Professor Z. Xiao Guo
Xiao Guo’s research interest focuses on multiscale simulations and syntheses of materials and nanostructures for applications in clean energy, hydrogen storage, energy catalysis, biofuel cells and biointerfaces. Fundamental theories are coupled with ab initio, molecular dynamics, cellular automata and finite element simulations for materials discovery, while selected materials are synthesised and tailored by mechanochemical alloying, self-assembly, deposition and precipitation methods.
A. Research Activities in Energy/Hydrogen Storage and Generation:
A1. Predictive Design and Synthesis of Hydrogen Storage Materials and Nanostructures
Climate change, limited oil & gas fuels, and pollution have led to a worldwide drive for the development of clean and renewable energy resources. Hydrogen is a clean energy vector, as it is the most abundant element in the universe, has the highest energy per unit weight of any chemical fuel, and is non-polluting. Material hydrides offer safe, compact and low pressure storage of hydrogen for many potential applications, e.g. fuel cells / batteries in future electronics and transportation. However, much of the technology is hindered by high-cost and low weight-specific power. The research aims to develop hydrogen storage nanostructures and systems of desirable properties, guided by theoretical predictions. Systems under consideration include LiH, MgH 2, LiNH 2, LiBH 4, LiAlH 4 and doped carbon nanostructures. Selected multi-component systems (Li, B, C, Mg, Al) are synthesised in an ultra-clean clean environment, modified by mechanical, chemical and catalytic means and by the design of reaction paths. Characterisations of particle size, lattice parameter, microstructure, and phase composition are performed using SEM, TEM, X-Ray diffraction and quantitative Rietveld analyses. Hydrogen desorption/absorption properties are evaluated using P-C-T facilities and coupled Thermogravimetry (TG), Differential Scanning Calorimetry (DSC), Mass Spectrometry (MS) and FT-IR techniques. The research activities are currently sponsored by the EPSRC SUPERGEN Initiative - UK Sustainable Hydrogen Energy Consortium Grant, in association with the International Energy Agency – Task 22
A2. Electronic Simulations of H 2 /CO 2/H 2O Interactions with Nanostructures
The overall aim is to clarify the nature of H 2, CO 2 and H 2O interactions with various host structures and surfaces, so as to identify the most-effective H-storage systems, CO 2 sorbents, water-splitting catalysts. Considerations are given to the influences of structural geometry, defects, charge and doping of nanostructures from first principles electronic structural simulations. Stability of nanostructures is evaluated from the electronic structures and binding energies, and energy barriers are determined from the Nudged Elastic Band method. Relative stabilities of different sorption sites and configurations are assessed for further clarification of H 2 /CO 2 sorption mechanisms. Well-tested first principles codes, e.g., WIEN2K and VASP, are used for the studies. The research activities are currently sponsored by the EPSRC SUPERGEN Initiative - UK Sustainable Hydrogen Energy Consortium, an EPSRC Platform Grant, in association with the International Energy Agency.
A3. Integration of Hydrogen Storage Materials into Power Systems
The focus here is to incorporate modified hydrogen storage materials or hybrid systems into storage tanks and then with fuel cells. The project builds on the current research activities to develop optimised hydrogen storage systems, which is integrated into storage tank designs and development with collaborating partners. Material stability and degradation due to hydrogen and temperature exposure are studied. There is a need for integration of tank design, heat transfer requirements, heat management, system geometry, and choice of materials for tank casing. Furthermore, hydrogen delivery issues to fuel cells are evaluated to ease of installation, energy efficiency, response time, safety and reliability. Part of the project is currently sponsored by a EU funded HyTRAIN consortium
A4. Chemical Synthesis of Cathode Materials for High Power Density Li-Ion Batteries
Due to continued industrial demand for high-performance Li-ion batteries, LiCoO 2-based cathode materials have been under popular investigation for enhanced electrochemical capacity. Here, doped LiCo (1-x)M xO 2, was synthesized by co-precipitation followed by freeze drying, milling and calcination. TG/DSC studies were performed on the ball-milled and freeze-dried precursors. The morphologies and structures of the as-prepared compounds were characterized by SEM and XRD, respectively. FTIR was also employed to investigate the compound structures in detail. The chemical method requires far less time than the traditional route, leading to much improved electrochemical performance.
