The behavior of Si electrodes in aqueous alkaline media has been investigated by voltammetric and impedance
techniques. The flatband potential has been estimated on the basis of Mott−Schottky plots and photocurrent
onset as E
FB = −1.15 V (SCE) for n-Si and E
FB = −0.45 V(SCE) for p-Si. A dissolution/passivation mechanism
is proposed, assuming: (1) irreversible electrochemical oxidation of H-terminated Si to a monohydroxylated
surface species, which may undergo either (2) irreversible electrochemical oxidation to a dihydroxylated
species responsible of 2D surface blocking or (3) chemical dissolution as Si(II) regenerating an H-terminated
surface; furthermore, (4) the blocking species may be dissolved chemically as Si(IV); (5) a chemical reaction
with water generating monohydroxilated Si (and H2) is also considered. A kinetic model is developed for the
case of n-Si, assuming Helmholtz-layer control. The model reproduces the essential experimental features of
both J
−
E curves and impedance diagrams in the active dissolution and passivation regions but is not expected
to be realistic in the passive region where 3D surface blocking should be considered.