Watervoltaic materials and energy conversion device based on carbon nanomaterials

Abstract

Harvesting renewable energy and realizing its transformation into electricity is one of the effective ways to solve energy crisis and environmental problems. Hydroenergy has been considered as a promising energy with enormous development potential and application value because of its great advantages of large reserves, wide distribution, and environmentally friendly. Nowadays, the development and utilization of hydropower resources mainly rely on dams, generators and other steel facilities to convert mechanical energy to electricity, with inherent defects of inefficiency and damage to the ecological environment. Therefore, developing new types of watervoltaic materials and devices with diverse application environments, high energy conversion efficiency and low power generation costs is an effective improvement and complement to current water energy utilization condition. Carbon nanotube flow sensor reported by Shankar Ghosh in 2003 first proved the property of carbon nanotube that it can generate electricity in floating water, promoting the research of carbon nanomaterials for power generation in fluids. In the following years, several kind of carbon nanomaterials with different dimensions including carbon nanotube, graphene, et al. were successively confirmed that they have similar character to convert hydroenergy to electricity. Various theories including phonon dragging were proposed to explain this phenomenon as well as the form of electric double layer (EDL) and electrokinetic theory fit it reasonably both in charge transfer and electrical output. Related devices were also designed and assembled to convert energy in liquid water, such as ion water drops, saline solution, et al., to electricity, increasing electrical output from initial a few millivolts to a few volts with a small number of devices in series, which is enough to drive small loads. Subsequently, carbon nanomaterials/polymer conducting composite film was designed to harvest energy from real raindrops and seawater waves, making a great progress of watervoltaic materials and devices in practical application. In addition to converting energy in liquid water, devices based on carbon nanomaterials with different dimensions including quantum dots, nano-carbon film and graphene oxide can harvest energy in water vapor and water evaporation, making it possible to collect and convert energy in gaseous water in nature. Unique structures of holes, elemental concentration gradient, et al. were considered to make contributions to capture water molecule and transfer charges, resulting of the electrical output between electrodes. The combination of nano-carbon electrode and all inorganic perovskite solar cells realizes simultaneous collection of water vapor energy and solar energy, making great significance for implementing multi-energy integration of devices. Since carbon nanomaterials were confirmed to be able to convert extensive water energy in natural into electrical energy, different materials and devices were designed and manufactured to increase the electrical output, improve stability and reduce power generation costs. However, there are also challenges including unclear working mechanism, high environmentally demanding and difficulty to integrate devices on a large scale need to be overcomed in the future. Despite this, watervoltaic materials and energy conversion devices have become promising green energy capture technologies due to their high conversion efficiency, wide application environment, and simple device structure. Improving usability is one of the directions of watervoltaic devices development.