Elevated atmospheric CO2 concentrations are changing the radiative balance of the Earth’s atmosphere while incomplete combustion of hydrocarbons, e.g. leading to smog, has caused large degradation of environmental quality. These realities clarify the need to transition to an alternative energy economy. One attractive possibility is an economy based on the combustion of molecular hydrogen (H2). H2 is rare at the Earth’s surface. However in most locales the most abundant source of elemental hydrogen, i.e. H, is water, H2O. It’s thus natural to ask why not generate H2 by water splitting? This reaction is strongly unfavourable but if a renewable source of energy is used to induce it this is not a conceptual obstacle.
Water-splitting devices require solids that can donate electrons to and accept electrons from liquid H2O. The importance of such solids has been appreciated for decades but finding them has proven surprisingly challenging. The logic of SOLWET is that this materials quest has been limited by a lack of physical insight into the mechanism by which electrons move across the solid/water interface. Even for the most studied systems well established experimental observations exist that are difficult to rationalise with existing mechanistic understanding.
SOLWET addressed this challenge by performing experiments in which we watch the journey of the electron either from water to solid or solid to water, for the prototypical water splitting materials platinum and hematite (alpha-Fe2O3), in real time. We did this by initiating electron transfer in either direction using femtosecond optical pulses and probing the journey of the electron, and its correlated chemical change, using nonlinear optical and optoelectronic spectroscopies. This program has enabled the development of a new toolbox and in so doing offered insight into the curious catalytic effectiveness of platinum and quantified loss mechanisms in Hematite photocatalysis.
