Language:
Engilsh

Registration:
Please register at https://cap.cityu.edu.hk/studentlan/postDetail.aspx?id=K11i2820c180208M683307

Enquiry:
see.enquiry@cityu.edu.hk (email) or 3442 2414 (Tel.)

About the Workshop

The Workshop on Energy Conversion and Storage with the theme ‘Energy Materials in Addressing Global Challenges’ will be hosted by the School of Energy and Environment, City University of Hong Kong, to promote and enhance the scientific knowledge on materials science, physical chemistry, and energy applications.

The workshop will cover topics on materials science and engineering, materials and devices, perovskite materials, photocatalysts, fuel cells, battery materials, molecular simulation, and so forth. Scholars and experts will share with the audience their expertise in materials science, physical chemistry and energy applications.

Programme

Abstracts and Speakers

Stability of Perovskite Solar Cells

Prof. Aleksandra B. Djurišić, Professor and Associate Dean. Department of Physics, University of Hong Kong

Abstract

The record efficiency of perovskite solar cells currently exceeds 22%, which is comparable or higher than that of well established technologies, such as CIGS, CdTe and multicrystalline Si. However, despite high efficiencies and promising reports of long term stability with dark storage, the stability of these devices remains a concern. In this talk, the stability of the commonly used CH3NH3PbI3 perovskite and the solar cells based on this material will be discussed in detail, including the effect of the deposition conditions on material properties and stability upon ambient exposure under illumination. The other factors contributing to the device stability, such as charge transport layers and electrodes in different device configurations will also be discussed. Finally, encapsulation of the devices to ensure stable performance and the measurement protocols for stability characterization will be discussed.

About the speaker

Prof. Aleksandra B. Djurišić obtained PhD degree in Electrical Engineering from the School of Electrical Engineering, the University of Belgrade in 1997. After finishing her PhD studies, she worked as a postdoctoral fellow at University of Hong Kong and as an Alexander von Humboldt postdoctoral fellow at TU Dresden. She joined the Dept. of Physics at the University of Hong Kong in 2003 as assistant professor and she is currently a professor. Her research interests include nanomaterials, wide-bandgap semiconductors, and organic materials, and their applications in areas related to energy and environment, such as photocatalysis, antimicrobial materials, solar cells, and batteries. She has published 337 research articles including reviews, and has been cited over 13800 times. Her h-index is 53.

Photocatalytic Fuel Cell: Prospects and Challenges

Prof. Michael K. H. Leung, Professor. School of Energy and Environment, City University of Hong Kong

Abstract

Photocatalytic fuel cell (PFC) is primarily a synergistic integration of two emerging technologies, namely, photocatalysis (PC) and fuel cell (FC). Solar PC can decompose organic compounds while FC provides an electrical potential gradient to facilitate transport of electrons. Therefore, PFC can be effectively applied to utilize solar energy for wastewater treatment and recovery of energy chemically stored in wastewater. It is a promising technology for solving both environmental and energy problems. In order to conduct proper research for rapid development of PFC, we need to have good knowledge about the material properties and clearly understand the cell mechanisms of PFC. The Fermi level between the photoanode and the cathode forms interior bias that inhibits recombination of photogenerated electrons and holes, resulting in increase in visible-light activation of PFC. Modification of photoelectrocatalysts and use of microfluidics are effective strategies for improving the PFC performance. The PFC effects can also be manipulated by the system configuration, design and control for specific outputs and reaction rates. In this talk, the speaker will present the fundamentals, latest development of PFC, and upcoming R&D challenges needed for enhancing the PFC technology.

