Computational Studies Of Halogenated Carbon Based Nanomaterials As Multifunctional Catalysts

Nanostructured carbon materials(NCMs)have garnered much interest in various fields,owing to their unique structural and electronic properties.Notably,NCMs have shown to be suitable supports for heterogeneous catalysis,due to a series of features comprising high thermal stability and mechanical resistance.However,the inert nature of NCMs instigates the need to structurally modify NCMs for improved catalytic properties at the design stage.One of the design strategies for adjusting the surface morphology and properties of NCMs is by halogenations,and the other is by heteroatom doping and creation of defect in the carbon lattice.When the halogen is doped on the NCMs lattice,it converts the sp2 carbon bonding into a sp3 state,which produces drastic distortions in the electronic and geometric structures of NCMs.With halogen doping,the band gap level of NCMs can be modulated and other intrinsic properties such as conductivity and carrier mobility are significantly enhanced.Apparently,halogenated-NCMs have excelled in many fields of research for wide range of applications,however,the nature of interaction and weak binding strength of halogen-NCMs system remains a significant challenge.Therefore adjustment of halogenated-NCM relies on effective strategies such as heteroatom doping which is vital for the development of halogenated-NCMs.Obviously,boron and nitrogen are two most often used dopants because they have similar atomic radius with carbon which can potentially enable them to enter carbon matrix.On the other hand,boron and nitrogen have one less or more valence electrons than carbon which resembles p or n type doping.Defects in NCM are found to modulate the local electronic environment and perturbed the surface properties of the NCM.The incorporation of halogen can effectively enhance the binding energy of TMs to NCM compared with the NCM without halogen.Although various research efforts have been established on the doping mechanism of halogen on the surface of NCMs,however,the synergistic effect of heteroatom doped on halogenated-NCMs is still yet to be fully understood.Here by using computer simulation we clarified tuneable effect of halogens on the catalytic performance of NCM and also the synergistic coupling effects endow on it by heteroatoms doping.Similarly,we rationalize the role halogens and defects played in tuning the catalytic property of supported metal on the NCM.This PhD thesis investigates the catalytic performance of halogenated NCM synergized by heteroatom doping and also transition matal-halogen supported/defected NCM for several types of catalytic reactions such as lithium polysulfide interfacial reactions in Li-S batteries technology,small molecules adsorption and oxygen reduction reaction(ORR)using ab initio DFT calculations.The first aspect of this thesis investigates the role of heteroatom doping on the halogenation of graphene.Halogenation is one of the most important ways to tailor the properties of graphene.Halogen doping of graphene can break the relative inertness of graphene and endow it with chemical reactivity due to their high electronegativity compared with carbon.Our analysis revealed that the halogen intercalation on graphene surface featured with weak binding energy which does not really helpful to bind halogen molecules and subsequently undermine the formation of halogenated graphene derivatives.Heteroatom doping with boron and nitrogen dopants is an effective strategy to strengthen the interaction between graphene and halogen.With the introduction of boron and nitrogen,the interaction between halogen molecule and graphene was tuned and adjusted in a wide range.The tuneable effect of boron and nitrogen doping on the interaction of diatomic molecules and graphene can be attributed to induced spin density and orbital polarization of the doping atoms.It is found that nitrogen and boron doping does not only increase the binding energies of Cl2,Br2,and I2 but also induces the spontaneous dissociation of F2.The doping mechanism of graphene by nitrogen and boron is expected to open the opportunities for rational design of halogenated graphene derivatives as this work demonstrates that the doping is a valid method for the facile halogenation of graphene and pave the way for the further application of halogenated graphene.The second aspect investigated in this thesis is the inhibition of polysulfide shuttle in Li-S battery by chemical modification of carbon cathode via heteroatom-doping.Lithium-Sulfur batteries(Li-S)are currently the premier rechargeable battery,due to their extremely high specific energy density and theoretical specific capacity.The major set of the Li-S battery technology is the issue pertaining to complex diffusion of lithium polysulfide intermediates,which is also called shuttle effect.The halogenated functionalized carbon host has shown an optimum performance to address the shuttle and kinetics issues of Li-S battery cathode.Our calculation revealed that halogen dopants(F,Cl,Br,I)significantly modify the local electronic structure of adsorption site and further induce a polarization to trap the polysulfides.Moreover,boron as second dopant further strengthened the interaction between halogenated graphene and polysulfide molecule.Boron induces charge accumulation on halogens which consequently create a strong dipole for adsorbing lithium polysulfides.This work suggests halogenations as a veritable strategy verified to regulate the adsorption of lithium polysulfide and also enhance the reaction kinetics of the Li-S battery systemThe third aspect investigated in this thesis is the sensitivity and electrocatalytic activity of novel halogen-doped/undoped Fe-embedded carbon nanotube single-atom catalysts(Fe-SWNT and Fe-X-SWNT,X=Cl,Br,I)for small molecules adsorption and oxygen reduction reaction(ORR)catalysis under the framework of first principles density functional theory(DFT)study.The chemical modification of SWNT either by halogen doping or creating defects can enhance the catalytic reactivity of Fe atoms,which subsequently provides high binding with small molecules and ORR intermediates compared to pristine one.Similarly,Fe-Cl-SWNT presents the greatest catalytic performance towards oxygen reductions and small molecule's adsorption,due to the inductive effect and electronegative strength of Cl element embedded into the divacancy defect in SWNT.The enhanced performance also corresponds with the high d-band value of the active Fe atom,which is closer to the Fermi level of Fe in Fe-Cl-SWNT.This work provides a new insight to rational design of ultra-high activity catalyst for environmental monitoring of poisonous gases and ORR catalysis.The outcome of this thesis is expected to tackle the current global environmental challenges and provide alternative catalyst for monitoring and trapping poisonous gases.This research provides in-depth mechanistic insights into rational designing of multifunctional based catalysts for most relevant industrials process such oxygen reduction reaction and polysulfide interfacial reactions in Li-S batteries technology based on their remarkable electronic properties.The results achieved will provide useful information to researchers and industrialists and also serve as a guide or benchmark for futuristic screening of high performance catalyst for the most relevant industrial processes.