At the heart of addressing energy issues are efficient systems that convert one form of energy into another. Living things have evolved spectacular systems for doing this: a plant uses the process of photosynthesis to capture solar energy and convert it into chemical energy, stored as sugars; a human eats that plant and converts the chemical energy in those sugars to heat and high energy molecules that fuel the thousands of reactions in the body.
Nature’s energy conversion systems are very efficient. They’re some of the most complex. Scientists at ENSI are striving to understand what, at the molecular level, makes natural systems efficient, and how we might emulate their tricks.
“One question that ENSI is tackling is, ‘Do you mimic the biological system or do you look at how the biological system operates and then transfer the concepts?’ ” says UC chemistry professor and ENSI co-director Omar Yaghi. “We have the advantage that we can study these biological systems and try to make use of millions of years of evolution. We can see how these systems should be put together and the principles under which they operate.”
The systems Yaghi envisions scientists designing can start with solar, chemical, heat, or other kinds of energy. The end product is a fuel or product that allows us to do accomplish something faster, using fewer resources. “The process in the middle,” he says, “is a lot of chemistry that needs to be developed.
“The question here is what happens to energy at the nanoscale?” Yaghi adds. The conversion of energy from one form to another is a well-known aspect of first-year chemistry and physics. But how does that transformation happen in the quantum world of the nanoscale? Being able to answer that question can help researchers develop new, synthetic systems that can carry out energy transformations as efficiently as biological systems, but allow for more flexibility.
Yaghi points to enzymes, the energy transformers of the biological world. Enzymes catalyze chemical reactions, making one set of molecules into a different set of molecules, often releasing energy in the process. That energy is used to power cell functions. Enzymes are highly specific, meaning they start with a very specific product and end with a very specific product. This quality is important to chemists, because it points to a way of producing very pure compounds.
But biological systems are finicky about their environments. Most energy transformations in the living world require watery surroundings that are at a particular temperature and pH. Yaghi envisions designing simpler systems that can function efficiently in a wider range of conditions. “This is the big challenge,” he says. “How does one design a system that is exquisitely controlled and very efficient, like an enzyme, while at the same time is as stable as something like a steel engine? We need ways to bridge that gap.”
To that end, Yaghi has been designing what he calls "metal organic frameworks,' or MOFs, which contain tiny spaces were catalysis can occur. “In a MOF,” Yaghi explains, “you have a backbone that can be rigid and stable. And within it you can dangle molecules that can carry out transformations that are dynamic, that can do many things that the backbone should not do.” That’s the type of structure, he believes, that scientists will need to use in designing new systems for energy capture, storage, and transformation. They will need to be heterogeneous, with parts that have different nanoscale characteristics.
Yaghi notes that we’ve become adept at making single nanoscale objects. They’re now not uncommon, and that’s a great advance. “But creating a whole system at the atomic or molecular level remains a great challenge,” he says. “Designing at that tiny level is hard. Designing a nanoparticle or system with directionality is hard. We need to learn to do these things so that we can really tackle the questions of energy transformation.”