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

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

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

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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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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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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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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