About the Speaker

Prof. Michael Leung received his PhD degree in Mechanical Engineering from the University of Florida, Gainesville, Florida, U.S.A. in 1995. He was an Assistant Professor in the Department of Mechanical Engineering at the University of Hong Kong before joining the City University of Hong Kong in 2010. Presently, Prof. Leung is a Professor in the School of Energy and Environment at CityU and the Director of Ability R&D Energy Research Centre at CityU. Prof. Leung's main research interests are solar photocatalysis, fuel-cell electrochemistry and advanced refrigeration and air-conditioning. He has published 130+ journal papers, 16 books/book chapters, and 6 patents. He is listed in the Most Cited Researchers in Energy Science and Engineering by Shanghai Ranking’s Global Ranking of Academic Subjects by Elsevier. The research grants received add up to a total above HK$40M. Prof. Leung is also the Chairman in the Education and Examinations Committee of the Hong Kong Institution of Engineers, a Past Chairman of the Energy Institute (Hong Kong Branch), a Chartered Engineer, and a Registered Professional Engineer.

Perovskite Photovoltachromic Supercapacitor with All-Transparent Electrodes

Dr. Yang Chai, Assistant Professor. Department of Applied Physics, The Hong Kong Polytechnic University

Abstract

Photovoltachromic cells (PVCCs) are of great interest for the self-powered smart windows of architectures and vehicles, which require widely tunable transmittance and automatic color change under photostimuli. Organolead halide perovskite possesses high light absorption coefficient and enables thin and semitransparent photovoltaic device. In this work, we demonstrate co-anode and co-cathode photovoltachromic supercapacitors (PVCSs) by vertically integrating a perovskite solar cell (PSC) with MoO3/Au/MoO3 transparent electrode and electrochromic supercapacitor. The PVCSs provide a seamless integration of energy harvesting/storage device, automatic and wide color tunability, and enhanced photostability of PSCs. Compared with conventional PVCC, the counter electrodes of our PVCSs provide sufficient balancing charge, eliminate the necessity of reverse bias voltage for bleaching the device, and realize reasonable in situ energy storage. The color states of PVCSs not only indicate the amount of energy stored and energy consumed in real time, but also enhance the photostability of photovoltaic component by preventing its long-time photoexposure under fully charged state of PVCSs. This work designs PVCS devices for multifunctional smart window applications commonly made of glass.

About the speaker

Dr. Yang Chai is an Associate Professor at the Hong Kong Polytechnic University. He received his PhD degree from the Hong Kong University of Science and Technology in 2009. After he conducted his Postdoctoral studies at Stanford University and University of Illinois at Urbana &Champaign, he joined the Department of Applied Physics in the Hong Kong Polytechnic University in 2012. He is a recipient of RGC Early Career Award in 2014, the IEEE Distinguished Lecturer since 2016, and the Semiconductor Science and Technology Early Career Research Award in 2017. His current research interest includes low-dimensional material for electron devices.

Advanced Nanotechnology for High-Performance Photovoltaic Devices

Prof. Feng Yan, Professor. Department of Applied Physics, The Hong Kong Polytechnic University

Abstract

High-performance organic solar cells have been developed by our group based on various nanotechnology in recent years. First, the efficiency of organic solar cells has been improved by introducing plasmonic nanoparticles, high mobility conjugated polymers or 2-D materials. Pronounced effects have been observed in the devices due to the improvement of the carrier mobility or light absorption in the active layer. Graphene has shown promising applications in photovoltaic devices for its high carrier mobility and conductivity, high transparency, excellent mechanical flexibility and ultrathin thickness, and can be used in solar cells as transparent electrodes or interfacial layers. Package-free flexible organic solar cells are fabricated with multilayer graphene as top transparent electrodes, which show high power conversion efficiency, excellent flexibility and bending stability. Semi-transparent organic solar cells and perovskite solar cells were prepared by using graphene transparent electrodes. For the perovskite solar cells, the devices show high power conversion efficiencies (~12%) when they are illuminated from both sides. Considering the poor stability of perovskite solar cells in ambient air especially with high humidity, we have recently developed a novel technique to improve the device stability by introducing SCN- to partially replace I- in the perovskite material, which can dramatically improve the lifetime of package-free device in air. All of the techniques will be very useful for the practical applications of the novel photovoltaic devices.

