Efficient solar-powered water splitting
Relieving dependence on the combustion of fossil fuels for energy production has numerous benefits. It could eliminate the geopolitical differences that threaten energy security and reduce emissions widely accepted to be the main cause of global climate change. Hydrogen as an energy carrier has been the focus of intensive research and development. Although hydrogen production is a large and growing industry, almost all techniques rely on hydrocarbons (fossil fuels) as the hydrogen source. Scientists launched the EU-funded project 'Modular ligands for water splitting' (WATERSPLIT) to develop novel, improved catalysts for the complex proton-coupled multi-electron transfer associated with solar-powered water splitting. In particular, they sought to create catalysts of water oxidation to oxygen and water reduction to molecular hydrogen (H2) with higher activities, specificities and efficiencies than those currently available. They focused on the use of abundant, environmentally benign and inexpensive transition metal elements. These were used to create homogenous coordination complexes consisting of a central metal cation to which negatively charged ligands are bound. Studies of product formation mechanisms and characterisation of catalytic properties led to identification of new families of highly efficient water-oxidation catalysts (WOCs) and water-reduction catalysts (WRCs). WATERSPLIT's WOCs are based on abundant and benign iron. The team provided insight into characteristics of the metal centre that affect activity, which will be useful in development of other catalyst systems and catalytic transformations. In addition, researchers identified a reaction intermediate that can be used as a model of the photosystem II complex, the first step in the photosynthetic pathway. The WRCs, based on cobalt, are equally capable of acting as photocatalysts and as electrocatalysts. Mechanistic insight and characterisation of WOCs and WRCs formed from abundant and environmentally friendly transition metal elements paves the way to rational design of more efficient catalysts. Higher efficiency of solar-powered water splitting to produce H2 could make this virtually no-emission.
Keywords
Solar-powered, water splitting, hydrogen, catalysts, modular ligands
