Researchers Quest for Green Hydrogen
Last week, we talked about ultra-capacitors, and their potential for handling high power demands in electric vehicles, allowing battery chemistry to move towards higher energy formulations that could ultimately extend cruising range. But even with this enhancement, battery-powered EVs will have competition. Vying for the lead role in a carbon-free travel future are hydrogen fuel cell electric vehicles that offer the advantage of a quick fill-up/recharge that plug-in electric vehicles will likely never have.
Likewise, in the utility sector, with wind and solar playing increasingly significant roles, there will be an ever-growing need for storage on a large scale. If a clean, cost-effective means of producing hydrogen in large quantities can be developed, it could potentially form a bridge between renewable electricity and transportation that could complete the picture of a no-compromise clean energy future.
Most people don’t realize that hydrogen is already a $100 billion market, being used, for gasoline refining, jet fuel, metals, ammonia, hydrogenated foodstuffs, and more. It is mainly produced through steam reformation of natural gas or coal, a process that produces CO2 as a byproduct. Hydrogen can also be produced by splitting water into its constituent parts through electrolysis, which is theoretically clean, but energy-intensive. This is why the search for a scalable, clean process with lower energy demands has taken grail-like significance in certain research circles.
Followers of Biomimicry might ask, how does nature do it? The answer is photosynthesis, an energy storage process that has evolved over billions of years, which uses sunlight to split water, though the hydrogen is incorporated into an intermediate molecule called NADH, a precursor to the production of carbohydrates. And while it’s not super-efficient, given the abundance of natural sunlight, it really doesn’t have to be.
I took a little trip through the world of hydrogen research, and here’s what I found.
A company called H2OPE is developing a bio-hydrogen process using algae. They have a patent for a process that modifies hydrogenase, the enzyme that creates hydrogen, making it more productive. Ordinarily algae only produce hydrogen in the absence of oxygen. But H2OPE’s modified enzymatic process is far more tolerant of oxygen, which is a natural waste product of photosynthesis. They have already demonstrated a 400-fold increase over the natural photosynthetic process and are hoping to squeeze out another factor of 10 using a bio-engineering process call directed evolution, a technique that allows hundreds or even thousands of variants to be evaluated at a time. I asked Scott Plummer, CTO, if improvements are getting progressively more difficult. He said, not necessarily. It’s a bit like a game of Battleship. Once you get a hit, you have a much better idea where to aim.
The company is still in the early stages of development. They have relocated from Denver to Delaware where they will continue to refine their process.
Here’s how it would work. You get a large vat and start breeding algae in it. It could be indoors or outdoors. The algae do well at room temperature (59-95ºF). They require light, and some form of carbon-based food which could be carbon dioxide, presenting an opportunity to provide sequestration. Some have suggested combining algae production with a fossil fuel power plant, though it’s not clear whether contaminants (e.g. NOx, SOx) would be toxic to the algae. Since the algae give off oxygen, another possibility is a pairing with wastewater treatment facilities that need oxygen to help treat the waste. This is already being done.
One other key factor is that hydrogen production from algae is a continuous process, unlike most other biofuels that involve batch processes. In a sense, it’s more like a dairy than a beef operation. The algae continuously produce the gas, except for a brief time when they are reproducing. Ultimately, hydrogen produced from algae in this way, could prove to be less expensive, and greener, than hydrogen derived from natural gas. The projected combined capital and operating cost required to produce 5 million scf of hydrogen annually from algae will be $7.8 million, compared with $27.6 million to produce the same amount from natural gas.
At the University of Rochester, Rich Eisenberg and Todd Krauss have made several key advances in developing a form of artificial photosynthesis that could also potentially meet the hydrogen production challenge. According to Eisenberg, “The goal is just to take water, sunlight, and some black box that will convert that into oxygen and hydrogen which could then be fed into a fuel cell so that you could then get useful electrical work out. We’ve focused our efforts on the half-reaction that produces hydrogen from water. In order to do this you need three components: a light absorber, a catalyst and a source of electrons that will take protons from water and make it into H2. This has been standard practice for some time, but generally, the light absorber and the catalyst, in the past have contained precious metals. So, one focus of our research has been to find materials that are more abundant and less expensive.”
Using nano-particles, also known as quantum dots, they were able to create a low-cost light absorber that works well with a durable water-soluble nickel catalyst (see video). Nickel is quite abundant and far lower in cost than any of the precious metals used previously. With this “homogeneous catalysis” process, they have achieved over a million turnovers, which is the number of reactions taking place before any components need replenishment. At the same time they have seen quantum yields in excess of 35 percent, which is seven times higher than natural photosynthesis. These are significant milestones; though more work needs to be done in developing the oxygen half-reaction that will provide the electrons required to make this a closed-loop process. In the mean time, they need to add ascorbic acid to the solution to provide this function. Even so, they have attracted some interest from a major energy company.
Also exciting, is work being done by Y.H. Percival Zhang, an associate professor of biological systems engineering at Virginia Tech, producing hydrogen from the simple and abundant plant sugar xylose. The results were achieved using a novel enzyme cocktail that was produced by separating several enzymes from their native micro-organisms. These enzymes, when combined with xylose and a polyphosphate, use the energy stored in xylose to split water, producing about three times as much hydrogen as other hydrogen-producing microorganisms
This reaction occurs at low temperatures, generating hydrogen energy that is greater than the chemical energy stored in xylose and the polyphosphate — a net energy gain. The key significance of this breakthrough is the prevalence of xylose. Jonathan R. Mielenz, a biosciences expert at the Oak Ridge National Laboratory, feels that this process could reach the market in as little as three years.
Finally, researchers in Sweden, have developed a process to make hydrogen from ash. Aamir Ilyas, of Lund University has found that combining ashes and water in an oxygen-free environment can produce sizable amounts of hydrogen. He proposes using ash from municipal incinerators, which he estimates, can yield 20 billion liters of hydrogen.
That would be enough to power approximately 6 million cars, which is coincidentally, about the number of cars and trucks in Sweden.
It will be interesting to watch for news of these promising approaches as they progress.