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  Invitation of Applications for the Second Round of the
Theme-based Research Scheme

  Partial Nitrification from Ammonia to Nitrite by Enriched Ammoniaoxidizing
Archaea in Sewage

  FlexiBOL®: Flexible Street Bollard and Railing System for New and Changing Urban Environment

  Development of Highly Efficient Semiconductor Nanoparticles as
Photocatalysts for the Degradation of Organic Pollutants in Water under
Visible Light

  Coupled Heat and Mass Transfer in Passive Silicon-based Direct Methanol Fuel Cells

  Liquid-filled Glazing Technology

  A Novel Magnetic-geared Electronic-continuously Variable Transmission
Propulsion System for Hybrid Electric Vehicles

  Areas of Excellence Scheme Project: Achievement Summary of The Institute
of Molecular Technology for Drug Discovery and Synthesis

  Areas of Excellence Scheme Project: Molecular Neuroscience: Basic
Research and Drug Discovery

The topic:
Environmental concerns and sustainable development call for a new generation of energy-conversion technologies to replace the existing fossil-fuel, combustion-based energy systems. Due to their inherent advantages, such as high efficiency and low/zero emission, fuel cells have become one of the most attractive energy-conversion technologies. Hydrogen is the cleanest and most efficient fuel for fuel cells. However, the widespread commercialization of hydrogen-fed fuel cells is limited by the significant challenges in the production, transportation and storage of pure hydrogen. Liquid methanol is an ideal alternative to hydrogen. This hydrogen-rich fuel offers multiple advantages over pure hydrogen, including higher energy density and ease of transport, storage and handling. For this reason, interest in developing direct methanol fuel cells (DMFCs) has grown rapidly all over the world in the past decade.

One of the key challenges to the widespread
commercialization of this type of fuel cell, however, is its low power density. In addition
to the sluggish electrochemical oxidation of methanol and the methanol crossover problem, two challenging problems lead to low power densities in conventional DMFCs. One is the cell’s inability to handle the crossing over of excess water that evolves during fuel cell operation to the cathode. The other is that conventional designs render too much heat loss, resulting in a rather low cell operating temperature. Solving these two problems requires extra attention to be given to thermal and water management.

A model car powered by our prototype micro-DMFC

Methodology used:
In this project, we set about solving the abovementioned problems. First, we designed and fabricated a prototype micro-DMFC using microelectromechanical system techniques. The micro-DMFC not only facilitates the effective removal of water from the cathode, but also provides a higher cell operating temperature. We then developed a theoretical model that incorporates the effects of coupled heat and mass transfer, and electrochemical kinetics as a simple but robust tool for the design and optimization of the passive micro- DMFC. Finally, we investigated theoretically and experimentally its heat and mass transfer behavior.




Prof Tianshou Zhao

Key findings and implications:
A New Type of Fuel Cell: We have developed a new type of DMFC that requires neither liquid pumps nor gas compressors. This type
of passively operated fuel cell can achieve a maximum power density of about 30 mW/cm2, which is the highest performance reported in the open literature. This work has been published in Electrochemistry Communications, one of the most prestigious journals in the field of fuel cells. The paper has been awarded the Most Cited Article Award of the Journal. In addition, since this type of DMFC is the most competitive candidate to replace conventional batteries, the prototype was the subject of a feature article in Fuel Cells Bulletin (ISSN 1464- 2859, February 2005), an international newsletter that publishes technical and business news for the worldwide fuel cells sector.

A New Hydrogen Generation Technique: According to conventional wisdom, the DMFC is an electrochemical device that generates electricity. However, we recently discovered that hydrogen can evolve spontaneously from the DMFC. We proposed a theory that predicts the peculiar phenomenon of hydrogen evolution. This work has been published in Electrochemical and Solid-State Letters , a top-rated electrochemistry journal. This discovery has led to a new technique for producing hydrogen at room temperature without the emission of carbon monoxide species which is common with conventional methanol-reforming technologies. In addition, the discovery of hydrogen evolution in the DMFC has led to many other inventions in our lab, for example, a new method to activate DMFCs (Electrochemical and Solid-State Letters 8 A549-A553, 2005), a new method for measuring the rate of methanol crossover (Journal of The Electrochemical Society 152 (11) A2238-A2245, 2005), and an accurate method for measuring the electric potential of anodes and cathodes (Electrochemical and Solid-State Letters 8 A211-A214, 2005).

Prof Tianshou ZHAO
Department of Mechanical Engineering
The Hong Kong University of
Science and Technology