Ag 2 S Quantum Dots as an Infrared Excited Photocatalyst for Hydrogen Production

H 2 production using nanoscale semiconductors via photocatalytic water splitting is a much sought-after technology to curb carbon dioxide emission. Among the many challenges found to date is the search for a stable semiconductor photocatalyst responding to visible and preferably visible and IR light. Ag 2 S is a narrow bandgap semiconductor with a bulk electronic gap smaller than that needed to split water. In this work, using a solvent thermal strategy, we have increased its bandgap energy by shifting up the conduction band edge to make it suitable for the electron transfer reaction to hydrogen ions. The Ag 2 S quantum dots (QDs) were tested as both electrocatalysts and photocatalysts. As electrocatalysts, Ag 2 S QDs with an absorption peak at 800 nm (QD800) showed the highest H 2 evolution activity with a Tafel slope of 89 mV/dec with an overpotential of 0.32 V. As photocatalysts, H 2 was produced at a rate of 858 μmol h –1 g catal –1 under a white light flux of 100 mW cm –2 . Moreover, QD800 was also found to be active under only near-infrared excitation (800 ± 20 nm). This is the longest wavelength reported so far to excite a semiconductor and generate H 2 .