Nature Inspires High Speed Hydrogen Production
Chris - We're joined by Dr. Morris Bullock, one of the scientists behind the work. Hello, Morris.
Morris - Hello.
Chris - Thank you for joining us on the Naked Scientists. Kick off if you would, and tell us, what was the actual goal of the work when you started? Why were you doing this?
Morris - The goal of our research is to develop ways to convert between electrical energy and chemical energy. And the reason is that we all hope that in our future we'll be using a lot more renewable sources, such as solar power and wind power. To make that as effective as possible we need to have ways to store the energy. Of course there are going to be times that we want to have energy usage or electricity available when the sun's not shining, or when the wind is not blowing, and so it's important to have a greater use of these renewable sources, and that we find a way to convert electrical energy to chemical energy.
Chris - So in other words, you put the electricity into hydrogen, and you want to be able to do that efficiently, and then get the energy back out of the hydrogen again later when the sun's not shining.
Morris - That's exactly correct. We're taking electricity. We're doing an electrochemical experiment. We convert the electricity; we take two electrons and two protons and we convert them into hydrogen. That way we store the electrical energy in the form of a chemical fuel that is, in our case, in hydrogen. Then we have that hydrogen. It would be available at the time that you need electricity, and then we would run the reaction in exactly the opposite way. That's what happens in a fuel cell, you run hydrogen into the fuel cell to get electricity back out. And so, the catalyst that we just recently developed converts electricity into hydrogen much more quickly than the previous catalysts.
Chris - What exists in nature to do this and what's wrong with the natural form? Why can't we just use that?
Morris - Well, the ones that nature has are amazingly efficient. They're terrific catalysts, but they exist in hydrogenase, that's found in microbes, and that kind of thing in nature. The problem is they exist in a very specific biological environment and are not often that stable outside of their natural environment.
Chris - So what is it that you've been able to do and how have you used what those bacteria, those microbes with hydrogenases, do to inform building this new catalyst?
Morris - What we've done is to look at what the hydrogenase enzymes look like. Then what we tried to do is to emulate just the important functional features. In particular, we know that the hydrogenase enzymes are based on metals like iron or nickel, and so these are cheap metals as opposed to a precious metal like platinum. The second key feature of what we've seen is that one of the key chemical features of the hydrogenase enzyme is what we call a pendant amine. That's just the nitrogen containing group that has a basic site and that helps to move the protons. What we've done is to incorporate that amine functionality, that basic site to move protons into the structure, and we found that being able to move protons more efficiently makes a huge difference in having a fast catalyst.
Chris - So rather than having to rely on an enzyme, which is protein based and therefore more difficult to work with, you've been able to make a solid state. Basically, a crystal architecture, with various chemicals in just the right places to do this chemical reaction. But how do you build that catalyst? How do you get those chemical groups, including the nickel and the iron you mentioned, in just the right place? So that the reaction happens as well as it does, or better, with the enzyme, but without having to use an enzyme?
Morris - These were just made up in the laboratory, so these are completely synthetic molecules. We assemble a ring containing two phosphorus atoms to bind to the metal, and then between the two phosphorus atoms is a nitrogen that has the amine. And so then we attach that to a nickel. In this case it's just a nickel catalyst, not any iron involved in this so it's just one nickel molecule that has two - what we call ligands - that is a chemical attachment to the metal, and has the amine attached. We synthesise that in the lab and then we do the experiments where we look at the conversion of electricity to hydrogen.
Chris - And how good is it compared with what microbes can do?
Morris - The fastest reported rate for natural hydrogenase enzymes is a turnover - that's we call the turnover frequency - of 9,000 per second. The one that we have recently made turns over at 100,000 times per second, so it's approximately 10 times faster than the natural hydrogenase enzyme.
Chris - And is it economically and scientifically viable to actually make this stuff on the kind of scale that we would need if we were to try and do this industrially?
Morris - I think this one would not be economically viable to use in its present form. We're studying fundamental science and we think that the discoveries that we've made will be helpful in showing us how to take the next step of making one that would be even better, but even though this is a very fast rate, the efficiency is not good enough at this point to really make it so viable for implementation in an industrial type of setting at this point.
Chris - So a little bit more work to do, but still, congratulations - a wonderful study. Morris Bullock there. He's from the Pacific Northwest National Laboratory in Washington State and you can find that paper published this week in the journal Science.