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The former follows steps (1) to (5), whereas the latter follows steps (6) to (8) combined with step (1).In addition, the red arrow denotes the recombination reaction (2) photo-oxidation to occur, an adsorption step that involves the long-lived Fe-OH species is expected to precede the step in which the adions interact with the Fe = O intermediates, as suggested in (c).
At higher H concentrations (10 m M) j increases almost linearly with U, indicating that the flux of photo-generated holes arriving at the surface is proportional to the applied potential.
concentrations ranging from 0 to 500 m M in alkaline solution (1 M Na OH in deionized water).
The photocurrent density, j, is the current measured under illumination after subtraction of the dark current (at the same potential), divided by the aperture area of the PEC cell.
To distinguish the bias-dependent interfacial charge transfer at the photoanode|electrolyte interface from the bias-dependent hole flux from the bulk to the surface, the photocurrent voltammograms were normalized by the photocurrent obtained at the highest H concentrations (from 1 to 5 m M) wherein the normalized photocurrent first increases at low potentials, secondly decreases at moderate potentials, thirdly exhibits a steep rise at the onset potential around 1.1 V concentrations marked by points (i) to (vi) in Fig. The IMPS spectra of the complex photocurrent admittance, Y(ω) = j(ω)/Φ(ω), where ω is the ac frequency and Φ is the light intensity, display two main features: upper (positive imaginary part) and lower (negative imaginary part) semicircles.
The diameter of a lower semicircle corresponds to hole flux to the surface, whereas the diameter of the upper semicircle corresponds to surface recombination in the electrolyte, the upper semicircle at low potentials (point (i)) is large, indicating strong surface recombination.