To make sunlight practical as a dominant source of energy a viable storage technology needs to be developed. One promising area of research is imitating the process of photosynthesis to separate the hydrogen and oxygen atoms in water to create hydrogen fuel. An MIT team led by Daniel Nocera is now reporting that nickel borate can efficiently and sustainably function as the oxygen-producing electrode in such a process, bringing the dream of energy storage systems that would allow buildings to be completely independent and self-sustaining.

Like many people, Nocera, the Henry Dreyfus Professor of Energy and Professor of Chemistry at MIT, believes that solar energy is the only feasible long-term way of meeting the world’s ever-increasing needs for energy. That is why he has focused his research on the development of an efficient way to split water using electricity that could form the basis for new energy storage systems. The systems would use energy from intermittent sources like sunlight or wind to create hydrogen fuel, which could then be used in fuel cells or other devices to produce electricity or transportation fuels as needed.

Nocera pictures small-scale systems in which rooftop solar panels would provide electricity to a home, and any excess would go to an electrolyzer to produce hydrogen, which would be stored in tanks. When more energy was needed, the hydrogen would be fed to a fuel cell, where it would combine with oxygen from the air to form water, and generate electricity at the same time.

For such systems to become viable they must be cheap and reliable. So Nocera has concentrated on the development of less-expensive, more-durable materials to use as the electrodes in devices that use electricity to separate the hydrogen and oxygen atoms in water molecules.

Now, along with postdoctoral researcher Mircea Dincă and graduate student Yogesh Surendranath, he is reporting the discovery of yet another material that can efficiently and sustainably function as the oxygen-producing electrode. This time the material is nickel borate, made from materials that are even more abundant and inexpensive than an earlier cobalt-based electrode.

Even more significantly, Nocera says, the new finding shows that the original compound was not a unique, anomalous material, and suggests that there may be a whole family of such compounds that researchers can study in search of one that has the best combination of characteristics to provide a widespread, long-term energy-storage technology.

“Sometimes if you do one thing, and only do it once,” Nocera says, “you don’t know - is it extraordinary or unusual, or can it be commonplace?” In this case, the new material “keeps all the requirements of being cheap and easy to manufacture” that were found in the cobalt-based electrode, he says, but “with a different metal that’s even cheaper than cobalt.”

But the research is still in an early stage. “This is a door opener,” Nocera says. “Now, we know what works in terms of chemistry. One of the important next things will be to continue to tune the system, to make it go faster and better. This puts us on a fast technological path.” While the two compounds discovered so far work well, he says, he is convinced that as they carry out further research even better compounds will come to light. “I don’t think we’ve found the silver bullet yet,” he says.

John Turner, a research fellow at the National Renewable Energy Laboratory in Colorado, calls this a nice result, but says that commercial electrolyzers already exist that have better performance than these new laboratory versions. “The question then is under what circumstances would this system provide some advantage over the existing commercial systems,” he says. For large-scale deployment of solar fuel-producing systems, he says, “the big commercial electrolyzers use concentrated alkali for their electrolyte, which is OK in an industrial setting were engineers know how to handle the stuff safely; but when we are talking about thousands of square miles of solar water-splitting arrays, and individual homeowners, then an alternative electrolyte like this benign borate solution may be more viable.”

The original discovery has already led to the creation of a company, called Sun Catalytix, which aims to commercialize the system in the next two years. The latest research findings appear in the journal Proceedings of the National Academy of Science (PNAS).