Ag2S Quantum Dots as an Infrared Excited Photocatalyst for Hydrogen Production

H2 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. Ag2S 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 Ag2S quantum dots (QDs) were tested as both electrocatalysts and photocatalysts. As electrocatalysts, Ag2S QDs with an absorption peak at 800 nm (QD800) showed the highest H2 evolution activity with a Tafel slope of 89 mV/dec with an overpotential of 0.32 V. As photocatalysts, H2 was produced at a rate of 858 μmol h–1 gcatal–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 H2.