About the Speaker

Prof. Feng Yan has research interests on organic electronics, 2D materials, solar cells, thin film transistors, biosensors and smart materials. He received his PhD degree in physics from Nanjing University in 1997 and then worked at the Department of Physics of Nanjing University as Associate Professor. He joined the Engineering Department of Cambridge University in Feb 2001 as a Research Associate and joined National Physical Laboratory in UK in April 2006 as a Higher Research Scientist. He became an Assistant Professor at the Department of Applied Physics of the Hong Kong Polytechnic University in September 2006 and was promoted to Full Professor in 2016. He has published more than 180 papers in peer-reviewed journals, including Adv. Mater., Nature Commun, Nano Lett. JACS, and given more than 50 invited talks in international conferences.

Improving Stability and Capacity of Sodium-ion Cathode Materials

Dr. Denis Y. W. Yu, Associate Professor. School of Energy and Environment, City University of Hong Kong

Abstract

Na-ion battery (NIB) is an attractive alternative to lithium-ion battery (LIB) because sodium is more abundant and cheaper than lithium. However, sodium-ion based cathode materials typically show low capacity, low voltage and poor cycle performance. In this presentation, we will outline our strategies to improve the stability and capacity of these materials through doping, surface coating and utilization of anionic reaction.

About the Speaker

Dr. Denis Yu is an associate professor at the School of Energy and Environment at City University of Hong Kong. He received his PhD in Applied Physics from the School of Engineering and Applied Sciences at Harvard University in 2003. He then worked as an engineer at SANYO Electric Co. Ltd. in Japan for 8 years, developing cathode and anode materials for Li-ion batteries. Afterwards, he led the battery activities at the Energy Research Institute at Nanyang Technological University and TUM CREATE Centre for Electromobility in Singapore as a senior scientist for two years before joining City University of Hong Kong. His research interests include fabrication, development and characterization of materials and electrodes for energy storage applications.

Chloride Enhances Fluoride Mobility in Anion Exchange Membranes

Dr. Ying-Lung Steve Tse, Assistant Professor. Department of Chemistry. The Chinese University of Hong Kong

Abstract

Anion exchange membrane fuel cells have received particular attention in recent years because they can overcome the problems of electrolyte leakage and carbonate precipitation in traditional alkaline fuel cells. Often, because perfect ion exchange in syntheses of fuel cell membranes is not possible, multiple ions can coexist in the membranes. Such co-ionic systems have non-trivial transport properties due to the competition between ions. In this presentation, I will talk about an anion exchange membrane with different ratios of fluoride and chloride ions. At 300 K, our molecular dynamics simulation results showed that the self-diffusion constant of fluoride increases by about 70% when fluoride content decreases from 100% to 40% (and 60% Cl), and it increases by about 140% when fluoride content decreases from 100% to 10%. We provide evidence that the enhancement in fluoride mobility is due to the larger size of the chloride ion, which more readily loses its water solvation shells because of a lower surface electric field. This in turn frees up more water for ion transport. I will also show such co-ion effects are more general than just the fluoride/chloride case discussed.

About the speaker

Dr. Steve Tse received his PhD degree in theoretical chemistry at Stanford University in 2011. He then spent four years at The University of Chicago from 2011 to 2015 to carry out postdoctoral research in the areas of renewable energy and acid-base systems. He returned to Hong Kong in 2015 to start working as an Assistant Professor in the Department of Chemistry at the Chinese University of Hong Kong. His current research involves using statistical mechanics and computer simulations to study different anion/proton exchange membrane systems and interfacial systems.

