Photoreduction at illuminated p-type semiconducting silicon photoelectrodes. Evidence for Fermi level pinning
Studies of p- and n-type Si electrodes are reported which show that semiconducting Si electrode surfaces do not allow efficient H/sub 2/ evolution in the dark (n type) or upon illumination with band gap or greater energy light (p type). The key experiment is that N,N'-dimethyl-4,4'-bipyridinium (PQ/sup 2 +/) is reversibly reduced at n-type Si in aqueous media at a pH where H/sub 2/ should be evolved at nearly the same potential, but no H/sub 2/ evolution current is observable. The PQ/sup 2+/+/.system may be useful as an electron-transfer mediator, since PQ/sup +/.can be used to effect generation of H/sub 2/ from H/sub 2/O using a heterogeneous catalyst. The PQ/sup +/.can be produced in an uphill sense by illumination of p-type Si in aqueous solutions. Studies of p-type Si in nonaqueous solvents show that PQ/sup 2 +/, PQ/sup +/., Ru(bpy)/sub 3//sup 2 +/, Ru(bpy)/sub 3//sup +/, and Ru(bpy)/sub 3//sup 0/ are all reducible upon illumination of the p-type Si. Interestingly, each species can be photoreduced at a potential approx. 500 mV more positive than at a reversible electrode in the dark. This result reveals that a p-type Si-based photoelectrochemical cell based on PQ/sup 2+/+/., PQ/sup +/l/sup 0//, Ru(bpy)/sub 3//sup 2+/+/, Ru(bpy)/sub 3//sup +/0/, or Ru(bpy)/sub 3//sup 0/-/ would all yield a common output photovoltage, despite the fact that the formal potentials for these couples vary by more than the band gap (1.1 V) of the photocathode. These data support the notion that p-type Si exhibits Fermi level pinning under the conditions employed.Surface chemistry is shown to be able to effect changes in interface kinetics for electrodes exhibiting Fermi level pinning.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge
- OSTI ID:
- 5112901
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 102:11
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
08 HYDROGEN
PHOTOANODES
FERMI LEVEL
PERFORMANCE
PHOTOELECTROCHEMICAL CELLS
ELECTROCHEMISTRY
SILICON
AQUEOUS SOLUTIONS
BIPYRIDINES
CHEMICAL PREPARATION
ELECTRODES
EXPERIMENTAL DATA
HYDROGEN PRODUCTION
ORGANOMETALLIC COMPOUNDS
P-TYPE CONDUCTORS
PHOTOELECTROLYTIC CELLS
REDUCTION
RUTHENIUM COMPLEXES
SOLAR ENERGY CONVERSION
VOLTAMETRY
ANODES
AZINES
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
CONVERSION
DATA
DISPERSIONS
ELECTROCHEMICAL CELLS
ELECTROLYTIC CELLS
ELEMENTS
ENERGY CONVERSION
ENERGY LEVELS
EQUIPMENT
HETEROCYCLIC COMPOUNDS
INFORMATION
MATERIALS
MIXTURES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PYRIDINES
SEMICONDUCTOR MATERIALS
SEMIMETALS
SOLAR EQUIPMENT
SOLUTIONS
SYNTHESIS
TRANSITION ELEMENT COMPLEXES
140505* - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)
400500 - Photochemistry
080101 - Hydrogen- Production- Electrolysis