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 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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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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