Graphene and its composite as solar sponge for water- splitting

Dr. Manas Roy
Department of Chemistry
Indian Institute of Engineering Science and Technology, Shibpur

 

It is the billion year challenge of some early living microbes in fixing carbon dioxide to create food under geothermal and finally with solar radiation since the earth has been created. These chemo auto-trophs slowly evolved as photo –autotroph like purple bacteria and cyanobacteria to trap solar energy to fix carbon dioxide using hydrogen sulfide and finally stabilized by using water. The production of reducing equivalent or hydrogen from light-driven water splitting is the product of an environmentally clean efficient natural work machine which is one of the most enthralling aspects of the current research to mimic. To develop “artificial leaf” for water- splitting various approaches are currently being made including molecular design of ligands, semiconducting inorganic nano materials with surface modification, but there are limitations in terms of cost hurdle, sustainability and catalytic efficiency and reusability. This project aimed to catalytically produce hydrogen using visible light. Our current research led to the production of reduced graphene oxide (rGO) using ingenious inexpensive method with conductance limit similar to indium coated tin oxide glass (ITO). In addition, this rGO is stable in highly alkaline and acidic solution unlike ITO which is etched in acidic medium. This has inspired us to look at cheaper sources for isolation of graphene oxide. The composite layer of graphene and /or with varied metallo porphyrins absorbs the entire visible solar radiation. This layer may be short circuited with the ITO layered with inorganic metal oxo clusters on the opposite side. Water, as loosely attached to the metal center creating acidic proton may release electron generated by graphene/porphyrin will produce hydrogen and the oxide (hydroxide) ion from water would reach the graphene and or cationic radical of porphyrin to de-load its electron regenerating the initial state of the graphene- porphyrin composite with the evolution of oxygen and thus this will create an effective catalytic cycle.