Direct electron transfer to hydrogenase for catalytic hydrogen production using a single-walled carbon nanotube forest

The production of hydrogen through the direct electron transfer from electrode to hydrogenase was successfully performed using hydrogenase combined with a single-walled carbon nanotube forest (SWNT-forest). The SWNT-forest has a unique structure comprising dense and vertically aligned SWNTs with millimeter-scale height. The vertically aligned SWNTs became rearranged into a wall-like architecture after immersing in water. Hydrogenase was spontaneously incorporated within the SWNT-forest and confined on the sidewall of the rearranged architecture. The SWNT-forest was a very stable protein carrier in aqueous solution, and an SWNT-forest integrated with hydrogenase could easily be constructed. With a hydrogenase assembled SWNT-forest we were able to electrochemically produce hydrogen with an electron transfer efficiency exceeding 30% without the use of any chemical mediator. Furthermore, a reverse oxidative reaction of hydrogen was also successfully performed using the same device. Thus, the SWNT-forest can work as an effective and direct electron mediator for the oxidation/reduction reaction of hydrogenase. The usefulness of the SWNT-forest as a beneficial material for electrochemistry was demonstrated, underlining the potential of protein assembled SWNT-forests in fabricating highly efficient biofuel cell devices.