Direct Alcohol Fuel Cell - A Sustainable Energy Technology R. Chen and T.S. Zhao Dept of Mechanical Engineering The Hong Kong University of Science & Technology Email: metzhao@ust.hk
Main Messages Background Why fuel cells Clean and efficient Challenges of H2-fuel cells H2 production, transportation, and storage Direct alcohol fuel cell technology Why DAFC Opportunities and challenges Our research activities Our prototypes - applied Summary
Background
Traditional Energy Conversion Electric current Electric generator Mechanical energy Turbine or IC engine Heat NOx, SOx Particulates CO 2 O 2 Combustion Fuel
Why so polluted? The use of fossil fuels Traditional energy conversion technologies
Fuel Cells
Fuel Cell Stack Cathode catalyst Anode catalyst H 2 O 2 Stack of several hundred Electrolyte frame Bipolar plate
What s s the big deal? Fuel is used directly, not burned! 100% emission free - only byproducts are pure water and heat. Cycle is continuous as long as fuel and oxidant are supplied, can run indefinitely. No moving parts, reliable, silent Versatile and scalable cells can be stacked to reach any desired power output - from microwatts to megawatts (Covers all markets: Batteries; vehicles; Stationary power) Efficient!
Efficiency Heat engine ruled by Carnot cycle. Max efficiency given by 1- Tc/Th. Combustion engines typically reach about 30 % chemical to mechanical efficiency. Fuel cell not restricted by Carnot cycle. Up to 70% chemical to electrical efficiency, and up to 90% system efficiency if waste heat is used.
Hydrogen Problems Producing hydrogen Electrolysis, reforming of natural gas (methane), methanol. takes more energy than to make gasoline (but more efficient). More expensive than gasoline Is it safe? Storage Energy carrier
Direct Alcohol Fuel Cell (DAFC) Tech
How does DAFC work? Methanol, Ethanol Alcohol solution Direct Alcohol Fuel Cell
Single cell structure + Load - Anode flow channel Cathode flow channel CO2 bubble e - e - Water H + e - e - Alcohol Flow field plate Cathode diffusion layer Cathode catalyst layer Polymer Electrolyte Anode catalyst layer Anode diffusion layer Flow field plate Oxygen or air with water Catalyst particle on carbon support Diffusion layer Water/Alcohol Carbon
Nafion membrane MEA Carbon cloth ~850 µm
Why alcohol? Simple molecule Less demanding on catalyst. Made from natural gas or renewable resources Low cost, sustainable. Liquid at room temperature and ambient pressure. - High energy density; readily available fuel infrastructure.
Why DAFC? The DAFC system: Greatly simplified system design (no reformer, no humidifier) Promise of high efficiency Silent operation (no noise) Operable at room temperature
Applications of DAFC Ideal for mobile applications such as laptops, cellular phones Also of great interest to the military to power individual soldiers electronics Next generation of road vehicles Distributed power generation.
Technical Challenges for DAFC 1.2 Cathode electrode Kinetic loss (200-300 mv) Catalyst development Electrode resistance Electrode potential / Voltage OCV loss due to alcohol crossover Rapid drop-off due to activation losses Linear drop-off due to ohmic losses Mass transport losses Oxygen transport (>100 mv) Alcohol crossover (25-150 mv) Electrolyte resistance Alcohol transport (25-150 mv) Electrode resistance Electrode material development Membrane modification and development Electrode material development Anode electrode Kinetic loss (200-400 mv) Catalyst development Current density
Our Activities - Overview
Our Current Focuses Material Development Nano-catalysts Membrane modifications Transport phenomena Experimental Theoretical Component design & system development
Single DMFC Power density: 250 mw/cm 2
MEA Gasket Bipolar plate Transparent enclosure
Active DMFC Stack
Micro DMFC 1x1 cm 2 MEA (1x1 cm 2 ) Silicone flow channels 1x1 cm 2 Standard steel flow channels
Our Prototypes - Applied
Fuel Cell Powered Toy Car
Fuel cell powered toy car Six-cell stack (in series) Passive operation no pump/blower Running 6 hours on 5-cc 5 methanol Rapid recharging Rapid start 5 cc
Fuel Cell Powered Fan
Twin-cell stack Passive operation Running 20 hours on 2-cc 2 methanol Rapid recharging Rapid start Fan
Fuel Cell Powered MP3 Player
Eight-cell stack (in series) Passive operation Playing for 20 hrs on 2-cc 2 methanol Rapid recharging Rapid start MP3 Player
Fuel Cell Powered Toy Train
Six-cell stack (in series) Passive operation Running 8 hours on 5-cc 5 methanol Rapid recharging Rapid start Toy Train
MP4 Player
MP4 Player
Looking ahead DAFC s have the ability to replace most power supplies Promise of clean and efficient power Cheaper catalysts needed Higher power output needed DAFC will make tremendous impacts on energy and power industries in this century
Lab Website http://www.me.ust.hk/~mezha www.me.ust.hk/~mezhao