Water evaporation is a ubiquitous natural process that harvests thermal energy from the ambient environment. It has previously been utilized in a number of applications including the synthesis of nanostructures and the creation of energy-harvesting devices. Here, we show that water evaporation from the surface of a variety of nanostructured carbon materials can be used to generate electricity. We find that evaporation from centimetre-sized carbon black sheets can reliably generate sustained voltages of up to 1 V under ambient conditions. The interaction between the water molecules and the carbon layers and moreover evaporation-induced water flow within the porous carbon sheets are thought to be key to the voltage generation. This approach to electricity generation is related to the traditional streaming potential, which relies on driving ionic solutions through narrow gaps, and the recently reported method of moving ionic solutions across graphene surfaces, but as it exploits the natural process of evaporation and uses cheap carbon black it could offer advantages in the development of practical devices.

Converting environmental "waste energies" into electricity via a natural process is an ideal strategy for environmental energy harvesting and supplying power for distributed energy-consuming devices. This paper reports that evaporation-driven water flow within an all-printed porous carbon film can reliably generate sustainable voltage up to 1 V with a power density of ≈8.1 µW cm −3 under ambient conditions. The output performance of the device can be easily scaled up and used to power low-power consumption electronic devices or for energy storage. Furthermore, the device is successfully used without electric storage as a direct power source for electrodeposition of silver microstructures. Because of the ubiquity of water evaporation in nature and the low cost of materials involved, the study presents a novel avenue to harvest ambient energy and has potential applications in low-cost, green, self-powered devices and systems.

Solar-enabled steam generation has attracted increasing interest in recent years because of its potential applications in power generation, desalination, and wastewater treatment, among others. Recent studies have reported many strategies for promoting the efficiency of steam generation by employing absorbers based on carbon materials or plasmonic metal nanoparticles with well-defined pores. In this work, we report that natural wood can be utilized as an ideal solar absorber after a simple flame treatment. With ultrahigh solar absorbance (∼99%), low thermal conductivity (0.33 W m K), and good hydrophilicity, the flame-treated wood can localize the solar heating at the evaporation surface and enable a solar-thermal efficiency of ∼72% under a solar intensity of 1 kW m, and it thus represents a renewable, scalable, low-cost, and robust material for solar steam applications.