In this work, hematite thin films are utilised as a model system to understand the effect of variation in the synthesis process on the water splitting performance [3]. Thin films of 40-50 nm thickness are prepared by DC and reactive RF sputtering, followed by annealing at 800°C. It is observed that the DC sputtered films exhibit higher PEC performance with 40 times higher photocurrent at 1.23 V (versus RHE) and 300 mV lower onset potential, as shown in figure 1(a).
From electrochemical impedance spectroscopy (EIS) measurements we find that the DC sputtered thin films exhibit faster charge transfer kinetics as shown by the higher charge transfer rate constant for the oxygen evolution reaction (figure 1(b)). Intensity modulated photocurrent spectroscopy (IMPS) and hole scavenger measurements show that DC sputtered films also have lower surface and bulk recombination effects, respectively, as compared to the reactive RF sputtered films. The variation in the PEC properties is related to the large differences observed in the morphology, surface chemistry and optical properties of the DC and RF sputtered thin films as studied by techniques such as cross-sectional TEM, SEM, XPS and UV-Vis spectroscopy.
References
[1] M.G. Walter, E.L. Warren, J.R. McKone, S.W. Boettcher, Q. Mi, E.A. Santori, N.S. Lewis, Chemical Reviews, 110 (2010) 6446-6473.
[2] K. Rajeshwar, A. Thomas, C. Janáky, Photocatalytic Activity of Inorganic Semiconductor Surfaces: Myths, Hype, and Reality, The Journal of Physical Chemistry Letters, 6 (2015) 139-147
[3] R. Sinha, R. Lavrijsen, M. C. M. van de Sanden, A. Bieberle-Hütter, In Preparation