Dynamics of the Oxygen‐Evolving RuS2/Electrolyte Interface: An Electroreflectance Study

Abstract

Systematic studies of electrolyte electroreflectance (EER) on n-type RuS 2 electrodes in contact with acqueous electrolyte makes it possible to distinguish between two different signals from phases which compete for applied electrical potential. They could be attributed to the space-charge region (EER-b) and to a surface oxide layer (EER-s), respectively. Both signals coexist on electroactivated RuS 2 samples with moderate doping level, where EER-s is observable under accumulation of photogenerated holes at the RuS 2 /RuO,2, interface. On degenerate RuS, samples, the EER-s signal is the only one observed in the spectrum, whereas on low-doped samples EER-b predominates. A minimum observed for the intensity of the EER-s signal on potentiodynamic measurements is attributed to the condition of zero electric field at the surface oxide. A change of sign of this electric field is necessary for oxygen to evolve from water at the RuS,/electrolyte interface. According to the EER measurements, this happens at more negative potentials on the degenerate rather than the moderately doped RuS, sample, explaining why oxygen evolution in the dark is more efficient for highly doped RuS,.

Ruthenium sulphide thin layers as catalysts for the electrooxidation of water

“…It must be noted that this high value most likely points to upstreamed slow chemical reaction steps like adsorption processes and do not reflect the kinetics of the electron transfer. In analogy with detailed measurements on RuS 2 single crystals 10,11 we concluded also for the sputtered material an electrooxidation of the RuS 2 surface within the first scans which comes to an end after the whole interface is totally occupied with an oxide layer. The formation of this layer is confirmed by analysis of the O1s-XPS spectrum which shows a significant increase of the oxygen peak (531.1 eV) measured at the electrochemical treated surface.…”

“…[8][9][10] This is also verified by XPS and electroreflectance measurements. 10,11 By this surface oxidation the semiconducting property of the RuS 2 as absorber is combined on an atomic level with the Ru-oxide's outstanding catalytic activity for water oxidation. Nevertheless, due to the indirect low band gap in general the photovoltage obtained on RuS 2 is too small to split water and an additional bias voltage has to be applied to evolve oxygen.…”

Shining a light on transition metal chalcogenides for sustainable photovoltaics

“…Binary transition metal chalcogenides have the form M x E n (M transition metal, E = S, Se, Te). There are a vast range of binary TMC systems that have demonstrate suitable properties for photovoltaic systems, including: FeS 2 , 34 , 35 CdS, 36 Cu x S, 37 , 38 CuSe, 39 MoS 2 , 40 , 41 RuS 2 , 42 – 45 ZrS 2 /Se 2 , 46 TaS 2 ( ref. 47 ) and AgS.…”

“…Single crystals of RuS 2 have been shown to oxidise H 2 O upon illumination, but it is thought that RuO 2 is probably responsible. 42 The single crystals show a limited photocurrent, but deposited thin films do not, possibly due to a high electron/hole re-trapping and combination rate. 44 , 45 …”

Electrolyte electroreflectance study of TiO2 films modified with metal nanoparticles

“…When the modulated electric field is sufficiently low, the line shape of the EER spectrum of a nondegenerate semiconductor is determined by the modulation-induced effect of populationdepopulation of the electronic surface states (in the sub-band-gap absorption range) or is closely related to the third derivative of the dielectric function (in the bandgap absorption range). 1 This spectroscopic technique was used to determine the potential distribution inside the nanocrystalline films 2 and between the space charge layer and Helmholtz or surface oxide layer, [3][4][5] to study the evolution of space charge region in the degenerated semiconductors contacting with the electrolyte solution, 6 to measure flat-band potentials, 4,7,8 and to obtain information on the degree of inhomogeneity of an electrode surface. 8,9 The EER measurements have also proven to be particularly useful as a means for the identification of the electroactive surface states.…”