poisson method, we establish a transport regime classification based on an Advection Diffusion Index (ADI) and a novel Electrodiffusivity Index (EDI) for a two-dimensional (2D) microchannel model under various electric potentials, pressure gradients, and concentration conditions. The resulting transport regimes can be well controlled by changing the applied electric potential, the pressure field, and the injected ions concentration. Furthermore, we conduct numerical simulations in a synthetic 2D porous media and an x-ray microcomputed tomography sandstone image to validate the prevailing transport regime. The simulation results highlight that the defined transport regime observed in our simple micromodel domain is also observed in the synthetic two- and three-dimensional domains, but the boundary between each transport regime differs depending on the variation of the pore size within a given domain. Consequently, the proposed ADI and EDI emerge as dimensionless indicators for controlled ion transport. Overall, our proof-of-concept for ion transport control in porous media is demonstrated under advection–diffusion–electromigration transport, demonstrating the richness of transport regimes that can develop and provide future research directions for subsurface engineering applications.@en

Constructing thick electrodes with high Li+ adsorption capacity and excellent kinetic performance effectively addresses the low efficiency of lithium extraction from salt lake brines. However, an increase in the content of active material can hinder the Li+ mass transfer within the electrode, resulting in polarization and reduced kinetic performance, which ultimately affects the extraction efficiency. This study synthesized a three-dimensional(3D) conductive network-incorporated thick electrode (∼20 mg/cm2) composed of the redox graphene oxide-loaded LFP(LFP/rGO) composite through an in situ hydrothermal method. The electrode material showed excellent kinetic performance and a high adsorption capacity for Li+ in salt lake brine. Under a constant voltage of 0.8 V in Li+ solution, the Li+ adsorption capacity reached 36.78 mg·g−1 within 10 min, exhibiting an average coulombic efficiency of over 83.53 %. Furthermore, the LFP/rGO composite thick electrode exhibited a Li+ adsorption capacity of 32.82 mg·g−1, along with an average coulombic efficiency of 74.6 %, even in the West Taijinar old brine solution. Additionally, the electrode material demonstrated remarkable cycling stability, maintaining a capacity of 172.09 mAh·g−1 after 50 cycles at a 0.2C rate in a high-concentration salt lake brine. Our preparation strategy offers novel insights for high-performance lithium extraction electrodes.@en

The electrochemical C-N coupling process, facilitating the production of organic nitrogen substances (such as urea, methylamine, formamide, and ethylamine) via the simultaneous reduction of carbon dioxide (CO2) and small nitrogen-based substances, stands at the forefront of advancing carbon neutrality and the artificial nitrogen cycle. This method has garnered substantial interest due to its potential economic and environmental benefits. Although considerable progress has been achieved in this emerging field, it still faces challenges, including slow reactant adsorption, competing side reactions, and complex multi-step pathways, resulting in low yields and selectivity. Strategically designing and developing low-cost and exceptionally performant catalysts is crucial for cost-effective and precise electrochemical C─N bonding. This article offers an in-depth review of the electrosynthesis of valuable organic nitrogen compounds at ambient conditions from earth-abundant resources/wastes, such as CO2 and small nitrogenous molecules (nitrogen: N2, nitrite: NO2−, nitrate: NO3−, ammonia: NH3, etc.), via electrochemical C─N bond formation reactions, especially using carbon-based catalysts. The relevant electrochemical C─N bond formation mechanisms, the design principles of advanced carbon-based electrocatalysts, and the impact of different electrolyser designs are discussed, along with the present obstacles and upcoming prospects in this dynamic field.@en

