Trapping carrier dynamics in hetrostructured photoelectrodes by frequency modulated illumination operando XAS

Metal oxides photoanodes, such as WO3/BiVO4 heterostructures, represent the state of the art towards photoelectrochemica (PEC) water splitting, although their efficiency is still hampered by the sluggish oxygen evolution reaction (OER) and limited charge separation efficiency. Mixed Cobalt-Iron co-catalysts proved to be effective to temper such issues, however, a full comprehension of the catalytic cycle underlying such enhancement is yet to be achieved.
To this aim, steady-state operando XAS measurements proved to be a powerful tool to probe the catalyst structural and electronic features under working conditions, but fail in probing transient catalystic sites. Here, we propose a new kind of fixed energy X-ray fluorescence, where light intensity is modulated at a fixed frequency to “block” transient states in a fixed oxidation state, which now can be easily probed by continuously measuring the fluorescence signal at the edge of the absorption of the specific element.