Bio-inspired Synthesis of Ultrathin Hematite Nanowires for Photoelectrochemical Water Splitting

Abstract

Hematite (a-Fe2O3) is one of the most promising photoanode materials for photoelectrochemical water oxidation due to its small band gap and abundance. However, there still remain many problems to be solved for its practical application such as its short hole diffusion length (on a few-nanometer scale) and high overpotential for water oxidation. In principle, these problems can be easily solved by synthesizing ultrathin nanostructure of hematite and modifying its surface with water oxidation catalysts. While the latter issue can be easily addressed, the former cannot be done because of the difficulty to synthesize ultrathin hematite nanostructures. In this regard, we have studied the bio-inspired synthesis of ultrathin hematite nanowires by using ultrathin M13 virus nanowires as a template for the controlled hydrolysis and condensation of the sol-gel precursor for its synthesis. By incubating the positively charged precursor molecules with negatively charged viral nanowires at low temperatures overnight, we could concentrate the precursor molecules near the viral nanowires and readily grow ultrathin nanowires of FeOOH, which can be converted to hematite by annealing at high temperatures in air. It was found that the diameter of hematite nanowires can be easily controlled from few tens of nanometers to hundreds nanometers by varying the concentration of the precursor solution and reaction temperature. We also found that our ultrathin hematite nanowires have a high photocatalytic activity for water-splitting. We believe that our findings provide an green and alternative ways to fabricate ultrathin nanowires of various functional materials.