High-Efficiency MAPbI3 and Cs0.15FA0.85PbI3 Perovskite Solar Cells Made in a Humid Air with a Relative Humidity of 70%

Dr. Sai-Wing Tsang, Assistant Professor. Department of Materials Science and Engineering, City University of Hong Kong

Abstract

Understanding air-processing limitations and developing facile strategies to fabricate high-performance air-processed perovskite solar cell (PSC) is appealing yet challenging for the low-cost industrial deployment. Here, we demonstrate that besides the general wisdom of the moisture effect, oxygen induces a de-wetting behavior during the spin-coating of PbI2 precursor solution, both of which leads to the failure of desirable PbI2 deposition in air. Interestingly, by simply preheating the substrate and PbI2 solution, uniform PbI2 films can be deposited in air with a relative humidity (RH) of 70%. This is probably due to the rapid solvent evaporation at high temperature, reducing the ingress of oxygen and moisture. With the preheating approach, PSCs based on MAPbI3 achieves an encouraging power conversion efficiency (PCE) of 18.11%. More importantly, we found that the combination of preheating and a PbI2-(CsI)0.15-(FAI)x intermediate complex can unlock the processing limitation and facilitate the growth of high-quality FA based perovskite films in humid air (RH: 70%). With the coupled method, a low-temperature air-processed planar Cs0.15FA0.85PbI3 PSCs achieves a high PCE of 15.56% with superior thermal-stability and photo-durability. Our work not only reveals the origin of the detrimental effects on perovskite formation in humid air, but also provides practical strategies for high-efficiency air-processed MA or FA based PSCs for future commercialization.

About the speaker

Dr. Stephen Sai-Wing Tsang is an assistant professor in the Department of Materials Science and Engineering at the City University of Hong Kong. Dr. Tsang received his PhD in 2009 in the Materials Science and Engineering Department at the University of Toronto, Canada. His PhD was focused on developing experimental approaches and models to investigate the charge carrier transport across organic heterojunction, under the supervision of Prof. Zheng-Hong Lu. After his PhD, he joined the National Research Council (NRC) Canada as an Assistant Research Officer to develop solution processed quantum dots for photovoltaic applications. At 2011, he joined Prof. Franky So’s group at the University of Florida as a Postdoc Fellow to develop high efficiency polymer solar cells and investigate the corresponding device physics. Before joining CityU, he joined the Nano and Advanced Materials Institute (NAMI) in Hong Kong as an Assistant Technical Manager in the Energy division to develop CIGS and a-Si photovoltaic cells. His expertise is on photovoltaic technology, organic and nano electronics, and development of advanced opto-electronic characterization techniques.

Computational Study of Novel Materials for Energy Conversion and Storage

Dr. Patrick Sit, Assistant Professor. School of Energy and Environment, City University of Hong Kong

Abstract

Quantum mechanical simulations have become increasingly powerful tools for materials design and development thanks to the ever-increasing computer power, and the development of more efficient and accurate methodologies. As the state-of-the-art approach, density functional theory techniques have been extensively used to provide atomic-scale understanding and realistic prediction of materials properties. In this talk, I will highlight several examples of the study of nanoscale materials important in energy storage and conversion. In particular, I will present the theoretical study of the degradation of the hybrid perovskite materials in perovskite solar cells (PSCs). This provides crucial insights into the design of robust perovskite materials in photovoltaic applications. Moreover, density functional theory simulations also play an important role in catalyst design. I will discuss our studies of electrocatalysts for reactions including hydrogen production and oxygen reduction. These are important for the development of efficient and clean means for energy storage.

About the speaker

Dr. Patrick Sit is an assistant professor in the School of Energy and Environment at the City University of Hong Kong. He received his undergraduate degree in Physics from the University of Oxford and his PhD in Physics from MIT. Prior to joining CityU, he was a post-doctoral associate in the Department of Chemistry at the University of Pennsylvania and an associate research scholar in the Department of Chemistry at Princeton University. Dr. Sit’s research focuses on the development of novel computational methodologies and application of state-of-the-art ab initio simulation methods to study fundamental processes in energy-related systems.