Breaking through water-splitting bottle-necks over carbon nitride with fluorination

Graphitic carbon nitride has long been considered incapable of splitting water molecules into hydrogen and oxygen without adding small molecule organics despite the fact that the visible-light response and proper band structure fulfills the proper energy requirements to evolve oxygen. Herein, through in-situ observations of a collective C=O bonding, we identify the long-hidden bottleneck of photocatalytic overall water splitting on a single-phased g-C3N4 catalyst via fluorination. As carbon sites are occupied with surface fluorine atoms, intermediate C=O bonding is vastly minimized on the surface and an order-of-magnitude improved H2 evolution rate compared to the pristine g-C3N4 catalyst and continuous O2 evolution is achieved. Density functional theory calculations suggest an optimized oxygen evolution reaction pathway on neighboring N atoms by C-F interaction, which effectively avoids the excessively strong C-O interaction or weak N-O interaction on the pristine g-C3N4.