New Insight Into the Role of Cobalt Phosphate Surface Coating in Water Photo‐Oxidation Over Hematite Electrodes
Shufeng Zhang, Wenhua LengABSTRACT
Addition of surface coating CoPi on hematite ( α ‐Fe 2 O 3 ) photoelectrode has been widely reported to be a promising strategy to enhance the rate of photoelectrochemical oxidation water. However, it is not fully understood regarding the role of CoPi in water photo‐oxidation over this material from the point of view of chemical kinetics. In this work, the impact of CoPi on the surface states and the charge transfer kinetics of Ti doped α ‐Fe 2 O 3 are quantitatively investigated by a combination of (photo‐) electrochemical techniques. It was demonstrated that the enhancement in photocurrent is predominately resulted from the improved charge transfer rate constant ( k ct ), though the surface recombination rate constant ( k sr ) is also increased. An unconventional relationship between k ct and the density of surface reactive hole was found, and the basic origin for the increase in k ct is attributed to greater hole flux toward the electrode surface which is resulted from a larger band bending due to a negative shift of the flatband potential. These findings thus may provide insights into the function of CoPi in water photooxidation on Ti–Fe 2 O 3 electrodes and may be inspiring to the design of more efficient photoanode through surface modification.