A Long Life Moisture-Enabled Electric Generator Based on Ionic Diode Rectification and Electrode Chemistry Regulation

Abstract

Considerable efforts have recently been made to augment the power density of moisture-enabled electric generators. However, due to the unsustainable ion/water molecule concentration gradients, the ion-directed transport gradually diminishes, which largely affects the operating lifetime and energy efficiency of generators. This work introduces an electrode chemistry regulation strategy into the ionic diode-type energy conversion structure, which demonstrates 1240 h power generation in ambient humidity. The electrode chemical regulation can be achieved by adding Cl^-. The purpose is to destroy the passivation film on the electrode interface and provide a continuous path for ion-electron coupling conduction. Moreover, this device simultaneously satisfies the requirements of fast trapping of moisture molecules, high rectification ratio transport of ions, and sustained ion-to-electron current conversion. A single device can deliver an open-circuit voltage of about 1 V and a peak short-circuit current density of 350 µA cm^-2. Finally, the first-principle calculations are carried out to reveal the mechanism by which the electrode surface chemistry affects the power generation performance.

Keywords: electrode chemistry regulation; hydrovoltaic; ionic diode; long lifetime; moisture.

Figure 1

a) Schematic diagram of MEG structure. b) Schematic diagram of MEG working principle. c) Two strategies of electrode passivation layer suppression. d–f) MEG with and without calcium chloride: respective I–V curve comparison, current density comparison, and charge/discharge output current density curve comparison. g) Ultra‐long operation curve of a single device under coupling mode of hygroelectricity and photovoltaic charging.

Figure 2

a) Ionic I–V curve of MEGs with nanofluidic diode effect under different concentrations of additives. b) MEG rectification ratio values under different concentrations of additives. c) Open circuit voltage of devices with double carbon material electrodes at different concentrations of additives. d) Mott–Schottky plots of the passive films formed on the EGaIn electrode with different concentrations of additives. e) EDS mapping of EGaIn electrode oxide. f) Tafel plots of EGaIn electrode in different concentrations of additives.

Figure 3

a) Effect of relative humidity on device performance. b) Device performance corresponding to different additive concentrations under moisture conditions. c) Effect of nanopore size on device performance. d) V _OC and J _SC changes with different external load resistances for the device with a working area of 0.28 cm², the inset being the actual test circuit diagram. e) The corresponding output power density varies with the load resistance. When the external resistance is 10 kΩ, the device has the best output performance. f) Performance comparison between the MEG device and some recently reported moisture‐enabled electric generators.

Figure 4

a) The adsorbed structures of Cl⁻ on the surface of GaOOH(001) at the coverage of 22.2% (aI), 77.8% (aII). Greenish atoms, hydrogen; Dark green, gallium; Pink, hydroxyl; Dark red, oxygen. b) The inserted structures of Cl⁻ into GaOOH(001) surface at the coverage of 22.2% (bI), 77.8% (bII). c) Electronic band structure plots of GaOOH(001) surface at the Cl⁻ adsorption coverage of 22.2% (cI) and 77.8% (cII), and at the Cl⁻ insertion coverage of 22.2% (cIII) and 77.8% (cIV). d) Short‐circuit current density of the device during short‐time charging and follow‐up discharging, the illustration on the right is the enlarged current density diagram. e) Long‐term cycling performance of devices with different additive concentrations at 1 µA cm⁻². f) Comparison of device Nyquist curves before and after charging. g) EDS mapping image of EGaIn under different cycle conditions. h) Mass ratio of EGaIn in different cyclic states.

Figure 5

a) Voltage‐time curves of different commercial capacitors charging by a single MEG. b) Three devices in series are used to light two commercial LEDs in series. c) Four devices in series can light ten LEDs in parallel. d) Five devices in a series can light a commercial scientific calculator. e) Schematic diagram of the practical applications of the forest fire monitoring system. f) The demonstration experiment showing humidity sensing, at low humidity, the LED arrays could be lit.