Study on solar hydrogen generation from water

Abstract

Water splitting for hydrogen production under solar light irradiation is an ideal system to provide renewable energy sources and to reduce global warming effects. Even though significant efforts have been devoted to fabricate advanced nanocomposite photo-catalysts, the main challenges persist, are slow reaction, lower rate of H2 evolution, high recombination rate of photogenerated electrons and holes, metal loss of powder form of photocatalyst and lower retention of reacting species on these photocatalyst that limits the feasibility of continuous mode of operation. These issues are addressed introducing alginate-based hydrogel having higher water adsorption and retention capacity to encapsulate different photocatalysts namely CdS, rGO-CdS and to form beads like Photocatalysts. The powder form of CdS and rGO-CdS as well as the beads form of alginate encapsulated photocatalysts (CdS-alginate, rGO-CdS-alginate) are successfully synthesised, characterized and tested for photocatalytic hydrogen generation under full band solar irradiation using a solar simulator. Among all the synthesised catalysts, CdS-rGO-alginate exhibits the maximum photocatalytic activity of 79.6 mmol/g. hr which is more than that of CdS -alginate (55.62 mmol/g.hr) and remarkably higher than that of pristine CdS powder catalyst (4.88 mmol/g.hr). Band pass filter of 420 nm is used in the system to evaluate the apparent quantum yield (AQY) of the process. Among all the synthesized catalysts, rGO-CdS -alginate exhibits the maximum AQY of 18.24% at 420 nm of band pass filter. It may be inferred that use of alginate having plenty of OH- groups promotes the water adsorption into its confined porous structure and causes the chemisorption of water molecules on the surface of photocatalyst (CdS/ rGO-CdS).