Effect of morphology on the photoelectrochemical performance of nanostructured Cu2O photocathodes.

Cu2O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (Jph), onset potential (Eonset), band edges, carrier density (NA), and interfacial charge transfer resistance (Rct) are affected by the morphology and method used to deposit Cu2O on a copper foil. Mesoscopic and planar morphologies exhibit large differences in the values of NA and Rct. However, these differences are not observed to translate to other photocatalytic properties of Cu2O. Mesoscopic and planar morphologies exhibit similar Eg and Efb values of 1.93±0.04 eV and 0.48±0.06 eV respectively. Eonset of 0.48±0.04 eV obtained for these systems is close to the Efb indicating negligible water reduction overpotential. Electrochemically deposited planar Cu2O provides the highest photocurrent density of 5.0 mA cm-2 at 0 V vs RHE of all the morphologies studied. The photocurrent densities observed in this study are among the highest reported values for the bare Cu2O photocathodes. Although different deposition methods show a similar average photocurrent density 2.8±0.3 mA/cm2 at 0 V vs RHE, large variations in the photocurrent density are observed for samples prepared under nominally identical deposition methods.