Graphene oxide and carbon black synergistic coated cotton fabric for enhancing energy harvesting from water droplets

Hydrovoltaic generators (HGs), which harness sustainable energy directly from water flow have garnered tremendous interest worldwide due to their cost-effectiveness, eco-friendliness and potential for powering wearable electronics. However, current HGs generally suffer from poor ion selectivity and resistance matching resulting in low output current, limiting their application scenarios. Herein, a flexible cotton fabric based hydrovoltaic generator (CFHG) fabricated by successive modification with carbon black (CB) and graphene oxide (GO) is proposed, contributing to a simple yet effective performance improvement. Benefiting from the enhanced charge transfer efficiency, ion selectivity and fast capillary flow contributed by CB, GO and fiber network respectively, a considerable open-circuit voltage (Voc) of ∼0.75 V and a short-circuit current (Isc) of ∼8.7 μA are obtained when exposed to water droplets. Experimental results indicate that the power generation performance is influenced by various factors, including the amount of GO, cation size, liquid volume, polarity and pH, as well as temperature and humidity. Moreover, excellent flexibility and porosity of the CF substrate facilitate unconventional serial or parallel connections, providing sufficient power supply for commercial devices and wearable electronics. This research is highly significant for designing versatile power supplies for next-generation intelligent wearable electronics.