Hydrogen fuel cells are in the spotlight, but is there a dark horse in the race?
Michael Antal believes that, in the search for global energy efficiency, hydrogen fuel cells may not be the only fuel cell contender. The University of Hawai‘i researcher is betting on carbon, or more specifically, charcoal. For 38,000 years humans have been cutting down trees and burning them down to highly concentrated forms of carbon, or charcoal, to use as a fuel source. It is well known that carbon fuel cells have the potential to produce power more efficiently than the current generation of commercialized hydrogen cells. To demonstrate their theoretical potential, Antal and his team at the Hawaii Natural Energy Institute (HNEI), which is part of the University of Hawai‘i, have developed a carbon fuel cell powered by charcoal.
Purified charcoal has useful properties for fuel cells. Unlike hydrogen, carbon is extremely stable and easy to store and produce. Charcoal conducts electrical current and—unlike graphite and coal—charcoal burns easily. Antal’s carbon cell comprises a positively charged anode terminal and a negatively charged cathode terminal, like hydrogen fuel cells. In Antal’s design, these terminals reside in a liquid electrolyte solution of alkaline potassium hydroxide. The solution is pressurized to prevent it from turning to gas. The cathode is made of nickel and silver or platinum. The anode is a porous cylinder made of a ceramic compound and filled with compacted charcoal powder. A piston compacts the charcoal inside the cylinder. The piston is also used as an electrical connection point.
The electrolyte supplies hydroxide ions that interact with the carbon, creating water and carbon dioxide (CO2) and releasing energy in the form of heat. The cell takes air from the atmosphere for new oxygen and vents CO2, which is a greenhouse gas. However, unlike fossil fuels, biomass charcoal is renewable, and the plants that supply this fuel source also remove CO2 from the atmosphere. The primary difficulty with the carbon cell is uncertainty concerning the life of the aqueous alkaline electrolyte. This is a subject of intense current work. Antal envisions his fuel cell first being adapted for industrial uses. In time, Antal believes, carbon cells could be used to power cars, the Holy Grail of the fuel cell sector.
Charcoal In A Flash
As a complement to carbon fuel cells, Antal has also developed a technology that can use virtually any type of green waste, including corn cobs, coconut husks, and switchgrass, to produce fuel cell grade charcoal. His patented flash carbonization reactor consists of a vertical cylinder with an ignition element at the bottom that is enclosed by a pressure chamber. The chamber is stuffed with 1,000 to 1,500 pounds of green waste and then pressurized with air to 150 pounds per square inch. The contents are ignited and pressurized air is pushed through the canister. This causes a high-temperature flash fire that rapidly incinerates the green waste, converting it into charcoal. The process is extremely fast and efficient. Antal has reduced undesirable byproducts of the process, such as tar and combustible gases, to negligible amounts through the introduction of additional oxygen into the carbonization process.
The process can also convert other carbon-rich waste, such as automobile tires, into charcoal. The charcoal produced in Antal’s kiln can be used as a metal reductant, fertilizer, cooking charcoal, or to replace fuel coal. Antal has received more than $2 million in grants from the National Science Foundation, the North Atlantic Treaty Organization, Arrow Industries, Pacific Carbon & Graphite, the Carbon Diversion Corporation, the UH Accelerated Research Commercialization Program, and the Consortium on Plant Biotechnology Research to develop the technology. The Office of Technology Transfer and Economic Development at UH licensed the flash carbonization technology to two companies, including one Hawaii firm that plans to build flash carbonization reactors in West Oahu.
Michael Antal, Ph.D., is the Coral Industries Professor of Renewable Energy Resources at Hawai‘i Natural Energy Institute (HNEI). According to the ISI Essential Science Indicators, Antal’s publications are among the top 1% in terms of total citations earned in all fields of engineering. To conserve energy Antal uses a clothesline instead of a clothes dryer and rides the bus.