Effect of Wavelength-Scale Cu2O Particles on the Performance of Photocathodes for Solar Water Splitting

Abstract

Grain particle size-controlled Cu2O structures were fabricated by oxidizing copper microfilms by soaking them in a 4 M NaOH solution. A microfilm of Cu2O was obtained from one-step heating (80 degrees C for 1 h) of a multilayered film of Cu/Au/Ti (1000/50/10 nm) on a glass substrate followed by naturally cooling under ambient conditions. On the other hand, molding by a micro contact stamp during fabrication of the Cu2O structure was carried out to obtain Cu2O structures with a relatively smaller particle size than that of the Cu2O microfilm, which was obtained by confinement of the Cu2O crystal growth within the molded space of the micro contact stamp. The Cu2O phases in the microfilm and the molded Cu2O samples were confirmed with X-ray diffraction, micro-Raman spectroscopy, and diffuse reflectance spectroscopy. The light absorption capabilities of the Cu2O samples were characterized by finite-difference time-domain simulations; the wavelength-scale particle size resulted in absorbance enhancement near the Cu2O band gap, and the mirror effect of the Au film underneath the Cu2O samples strengthened the absorbance over the entire monitored wavelength region. Moreover, photoelectrochemical characterization proved that the photocurrent of the wavelength-scale Cu2O particles (obtained with the molding procedure) increased by approximately 2-5 times in the cathodic process, and the onset potential decreased by approximately 0.3 eV compared to that of the Cu2O microfilm. The enhanced light absorption and relatively large surface area, due to the wavelength-scale particle size of Cu2O in the molded sample, would result in an enhancement of the photocatalytic activity of Cu2O materials.