Electrokinetic effect and H2O2 boosting in synthetic graphene/α-FeOOH aerogel films for the generation of electricity

Abstract

Harvesting and transforming water energy into electricity via nanostructured materials, which is termed hydrovoltaic power generation (HPG), has attracted increasing interest in the past few decades. However, the current limitation of HPG devices taking advantage of the electrokinetic effect is their poor power density within microwatts per square meter. Herein, a novel catalytic graphene aerogel film decorated with an interlayer catalyst of α-FeOOH was developed successfully. Upon the addition of H₂O₂ to a saline (NaCl) droplet, an exceptionally high voltage of 0.63 V was achieved, which is around 20 times higher than the previously reported value using single-layer graphene. The experimental and theoretical results showed that the high hydrovoltaic performance originates from three contributions. Firstly, the large droplet/graphene interfaces, benefitting from the high specific surface area of the aerogel and the bubbling effect produced by the catalytic decomposition of H₂O₂via α-FeOOH. Secondly, the enhanced electrokinetic effect, i.e., increased hydrated ion radius of NaCl and suppressed shielding effect between cations and anions in the presence of H₂O₂, which dramatically extends the NaCl concentration window from 0.6 M to 5.0 M. Thirdly, utilizing the advantage of electrochemical reactions related to H₂O₂ in the saline (NaCl) droplet to greatly increase the short-circuit current of the HPG device. The outcome of these contributions is a much higher ion utilization efficiency under a high saline concentration, which breaks the output bottleneck of power density caused by using a low saline concentration. Our work extends the device component from single-layer graphene to a 3D porous graphene aerogel, making a significant step forward for the future development of HPG devices.