Transition Metal Based Coordination Complexes as Catalysts for Water Oxidation An Overview

Catalysts for efficient water oxidation are critical to lowering CO2 emissions that cause global warming and future sustainable energy technologies. In nature, catalytic oxidation of water into oxygen occurs at the oxygen-evolving center of photosystem II (PSII). Not with standing its importance in biology and renewable energy, the mechanism of this reaction is not completely understood to date. Transition metal based water oxidation catalysts are one of the most active areas of research across many divisions of chemistry to investigate and extract the crucial information about the precise mechanistic pathways of this complex reaction. A detailed understanding of the mechanism of water oxidation in PSII, i.e., mechanistic pathways of water oxidation in the oxygen-evolving complex (OEC), is vital for the rational design of an artificial model. Moreover, water oxidation is a thermodynamically uphill and kinetically slow reaction. Therefore, this reaction causes a bottleneck in large-scale water splitting. Consequently, developing new and competent water oxidation catalysts (WOCs) has attracted extensive importance. This review article summarizes the progress in research on molecular catalysts based on transition metals in the homogeneous phase, emphasizing the current mechanistic understanding of the water oxidation reaction. The factors that influence the character of WOCs, such as reaction conditions, attached ligands, and transition metal centers, are discussed as well.