Theortical Simulation Studies Of Exothermic Reaction Of Al/Ni Composite And Properties For Water Splitting Of G-C₃N₄

With the progress in computer technology and numberical methods, moleculardynamics simulation and first-principles calculations have become the powerful toolsfor investigation of material properities and greatly promote the progress ofcomputational materials science. The results obtained from researches are thefollowings:Molecular dynamics simulations indicate that the ignition temperature is at about913K. Reducing the size of Al/Ni clad particles makes the propagation velocity ofreaction front increase but lowers both the adiabatic combustion temperature andpressure of the system. However, increasing either mass density or ignitiontemperature makes the propagation velocity of reaction front increase and raises theadiabatic temperature and pressure as well. The NiAl compound is an intermediateproduct in the reaction of Al/Ni （atomic ratio1:3） clad particles. The effect ofparticle size on the propagation of reaction is considered. For the system with largerparticle size （>4nm）, part of the NiAl compound forms the phase of B2―NiAl bynucleation. The presence of NiAl precipitate retards the propagation of reaction. Theformation of the NiAl phase is dependent on the temperature below a certainthreshold. For longer time, the phase of B2―NiAl gradually transforms into Ni3Alcompound that is the final product of Al/Ni （atomic ratio1:3） clad particles.Using method we optimized the force field parameters of copper based on theexperimental and theoretical value. The training sets include the volume module,lattice energy, dissociation energy of copper dimer.and the equation of state （EOS） ofA15, fcc, bcc, and sc phase and so on. To ensure reliable force field parameters, theforce field parameters have been tested extensively. The tests show that the force fieldparameters can have a good description of the propertities of copper.The properties of single g-C₃N₄sheet, the water adsorption on single g-C₃N₄sheetand the role of defect in water adsorption and dissociation were thoroughly exploredbased on density functional theory （DFT） calculations. The results shows that single g-C₃N₄sheet can be either flat or buckle, and the buckle one is more stable.Interestingly, when water molecules adsorb on one side of the planar single g-C₃N₄sheet, the initial planar g-C₃N₄automatically becomes buckle one, while watermolecules adsorb on both sides of g-C₃N₄can avoid the presence of buckle structure.Fascinatingly, the flat g-C₃N₄is indirect semiconductor, but the band structure ofg-C₃N₄changes from indirect semiconductor to direct one because structuretransforms from flat to buckle one because of the water adsorption. Water moleculeprefers to adsorb around the intrinsic vacancy of single g-C₃N₄sheet at the lowcoverage, and further adsorbed water molecules will stay around this site because ofhydrogen bond between water molecules. More importantly, water can help todecrease the valence band maximum and conduction band minimum of g-C₃N₄, whichwill greatly promote the splitting of water. Water monomer, dimer, and clusters withthree and four molecules at the defect site can form a stable coplanar structure withthe g-C₃N₄sheet. The clusters help to stabilize the adsorption at the defect site.Molecular dynamics simulations show that on the perfect g-C₃N₄sheet water does notdissociation but on the defect g-C₃N₄sheet do. There are two reoriented water layersnear the g-C₃N₄sheet because of the interaction between water and the g-C₃N₄sheet.Our findings indicate that the defect within g-C₃N₄play a key role in the adsorptionand dissociation of water. These results not only help to design the new type of metal-freecatalyst for water-splitting.