Executive Summary : | To combat world’s increasing energy demands due to continuous depletion of petroleum reservoirs and the impact of rising CO2 emissions globally, development of sustainable and carbon-neutral alternatives to fossil fuels is highly demanded. Of the possible sustainable energy sources, only solar energy has the potential to meet the global energy demands. In this context, an attractive way of harnessing solar energy is artificial photosynthesis, where solar energy is employed to split H2O into O2 and a fuel, H2. Owing to its natural abundance, H2O would be the ideal source of reducing equivalents, i.e. protons and electrons. However, the development of efficient catalysts for the oxidation of H2O remains a bottleneck in the development of technologies for the conversion of solar energy into fuels. The light-driven H2O splitting requires the cooperation of several intricate processes, such as (i) light absorption, (ii) charge separation, (iii) oxidation of H2O and (iv) reduction of the generated protons. To catalyze such an energy demanding reaction as H2O oxidation, the catalysts should be able to accumulate several oxidizing equivalents, forming the essential O–O bond, and operate close to the thermodynamic potential. The design of artificial water oxidation catalysts (WOCs) thus represents a fundamental challenge in schemes for artificial photosynthesis and has therefore been the major focus of research. Another the most promising approach for hydrogen fuel generation is electrochemical water-splitting to store renewable electricity in the form of H2. Hydrogen can be generated in a water electrolyser consisting of a hydrogen evolution reaction (HER) cathode and an oxygen evolution reaction (OER) anode. Recent developments on electrochemical water splitting catalyst mainly based on metal-oxide and nanostructured catalyst, however development of cost-effective efficient water oxidation catalyst is a key challenge which is yet to be addressed. In this work we will try to develop new types of electrochemical/photochemical catalysts for water oxidation/splitting using cheap 3d -transition metals like (Mn, Fe, Ni, Co, Cu). The introduction of the organic or metal-based chromophore site in the catalyst ligand framework will act as antenna to harvest light energy that will help to achieve and stabilize higher oxidation states of the catalyst metal-center, the actual sight of photochemically driven water oxidation. The use of mono, bimetallic centres with pincer and open and/or cyclic Nn-, NnOn- type ligands systems of varying denticity and the ability of ligand modifications at the carbon skeleton will effectively tune the redox potentials of the water splitting catalyst. Efforts to trap and characterize reactive metal-oxygen species proposed the catalytic cycle of the water oxidation reaction will also help us understand the mechanistic insight of O-O bond formation and H2 evolution reactions. |