B. Research Activities in Biofuel Cells and Biointerfaces:
B1. Synthesis and Modifications of Electrode Materials for Biological Fuel Cells
The project aims to develop high power density biological fuel cells, converting chemical / biochemical energy into electrical energy using biocatalysts, generating fuel through metabolic processes or catalysing electron transfer between the fuel and the bioelectrode. A fuel cell is an electrochemical device that converts chemical energy to electricity. Unlike conventional fuel cells, a biological fuel cell converts biological matters into and/or uses bio-catalytic enzymes for electric energy. BioFCs operate at ambient temperatures, atmospheric pressure and neutral pH, of benefit to the environment, waste management, portable electronics and implantable medical devices. This multidisciplinary project aims at developing highly conductive and robust electrodes for biological fuel cells. Such biofuel cells may be implanted into human body to power medical devices at a very small scale, or set up in biomass and waste-water streams for electricity generation and water/waste treatment. Here, we are synthesising the important electrode structures, examination of the structures by SEM / XRD, and measurement of mechanical and electrical properties. The activities are currently sponsored by the EPSRC SUPERGEN Initiative – UK Biological Fuel Cells consortium
B2. Molecular Dynamics Simulations of Electrodes and Enzymes in Biofuel Cells
This project is orientated for biological fuel cells that can directly convert biological matter into energy – electricity, making use of the unique capabilities of Molecular Dynamics (MD) to simulate interactions of inorganic and bio-molecular substances for understanding and design of biointerfaces with much improved immobilisation of catalytic enzymes and electronic transfer from the bio-substrate to the electrode. The activities are currently sponsored by the EPSRC SUPERGEN Initiative – UK Biological Fuel Cells consortium.
B3: Self-Assembly for Surface Coatings of Improved Biocompatibility:
Titanium and its alloys are frequently used as surgical implants in load bearing situations due to their good biocompatibility. However, the materials do not readily bond to bone in the early post-implantation stage. Various methods have been proposed to introduce calcium phosphate (CaP) coatings onto metal implant surfaces to improve and accelerate their integration with bony tissue, but none of the methods offers satisfactory results. A self-assembly technique is under development here to modify the surfaces of titanium and its alloys so as to improve their biocompatibility. Several kinds of molecules with specific bioactive functionalities were immobilised on spontaneously formed nanoscale self-assembled monolayers (SAMs). Titanium based samples were first treated with concentrated H 2SO 4 and 30%H 2O 2 to form titania and then immersed in silane solutions and organic solvents to generate monolayers with –OH, –COOH, –NH 2 and –PO 4H 2 terminal groups. Atomic force microscopy and contact angle goniometer were used to characterise the SAM surfaces and confirm the presence of various functional groups. Simulated body fluids (SBFs) were utilised to generate calcium phosphates over these functional groups. Scanning electron microscopy and X-ray diffraction were applied to characterise the calcium phosphate layer. The results clearly show that the SAM modified surfaces greatly enhance the formation of calcium phosphates . This low-temperature process is able to produce uniform coatings onto complex-shaped and/or micro-porous samples and the phases and crystallinity of the deposited material can be readily controlled, even with possible addition of growth-factors.
B4. Molecular Dynamics Simulations of Biointerfaces
Biointerfaces refer to those between a physiological environment and an inorganic material, such as implant/tissue and biosensor/bio-fluid interfaces. Understanding of such interfaces is very important in improving the biocompatibility of implants and in optimising the design and function of drug delivery / bio-sensory devices and gene chips. The aim of this project is to use molecular dynamic simulations to study the complex interactions across the bio-interfaces, so as to provide some insight into the specific area of bio-interface science. The interfaces between selected proteins and a titanium alloy will be simulated using InsightII, in order to identify: 1) the reorientation of proteins after contact with the biomaterial; and 2) effects of surface chemistry, topography and voids on protein apposition on titanium. Comparison between empirical method and semi-empirical method or quantum mechanical simulations will be made, mainly using InsightII and DL-Poly.
