MIT chemistry professor Daniel Nocera (pictured at lower right) and post-doc Matthew Kanan recently unveiled a discovery that may represent a major energy breakthrough: a new compound that promises to enable large-scale adoption of truly decentralized, at-home solar power. The researchers focused on harnessing solar energy, since it enables clean, carbon-free power generation and is abundantly available. In this video clip on the discovery, Nocera puts the promise of solar in context: “In around one hour, the amount of sun that hits the face of the earth is what we use in an entire year globally for our energy.” (See the MIT Technology Review cover story on Nocera's research here.)
Until now, however, solar has been constrained by its inherent intermittency; power is only generated when the sun is shining, and storing any excess power produced during the day has been prohibitively expensive for at-home use. Batteries are costly, and solutions such as compressed air storage do not represent feasible options in small-scale applications. In places where the energy infrastructure allows it, excess power can be sold back to the grid, but this stop-gap solution is still reliant on the relative inefficiencies of our 20th-century energy system.
In contrast, the catalyst Nocera and Kanan discovered represents the crucial new component of a simple, inexpensive, and reportedly highly efficient water electrolysis system with negligible maintenance and replacement costs.
How does it work? Excess solar energy is used to split water molecules into hydrogen and oxygen for separate storage and subsequent re-combination in fuel cells when energy is needed. As Nocera points out in the video linked above, the researchers are hoping that their discovery will lead to homes that capture solar energy themselves by using their efficient process to convert sunlight into chemical energy for use when the sun is not shining.
While the electrolysis of water is a well-known process, it has traditionally been expensive due to reliance on noble metals and the inefficiencies of oxygen extraction in non-benign environments. The new catalyst that extracts oxygen consists of cobalt and phosphate covering a conducting material such as glass or graphite. These materials are widely available and thus cheap. Placed in water, cobalt and phosphate ions form a thin film on the electrode when a positive potential is applied and produce oxygen gas.
The new catalyst works well in neutral water at room temperature and under normal atmospheric pressure – in contrast to the traditional industrial water electrolysis process. The solution looks to create precisely the benign, inexpensive, and easy-to-set-up environment preferable for at-home use.
Scientists have been able to extract hydrogen from water easily for a long time, but only the simultaneous extraction of oxygen avoids the production of undesired hydroxide. Hydrogen is typically produced using platinum-based electrodes, but Nocera also announced plans for a full system design that includes a replacement for the noble metal, which would decrease the price of the energy storage system further.
Two additional aspects make the technology even more elegant. First, the cobalt and phosphate ions on the cathode exhibit a “self-repair” interaction that allows for repeated use. Second, the inputs – energy and water – ultimately yield energy and water again. Since this water can then be reused, an entire closed-loop system might be within reach.
The impact of Nocera and Kanan’s discovery can only be forecasted at this point. James Barber, professor of biochemistry at Imperial College London, gushes: “This is a major discovery with enormous implications for the future prosperity of humankind. The importance of their discovery cannot be overstated since it opens up the door for developing new technologies for energy production thus reducing our dependence for fossil fuels and addressing the global climate change problem.”
Notwithstanding, as with any emerging technology, this energy storage enabler needs to be vetted in further research and prove its economic potential for scalability. Also, the storage of hydrogen and oxygen and their recombination in fuel cells needs to become safer for reliable at-home use.
Nocera, though, is convinced: “This is the nirvana of what we've been talking about for years. Solar power has always been a limited, far-off solution. Now we can seriously think about solar power as unlimited and soon.”
Indeed, this technology could be the final link in an emerging energy system that includes distributed photovoltaics and fuel cells, electric cars, and new regulation that favors at-home energy generation. Commercializing this system will be a challenge (though we have theories on the best way to do this – see this article and chapter 5 of The Innovator’s Solution), but true clean energy decentralization, which promises enormous efficiency and environmental benefits, could be closer than commonly assumed.
