Doped Framework Iron Hydroxyl Phosphate as Photocatalyst for Hydrogen Production from Water/Methanol Mixtures

In the search for novel photocatalysts for hydrogen production and with the alpha-Fe2O3 photoelectrocatalyst as a recent precedent, we report herein the preparation, semiconductor properties and photocatalytic activity of metal-doped (0.1-5 wt.-% loading) iron hydroxyl phosphate (FeP). X-ray diffraction analyses of FeP samples subjected to extended photocatalytic irradiation showed the stability of this framework phosphate under photocatalytic conditions. Doping increased the photocatalytic efficiency of FeP for all dopants, with the optimal doping level between 0.1 and 1%. Under the optimized conditions (Cr at 1% doping), the photocatalytic activity of FeP reached a hydrogen production rate of 35.82 mu molg(Fe)(-1) in the absence of platinum as co-catalyst. The conduction flat band potential was estimated by photocurrent measurements or impedance spectroscopy to be 0.1 eV versus NHE and the charge carrier density 2.6 x 10(20) carriers cm(-3). Transient absorption spectroscopy revealed a transient species decaying on the microsecond time-scale characterized by a broad band spanning 300-750 nm. This transient was attributed to the charge-separated state. These results are promising for the development of novel photocatalytic materials based on framework metal phosphate.