Channel Topology Design And Permeation Energy Conversion Performance Of Two-dimensional Nanofluidic Membrane

With the excessive consumption of fossil energy and its crisis,the development of green clean energy has reached an urgent level.The development of salt difference energy is an effective potential means to solve the problem of decreasing non-renewable resources and increasing environmental pollution.The reverse electrodialysis(RED)method is the most promising salt difference energy conversion method at present.By inserting an ion exchange membrane between two liquids with a concentration difference,high-concentration counterions can be transported to the low-concentration side through the film to convert this Gibbs free energy present in the salt difference into electrical energy.As a kind of power generation technology,RED has attracted much attention,It has the advantages of flexible device design,high energy conversion power and no environmental pollution.The membrane device is the core device of RED technology for salt difference power generation.In the past decade,polymer materials have attracted much attention as permeable energy harvesters due to their high cost-effective and large-area preparation.However,the properties of polymer materials and the phase separation preparation method of their films make them unable to have customizable physical and chemical properties.For example,the number of surface charges on the film and the regularity of the ion transport channel limit its application prospect in the field of osmotic energy conversion.Two-dimensional materials provide an ideal platform for studying new physical and chemical phenomena.Compared with polymer materials,two-dimensional materials can stack two-dimensional nanosheets layer by layer to form a regular multi-layer ion channel film with nano-confined regions by a simple method.Recent studies have shown that thin films with nano-flow ion channels assembled by two-dimensional materials can effectively improve the actual performance of salt-difference power generation.But at the same time,films stacked by two-dimensional material nanosheets also face many challenges in applications.For example,the ions transport rate of two-dimensional material films represented by graphene-based films is very low,much lower than that of commercial Nafion ions transport films;The main challenge is that ions or hydrated ions can only be transported along the ion channels stacked by two-dimensional nanosheets or at material defects.The lower nanochannel density and relatively long ion diffusion distance lead to limited ion transport dynamics.Most of the energy is consumed in the form of thermal energy,and the actual output power is still low.In order to solve the problem of long path and bending of nanofluidic films constructed by two-dimensional materials,in order to solve the shortcomings of the films composed of two-dimensional materials in the application of osmotic energy conversion and explore its application potential in reverse electrodialysis salt difference power generation,this paper mainly studies the preparation of porous graphene oxide films,the extraction of salt difference energy and the design of bionic intercalation structure.The main work is as follows:(1)Preparation of porous graphene oxide film.In order to solve the problem of low power density of osmotic energy conversion caused by the long and curved ion channels assembled by traditional two-dimensional nanosheets,a convenient and mild hydrogen peroxide etching method was explored in this paper.The in-plane nanoporous structure was prepared on the two-dimensional material graphene oxide nanosheets,and then the porous layered structure film was prepared by flow field driven self-assembly method.Through the BET test data,it was found that the etched nanosheets showed a significant increase in specific surface area and pore size,and the EDS test found that the porous graphene oxide film had more counterion adsorption capacity,indicating that the in-plane pores formed by etching can provide more counterion adsorption sites for the film,thereby increasing its ion flux,making the porous graphene oxide film The salt difference power generation power density of the film is higher,highlighting the important influence of different morphologies of the ion channel on ion transport.(2)Research on RED salt difference power generation.In this experiment,the effects of etching time,etchant content and film thickness on salt-difference power generation were investigated.The corresponding films were prepared under the conditions of etching time of 0,2,4,6 h and etchant content of 0,2.5,5,7.5 m L,respectively.Through the data comparison and analysis of the salt-difference power generation experiment of reverse electrodialysis,the results show that the power density shows a trend of increasing first and then decreasing,and the power density reaches the maximum when the etching time is 2 h,the etchant content is 5 m L and the film thickness is 11μm.This indicates that the ion channel structure prepared under the optimal experimental conditions is most conducive to promoting ion transport.(3)Preparation of intercalated graphene oxide film.When constructing artificial ion channel films,it is often limited by the mutual restriction of ion selectivity and ion flux.In this paper,inspired by the structure of bamboo film,a simple intercalation sequence was constructed by bionic structure design with graphene oxide nanosheets and porous graphene oxide nanosheets as two sequences.In the experiment,through the regulation of the content of graphene oxide nanosheets and porous graphene oxide nanosheets,the intercalation films with different sequences were prepared by the ordered flow field driving method.It was found that the intercalation films prepared under certain conditions can break the restriction of ion selectivity and ion flux during ion transport.(4)Study on salt difference power generation of intercalated graphene oxide film.Through the study of the power generation performance of two different intercalation sequence films,we found that when two layers of porous graphene oxide film were inserted into the graphene oxide film,the power density reached 6.78 W/m~2,and through the comparison of experimental data of different intercalation films,we proposed a research strategy for the development of nanoflow equipment for the efficient conversion of osmotic energy:under the premise of little change in ion selectivity,high-throughput ion transport can maintain its high salt difference power generation performance,on the contrary,its salt difference power generation performance changes greatly.In this study,we demonstrated that the introduction of in-plane pores on two-dimensional nanosheets can effectively promote the transport of ions through the formed layered film.This fast diffusion kinetics is mainly attributed to the change of channel morphology,which not only increases the concentration of counter ions,but also shortens the path length through the membrane.Therefore,in terms of osmotic energy conversion,the porous graphene oxide film exhibits enhanced performance relative to the graphene oxide film.In addition,the biomimetic multilayers assembled sequentially by the graphene oxide film layer and the porous film layer can provide an optimized combination of selectivity and permeability,resulting in a power density higher than the commercial benchmark of industrial development.This work highlights the importance of ion channel morphology and proposes a general strategy for effectively improving ion transport through two-dimensional layered membranes for high-performance nanofluidic devices.