A new production process for hydrogen could finally make widespread commercial use of hydrogen power practical and cheap. Using the power of the sun and ultrathin films of iron oxide (commonly known as rust), Technion researchers have found a novel way to generate power to split water molecules to hydrogen and oxygen.
The breakthrough, published in the online scientific journal Nature Materials, could lead to less expensive, more efficient ways to store solar energy in the form of hydrogen-based fuels. This could be a major step forward in the development of viable replacements for fossil fuels, said experts in the field.
Alternative energy technology for motor vehicles have in recent years followed a “flavor of the month” pattern, says Associate Professor Avner Rothschild of the Technion. “Now, electric cars are the technology everyone is counting on to replace fossil fuels, but a few years ago, hydrogen was the preferred solution.” This yin-yang between the two alternative energies has been going on for decades; and while solar and hydrogen duke it out, gasoline and diesel fuel continue to dominate.
The reason for that is the fact that both battery and hydrogen have their own problems. For electric battery technology, the biggest problem is producing a battery that has the enough power to allow drivers to travel hundreds of miles on a single charge, as they can with a single tank of gas. The best of today’s batteries can provide a range of only up to about 100 miles of highway driving between charges; producing batteries with a greater range using today’s technology would result in a heavier battery, which would make the vehicle carrying it heavier. The heavier the vehicle, the more battery power it needs, so the extra power wouldn’t go toward increasing the vehicle’s range.
Hydrogen fuel-cell vehicles have their own issues, such as the high cost to produce them (several of the large car manufacturers have been experimenting with hydrogen cars, and have gotten production costs down to $100,000 – still too expensive for consumers). Although hydrogen would appear to be a perfect alternative to gasoline — there’s certainly enough of it in the world, and it produces zero emissions when “burned” — hydrogen contains less energy than gas or diesel fuel, so you need a lot more hydrogen fuel than gas to go the same distance. And the fuel cells themselves are very expensive, because they use a lot of platinum.
Despite the reputation that both electric batteries and hydrogen have as “green” technologies, neither of them really is: It takes energy to produce energy, and the energy used to produce the electricity stored in batteries, as well as the power needed to split hydrogen from water to supply fuel cells, use good old oil and natural gas. Instead of eliminating the pollution associated with fossil fuels, both battery technology and hydrogen fuel cell technology, as they are used today, simply shift the pollution problem from vehicle tailpipes to the power plant.
The Technion’s hydrogen innovation has the potential to solve the problems with current production. “Our nanotechnology innovation is green, cheap, and easy to implement,” said Rothschild. “It could definitely be used for hydrogen-powered vehicles, making them much cheaper to build and operate.”
In order to produce hydrogen, you need to split water into its components, oxygen and hydrogen. In commercial hydrogen production, that work is done at hydrogen production plants powered by fossil fuels, with the hydrogen transported to where it can be used — itself a major headache, because you have to build special, expensive pipes to resist hydrogen’s corrosive properties. The Technion-developed solution avoids both those issues by utilizing the process of photoelectrolysis, using solar power to generate power to divide water molecules. Using photoelectrolysis, the Technion team’s approach solves both the storage and the electricity generation problem in hydrogen production, said Rothschild. “Our approach is the first of its kind. We have found a way to trap light in ultrathin films of iron oxide that are 5,000 thinner than an office paper. This enables achieving high solar energy conversion efficiency and low materials and production costs.”
Iron oxide is a common semiconductor material, inexpensive to produce, stable in water, and — unlike other semiconductors such as silicon — can oxidize water without itself being oxidated, corroded, or decomposed. But it also presents challenges, the greatest of which was finding a way to overcome its poor electrical transport properties. “For many years researchers have struggled with the tradeoff between light absorption and the separation and collection of the photogenerated charge carriers before they die out by recombination,” said. Rothschild. “Our light-trapping scheme overcomes this tradeoff, enabling efficient absorption in ultrathin films wherein the photogenerated charge carriers are collected efficiently.”
The cheap iron oxide collects the sunlight and converts it into energy which is then used to manufacture hydrogen. This can all happen on board a vehicle, with a small sheet of the nano-sized iron oxide film, which, combined with photovoltaic solar cells, could store solar energy for on demand use, 24 hours per day. This is in strong contrast to conventional photovoltaic cells, which provide power only when the sun is shining (and not at night or when it is cloudy).
While the technology is still at a very early stage, there has been much interest by commercial interests in what the Technion has been doing, said Rothschild. “Hydrogen has a lot of promise of an alternative fuel, but it is hard to produce and hard to store,” he said. “Our process makes both easier, enabling hydrogen to live up to its promise.”