Structural improvement of CaFe₂O₄ by metal doping toward enhanced cathodic photocurrent.

Various metal-doped p-type CaFe2O4 photocathodes were prepared in an attempt to improve the low quantum efficiency for photoreaction. CuO and Au doping enhanced the photocurrent by expansion of the absorption wavelength region and plasmon resonance, respectively. X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) analysis showed that doping with these metals further disturbed the originally distorted crystal structure of CaFe2O4. In contrast, doping with Ag relaxed the distorted crystal structure around the Fe center toward symmetry. Ag doping resulted in improvement of the carrier mobility together with a red-shift of photoabsorption with Ag-doped CaFe2O4 having a 23-fold higher photocurrent than undoped CaFe2O4.