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Modified P‐Type Si Photocathodes for Photochemical Hydrogen Generation: Surface Texturing, Molecular Derivatizing Reagents, and Noble Metal Catalysts for Multi‐Electron Processes
Author(s) -
Bruce James A.,
Wrighton Mark S.
Publication year - 1982
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198200036
Subject(s) - chemistry , photocathode , reagent , electrolyte , redox , etching (microfabrication) , photoelectrochemistry , catalysis , water splitting , electron acceptor , photochemistry , electrochemistry , electrode , photocatalysis , inorganic chemistry , electron , organic chemistry , physics , quantum mechanics , layer (electronics)
Modification of single‐crystal (100), p‐type Si photocathode material to improve photoelectrochemical H 2 generation from H 2 O is reported. The (100) surface has been first modified by chemical etching to reveal pyramids (1–5 μM in height) having (111) sides to give a “textured” surface having lower specular reflection losses than polished (100) or (111) single‐crystal Si. Second, the textured surface has been derivatized with {N,Nî‐ bis ‐[3‐trimethoxysilyl)propyl]‐4,4′‐bipyridinium}dibromide, I , to yield large coverages (0.5–5 × 10 −8 mol/cm 2 ) of redox centers [PQ 2+/+ ] surf in a polysiloxane network. The surface redox polymer is a fast electron acceptor and can be reduced photoelectrochemically, [PQ 2+ ] surf → [PQ + ] surf , by ≥ E g = 1.1 eV light at ∼0.0 to ‐ 0.1 V vs. SCE in aqueous electrolyte solution, or ∼ 500 mV more positive than on a reversible electrode such as Pt. Third, the surface polymer is then further modified by depositing Pd(O) or Pt(O) onto the outermost surface to catalyze the reaction 2[PQ + ] surf + 2H + → 2[PQ 2+ ] surf + H 2 . Energy conversion efficiency from the modified photocathodes for 632.8 nm (∼ 10 mW/cm 2 ) light‐driven H 2 evolution is ∼ 5% at pH = 4, representing significant improvement compared to polished, (100) or (111) p‐type Si‐based photoelectrochemical devices where the surface of the p‐type Si is not modified.