2001
Role of Surface Amorphization in CuO-Cu2o Core-Shell Nanowire Array for Photoelectrochemical Water Splitting

Tuesday, 26 May 2015: 11:40
Conference Room 4D (Hilton Chicago)
F. Wu Sr. (Washington University in St. Louis), S. Banerjee, Y. Myung (Washington University in St.Louis), and P. Banerjee (Washington University in St. Louis)
We demonstrate spatial (i.e., where) and stoichiometric (i.e., how much) control of dense CuO core - Cu2O shell nanowires (NWs). These NWs are then used as photocathodes for water splitting. CuO has a narrower band gap (1.53 eV) and a higher conduction band edge compared to Cu2O (2.0 eV), thus enabling an efficient way to absorb light and convert solar energy.

Thermally grown CuO NWs under carbothermal reduction conditions lose oxygen from the surface.[1] The out-diffusion of oxygen makes single crystalline CuO transform to Cu2O. However, a 2 to 3 nm transition, amorphous Cu2O layer on the surface is formed. This transition, surface amorphous Cu2O layer crystallizes under longer reduction time. We tune the CuO core/Cu2O shell ratio by controlling the temperature and time of reduction to study the CuO NW phase transformation kinetics. We examine the phase transformation (oxygen loss) in the NWs using Raman spectroscopy and model it within the framework of the Johnson-Mehl-Avrami equation. The nature of the transformation under oxygen loss conditions in narrow 1D NWs will be presented.

The as-synthesized CuO-Cu2O core-shell NW array is systematically used to examine water splitting performance. The maximum photocurrent density measured is 2.69 mA/cm2 at 0.6 V vs. Ag/AgCl for the CuO-Cu2O core-shell NW structure with a 2-3 nm transition, surface amorphous Cu2O layer. Once the amorphous layer crystallizes, photocurrent density decreases to 0.3-0.4 mA/cm2 range. This data indicates that amorphous protection layers can improve the photocathodic performance CuO NWs.