Sorption-based atmospheric water harvesting (SAWH) followed by solar-driven desorption is emerging as a promising energy and cost-effective solution to alleviate the worldwide freshwater scarcity. To achieve efficient atmospheric water harvesting, a SAWH system with low water transfer resistance and high sorption-desorption kinetics that integrates photothermal properties is demanded. Herein, inspired by nature, a sodium alginate (SA)-based SAWH hemisphere with spatially centripetal conical channels loaded with CaCl ₂ crystals is designed. The device demonstrates unidirectional water transfer properties and high moisture absorption capacity. To enable solar-driven water desorption, the device is engineered with a photothermal layer by chelation of tannic acid (TA) with Fe ³⁺. The multifunctional SAWH device with a special channel structure presents a superb water absorption of 0.90-2.29 g g ⁻¹ within a wide range of relative humidity (RH) (40-90%) and a fast solar-driven water desorption rate of 1.77 kg m ⁻² h ⁻¹ under one sun illumination. In outdoor tests, 82.3% of the water absorbed overnight could be released during the daytime under natural sunlight, achieving an ultrahigh daily water production of 3.72 L per m ² that is superior to that of most previously reported all-in-one SAWH systems. This proposed design strategy provides an effective solution for collecting water from the air by SAWH followed by solar-driven water desorption.

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Wastewater recycling is a solution to address the global water shortage. Phenols are major pollutants in wastewater, and they are toxic even at very low concentrations. Advanced oxidation process (AOP) is an emerging technique for the effective degradation and mineralization of phenols into water. Herein, we aim at giving an insight into the current state of the art in persulfate-based AOP for the oxidation of phenols using metal/metal-oxide and carbon-based materials. Special attention has been paid to the design strategies of high-performance catalysts, and their advantages and drawbacks are discussed. Finally, the key challenges that govern the implementation of persulfate-based AOP catalysts in water purification, in terms of cost and environmental friendliness, are summarized and possible solutions are proposed. This work is expected to help the selection of the optimal strategy for treating phenol emissions in real scenarios.

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Mixing, homogenization, separation, and filtration are crucial processes in miniaturized analytical systems employed for in-vitro biological, environmental, and food analysis. However, in microfluidic systems achieving homogenization becomes more challenging due to the laminar flow conditions, which lack the turbulent flows typically used for mixing in traditional analytical systems. Here, we introduce an acoustofluidic platform that leverages an acoustic transducer to generate microvortex streaming, enabling effective homogenizing of food samples. To reduce reliance on external equipment, tubing, and pump, which is desirable for Point-of-Need testing, our pumpless platform employs a hydrophilic yarn capable of continuous wicking for sample perfusion. Following the homogenization process, the platform incorporates an array of micropillars for filtering out large particles from the samples. Additionally, the porous structure of the yarn provides a secondary screening mechanism. The resulting system is compact, and reliable, and was successfully applied to the detection of Escherichia coli (E. coli) in two different types of berries using quantitative polymerase chain reaction (qPCR). The platform demonstrated a detection limit of 5 CFU g ⁻¹, showcasing its effectiveness in rapid and sensitive pathogen detection.

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The ubiquitous and continuous natural processes of water absorption and evaporation have stimulated interest in generating electricity through the creation of a flow of electrical charge, which can then be collected and stored. However, the resultant low output power density as well as the complicated fabrication and operation processes have hindered the practical applications of this technology. Herein, we demonstrate a highly efficient self-operating hydroelectric nanogenerator (HENG) that produces electricity through the absorption and evaporation of seawater. The single HENG consists of a hydrophilic wool cloth stripe functionalized with ketjen black powders and equipped with two electrodes affixed at its ends. The continuous absorption and evaporation of seawater results in the generation of electricity that can be stored in a capacitor. A series of 16 HENGs, each consisting of 10 stacked wool cloth stripes, can generate sufficient power to charge a supercapacitor to 1.6 V within 5 h 30 min under ambient conditions, outperforming most comparable devices reported. The superior performance observed for the HENG is attributable to the hydrophilicity and porosity of wool cloth which can continuously absorb seawater at a desired rate as well as the 2D structure of ketjen black and its high conductivity. This work paves the way to facilitate the development of HENGs for practical applications.

