A highly ordered material architecture appears an ideal one for transfer of electronic charge in that the electrons can move about with great ease. Hence, in the applications noted above—dye solar cells, water photoelectrolysis, gas sensing, biofiltration, etc.—the facile movement of electronic charge leads to remarkable electronic device efficiencies. As an analogy, consider your ability to move through a (normal) randomly oriented forest in comparison with how easily you can move through a forest of trees planted in straight rows.

Furthermore, each TiO2 nanotube of an array has the same properties as the other nanotubes, so device repeatability is excellent. You don't get into a situation akin to that of single-wall carbon nanotubes, where properties vary from tube to tube in an uncontrolled and unpredictable fashion.

I entered the field by happenstance. The obstacles were simply that we were doing something for the first time, with no road maps of where we were going, just a goal.

Yes indeed. Under UV illumination nanotube arrays of extended length, we have now achieved nanotube arrays of 134 micron length (J. Phys. Chemistry, in press), which demonstrate a 16.25% water photolysis photoconversion efficiency rate (sunlight into chemical energy). This is remarkable photoconversion efficiency for such a readily synthesized, single bandgap material.

If someone could figure out how to shift the bandgap of the material so that it responded to visible spectrum light while maintaining the remarkable charge transfer properties, it would offer a practical means for putting the hydrogen in the hydrogen economy in a renewable, non-polluting, no CO₂, evolving manner.