Electrochemical characterization of p-type semiconducting tungsten disulfide photocathodes: efficient photoreduction processes at semiconductor/liquid electrolyte interfaces
Single-crystal p-type WS/sub 2/(E/sub g/ approx. = 1.3 eV) has been synthesized and characterized as an electrode material in CH/sub 3/CN/0.1 M (n-Bu/sub 4/N)ClO/sub 4/ and in aqueous electrolytes containing a variety of one-electron redox reagents having different E/sub 1/2/ values. In either CH/sub 3/CN or H/sub 2/O solvent the flat-band potential, E/sub FB/, is measured to be approx. + 0.95 vs SCE. In aqueous I/sub 3//sup -//I/sup -/ the E/sub FB/ is shifted more negatively by at least 0.3 V as is found for n-type WS/sub 2/ photoanodes. Capacitance measurements of the WS/sub 2//electrolyte interface to determine E/sub FB/ accord well with electrochemical measurements. For E/sub 1/2/ more negative than E/sub FB/ the p-type WS/sub 2/ behaves as a photocathode giving an open-circuit photovoltage, E/sub v/(oc), up to approx. 0.8 V depending on E/sub 1/2/. For E/sub 1/2/ between +1.3 and -0.1 V vs SCE, E/sub v/(oc) varies as expected: for E/sub 1/2/ more positive than E/sub FB/ the p-type WS/sub 2/ behaves as a metallic electrode while for E/sub 1/2/ more negative than E/sub FB/ we find E/sub v/(oc) approx. = vertical bar E/sub 1/2/ - E/sub FB/ vertical bar. It appears that for negative redox couples carrier inversion results at the p-WS/sub 2/ surface, but for E/sub 1/2/ more negative than -0.1 V vs SCE E/sub v/(oc) declines, a result associated with junction breakdown at sufficiently negative potentials. p-Type WS/sub 2/-based photoelectrochemical cells can be used to effect the sustained conversion of visible light (632.8 nm) to electricity in H/sub 2/O or CH/sub 3/CN with efficiencies of up to approx. 7%. In H/sub 2/O the photochemical reduction to H/sub 2/ can be effected by illumination of p-type WS/sub 2/ modified by depositing approx. 10/sup -7/ mol/cm/sup 2/ of Pd(0) or Pt(0) onto the surface as an H/sub 2/ evolution catalyst. Efficiency for H/sub 2/ evolution from 6 M H/sub 2/SO/sub 4/ is typically 6 to 7% for 632.8 nm (50 mW/cm/sup 2/) intensity.
- OSTI ID:
- 5718371
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 105:8
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
08 HYDROGEN
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
HYDROGEN PRODUCTION
PHOTOCHEMICAL REACTIONS
SOLAR ENERGY CONVERSION
TUNGSTEN SULFIDES
ELECTROCHEMISTRY
AQUEOUS SOLUTIONS
CATALYSTS
COMPARATIVE EVALUATIONS
EFFICIENCY
FERMI LEVEL
MONOCRYSTALS
NONAQUEOUS SOLVENTS
P-TYPE CONDUCTORS
PALLADIUM
PHOTOCATHODES
PHOTOELECTROCHEMICAL CELLS
PLATINUM
REDOX POTENTIAL
VISIBLE RADIATION
VOLTAMETRY
CATHODES
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISTRY
CONVERSION
CRYSTALS
DISPERSIONS
ELECTROCHEMICAL CELLS
ELECTRODES
ELECTROMAGNETIC RADIATION
ELEMENTS
ENERGY CONVERSION
ENERGY LEVELS
EQUIPMENT
MATERIALS
METALS
MIXTURES
PLATINUM METALS
RADIATIONS
SEMICONDUCTOR MATERIALS
SOLAR EQUIPMENT
SOLUTIONS
SOLVENTS
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
TUNGSTEN COMPOUNDS
140505* - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)
080106 - Hydrogen- Production- Biosynthesis & Photochemical Processes
400500 - Photochemistry
400400 - Electrochemistry