Multistage coupling water-enabled electric generator with customizable energy output

Abstract

Constant water circulation between land, ocean and atmosphere contains great and sustainable energy, which has been successfully employed to generate electricity by the burgeoning water-enabled electric generator. However, water in various forms (e.g. liquid, moisture) is inevitably discharged after one-time use in current single-stage water-enabled electric generators, resulting in the huge waste of inherent energy within water circulation. Herein, a multistage coupling water-enabled electric generator is proposed, which utilizes the internal liquid flow and subsequently generated moisture to produce electricity synchronously, achieving a maximum output power density of ~92 mW m^-2 (~11 W m^-3). Furthermore, a distributary design for internal water in different forms enables the integration of water-flow-enabled and moisture-diffusion-enabled electricity generation layers into mc-WEG by a "flexible building blocks" strategy. Through a three-stage adjustment process encompassing size control, space optimization, and large-scale integration, the multistage coupling water-enabled electric generator realizes the customized electricity output for diverse electronics. Twenty-two units connected in series can deliver ~10 V and ~280 μA, which can directly lighten a table lamp for 30 min without aforehand capacitor charging. In addition, multistage coupling water-enabled electric generators exhibit excellent flexibility and environmental adaptability, providing a way for the development of water-enabled electric generators.

Fig. 1. Schematic diagram of the mc-WEG.

a Water absorption process of arid soil. The liquid flows along the tiny channels in the soil from wet region toward the dry region. At the same time, in areas where the liquid cannot flow through, water will be transferred in the form of moisture diffusion. b Schematic diagram of the structure of mc-WEG. c The water transportation track in mc-WEG. Bottom wf-layer utilize the flow of liquid to generate electricity, and the top md-layer is based on the moisture induced ion migration for electricity generation. A porous polyacrylonitrile membrane is placed between wf-layer and md-layer for water diversion.

Fig. 2. Structure and working principle of mc-WEG.

a SEM image of wf-layer and the element mapping images of Ca and Cl. b SEM image of PAN membrane on the porous Au mesh substrate. c SEM image of PVA-LiCl (0.5 M) membrane and the element mapping image of Cl. d Schematic diagram of multistage water transport process in mc-WEG. Navy blue arrows represent the direction of liquid flow, and the blue arrows represent the direction of moisture diffusion. e Photographs of water transport on wf-layer with PAN membrane before and after being exposed at 90% relative humidity (RH) under ultraviolet light. Scale bar: 1 cm. Green regions are the water infiltrated part. f Water absorption of PAN membrane on wf-layer (n = 3, error bars: standard deviation). g Moisture permeability test of PAN membrane. Inset displays the test diagram. h Water absorption of PAN membrane on Au mesh substrate and Au mesh only. i Dehumidification curves of PAN membrane (loaded on porous Au electrode) saturated with 10.08 mg ml⁻¹ CaCl₂ aqueous solution under different RH (25 °C). Inset displays the test diagram. Source data are provided as a Source Data file.

Fig. 3. Structure and electric generation of wf-layer.

a The voltage and current output of wf-layer (3 × 6 cm, width × length). The output can sustain 40,000 s under asymmetrical humidity (90% RH and 25% RH, the same below). Left inset exhibits the structure diagram of the wf-layer. Right inset shows the asymmetrical water absorption of wf-layer before and after being exposed in asymmetrical humidity. b Moisture absorption and desorption kinetics for CaCl₂ loaded region of wf-layer at 25 °C. c Voltage and current output of wf-layer (3 × 6 cm) in response to variation in RH in high RH side (25% RH for low RH side). d Bar graph of electricity performance of wf-layer (3 × 6 cm) with different CaCl₂ load ratio. e Current retention of wf-layer (3 × 6 cm) for different circulations. The wf-layer was dried by being placed at 80 °C for 1 h, and the output of the dried wf-layer can be restored by absorbing water again. f, g Voltage and current output in response to variation in length with the fixed width of 3 cm (f) and variation in width with the fixed length of 6 cm (g) under asymmetrical humidity. h Voltage, current and volumetric power density of wf-layer (18 × 6 cm, crimped state) with different electric resistance. Inset displays the schematic of circuit. Source data are provided as a Source Data file.

Fig. 4. Electric generation, working mechanism and the regulation of electricity-generating performance of md-layer.

a Scheme of the md-layer structure. The md-layer is composed of electricity-generating material (PVA-LiCl(0.5 M) membrane, H-PSS membrane and PVA-LiCl(0.01 M) membrane from bottom to top) and asymmetric Au electrodes. b Working mechanism of moisture-enabled electric generation in md-layer. c Current-voltage curve of md-layer after absorbing moisture for 1,330 s. Inset displays the schematic of circuit. d The maximum rectification ratio of md-layer, H-PSS membrane and md-layer without H-PSS. e Voltage and current output of md-layer (1 × 1 cm). The electrical-generated performance can sustain 10,000 s under 90% RH 25 °C. f Voltage and current output of md-layer in response to variation in RH. g Voltage and the current of md-layer with different area. h Voltage, current and area power density of md-layer (0.25 × 0.25 cm) with different electric resistance. Inset displays the schematic of circuit. Source data are provided as a Source Data file.

Fig. 5. Customized output and scalable integration of mc-WEG.

a Schematic diagram of the structure of mc-WEG and the“flexible building block” approach through size control, space optimization, as well as integration design. b, c Open-circuit voltage, short-circuit current (b) and volumetric power density with different electric resistance (c) of mc-WEG₁ in parallel connection (upper plot) and series connection (lower plot). d Variation of temperature, RH, as well as voltage and current generated by mc-WEG₂ during outdoor testing (Beijing in China: East longitude ≈116° and North latitude ≈ 40°; Time on August 27th~30th, 2022). e Voltage-time curves of commercial capacitors with various capacitance (0.47, 47 and 470 mF) charged by three mc-WEG₃ units connected in parallel. f Digital photo of the mc-WEG₃ pack before being folded (twenty-four mc-WEG₃ connected in series). g Schematic diagram of the designed auto-switchable adsorption and desorption generating setup (left diagram). Digital photos of the folded mc-WEG₃ pack (right). h The relationship between open-circuit voltage and number of mc-WEG₄ connected in series. i Digital photos of working table lamp (left) as well as LED strip (right) powered by mc-WEG₄ pack. Source data are provided as a Source Data file.