Theoretical Exploration On Porous Carbon Structures For Hydrogen Storage,Ions Batteries,and Water Desalination

In recent years,porous carbon nanomaterials have attracted a lot of attention because of their wide applications.Herein,we have summarized current status and most recent progresses of porous carbon nanomaterials for hydrogen storage,ion battery,and desalination,and theoretically explored potential applications of several porous carbon nanomaterials.Our theoretical workis mainly based on density functional theory(DFT),first-principles and classical molecular dynamics(MD),and grand canonical ensemble Monte Carlo(GCMC)method,which are described in detail. Hydrogen is an ideal clean energy source,and one of the key issues is to seek suitable materials which can safely and efficiently store hydrogen under practical conditions.To this end,we have constructed a model of B-doped graphene-interconnected framework(B-GIF),which shows good structural and thermal stability even after metal Li loading based on both DFT calculations and first-principles MD simulations.The average binding energy(2.64 eV)of adsorbed Li atoms on the proposed material is considerably larger than the cohesive energy per atom(1.60 eV)of bulk Li metal.This value is ideal for atomically dispersed Li doping in experiments.From GCMC simulations,high hydrogen storage capacities of 5.9 wt%and 52.6 g/L in the Li-decorated B-GIF are attained at 298 K and 100 bar.Li and Na ion batteries are two of the most widely studied rechargeable batteries due to their advantages in portability and energy efficiency.The key issue of ion battery application is to develop economic and efficient electrode materials with high capacity to meet the practical requirements.To search for such materials,we have chosen atwo-dimensional porous C2N structure as the anode material in Li and Na ion batteries,and studied Li and Na storage on this material via DFT calculations.We have found the saturated storage to be 10 Li and 9 Na atoms,forming Li10@C2N and Na9@O2N nanocomposites,respectively.These nanocomposites show good thermal stability by first-principles MD simulations at 300 K.The adsorption mechanism of Li and Na has been analyzed by partial density of states and charge density differences.The average binding energies of adsorbed Li and Na atoms in Li10@C2N and Na9@C2N are 2.54 and 1.95 eV,respectively,which are much larger than the cohesive energy per atom of bulk Li(1.60 eV)and Na(1.14 eV).These values are ideal for atomically dispersed Li or Na doping to avoid the metal clustering problems in experiments.Moreover,the charge capacities of L10@C2N and Na9@C2N have been estimated to be 1174.09 and 1056.68 mAh/g,respectively.The shortage in fresh water has become a global problem with the fast increasing population and the rapid development of economy.So far,desalination is one of the most promising techniques to supply fresh water.To find good membrane materials for desalination,we have performed classical MD simulations to investigate desalination by-H and-OH functionalized graphene of three nanopores under induced pressure.The potential of mean force has been calculated to analyze the desalination mechanism.At 298 K and 200.MPa,100%salt rejection of the-H and-OH functionalized P2 and P3 graphene membranes can be achieved,and the corresponding water fluxes are 36.9 × 104 kg·m-2·h-1 and 40.6 × 104kg·m-2·h-1.Therefore,the functionalized nanoporous graphene under induced pressure can supply fresh water rapidly.Another candidate for desalination is carbon molecular sieve(CMS)which is produced by random packing of one or more types of unit structures.We have carried out classical MD simulations on the desalination of CMS packed of 60 coronene(CR)platelets under induced pressure.The effects of CR orientation,density,flexibility,and type of construction units(corannulene)on desalination have been systematically investigated.The simulated results show a salt rejection of 100%and high water flux of 198 × 104 kg·m-2·h-1 through the flexible CR CMS with the density of 0.9 g/cc at 298 K and 200 MPa.