Improvement of Photoelectrochemical Properties by Surface Modification with Iron Oxide on p-Type Si Electrodes for Hydrogen Evolution from Water (original) (raw)
Related papers
International Journal of Hydrogen Energy, 2012
This study demonstrates solar driven oxidation of hydrazine hydrate and the simultaneous production of hydrogen and electricity in photoelectrochemical cells and photofuel cells, respectively, using a visible light active molybdenum doped BiVO 4 photoelectrode. The developed photoelectrodes exhibited tremendous efficiency towards anodic oxidation of hydrous hydrazine with continuous and stable hydrogen evolution at the Pt cathode under benign pH and zero bias conditions. Significantly, the photofuel cell containing hydrazine hydrate fuel has generated electricity with a high open circuit potential of 0.8 V. The presence of bicarbonate ions in the electrolyte has played a significant role in enhancing the kinetics of photoelectrochemical oxidation of hydrazine and improved the hydrogen and electricity generation efficiency thus avoiding the integration of an oxidation electrocatalyst. In addition, molybdenum doped BiVO 4 as a possible photoelectrochemical hydrazine sensor has been investigated and the electrode photocurrent was found to be linearly dependent on the concentration of the hydrazine hydrate in the range of 20-90 mM with a correlation coefficient of 0.9936.
Journal of Electroanalytical Chemistry, 2009
In this study we examined the rhenium photoelectroless deposition process onto p-Si(1 0 0) from HF solutions. In the first stage an energetic characterization through capacitance measurements (Mott-Schottky plots) of the p-Si/HF interface was done. Before the rhenium photoelectroless deposition process, a voltammetric and photovoltammetric analysis of p-Si in ReO À 4 =HF solutions was done. In this study, a decrease of the rhenium deposition charge was observed as a function of the increased HF concentration. This behavior was attributed to competition with the silicon dissolution process when an increased HF concentration was present in the electrolytic bath. A morphologic analysis was completed by means of atomic force microscopy (AFM) for the rhenium deposits obtained by photoelectroless process at different HF concentrations and different deposition times. X-ray photoelectron spectroscopy (XPS) technique was utilized to characterize the rhenium deposits, and it was concluded that the films formed by the photoelectroless process were metallic rhenium with only the uppermost atomic layer containing rhenium oxide species. The hydrogen evolution reaction (HER) on the different p-Si/Re electrode systems synthesized was studied. For the HER on p-Si(1 0 0)/Re electrode systems an overpotential decrease of 0.2 V and a photocurrent increase between one and two orders of magnitude, compared with p-Si(1 0 0) and metallic Re, was found. Additionally, the kinetic parameters of the cathodic reactions in the p-Si and p-Si/Re acidic media were estimated using intensity modulated photocurrent spectroscopy (IMPS). A brief analysis from this technique was done. According to these results, the p-Si/Re electrode system could be a potential photoelectrocatalyst for the HER.
Journal of Electroanalytical Chemistry, 2007
In this study we examined the rhenium electrodeposition process onto p-Si(1 0 0). The study was carried out by means of cyclic voltammetry (CV) and the potential-steps method from which the corresponding nucleation and growth mechanism (NGM) were determined. Both methods were performed under illumination for electron photogeneration. A 3D progressive nucleation, diffusion-controlled growth of rhenium films was found (PN3D Diff ). Furthermore, the photocurrent-time transients were fitted with an equation that takes into account redox reactions occurring simultaneously on the rhenium film surface, in this case proton reduction. Likewise, a morphologic analysis was completed for the deposits obtained at different potential values by means of atomic force microscopy (AFM). Finally, the hydrogen evolution reaction, HER, on different electrode systems was studied. An overpotential decrease of 0.2 V and a photocurrent increase by one order of magnitude for the HER on p-Si(1 0 0)/Re electrode system compared with p-Si(1 0 0) and metallic Re was found. According to these effects, this electrode system could be a photoelectrocatalyst for the HER.
In this work, we investigate the effect of the average size and density of Pt clusters on silicon on the photoelectrochemical production of hydrogen. The metallization of Si is performed via electroless deposition from aqueous HF solutions and from water-in-oil microemulsions. The first method enables control of the average diameter and density of Pt clusters by properly changing the deposition parameters like HF concentration and immersion times. However, on one hand, size dispersion is relatively wide and particles agglomeration may occur with this deposition technique. On the other hand, Pt islands with smaller dimensions at the nanoscale as well as with a narrower size distribution are deposited from reversed micellar solutions. Photoelectrochemical experiments show that the effect of Pt morphology on photoconversion efficiency strongly depends on light intensity. At low power of illumination (10 mW/cm 2 ), Pt islands with a mean diameter of 100 nm and a density of 15 particles/µm 2 , which can be obtained via electroless deposition from a HF-based solution, provide the best photoelectrochemical performance. Nevertheless, this configuration of Pt clusters yields an abrupt collapse of photoconversion efficiency from 31% to 11.8% when the light power is increased up to 100 mW/cm 2 . At this light intensity, Pt islands with a mean size and density of ∼40 nm and 75 particles/µm 2 , respectively, obtained via the microemulsion method, allow photoconversion efficiency as high as 20% to be achieved.
