Electrodeposition of α-Fe2O3 doped with Mo or Cr as photoanodes for photocatalytic water splitting

Electrochemical methods for the codeposition of Cr or Mo with alpha-Fe2O3 (hematite) have been developed to produce doped iron oxide films with varying compositions of Cr and Mo which are active photoanodes for photoelectrochemical (PEC) water decomposition ("water splitting"). The films were characterized by scanning electron microscopy, X-ray diffraction, UV-vis optical spectroscopy, and X-ray photoelectron spectroscopy to determine the effect of the dopants on the hematite structure and PEC performance. Upon doping, the microstructures of the films varied; however, no preferred crystallographic orientation or dopant phase segregation was observed. The best performing samples were 5% Cr and 15% Mo doped which had Incident Photon Conversion Efficiencies (IPCE's) at 400 nm of 6% and 12%, respectively, with an applied potential of 0.4V vs Ag/AgCl. These IPCE values were 2.2x and 4x higher than the undoped sample for the 5% Cr and 15% Mo samples, respectively. The increase in performance is attributed to an improvement in the charge transport properties within the films and not due to significant changes in the electrocatalytic rates due to dopants residing at the surface. The onset potential for photocurrent in all the samples was approximately -350 mV vs Ag/AgCl. The optical absorption spectra of the films showed bandgaps of approximately 2.0-2.1 eV for all samples regardless of doping.