London scientists catch a hidden leak in the solar fuel that could power green hydrogen

Solar water splitting — using sunlight to crack water into oxygen and hydrogen fuel — has long been judged by measuring electrical current. But Dr. Flurin Eisner and Dr. Daniele Benetti at Imperial College London built a custom instrument that actually watches oxygen being made in real time, and found the current was lying: in hematite, one of the most studied materials in the field, charge was quietly leaking into competing side reactions instead of making oxygen. They found a 'selectivity switch' — once enough charge builds up on the surface, oxygen production snaps to about 80% efficiency. The finding, published in the Journal of the American Chemical Society, gives researchers a far more accurate way to find and refine materials for solar fuels and green hydrogen.