Improving the battery: energy storage for a renewable world

12 December 2016

Professor TS Zhao, PhD, is Chair Professor of Mechanical & Aerospace Engineering and Director of the Energy Institute at the Hong Kong University of Science and Technology (HKUST). He is an internationally renowned expert in energy engineering and is distinguished for his seminal contributions in the areas of fuel cells, advanced batteries, multi-scale multiphase heat and mass transport with electrochemical reactions, and computational modelling.

Ironically perhaps, this eminent scientist, born in rural Shaanxi province, who is committed to creating clean energy production and storage devices for a sustainable future, commenced his scientific career studying the internal combustion engine at Tianjin University near Beijing.

"I loved cars, so the subject was interesting to me and in 1989 I did my Masters in the same field," says Zhao.

In 1990 he went to University of Hawaii at Manoa to study energy science and engineering and after a "very nice time in Honolulu," completed his PhD and came to HK in 1995 as an Assistant Professor in (what was then) the Department of Mechanical Engineering. He was appointed Chair Professor in 2011 but despite his teaching and managerial responsibilities, estimates that 50% of his time still remains firmly focused on research activities.

"We are doing very exciting research. I started in fossil fuels but with climate change and air pollution, we need clean and renewable energy," he says and explains that while the cost of solar photovoltaic (PV) and wind energy has dropped by a factor of ten, less than 5% of global energy needs are met by these two sources. Zhao believes this is primarily because these renewable power sources are inherently unstable and intermittent. Because the supply is fluctuating, it must be stored efficiently in order to use it effectively, making the need for a cost-effective long life power storage technology a pressing need.

"My research has been focused on this challenge," says Zhao and outlines the gap between installed power generation and on-grid power. Some 15% of all generated energy comes from wind and solar but only 4% of the on-grid power comes from the same source. This is the "missing link" between energy generation and storage and Zhao's team has been pioneering three specific technology areas.

Improved batteries

The direct alcohol fuel cell (DAFC) is an electrochemical energy conversion device which possesses the unique advantages of high-energy density-facile liquid fuel storage and simple system structure. His specific research is focused on electrochemistry and thermo-fluid flow in DAFC, nano-catalysts preparation, membrane modification, and system design.

"This is where electrochemistry meets thermo-fluid science," explains Zhao and he believes that an interdisciplinary approach is essential to make significant breakthroughs in this area. He demonstrates a fuel cell prototype vehicle that is able to run for 10 hours on just 5cc of fuel, which can be derived from biomass.

His team has achieved major breakthroughs in the innovation of new high-performance DAFC electrodes and their direct ethanol fuel cell breakthrough led to a world record in power density of 180 mW/cm².

He has also pioneered a solid state lithium-air battery with 5-6 times the capacity of lithium-ion batteries currently used in mobile phones. Its capabilities and applications for electrical vehicles are also apparent.

"I think electric cars will happen in HK- the distribution of charging points and battery life are the two key barriers," he says.

Perhaps the most exciting research area, because of its direct applications and suitability for the large scale energy storage required by renewable power sources, is the Vanadium Redox Flow Battery (VRFB).

A flow battery is charged and discharged by a reversible reduction-oxidation reaction between the two liquid vanadium electrolytes of the battery. Unlike conventional batteries, electrolytes are stored in separated storage tanks, not in the power cell of the battery. During operation, these electrolytes are pumped through a stack of power cells, in which an electrochemical reaction takes place and electricity is produced.

"Power and storage capacity are decoupled so the system becomes very easily scalable for large scale storage projects," says Zhao. This technology is widely regarded as the key to increasing the proportion of renewable energy on the grid, but there are still barriers to overcome. Efficiency loss due to species cross-over, low density due to insufficient active sites provided by electrodes and a lack of knowledge of coupled transport phenomena in trans-scale VRFB systems, are among the most difficult issues to address.

"If you were an investor, I would advise you to invest in all three technologies but maybe the flow battery first," admits Zhao.

"We are leading the world in this research. We have the unique theory of thermo-electrochemistry but this is half the story. My background is in heat transfer technology not pure chemistry and this area is the fusion of thermo-fluid science and electrochemistry," he says.

"It’s an interdisciplinary field that particularly applies to advanced energy storage systems. It's thermo-electrochemical theory," says Zhao and adds that it is the theoretical breakthroughs that have enabled significant improvements in these three key storage technologies.

Professor TS Zhao, PhD is Chair Professor of Mechanical & Aerospace Engineering, HKUST, Director of HKUST Energy Institute and Senior Fellow of HKUST Jockey Club Institute for Advanced Study. He is an elected Fellow of the American Society Mechanical Engineers (ASME), Fellow of the Royal Society of Chemistry (RSC), and a Highly Cited Researcher in Engineering by Thomson Reuters (2014, 2015 and 2016). In addition to four edited books, 10 book chapters, and over 60 keynote lectures at international conferences, he has published more than 280 papers in various prestigious journals. Prof Zhao received a Croucher Senior Research Fellowship in 2008.

To view Zhao's personal Croucher profile, please click here.