Harnessing Infrared Photons for Photoelectrochemical Hydrogen Generation. A PbS Quantum Dot Based “Quasi-Artificial Leaf”

Hydrogen generation by using quantum dot (QD) based heterostructures has emerged as a promising strategy to develop artificial photosynthesis devices. In the present study, we sensitize mesoporous TiO₂ electrodes with in-situ-deposited PbS/CdS QDs, aiming at harvesting light in both the visible and the near-infrared for hydrogen generation. This heterostructure exhibits a remarkable photocurrent of 6 mA·cm^–2, leading to 60 mL·cm^–2·day^–1 hydrogen generation. Most importantly, confirmation of the contribution of infrared photons to H₂ generation was provided by the incident-photon-to-current-efficiency (IPCE), and the integrated current was in excellent agreement with that obtained through cyclic voltammetry. The main electronic processes (accumulation, transport, and recombination) were identified by impedance spectroscopy, which appears as a simple and reliable methodology to evaluate the limiting factors of these photoelectrodes. On the basis of this TiO₂/PbS/CdS heterostructrure, a “quasi-artificial leaf” has been developed, which has proven to produce hydrogen under simulated solar illumination at (4.30 ± 0.25) mL·cm^–2·day^–1.