Fabrication Of Ion Conductors Using Two-dimensional Building Blocks And Their Applications

Developing electrochemical energy storage and conversion devices is an effective strategy for improving energy efficiency and developing clean energy.The ion conductor is the key component in the above electrochemical devices,and its performance determines the energy conversion efficiency of such devices.Therefore,the development of high-performance ion conductors is of significance for improving electrochemical efficiency.In this study,two-dimensional nanomaterials are used as building blocks to prepare high-performance ion conductors by hydrothermal assembly,vacuum assisted self-assembly and spray coating.The long-range and orderly two-dimensional ion channels are constructed to facilitate the rapid ion transport.The isotropic transport of ions in ion conductors is realized by optimizing the connectivity and orientation of the ion channels.In addition,we have demonstrated the application of as-prepared ion conductors in fuel cells,flexible touch panels and generators.The details are summarized as follows:The phosphorylated graphene monolith(PGM)with three-dimensional transport channels was prepared using phosphorylated graphene as building blocks by a hydrothermal method.The proton conductivity and electron conductivity of PGM simultaneously increase due to the introduction of phosphoric acid group during the reduction of GO.The highest values are 0.13 and 0.265 S cm^-1(35°C and 95%RH),respectively,which solves the trade-off effect between proton conductivity and electron conductivity.The 3D sulfonated GO(3D sGO)network was designed using sulfonated GO as building blocks by a freeze-casting method,and further fabricated composite electrolytes membranes by infusing polymer electrolytes into the 3D sGO networks.The prepercolating strategy avoids sGO nanosheets agglomeration and provides continuously proton-conductive pathways.Consequently,the composite electrolytes membranes exhibit a remarkable and simultaneous improvement in both in-plane and through-plane proton conductivity.Particularly,the highest through-plane proton conductivity of Nafion@3D sGO-2.4 reaches 0.29 S cm^-1,which is 91%higher than the recast Nafion.Covalent organic frameworks(COFs)membranes were prepared using two-dimensional COFs nanosheets as building blocks by a vacuum assisted self-assembly method.The one-dimensional nanopores in COFs membranes contribute channels for protons transport.At 80? and 98%RH,the proton conductivity of COFs membranes is 0.38 S cm^-1.In addition,the COFs membranes show good water retention capability owing to the capillary effect in one-dimensional channels,which significantly reduces the dependence of fuel cell performance on humidity.When the relative humidity decreases from 100%to 40%,the power density of single cell decreases by only 16%.The flexible and transparent vermiculite films were prepared using two-dimensional vermiculite nanosheets as building blocks by vacuum assisted self-assembly and spray coating methods.The inherently charged and ordered laminar microstructure renders an ultrahigh ion conductivity.At 80? and 100%RH,the Li⁺conductivity is up to 0.45 S cm^-1.We further demonstrate a touch panel based on vermiculite films that realize real-time,human-machine communicating by drawing and typing.The vermiculite films were prepared using vermiculite nanosheets as building blocks by a vacuum assisted self-assembly method.The mechanical properties and stability in water of vermiculite films are significantly enhanced by cross-linking of glutaraldehyde.The vermiculite films exhibit a typical surface charge-governed ion transport behavior.Based on the ion-selective transport characteristics,the osmotic energy was successfully harvested.The maximum output power density of the system can reach 0.6 W m^-2,when the salt gradient is 1000.