Analysis Of Zirconium Hydride ?ZrH₂?_n?N=5-24?and Doping Effects Of Transition Metals ?TM=Co,Cu And Ni? On ?ZrH₂?_n?N=5,11,19 And 24? In Nanocluster Sizes:DFT Calculations

The work presented in our thesis mainly focuses on the study of zirconium hydride and its doping with transition metals(TM=Co,Cu and Ni)in nano-sizes for the purpose of analyzing the behavior of the compound towards hydrogen storage potential.Since,fossil fuels are the main source of energy for every energy sector in the world because of not only its presence in larger amounts,but also they could provide high enough energy to make the whole process of driving energy from it,a feasible and inexpensive.Now,to replace such an energy source,because of its adverse effects to our environment and also its not sustainable for too long,other sources must be searched which could provide the same energy requirements.So,for this reason,hydrogen was considered the most feasible of energy sources because of its sustainability and providing more energy than that of fossil fuels.But,to utilize this energy source,there are few hurdles which needs to be addressed,in order to achieve the desired goals.Among these hurdles,one is its storage.There have been few methods suggested for its storage,which few of them proved to be unworthy of use,whereas two main processes which could be of great potential for the storage of hydrogen are physiosorption and chemisorption techniques.In this thesis work,we have approached to understand the storage capability for hydrogen by chemically bonding with zirconium and thus analyzing its properties in nanocluster sizes.We also studied the doping of transition metals(TM=Co,Cu and Ni)on the zirconium hydride(ZrH2)n nanoclusters and analyzed its properties and provide a comparative study.For the zirconium hydride(ZrH2)compound,different sized nanoclusters ranging from 15 to 72 atoms were studied i.e.(ZrH2)n(n=5-24).The properties for these structure sizes were observed and the behavior of each nanocluster size relating to the other were analyzed and a comparative analysis was provided.Also,for TM-doped(TM=Co,Cu and Ni)(Zrn-1H2n)(n=5,11,19 and 24)nanoclusters,their properties were calculated and a comparative study for the effects of each doped atom on the(ZrH2)n nanoclusters were observed.Hence,the probing of(ZrH2)n(n=5-24)nanoclusters was initiated with optimized initial structures,generated by artificial bee colony algorithm which was re-optimized and structural and electronic properties for(ZrH2)n(n=5-24),and nudged elastic bands(NEB)for(ZrH2)n(n=5 and 11)nanoclusters(NCs)were calculated using density functional theory.The analysis showed that Zr atoms of(ZrH2)n NCs,tends to occupy the edge positions with few of the atoms with increasing nanocluster sizes occupy the inner layer positions too,whereas majority of H atoms dissociate to the vertex sites.Furthermore,the resulting formation energies of(ZrH2)n(n=5-24)nanoclusters increases from(ZrH2)5 through(ZrH2)21 NCs,showing increased stability,with decreasing.trend later on.In partial density of states(PDOS)of(ZrH2)n,Zr 4d,5s and H 1s orbitals overlap over a wide range,showing stronger chemical bonding,which increases with increasing NC size.Nanocluster(ZrH2)2i,is the most stable NC,with the least formation energy-7.278 eV,and stronger Zr-H chemical bonding.Through electron localization function(ELF)perusal,it is observed that ionic bonding exists between Zr-H atoms of(ZrH2)n NCs.Also,through the analysis of Bader charge and charge density difference,we came across the fact that charges transfer from Zr to H atoms.Furthermore,the dissociation energies for nanoclusters(ZrH2)n(n=5-24)were studied to observe the maximal and minimal of energy requirements,for surface H2 atoms to expand the barrier and free from the Zr atomic absorptive energy field.Later,the bond strengths for the maximal and minimal of structures,(ZrH2)5 and(ZrH2)11 NCs,were analyzed,to understand the bonds strength relation with the dissipation energy.Moreover,the doping of transition metals(TM=Co,Cu and Ni)on the(ZrH2)n(n=5,11,19 and 24)nanoclusters showed manipulative results and the properties of(ZrH2)n nanoclusters were altered with distinctive effects.The formation energies calculated for the doped structures display an increasing behavior with the increasing nanocluster sizes as the formation energies of undoped(ZrH2)n nanoclusters.The Co-doped(Zrn-1H2n)(n=5,11,19 and 24)nanoclusters display increased formation energies than the other two neighboring transition atoms i.e.(TM=Cu and Ni),and also at nanocluster size(n=11),the Co-doped(Zrn-1H2n)nanocluster even have higher formation energy than the undoped(ZrH2)11.Furthermore,Co-,Ni-doped(Zrn-1H2n)nanoclusters display equal formation energies at(Zrn-1H2n)(n=24)nanocluster size.The reason for having increased stability for Co-doped(Zrn-1H2n)(n=11)nanocluster due to increased formation energy is because of having increased number of overlapping of orbitals,as from the partial density of state(PDOS)H 1s-,Zr 5s-,4d and(TM=Co,Cu and Ni)4s-,3d orbitals interaction analysis,the range of the overlapping were similar to the undoped(ZrH2)n nanoclusters overlapping,but the 3d orbital of the transition atoms increased the number of overlapping and thus the stability was increased more than the undoped(ZrH2)n nanoclusters.Also,the analysis of desorption energies for the TM-doped(TM=Co,Cu and Ni)(Zrn-1H2n)(n=5 and 11)nanoclusters,the dissipation energies were altered for both the nanocluster sizes,with decreased desorbing energies for(TM=Co and Ni)for(Zrn-1H2n)TM(n=5)nanocluster size,whereas for(TM=Co and Cu)at(Zrn-1H2n)TM(n=11)the desorption energies showed increased values.