Laser pulse studies on the photoresponse of oxygen-evolving iron ruthenium sulfide (FexRu1-xS2). Mechanistic aspects

Abstract

Semiconducting Fe^Ru^Sj (£0 =1.1 eV) is able to evolve oxygen from aqueous electrolytes during illumination. From time-resolved photopotential and photocurrent measurements at FexRu1_xS2/electrolyte junctions performed with light of different wavelengths, additional information on the electrode properties and reaction behavior has been derived. The most important results are the following: The photoelectrochemical behavior is determined by a high number of surface states. As a consequence the band edges are unpinned and can be shifted by changing the applied potential. In this range fast decay times of photocurrent transients (tj/2 = 30-400 ns) can be observed reflecting recombination processes. At more positive electrode potentials the surface states are energetically fixed by the electrolyte and an increase of band bending is possible. Thus, the recombination rate decreases and the photocurrent yield is raised. In this case slow decay times (t1/2 = 0.6-1.75 ¿is) are found. Whereas 530-nm excitation produces anodic photoresponses expected for n-type semiconductors, absorption of 1060-nm light leads to cathodic photocurrents and positive photopotentials. These differences in photoelectrochemical behavior for light of different wavelengths can be interpreted by an additional valence band in the band gap of pure RuS2. Thus, different reaction pathways of charge carriers are possible, if holes generated in the lower valence band do not tend to relax to the energetically higher energy bands.

Transient Photocurrent Measurements on Surface‐Modified p ‐ InP

“…will relax back to equilibrium prior to interaction with another laser pulse. The resulting decay observed for photopotential (open-circuit cell conditions) or photocurrent (short-circuit cell conditions) transients produced during such measurements have been used to probe interfacial kinetic parameters at a number of photoelectrodes including n-CdS (21)(22)(23)(24)(25), n-CdSe (22,23,33), n-WSe~ (31,35), n-MoSes (35,40), n-SnO2 (26,28,29), n-ZnO (27,28,30), n-Fe=Rul-xS2 (32), n-PtS2 (34), n-TiO2 (20,38,40), n-GaAs (39), n-InP (26,27), p-InP (36,37), and p-GaAs (40). Both photocurrent and photopotential techniques have demonstrated that the recorded transient photoresponse can be sensitive to the presence or absence of photoelectrode surface modifications .…”

Time‐Resolved Photocurrent of WSe2 Photoanode Studied with a Nanosecond Pulse Laser

“…The use of transient techniques in investigating photoelectrochemical cells has been introduced recently, in order to evaluate kinetic parameters in the p hotoelectrode processes (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). The relaxation of an open-circuit photopotential was examined theoretically for the special case where there is no interfacial electron or hole transfer (13).…”

“…Also, a dye-sensitized system, SnOJrhodamine B, has been studied (6). Photocurrent transients obtained under short-~ circuit condition have also been studied (6)(7)(8)(9)(10)(11)(12). From the measured dependence of the decay time on the value of load resistance and additional capacitances, it has been shown that the photocurrent decay was controlled by the RC time constant of the cell (7,9,11).…”

“…Photocurrent transients obtained under short-~ circuit condition have also been studied (6)(7)(8)(9)(10)(11)(12). From the measured dependence of the decay time on the value of load resistance and additional capacitances, it has been shown that the photocurrent decay was controlled by the RC time constant of the cell (7,9,11). But sometimes also faster components could be observed, which have been attributed to alternative reaction paths involving recombination (6)(7)(8)(9).…”