To dig small tunnels one needs small tools, so when you want to dig the smallest tunnels you need the smallest tools. Researchers at the Karlsruhe Institute of Technology and Rice University have successfully dug tunnels between one and 50 nm wide in a piece of graphite. Tunnels like these could be of great use in medical and battery technologies.
To dig the tunnels the researchers placed nickel nanoparticles on the graphite samples, and put the combination into chamber filled with hydrogen gas. Heating the chamber caused the nickel to act as a catalyst for the carbon and hydrogen, which combined to form methane. As carbon atoms from around the nanoparticle leave the graphite to become methane, a hole is formed which the nanoparticle is drawn into, allowing it to continue digging.
One of the potential uses for porous graphite is as the electrodes within lithium ion batteries. The tunnels increase the surface area of the electrode, which enables more lithium ions to attach to it either for charging for discharging. Also the tunnels could be used to store medicines that are to be released over long periods of time.