Onset Potential Shift of Water Oxidation in the Metastable Phase Transformation Process of beta-Fe2O3

Metastable iron oxide (beta-Fe2O3) has attracted wide attention in photoelectrochemical water splitting as a result of its ideal light absorption capacity and theoretical saturation photo-current. However, the poor crystallinity and high concentration of defects of beta-Fe2O3 prepared by the traditional method resulted in a high onset potential in photoelectrochemical water splitting. This work proved that gamma-Fe2O3 can be converted into beta-Fe2O3 under heating, which exploits a new synthetic route for beta-Fe2O3. beta-Fe2O3 obtained by this phase transformation method has a smaller particle size and better crystallinity, resulting in a significant reduction in defects. The beta-Fe2O3 photoanode exhibits an onset potential below 0.8 V-RHE, which is the lowest data thus far. This discovery breaks through the limited synthesis methods of beta-Fe2O3, thereby reducing the obstacles of preparing beta-Fe2O3 photoelectrodes.