Real-time oxygen measurements expose hidden losses in solar water splitting
A new technique developed at Imperial College London measures oxygen production in real time, revealing hidden losses in solar water splitting. The researchers found that electrical current did not always correspond to oxygen generation in hematite, one of the most widely studied materials in the field, revealing a previously unknown limitation in the reaction.
A groundbreaking technique developed at Imperial College London has revealed previously unknown limitations in solar water splitting, a process crucial for creating solar fuels and green hydrogen. Researchers discovered that electrical current does not always accurately reflect oxygen generation during this reaction on hematite, one of the most widely studied materials in the field.
Lead researcher Dr. Flurin Eisner, now at Queen Mary University of London, explained that at low current levels, electrical charge was diverted into competing surface reactions, reducing oxygen production. However, once sufficient positive charge accumulated at the material's surface, oxygen generation became highly efficient, reaching around 80% efficiency.
This "selectivity switch" was observed even when the reaction was driven electrically in the dark, suggesting it is a fundamental property of hematite rather than a light-specific effect. The findings challenge the common assumption that electrical current directly corresponds to oxygen production, offering researchers a more accurate method to identify and improve materials for solar fuel and green hydrogen technologies.
The study utilized a custom photoelectrochemical mass spectrometry (PEC-MS) platform developed at Imperial College's Royce facility in White City. This advanced technique allowed for real-time measurement of oxygen production while simultaneously illuminating the sample, measuring photocurrent, and monitoring oxygen generation throughout the reaction.
PEC-MS enabled the team to compare oxygen production with electrical current, uncovering behavior that would have remained hidden using traditional methods. Dr. Daniele Benetti, co-author from Imperial's Department of Chemistry, emphasized the importance of combining multiple techniques – electrochemistry, operando optical spectroscopy, and electrochemical mass spectrometry – to gain new insights into the reaction mechanism.
The researchers now plan to apply this approach to other metal-oxide materials and explore its potential in a broader range of energy-conversion reactions, such as carbon dioxide and nitrogen reduction.
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