Interaction At Solid-Liquid Interface Of Wrinkled Graphene And Its Application

Graphene has exceptional properties of excellent intrinsic carrier mobility,superior thermal conductivity,high optical transmittance,high tensile strength,large specific surface area,and flexibility.Due to the two-dimensional nature and ultra-thin structure of graphene,the formation of wrinkles is almost inevitable during the preparation,transfer,and application,which could greatly affect the electrical properties,mechanical strength and surface properties of graphene.On the other hand,the interaction at the solid-liquid interface of graphene plays a crucial role in applications such as energy conversion and storage,water treatment,sensing,and coating.Wrinkled graphene materials with a hydrophobic surface and uniformly distributed ring-like wrinkles have intrinsic advantages in utilizing the solid-liquid interactions,achieving outstanding performance in ultrafast humidity sensing,humidity-driven electricity generation,and sea energy harvesting.The humidity sensor with ultrafast responses can be a promising candidate for applications such as disease diagnostics,health status monitoring,and personal healthcare data collecting.However,prolonged exposures to high humidity environments usually cause device degradation or failure due to excessive water adsorbed on the sensor surface.A graphene film based humidity sensor with wrinkled graphene that exhibited excellent performances in breath sensing was designed and fabricated.The wrinkled morphology of graphene sensor was able to effectively prevent the aggregation of water micro-droplets and thus maximize the evaporation rate.The as-fabricated sensor responded to and recovered from humidity in 12.5 ms,the fastest response of humidity sensors reported so far,yet in a very stable manner.The sensor was fabricated into a mask and successfully applied to monitor sudden changes in respiratory rate and depth,such as breathing disorder or arrest,as well as subtle breath changes caused by talking and cough.In addition,a subtle change in humidity level caused by skin evaporation can also be detected.The sensor can potentially enable long-term daily monitoring of breath and skin evaporation with its ultrafast response and high sensitivity,as well as excellent stability in high humidity environments.Strong non-covalent cation-? interactions were discovered about three decades ago.However,the application of such interfacial behavior on carbon nanomaterials has been investigated only in recent years.A high-efficiency humidity driven electric nanogenerator based on the interfacial cation-? interaction was reported for the first time.The generator was prepared using the wrinkled graphene with intentionally increased defects and uniformly distributed wrinkles for ultrafast water evaporation,preventing excessive water accumulation and deposition of well-distributed salt crystals.A voltage of 15 m V with a current of 40 n A were generated by manipulating the formation of ionic liquid microdroplets on the graphene surface via the water adsorption and desorption of salt crystals as the humidity varied from 25% to 75%RH.The dynamic process of adsorption and desorption of ions during the condensation and evaporation of ionic droplets under humidity change cause the movement of the threephase contact line,leading to a potential difference due to the uneven distribution of the surface charge in graphene.The pinning effect of the wrinkles on the droplets promotes the formation of gradients in ion concentration resulting in a non-centrosymmetrically movement of the contact lines.The effects of orientations in humidity deposition,temperature,amount of salt crystal deposited,the size of the graphene area,the internal electrical resistance,and the ion species on the performance of power generation were investigated.Sea energy harvesting with carbon nanomaterials is an attractive renewable energy utilization strategy.Wrinkled graphene based highly sensitive and stable electric nanogenerator has been successfully developed and applied to multiple seawater movements with superior performances.The electric generation mechanism from the mechanical movements of seawater including droplet movement,boundary shift,and continuous flow was explored,and the corresponding electric generation performances were evaluated.The results suggest that the surface wrinkle nanostructure of graphene can enable energy harvesting from continuously flowing ionic liquid producing a maximum voltage output of up to 150 m V and a continuous current supply of 80 n A.The wrinkles have strong chemisorption and physical barrier effects,resulting in drifting and local enrichment of ions,hysteresis of ion migration,and gradient of flow velocity.Based on these results,a miniaturized sea energy harvesting system was successfully fabricated and evaluated with simulated seawater flow and tide waves.The as-fabricated nanogenerator exhibited high sensitivity and high voltage outputs,suggesting its great application potentials as a sea energy harvesting device.