Abstract: The establishment of multi-component catalytic systems on Fe₂O₃ photoanodes presents considerable potential for significantly enhancing the performance of photoelectrochemical water splitting systems. In this study, we hydrothermally synthesized a Fe₂O₃ photoanode. In addition, d-FeOOH synthesized via dip-coating and hydrothermally prepared h-FeOOH were used as cocatalysts and their synergistic combinations with cobalt phosphate (Co-Pi) were investigated. The synergy between h-FeOOH and Co-Pi was remarkable, whereas that between d-FeOOH and Co-Pi was negligible. For example, the onset potentials of the Co-Pi/h-FeOOH and Co-Pi/d-FeOOH dual catalysts, were cathodically shifted by 270 and 170 mV, respectively. Moreover, the photocurrent density of the Co-Pi/h-FeOOH/Fe₂O₃ anode was significantly higher than that of the Co-Pi/d-FeOOH/Fe₂O₃ one. The synergistic effect of Co-Pi and h-FeOOH could be attributed to the significantly inhibited recombination of surface charges owing to the formation of a p-n junction between β-FeOOH and Fe₂O₃ and the large contact area between the granular h-FeOOH and Co-Pi. However, the thin amorphous FeOOH layer of the Co-Pi/d-FeOOH/Fe₂O₃ anode acted as a hole-transfer medium, and weakly promoted the kinetics of the charge transfer process.

Key words: Fe₂O₃, Synergistic effect, Onset potential, Photoanode, Water splitting