Anodic photodissolution of n-InP, under electroless conditions

Evidence by Electrochemical Impedance Spectroscopy of Surface States Mediated SiMo12O404− Reduction at an n-InP Electrode

“…As previously demonstrated, , dissolution of n-InP immersed in a SiMo 12 acidic solution is observed under visible light illumination, in electroless conditions. Actually, under illumination electron−hole pairs are photogenerated, some electrons are captured by SiMo 12 avoiding the electron−hole recombination, and therefore some holes are available for the corrosion of n-InP.…”

“…After cathodic polarization, the concentration of the reduced form at the electrode/solution interface has increased; thus, the OCP is lower (Nernst equation). Progressively, the reduced species diffuse into the electrolyte bulk leading to an increase of the OCP until reaching its initial value …”

“…A classical Randles circuit (Figure C), as expected in the case of a direct electron transfer between the semiconductor conduction band and a redox species in solution (Figure A), did not allow us to simulate our experimental impedance data. The existence of a distribution of time constants suggests us considering a transfer mechanism via surface states (Figure B) since it has been shown that the SiMo 12 reduction occurs by electron capture (and not by hole injection into the valence band) . In fact, two time constants were used to well account for our impedance data, leading to the electrical equivalent circuit given in Figure D.…”

“…At an n-InP electrode, in 0.5 M H 2 SO 4 solution, for potentials between −0.25 and −0.65 V/MSE the reduction of SiMo 12 takes place according to the following reaction: SiMo VI 12 O 40 4 − + 2 e − + 2 H + → H 2 SiMo VI 10 Mo V 2 O 40 4 − Moreover, this process is diffusion-limited and irreversible . On the contrary, at a metallic electrode such as platinum electrode, in a potential range of 0 to −0.6 V/MSE, the voltammogram of SiMo 12 exhibits three reversible redox waves at potentials of −0.18, −0.3, and −0.48 V/MSE (see Figure ) …”

“…At an n-InP electrode, in 0.5 M H 2 SO 4 solution, for potentials between -0.25 and -0.65 V/MSE the reduction of SiMo 12 takes place according to the following reaction: 6 SiMo VI 12 O 40 4-…”