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Malodor is regarded as a very significant nuisance, 2nd only to noise pollution, in the developed world. It directly impacts people's health and wellbeing. The prevention of odor build-up is a key property for both interior textiles and active sportswear. Traditional approaches for odor elimination rely on textile surface treatment. However, the role of intrinsic morphology and chemical composition of fibers in odor elimination has not been taken into account. In this study, the adsorption characteristics and mechanisms of three common types of fibers (wool, cotton and nylon) for two typical odors of acetic acid and ammonia were systematically investigated through kinetic modelling, the inverse gas chromatography (IGC) technique, and density functional theory (DFT) calculations. Both acetic acid and ammonia adsorption onto fibers followed a pseudo-second-order kinetic model. Among all the tested fibers, wool showed the highest adsorption ability towards both acetic acid and ammonia. The adsorption behaviors of cotton and nylon were explored based on quantitative measurement of surface Lewis acid-base properties using the IGC technique. These findings were further corroborated by DFT calculations via the interactions between fibers and the adsorbed odor. This study provides a new insight into odor adsorption onto commonly used fibers and their interactions, which is a key step in developing fibrous materials for odor control, including body odor and indoor air pollutants.

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Hydroelectric nanogenerators (HENGs) are emerging devices towards sustainable and green energy production. The voltage produced by HENGs varies depending on several variables including the device size and architecture, the type of material used and the ambient conditions. Currently, HENGs have demonstrated the ability to generate voltage up to a few volts, making them well-suited for operating low-power electronics. This work gives a comprehensive review on the various aspects, including the working mechanisms of HENGs based on the phase transitions of water, different working modes (continuous or intermittent), and the materials used/developed to date. Factors that influence the device performance and durability/lifespan are analyzed and the potential applications of HENGs are recommended. Finally, the existing challenges and future trends of HENGs are discussed to guide the development of high-performance HENGs that can help meet the increasing electricity need for charging portable electronics. This review helps identify avenues for enhancing the efficiency and efficacy of HENGs by materials optimization and device design.

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Abstract: Electrokinetic in-situ recovery is an alternative to conventional mining, relying on the application of an electric potential to enhance the subsurface flow of ions. Understanding the pore-scale flow and ion transport under electric potential is essential for petrophysical properties estimation and flow behavior characterization. The governing physics of electrokinetic transport is electromigration and electroosmotic flow, which depend on the electric potential gradient, mineral occurrence, domain morphology (tortuosity and porosity, grain size and distribution, etc.), and electrolyte properties (local pH distribution and lixiviant type and concentration, etc.). Herein, mineral occurrence and its associated zeta potential are investigated for EK transport. The new Ek model which is designed to solve the EK flow in complex porous media in a highly parallelizable manner includes three coupled equations: (1) Poisson equation, (2) Nernst–Planck equation, and (3) Navier–Stokes equation. These equations were solved using the lattice Boltzmann method within X-ray computed microtomography images. The proposed model is validated against COMSOL multiphysics in a two-dimensional microchannel in terms of fluid flow behavior when the electrical double layer is both resolvable and unresolvable. A more complex chalcopyrite-silica system is then obtained by micro-CT scanning to evaluate the model performance. The effects of mineral occurrence, zeta potential, and electric potential on the three-dimensional chalcopyrite-silica system were evaluated. Although the positive zeta potential of chalcopyrite can induce a flow of ferric ion counter to the direction of electromigration, the net effect is dependent on the occurrence of chalcopyrite. However, the ion flux induced by electromigration was the dominant transport mechanism, whereas advection induced by electroosmosis made a lower contribution. Overall, a pore-scale EK model is proposed for direct simulation on pore-scale images. The proposed model can be coupled with other geochemical models for full physicochemical transport simulations. Meanwhile, electrokinetic transport shows promise as a human-controllable technique because the electromigration of ions and the applied electric potential can be easily controlled externally. Graphical abstract: [Figure not available: see fulltext.].

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