Gaku Kitahara

Nitrogen and transition-metal codoped titania nanotube arrays for visible-light-sensitive photoelectrochemical water oxidation.

Vertically aligned titanium dioxide nanotube (TNT) arrays codoped with nitrogen and 3d transition metals were successfully fabricated using anodization and nitridation processes. The codoping of N and Fe yielded the highest visible-light-induced photoelectrochemical water oxidation due to bandgap narrowing of impurity levels by N and Fe.

Efficient Catalytic Electrode for CO2 Reduction Realized by Physisorbing Ni(cyclam) Molecules with Hydrophobicity Based on Hansen's Theory.

An electrochemical electrode physisorbed with Ni(cyclam) complex molecules containing tetraphenylborate ions (BPh4(-)) as counteranions shows catalytic activity for the reduction reaction of CO2 to CO in an aqueous electrolyte, superior to that of an electrode physisorbed with conventional [Ni(cyclam)]Cl2 complex molecules. The BPh4(-)-containing Ni(cyclam) is inferred as having high hydrophobicity based on its Hansen solubility parameter (HSP), with an interaction sphere excluding HSPs of water in a three-dimensional vector space. The high hydrophobicity of BPh4(-)-containing Ni(cyclam) molecules inhibits their dissolution into aqueous electrolyte and retains their immobilization onto the electrode surface, which we believe to result in the improved catalytic activity of the electrode physisorbed with them. HSP analysis also provides an optimized mixing ratio of solvents dissolving BPh4(-)-containing Ni(cyclam) molecules.