Interface Engineering And Mechanism Research On Water-evaporation-induced Electricity Generation With Carbon Materials

To find an alternative renewable energy for the conventional fosil fuels is a pressing need for human beings at present and in the future.Recent advances in science and technology,especially the new finding in nanotechnology have provided new possibilities in the development of next-generation energy generating materials.The past decades have witnessed the rapid evolution of low-dimensional carbon materials such as graphene,carbon nanotubes and carbon nanoparticles,with extraordinary physical and chemical properties,which are ideal for electrical energy storage and generation.Tremendous progress has been made in the research on direct generation of electricity from influidic molecular interactions with various low dimensional carbon materials,after its first prediction was made in 2001 and was firstly experimental proven two years later.There has been an explosive surge in this research field and new findings with accompanied mechanisms have been proposed.However,there are three issues remained on the development of this research:(1)Most of the carbon-based fluidic electric generating devices need external kinetic energy input;(2)The power output in the electricity generation from influidic molecular interactions with carbon materials is low at this stage,like only a votage of milivolts or even microvolts can be generated,which hinders its potential application;(3)Most of the findings has been primarily phenomenological,without a consensus on the underlying physical mechanism that can explain the electricity generation.It is a research topic of significant value,and with great challenge to find a clear mechanism behind this fascinating nenergy conversion phenomenon with great complex in underlying physical or chemical process.According to the above issues,the main results in this paper are shown as follow:1.Water evaporation from a centimeter-sized carbon black sheet can produce significant high voltage up to 1 V and can sustain for over 160 hours under ambient conditions,enough to drive small electric device directly.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.Since the electricity is initiated by evaporation,environmental factors that affecting the water evaporation process also have significant influence on the induced electrical voltage,such as ambient temperature,relative humidity and air flow velocity.These factors have been thoroughly investigated by experiments.Further,we fabricate the porous carbon film devices by printing method,which greatly enhance the mechanical strength of the carbon film.Then,by introducing the superhydrophobic/hydrophilic interface on the porous carbon film,electricity can be spontaneously generated by adding water droplets on the interface under ambient conditions.The voltage can be controlled by modulating the direction of the droplet infiltration.With state-of-art device design,twelve 5 ?L water droplets can generate a voltage up to 5.2 V and illuminate a liquid crystal display.Based on the unique properties of the device,the results demonstrate that a porous carbon film can function as a cost-effective electricity generator for harvesting energy and self-powered sensing from natural resources.2.An evaporation-driven water flow nanogenerator based on a piece of flexible nanoporous carbon film was presented.The open-circuit voltage of one single-piece device can be tuned from-3 V to 3 V by manipulating the surface functional groups on the carbon nanoparticles.The effects of different modification molecules and solution concentrations were also investigated.By combining the modified carbon films with opposite surface charges,we enhanced the output of the generator to a maximum open-circuit voltage of 5 V and a short-circuit current of 1.5 ?A with a film size of 5 cm × 5 cm.Furthermore,the device can be easily integrated with carbon nanotube-based supercapacitors(CNT-SCs)to assemble the energy-storing and energy-harvesting devices into a self-sustaining power system.The electrical output of the device can directly power a liquid crystal display in an ambient environment and a blue LED with help of self-charged built-in SCs.This eco-friendly device,with its low cost and simple fabrication,shows great potential for future clean energy utilization and for extending the field of portable electronics.3.The step-by-step enegy conversion process in the carbon-based evaporation-induced electricity phenomenon is presented,we find the final energy conversion process from the kinetic energy of the flow liquid to electricity is the key step which is not fully unstood yet.After carfully and comprehensive literature reviewing on the mechanistically discussion of the direct generation of electricity from influidic molecular interactions with various low dimensional carbon materials,a comprehensive mechanism for the evaporation-induced electricity phenomenon is proposed with a set of carefully-designed experiments.The proposed theory is based on the electrokinetic effect on the carbon surface,after which the charge carriers can be directional transport within the carbon film via the intereaction with the hydrated ions in the inner-Helmholtz plain in a “ratchet-wheel” transportation model.This stream of charge carriers further induces the sustaining electrical current and corresponding voltage in the carbon film.The investigation of the working mechanism will guide the further expanded application of this energy conversion phenomenon.