Transformative times
The efficient storage of electricity for mobile devices, zero emission transport, renewable energy sources, and other applications is a hot topic in scientific circles. With advances essential for sustainable development and the evolution of smart cities, researchers are now looking beyond the lithium-ion batteries widely used in mobile phones and electric vehicles to uncover alternative technologies to improve performance and create larger capacity systems with potential for storing electricity generated by intermittent energy sources, such as solar and wind.
Professor Chan Kwong-yu (Croucher Research Scholarship 2010), of the Department of Chemistry, University of Hong Kong (HKU), is internationally recognised for his expertise in this field and for research into fuel cells and molecular simulation of electrochemical interfaces, which lie at the core of such innovation. His work is based on fundamental understanding and optimisation of transport-limited processes in multi-scale structured materials for electrochemical technologies, for example, fuel cells, batteries, super-capacitors, and ozone generation.
“I look at the comparative shortcomings of batteries in terms of driving range, operating cycle, and re-charging time,” Chan said. “I started off at the blue sky end of research with my PhD. But as my career has progressed, it has tended to become more practical.”
After school education in Hong Kong and Canada, Chan earned a bachelor degree in chemical engineering from the University of Alberta, before completing both his MSc and PhD at Cornell University. Chan subsequently held research posts in the US, Hong Kong and mainland China. He also worked in industry for a year. He first joined HKU’s Department of Chemistry in 1988 as a lecturer, rising to professor in 2008.
With lithium-ion batteries now used extensively in industry, Chan’s team has been examining ways of extending their capabilities by utilising oxygen (O2) from air. Such lithium-oxygen, or lithium-air, batteries are not yet ready for commercialisation but Chan’s leading research is helping to advance this goal by addressing some of the major challenges in utilising such batteries. For example, when a lithium-oxygen battery discharges, oxygen is converted into superoxide and then lithium peroxide, both reactive compounds that corrode the battery’s components over time. That, in turn, limits its recharging ability. Lithium-oxygen batteries also require extra components to manage the gas environment, in an open-cell configuration that is very different from conventional sealed batteries.
In 2017, Chan and his co-authors published a ground-breaking paper, “Advancing Lithium-Oxygen Battery Technology with an Iron-Nitrogen‐Doped Mesoporous Core-Shell Carbon Cathode Loaded with Ruthenium (IV) Oxide Nanoparticles” in Energy Technology. In this study he demonstrated that an iron‐nitrogen‐doped core-shell mesoporous carbon support loaded with a ruthenium (IV) oxide (RuO2) catalyst could be used as a lithium-O2 cathode, while corrosion and degradation problems were avoided by doping carbon with iron and nitrogen.
Lithium-air batteries are considered highly promising technologies for electric cars and portable electronic devices because of their potential for delivering high-energy output in proportion to their weight (high density). A lithium-air battery potentially has 15 times the specific energy of a lithium-ion battery.
Chan is interested in structuring composite materials at multiple-length scales to optimise the interfacial phenomena and degradation that take place in these applications. “We must make the material with the best structure for that interface. Carbon is one material that can be used with lithium,” he explained. The complexity of the pore structure and wall architecture affects electron conduction, ion transport in the pores, and interfacial charge-transfer, having a significant influence on electrochemical performance.
“I am gradually moving towards the materials side to improve the electro-chemical reaction,” said Chan, whose latest research into the interface structure is applicable to both lithium-ion and lithium-air batteries. And while fuel-cell technology is currently lagging behind the commercialisation of lithium batteries, a breakthrough on the materials side could propel it to the forefront of energy storage, according to the researcher. “It is the material science that is holding up the fuel-cell technology,” he noted.
In other research, Chan is investigating the feasibility of sodium-ion (Na-O2) batteries as an alternative to lithium-ion and lithium-air. Advantages of sodium-ion batteries include the greater abundance of sodium and a smaller voltage than lithium-ion, making them safer.
As co-lead investigator of an ambitious collaborative project with Nankai University in mainland China, he is seeking to construct a long cycle-life Na-O2 battery and study its reaction mechanism. The objective of the four-year project, launched in January 2018, is to develop long life-cycle sodium-air batteries which are safe, low cost, and sustainable. Critical anode and cathode components are due to be constructed with advanced multi-scale structured composite materials. There will be innovations in synthesis, configuration of electrochemical cells, and materials characterisation in situ of electrochemical reactions; and investigations into the sodium anode electrolyte interface, using advanced in situ characterisations, to try to reveal general molecular phenomena applicable to other heterogeneous solid-liquid reactions.
The enterprising HKU scholar is also working on flow batteries, which have properties of both conventional batteries and fuel cells, with energy stored as a charge difference between two electrolyte tanks. Electricity is produced when these electrolytes interact through a membrane in the flow battery. Energy is stored in a liquid and the liquid can be pumped out of the cell and stored in an external tank which, in principle, makes it suitable for storage of renewables with intermittent sources, such as solar power.
Behind these multiple research endeavours, and more, Chan and his team have a single aim in mind: to help to meet future energy needs of a sustainable economy.
Professor Chan Kwong Yu is an expert on fuel cells and the molecular simulation of electrochemical Interfaces. He earned his bachelor degree in chemical engineering from the University of Alberta, before completing both his MSc and PhD at Cornell University. Chan subsequently held research posts in the US, Hong Kong and mainland China. He also worked in industry for a year. He first joined HKU’s Department of Chemistry in 1988 as a lecturer, rising to professor in 2008.
To view Professor Chan's Croucher profile, please click here.