Theoretical Studies On The Applications Of Low Dimensional Nanomaterials In Clean Energy Conversion Process

With the rapid development of technology and economy,the global energy and environmental crisis caused by the shortage of resources and environmental pollution continues to increase.Hence,intensive efforts have been devoted to develop some sustainable applications of clean energy.Recently,a number of new energy materials,such as fuel cells and solar cells,have attracted more and more attention.The fuel cells can convert chemical energy into electric energy by electrochemical catalysis,looking for a sustainable,low cost,high catalytic activity of the electrocatalyst is essential for the widely use of fuel cells.The solar cells can convert solar energy into electric energy by photovoltaic effects,effective charge separation is the key to improve the efficiency of photoelectric conversion.For the development of clean energy,besides the new energy conversion technology,the hazards of polluting gases which produced during the development of new energy materials can not be ignored.With the enhancement of people's safety awareness,it is more and more important to detect and control the poisonous and harmful gases,which provides a powerful driving force for the development of various novel gas sensing technologies.In this paper,using density functional theory,we performed theoretical studies on the potential applications of some newly synthesized or predicted low-dimensional nanomaterials in energy conversion and gas sensing.The main contents and findings of this paper include:1.The potential application of novel boron-doped graphene nanoribbon(BGNR)as oxygen reduction reaction catalyst.The ORR active sites were identified on the boron atoms,which possess positive charge distribution.By comparing the activation barrier of different reaction pathways,we find that ORR prefers to proceed through a four-electron pathway.The formation of OH(Ea-0.38 eV)is the RDS for the whole reaction.The overpotential for ORR on BGNR is calculated to be 0.38 V,which is lower than that on the Pt-based catalysts(0.45 V).The increasing of boron content not only provides more ORR active sites but also significantly enhances the catalytic performance of BGNR.The results indicate that BGNR is a promising metal-free ORR catalyst for fuel cells.2.Using real-time time-dependent density functional theory combined with nonadiabatic(NA)molecular dynamics,we simulated the ultrafast charge transfer in MoS2/WS2 heterostructures.The results show that hole transfer time from MoS2 layer to WS2 layer is 74 fs,in excellent agreement with the experiment.Hole transfer is an order of magnitude faster than electron transfer,due to stronger donor-acceptor interaction and NA couplings.It is found that the A1g vibration mode(400 cm-1)plays an important role in the ultrafast charge transfer process.The theoretical work may be helpful for the design of new photovoltaics devices.3.Studies on the potential applications of novel SiC5 siligraphene(g-SiC5)in detecting and sensing air pollutants.In this paper,the adsorption mechanism of 12 common gas molecules on g-SiC5 was investigated.The results show that some air pollutants gas molecules could form stable chemisorption with g-SiCs.Among the 12 gas molecules,NO,HCHO and SO2 exhibit moderate adsorption energies in the range of 0.4-0.6 eV and would open up a considerable band gap due to the orbital hybridization,thus changing the conductivity of g-SiCs and making the sensing feasible.The further comparative researchs demonstrate that the g-SiCs is superior to Si-doped graphene and other siligraphenes in gas sensing,enabling g-SiCs to be a promising material as gas sensor for detecting NO,HCHO or SO2 from air mixture.