A novel method from Imperial College London allows scientists to measure oxygen production during solar water splitting in real time. This breakthrough has revealed hidden inefficiencies in the process, offering new insights for the development of clean hydrogen technologies.
The research team discovered that electrical current does not always directly correlate with oxygen generation in hematite, a widely studied material in this field. This finding challenges the long-held assumption that electrical current accurately reflects oxygen output, highlighting a previously unrecognised limitation in the reaction. The study, led by Dr Flurin Eisner and Dr Daniele Benetti, involved collaborators including Professor Ifan Stephens and Professor James Durrant.
The team identified a "selectivity switch" where, at low current levels, electrical charge was diverted to competing surface reactions instead of oxygen production. Once sufficient positive charge accumulated on the material's surface, oxygen generation became significantly more efficient, reaching approximately 80% efficiency. This behaviour was also observed when the reaction was driven electrically in the dark, suggesting it is a fundamental property of hematite.
This discovery was made possible by a custom photoelectrochemical mass spectrometry (PEC-MS) platform developed at the Royce at Imperial facility. This sensitive equipment provided the first direct comparison between oxygen production and electrical current under operating conditions, revealing behaviour that would have otherwise gone unnoticed. Dr Eisner noted the crucial role of the EC-MS equipment and the support for developing a light-compatible cell, stating its sensitivity was key to measuring oxygen at rates where current alone would have been insufficient. Professor Ifan Stephens expressed pride in the paper, highlighting how multiple techniques, including electrochemistry and mass spectrometry, can reshape mechanistic understanding.
The findings offer a new avenue for evaluating and optimising materials for solar fuel production by directly measuring oxygen generation. The team plans to apply this approach to other metal-oxide materials, such as bismuth vanadate and titanium dioxide, to determine if this behaviour is widespread. The technique could also serve as a screening tool for new materials, identifying currents that do not lead to the desired products. Further applications are being explored in carbon dioxide and nitrogen reduction reactions.
