Nanotech for energy

We have nanotech for medicine, manufacturing, and computation. Why not energy?

Nanotechnology is advancing in other fields

We don’t give it that name, but nanotechnology has been progressing rapidly in several fields.

For example, as I noted in Modular Peptide Nanotechnology, biochemistry is the original nanotechnology:

Proteins perform virtually all biological functions and are responsible for synthesizing every structure in your body. The fact that these biomolecules can be used to create motors, perform chemical synthesis, construct macroscale structures, and manipulate light suggests that they may be a good basis for nanotechnology.

Biotechnology has leveraged this towards developments in medicine, protein design, and gene editing that have been nothing short of miraculous. These breakthroughs are commonplace nowadays; the mRNA COVID vaccines leveraged two nanoscale innovations: lipid nanoparticles and designer mRNA, to save millions of lives.

Not to be outdone, semiconductor manufacturing has given us the ability to pattern materials at the nanoscale, mostly to make computers. The industry has roadmaps to produce better chips for another decade and has expanded into producing MEMS, metamaterials, microfluidics, and other incredible technologies. The future of lithography is bright, as I detail here.

In academia, chemists and materials scientists have moved to making ever more arcane structures such as metal-organic frameworks and topological insulators. On top of all this, research accelerants such as computational chemistry, computational design, and self-driving labs continue to improve.

But there’s something missing here; nanotechnology has contributed to medicine, manufacturing and computation but hasn’t really impacted energy, a pillar of society. What follows is a highly-speculative exploration of what it would take to change energy production with our newfound control over the nanoscale.

Photonics and metamaterials

One emerging opportunity is using nanotechnology to manipulate light. This falls under the heading of fields like photonics and metamaterials. Single-junction solar panels have an inherent efficiency limit of 33%. Multi-junction cells and solar concentrators can boost efficiency, but it’s looking difficult to break 50% efficiency with current techniques.

Fancy photonic designs can do much better, 87% in theory. Solar is so cheap right now that it doesn’t make sense to build these kinds of panels, but perhaps the cost of lithography could fall enough to make it worthwhile. Nanoimprint lithography could be used for roll-to-roll production of nanostructured films with higher efficiency while using less material.

High efficiency, narrow wavelength solar cells are also valuable for wireless energy transfer. If you can efficiently convert energy into laser light and hit a faraway solar panel, you can transfer energy between the two points. Alternatively, it’s possible to transfer energy over a fiber optic cable. Wireless power can help address the intermittency of renewable energy, or enable space-based solar, but I doubt these will be competitive with solar and batteries in the near term.

Nuclear batteries

Source

Nuclei can store incredible amounts of energy, if only we could control them better. Nuclear batteries are an attempt to utilize the incredible energy density of radioactive materials. Unfortunately, unlike nuclear reactors, these batteries cannot increase the rate of fission, meaning that we have to wait for nuclei to decay on their own. Unless you’re using something highly radioactive (read: dangerous and expensive), these batteries can only generate a trickle of energy¹.

Fortunately, nuclei can also store energy in metastable nuclear states. These states involve rearrangements of the protons and neutrons in nuclei, not destructive processes like fission or fusion. One of the most interesting elements in this regard is hafnium. However, further investigation into using hafnium to store energy haven’t been promising.

Ideally, we would find an nuclear state that we can “load up” with energy from gamma rays or x-rays and then stimulate the atom to give up this energy precisely when we want. Assuming we can find such a nuclear state, scaling energy storage into a small package requires several advances. The first step involves manipulating single atoms on a chip, this is already possible with some implementations of ion trap quantum computers. Next, planting these nuclei into a small metal cavity will help the atom interact strongly with incoming light. Finally, there needs to be a system of waveguides that can redirect and process the energy that the atom releases. This is particularly difficult because the x-rays and gamma rays coming out of the nucleus are inherently hard to control.

A similar system could potentially be used to do nuclear fission at the nanoscale, where the incoming gamma rays would induce fission and spent nuclei would be shuttled in and out of the chip and substituted for fresh ones. Scaling down fission is even harder because it typically releases energy in the form of neutrons. You need high temperatures to get any sort of efficiency, and high temperatures usually destroy nanostructures. Targeting a form of fission that doesn’t release neutrons could work, but it’s hard to see what advantage this would have over metastable nuclear states while adding a lot of complexity.

Fusion

The ultimate energy system would be a nanotechnological fusion device. Able to “store” massive quantities of energy in relatively abundant fuel, controlled fusion can quite literally take us to the stars. Miniaturizing fusion would bring science fiction to life. Hoverboards, laser pistols, you name it; packing a lot of energy into a small space is the main barrier to all sorts of bizarre gadgets.

Fusion requires incredibly high temperatures to get nuclei to collide at high speed and the energy output is usually in the form of neutrons. Like we discussed, both of these things are usually incompatible with nanostructures.

To avoid the problem of losing energy to neutrons, some form of aneutronic fusion would be necessary. Assuming that we can figure out how to do this at a large scale, miniaturizing it without high temperatures will require something like a chip-scale particle accelerator. One way to do this would be to miniaturize a plasma wakefield particle accelerator. This technology is still in its infancy, but if they become practical for particle accelerators, using a pair of them to smash nuclei together could work.

Antimatter

Antimatter has an energy density far higher than even fusion fuel. Fortunately, it’s hard to make the stuff, which is why we exist today. But small amounts of antimatter could power long lasting batteries and starships. The company positron dynamics is actually working on this application!

The process for producing antimatter seems too energy-intensive for nanotechnology to be of much help (though perhaps wakefield accelerators could find a use here too). However, moving and storing single atoms could be pretty useful for storage. Some nuclei produce positrons as part of their decay. An on-chip ion trap could potentially capture positrons from these atoms and recombine them with ordinary matter in a controlled fashion to produce energy, though capturing the high energy photons that result could be challenging.

Conclusion

The main thing separating us from sci-fi futures is being able to produce, move, and store huge quantities of energy at small scales. Better solar cells and batteries are one step in that direction, but the ultimate application would be unlocking the energy of nuclei at the nanoscale.

Looking at these challenges, it’s clear why nanotechnology hasn’t revolutionized energy. These ideas will have to wait for significant advances in lithography, cavity electrodynamics, and nuclear physics. As for what kinds of things can be researched in the near term, metastable nuclear states and plasma wakefield accelerators probably deserve more attention than they’re already getting.

1. This can still be useful in things like remote sensors and secure hardware. These batteries can last for a very long time!