Photoelectrochemistry of silicon in HF solution
Journal of Solid State Electrochemistry, 2013
Photoelectrochemical, photoelectrocatalytic, and electrochemical processes of silicon anodic oxidation and hydrogen evolution in aqueous HF solution are discussed in terms of thermodynamic stability of Si, oxides SiO, SiO 2 , and Si surface hydrides. It is shown that photoelectrochemical oxidation of n-type low-resistivity silicon to SiO 2 is catalyzed by Si + photo-hole formation, whereas in the case of p-type Si, the feasibility of this reaction is predetermined by p-type conductivity. It is suggested that anodic oxidation of Si goes through the stage of SiO oxide formation and its subsequent oxidation to SiO 2. Such mechanism accounts for chemical inertness of Si phase in HF solutions as well as for selective, anisotropic, and isotropic etching of Si within E ranges from −0.5 to 0.35 V, 0.35 − 0.8 V , and E > 0.8 V, respectively. Hydrogen evolution reaction on Si surface proceeds at very large overpotential (≥ 0.5 V) through the stage of surface Si hydride formation: Si + H 2 O + e − → (SiH) surf + OH − (the rate determining step) and (SiH) surf + H 2 O + e − → Si + H 2 + OH −. Illumination-related effects of surface reactions relevant to selective and anisotropic etching and nano/microstructuring of Si surface are discussed.
Si-based photocathodes for the photoelectrochemical purification of water
Comptes Rendus Chimie, 2006
Si-based photocathodes have been investigated for use as counterelectrodes in oxide-based photoelectrochemical water purification cells. Bare p-type silicon (either crystalline silicon or amorphous hydrogenated silicon a-Si:H obtained by plasma deposition) is found to exhibit poor catalytic properties for the photoelectrochemical reduction of dioxygen. Improvement in photocathode performance has been sought through the deposition of small amounts of platinum on the Si surface, and improvement in electrode stability has been sought through the formation of a thin organic layer covalently anchored to the Si surface, or through the deposition of a thin conductive-oxide film. Combining both treatments allows to obtain photocathodes with performances just slightly better than those of a bare Pt cathode. Much larger improvements in photocathode performance (+0.9 V shift in the voltammetric curves) have been obtained by using a p + /i/n + a-Si:H structure with similar coatings. The concept is readily scalable to large-area electrodes, which appears promising for practical sunlight powered water purification reactors. To cite this article:
Photoelectrochemical Hydrogen Evolution Using Copper-Indium-Sulfide Nanocrystalline Film Electrodes
Electrochemistry, 2011
. Panel (a) shows the J-E data collected for the electrode fabricated with 'enhanced' absorption due to light-trapping elements, in 0.5 M aq. H 2 SO 4 under ELH-type W-halogen solar simulation. Panel (b) shows a cross-sectional SEM image of the same sample. Panel (c) compares the spectral response collected for the sample with light-trapping elements ('enhanced') versus the spectral response for the normal sample. The red response in the 'enhanced' cell is significantly improved. Panel (d) shows the increased J sc with reduced angle dependence, for the enhanced sample compared to the normal sample. Panel (e) shows a digital photograph of a normal Pt/n + p-Si wire-array electrode evolving hydrogen under ~ 1 sun illumination. Small bubbles can be seen nucleating on the wire-array surface. The larger bubbles are stuck on the epoxy, and are the result of the coalescence of many small bubbles.
Nano letters, 2015
Amorphous Si (a-Si)/ crystalline Si (c-Si) heterojunction (SHJ) photoelectrochemical cells can serve as highly efficient and stable photoelectrodes for solar fuel generation. Low carrier recombination in the photoelectrodes leads to a high photocurrent and high photovoltage. Both SHJ photoanodes and photocathodes are designed for high efficiency oxygen and hydrogen evolution. The SHJ photoanode with sol-gel NiOx as the catalyst shows the current density of 21.48 mA/cm2 at the equilibrium water oxidation potential. The SHJ photocathode displays excellent hydrogen evolution performance with an onset potential of 0.640 V and a solar to hydrogen conversion efficiency of 13.26%, which is the highest ever reported for Si-based photocathodes.
Photoelectrochemical dissociation of water at silicon doped n-GaAs electrodes
International Journal of Hydrogen Energy, 1991
In continuation of our previous work on water photodissociation at semiconductor surfaces, we repori on the catalytic effects of hydrogen photogeneration due to metallic deposits on p-GaAs. These effects were investigated by measuring the current-voltage curves in 0.5 M H,SO, solution. Metallic coating was performed electrochemically by depositing an amount of a metal equivalent to five monolayers on GaAs. Such a coverage has achieved a maximum positive shift in the onset-potential of the photocurrent, E,. Etching GaAs electrodes in (H,SO, + H,O, + H,O) mixture improved the (J-E) characteristics, however temporarily by shifting E, towards positive potentials and also by increasing the value of the limiting photocurrent density by approximately w 15%. The effect of etching is for the surface with an elemental component, possibly, arsenic, due to the preferential dissolution of the other elemental component in the etching mixture. Coating with Pt, Ag and Cu gave a positive shift in E,, but coating with Pb gave a negative shift. Whereas the shift of the onset potential of the photocurrent was independent of the height of the Schottky barrier, which is expected to be created at the metal/semiconductor interface, the magnitude of this shift. towards positive potential, was proportional to the dark electrocatalytic activity for hydrogen evolution at the deposited metal. This activity has been found to be inversely proportional to the magnitude of the Tafel sl ope of the metal.