Flexible Moisture-Electric Generator Based on Vertically Graded GO-rGO/Ag Films

Abstract

Moisture-electricity generators (MEGs) hold great promise for green energy conversion. However, existing devices focus on the need for complex gradient distribution treatments and the improvement in output voltage, overlooking the important role of the graphene oxide (GO) oxidation degree and the response time and recovery time in practical application. In this work, we develop printed MEGs by synthesizing reduced graphene oxide/silver nanoparticle (rGO/Ag) composites and controlling the GO oxidation degree. The rGO/Ag layer serves as a functional component that enhances cycling stability and shortens the recovery time. Additionally, compared to conventional rigid-structure devices, these flexible MEGs can be produced by inkjet printing and drop-casting techniques. A 1 cm² MEG can generate a voltage of up to 60 mV within 2.4 s. Notably, higher output voltages can be easily achieved by connecting multiple MEG units in series, with 10 units producing 200 mV even under low relative humidity (RH). This work presents a low-cost, highly flexible, lightweight, and scalable power generator, paving the way for broader applications of GO and further advancement of MEG technology in wearable electronics, respiratory monitoring, and Internet of Things applications.

Keywords: graphene oxide; inkjet printing; moisture–electricity generators; nanogenerators.

Figure 1

Fabrication process of GO, rGO/Ag, and the MEG device. (a) Diagrammatic illustration of the GO preparation procedure. (b) Schematic illustration of rGO/Ag synthesis via liquid-phase reduction. (c) Preparation of GO and rGO/Ag functional inks and schematic diagram of the MEG device.

Figure 2

Structural and chemical characterization of graphene oxide (GO). (a) Raman spectra of graphite and GO; (b) XPS survey scan spectra; (c) C1s XPS spectrum of GO.

Figure 3

Characterization of rGO/Ag. (a) SEM image of rGO/Ag; (b,c) EDS elemental mapping images of rGO/Ag; (d) Raman spectra of GO and rGO/Ag; (e) C 1s XPS spectra of rGO/Ag; (f) Ag 3d XPS spectra of rGO/Ag.

Figure 4

XPS spectra of GO-1,GO-2 and GO-3. (a) Survey spectra of GO-1; (b) survey spectra of GO-2; (c) survey spectra of GO-3; (d) C1s spectra of GO-1; (e) C1s spectra of GO-2; (f) C1s spectra of GO-3; (g) O1s spectra of GO-1; (h) O1s spectra of GO-2; (i) O1s spectra of GO-3.

Figure 5

The MEG’s electrical output performance. (a) Optical image of one MEG unit; (b) output voltage cycles by a single MEG at ΔRH = 80%; (c) output voltage cycles of a single MEG unit at ΔRH = 80%; (d) voltage outputs of a single MEG under different humidity levels; (e,f) output voltage at different bending angles; (g) optical image of a printed MEG array; (h) voltage output of 10 MEG units connected in series under 40% RH; (i) output voltage of the arrays under ΔRH = 30%.

Figure 6

Power generation mechanism of MEG. (a) Diagrammatic illustration of droplet morphology; (b) diagrammatic illustration of power generation mechanism.

Figure 7

The effect of rGO/Ag transition materials. (a) Output voltage cycles of a single MEG without rGO/Ag; (b) voltage output of the MEG without rGO/Ag; (c) output voltage cycles of a single GO-rGO/Ag MEG; (d) voltage output of the GO-rGO/Ag MEG.