Uncommon characteristics of energy-harvesting by water droplet flowing on epitaxial graphene film

An uncommon power-generation phenomenon in droplet-driven electricity generation on high-quality epitaxial graphene films grown on SiC substrates was investigated. This phenomenon cannot be accounted for using conventional models. The measured voltage response was isotropic and independent of the droplet sliding direction and electrode geometry. In addition, electricity generation was independent of the graphene area and flow distance. The observed nonmonotonic voltage–ion concentration relationship, featuring distinct concentration-dependent peaks, together with the independence of the load resistance, is consistent with a microscopic, discontinuous generation process. These results highlight the role of nanoscale interfacial dynamics in the hydrovoltaic effect and indicate that atomic-scale control of the graphene substrate structure may inform the design of future energy harvesters.