Selected Publications :
- Y. Lei, Z.X. Guo, W. Zhu, S. Meng, and Z. Zhang (2007) , “Initial interactions between water molecules and Ti-adsorbed carbon nanotubes” , Applied Physics Letters , 91,161906.
- Kondo-Francois Aguey-Zinsou, Jinhan Yao, and Z. Xiao Guo (2007), “Reaction paths between LiNH 2 and LiH with effects of nitrides”, Journal of Physical Che mistry B , 2007, 111 (43), 12531 -12536.
- S.A. Shevlin and Z.X. Guo (2007), “Hydrogen storage in defective hexagonal boron nitride sheets and boron nitride nanotubes, Physical Review B, 76, 024104.
- Y.Song and Z.X. Guo (2006), “Electronic structure, stability and bonding of the Li-N-H hydrogen storage system ”, Physical Review B, 74, 195120.
- Y.Song and Z.X. Guo (2006), “Metastable MgH 2 Phase Predicted by First-Principles Simulations”, Applied Physics Letters, 89, 111911 .
- S. A. Shevlin and Z.X. Guo (2006), “Transition metal-doping enhanced hydrogen storage in BN systems”, Applied Physics Letters, 89, 153104.
- Y.Song, R. Singh and Z.X. Guo (2006), A First-Principles Study of the Electronic Structure and Stability of a Lithium Aluminium Hydride for Hydrogen Storage, Journal Physical Chemistry B, 110, 6906-6910 .
- C.S.Y. Jee, Z.X. Guo, S.I. Stoloarov and M.R. Nyden (2006), “Experimental and Molecular Dynamics Studies of Thermal Decomposition of a Polyisobutylene Binder”, Acta Materialia, 54, 4803-4813 .
- Y. Song, Z.X. Guo and R. Yang (2004), Influence of selected alloying elements on the stability of magnesium hydride for hydrogen storage applications: A first principles investigation, Physical Review B, 69, 094205.
- C.X. Shang and Z.X. Guo (2004), Effect of carbon on hydrogen desorption and absorption of mechanically milled MgH 2, Journal of Power Sources, 129 (1): 73-80.
- C.X. Shang, M. Bououdina, Y. Song and Z.X. Guo (2004), “Mechanical Alloying and Electronic Simulations of (MgH 2+M) Systems (M=Al,Ti,Fe,Ni,Cu and Nb) for H Storage”, International Journal Hydrogen Energy, 29,73-80.
- Z.X. Guo,Book Editor, “Multiscale Materials Modelling - Fundamentals and Applications”, ISBN978-1-84569-071-7, CRC & Woodhead Publishing Ltd, Cambridge, 2007.
- Z.X. Guo, Book Editor, “The Deformation and Processing of Structural Materials”, ISBN 1 85573 738 8, 352 pages, CRC & Woodhead Publishing Ltd, Cambridge, 2005.
- Editorial Boards : Journal of Nano Research; Journal of Multiscale Modelling; Materials Technology; Acta Metallurgica Sinica; Journal of Materials Science & Technology.
- Guest Professors : Institute of Metal Research /Chinese Academy of Sciences; Shanghai Jiao Tong University; Chong-Qing University; Chong-Qing Institute of Technology; Southeast University / Nanjing; Harbin Institute of Technology.
- Lee-Hsun Lecture Award , Institute of Metal Research / Chinese Academy of Sciences, 2002.
- Beilby Medal & Prize , jointly by the IoM 3, the Royal Society of Chemistry; and the Society of Chemical Industry, 2000.