Geometric Tuning for Enhanced Moisture-Driven Electricity Generation Enabled by Graphene-Oxide Flakes

In this work, we formulate water-based graphene oxide (GO) inks to fabricate moisture energy generators (MEGs) while a two-fold geometric tuning is proposed to encourage enhanced performance. Two GO-based structures with distinctly different thicknesses were prepared as the moisture absorbing layer: a GO-pellet (GOP) and a thinner GO-film (GOF). The effect of electrical contacts’ configuration on the MEG’s output voltage (Vo) was evaluated as a second geometric tunning approach by varying the surface area of the contacts and their orientation with respect to the GO plane, i.e., horizontal or vertical. GOF-based devices that employed a horizontal contacts’ configuration demonstrated champion Vo values (~350 mV) and the fastest response to humidity (3 min required to reach maximum Vo when the relative humidity, or RH, was increased). In GOP devices with horizontal point-like contacts, Vo is inversely related to the contacts’ distance, with a maximum Vo of ~205 mV achieved at a ~1 mm contacts’ distance. GOP-based MEGs with point-like contacts placed vertically to the GO-plane yielded a higher Vo value (~285 mV), while the humidity response time was 15 min. Replacing these contacts with large area electrodes in GOP devices resulted in devices with a slower response to humidity (~30 min) due to a smaller exposed GO surface area. These geometric tuning techniques allowed for the investigation of the optimum device configuration towards efficient moisture-based energy generation with a fast response.