A radically new way of producing hydrogen fuel from water — one that wasn’t even thought to be possible — has been developed by researchers at the University of Colorado Boulder. The researchers think that this new technique/system could pave the way for the mainstream use of hydrogen as a fuel.
The new technique is, essentially, is simply an enormous solar-thermal system — sunlight is concentrated on a tall central tower by a large array of mirrors, which heats the tower to temperatures as high as 2,500 degrees Fahrenheit, this heat is then redirected into a reactor containing chemical compounds known as metal oxides. As the metal oxide compound heats up, it then releases oxygen atoms, which change its material composition, causing the newly formed compound to seek out new oxygen atoms. With the “addition of steam to the system — which could be produced by boiling water in the reactor with the concentrated sunlight beamed to the tower — it would cause oxygen from the water molecules to adhere to the surface of the metal oxide, freeing up hydrogen molecules for collection as hydrogen gas.”
“We have designed something here that is very different from other methods and frankly something that nobody thought was possible before,” stated lead researcher and CU-Boulder Professor Alan Weimer. “Splitting water with sunlight is the Holy Grail of a sustainable hydrogen economy.”
As the researchers note, the key distinction between this new method and previous ones is that the new one makes it possible to conduct two chemical reactions at the same temperature. “While there are no working models, conventional theory holds that producing hydrogen through the metal oxide process requires heating the reactor to a high temperature to remove oxygen, then cooling it to a low temperature before injecting steam to re-oxidize the compound in order to release hydrogen gas for collection.”
“The more conventional approaches require the control of both the switching of the temperature in the reactor from a hot to a cool state and the introduction of steam into the system,” stated Associate Professor Charles Musgrave. “One of the big innovations in our system is that there is no swing in the temperature. The whole process is driven by either turning a steam valve on or off.”
“Just like you would use a magnifying glass to start a fire, we can concentrate sunlight until it is really hot and use it to drive these chemical reactions,” stated Christopher Muhich, a doctoral student at University of Colorado Boulder. “While we can easily heat it up to more than 1,350 degrees Celsius, we want to heat it to the lowest temperature possible for these chemical reactions to still occur. Hotter temperatures can cause rapid thermal expansion and contraction, potentially causing damage to both the chemical materials and to the reactors themselves.”
Something else to note — the conventional two-step process for water splitting is rather inefficient, wasting both time and heat. And as Weimer points out: “There are only so many hours of sunlight in a day.” So it’d be better not to waste those hours on inefficiency.
The University of Colorado at Boulder has more:
With the new CU-Boulder method, the amount of hydrogen produced for fuel cells or for storage is entirely dependent on the amount of metal oxide — which is made up of a combination of iron, cobalt, aluminum and oxygen — and how much steam is introduced into the system. One of the designs proposed by the team is to build reactor tubes roughly a foot in diameter and several feet long, fill them with the metal oxide material and stack them on top of each other. A working system to produce a significant amount of hydrogen gas would require a number of the tall towers to gather concentrated sunlight from several acres of mirrors surrounding each tower.
While the new technique sounds very promising now, it’s taken two years of hard work for the researchers to get to this point: “When we saw that we could use this simpler, more effective method, it required a change in our thinking,” stated Weimer. “We had to develop a theory to explain it and make it believable and understandable to other scientists and engineers.”
Regardless of the great potential of the new technique, the commercialization is probably still a couple of years off, according to the researchers. “With the price of natural gas so low, there is no incentive to burn clean energy,” stated Weimer, who’s also the executive director of the Colorado Center for Biorefining and Biofuels. “There would have to be a substantial monetary penalty for putting carbon into the atmosphere, or the price of fossil fuels would have to go way up.”
The research was partially funded/supported by the National Science Foundation and by the US Department of Energy.
The new research was just published in the August 2 issue of the journal Science.