Semiconductor quantum dot-sensitized rainbow photocathode for effective photoelectrochemical hydrogen generation

Significance Photochemical water splitting is the most desirable transformation in a non–carbon-based conversion of photon energy into stored chemical potential. The system described here to carry out this transformation is a photoelectrochemical (PEC) cell in which CdSe quantum dots (QDs) on a NiO surface serve as light absorbers, and a metal complex in solution acts to assemble the two protons and two electrons into H 2 . The present report extends prior work significantly with the construction of a “rainbow” photocathode by spin-coating different-sized QDs in a sequentially layered manner, thereby creating an energetically favorable gradient for charge separation. The resultant rainbow photocathode exhibits enhanced light-harvesting ability under white LED light illumination and an increased photoresponse relative to a single-sized CdSe QD-sensitized photocathode.