Laser‐Induced Photoelectrochemistry: Time‐Resolved Coulostatic‐Flash Studies of Photooxidation at n ‐ TiO2 Electrodes

Abstract

Coulostatic‐flash irradiation of semiconductor/liquid‐junction cells with a pulsed laser source has allowed time‐resolved measurements of photopotential transients in the submicrosecond time domain. In 1.0M electrolyte ∼12 nsec rise times were observed with several different normaln‐TiO2 electrodes. The dependences of transient photopotentials on the initial potential, pulsed laser intensity, and nature of electrolyte have been studied, and the measurement limitations defined by experimental and instrumental parameters have been described. Most importantly, the time dependence of photopotential transients has been characterized. Four possible contributions to the transient behavior are discussed: electron‐hole recombination, photoinduced charge transfer at the solution interface (oxidation), subsequent back‐reaction of photoproducts (reduction), and a transient expansion of the space charge layer due to rapid photoinduced charge injection.

Laser-induced photoelectrochemistry. Time-resolved coulostatic-flash studies of cadmium sulfide electrodes

“…In this respect these results are similar to those seen with n-Ti02 electrodes. 20 The potential dependence of the coulostatic response had an unusual dependence on laser power (vide infra); it was only at powers on the order of a few watts that the coulostatic potential dependence even began to resemble that of the dc photocurrent response. The coulostatic threshold does agree well with the dc photocurrent value; both values agree with the flat-band potential measured by capacitance techniques (Mott-Schottky plot).…”

“…We have obtained nanosecond time resolution of transient voltage excursions by using a coulostatic-flash technique. 19,20 The term "coulostatic" pertains to a type of electrochemical experiment in which an electrode-solution equilibrium is perturbed by an instantaneous pulse of charge.21 Before this perturbation our electrochemical cell is maintained under potentiostatic control. In a coulostatic-flash experiment a light pulse is used to generate that perturbing pulse of charge.…”

“…We have obtained ~200-ns time resolution in coulostatic-flash mercury photoemission studies19 and ~10-ns time resolution in photooxidation studies at n-Ti02 electrodes. 20 This paper presents the result of coulostatic-flash experiments with a regenerative solar electrochemical cell, namely, CdS in aqueous sulfide and polysulfide solutions. Additional pertinent results in nonaqueous solutions are also presented.…”

Time-resolved photoelectrochemistry. A laser-induced coulostatic flash study of n-titanium dioxide in acetonitrile

“…Although all previous studies of transient coulostatic effects have been conducted with aqueous electrolytes, nonaqueous solvents are often more suitable for photoelectrochemical studies employing ranges of redox couples because such solvents typically exhibit large solvent windows (e.g., 5 V for acetonitrile compared to 1.5 V for water) and because of the enhanced stability of many organic systems in nonaqueous solvents. Furthermore, the rate of photodissolution of low band gap semiconductors like GaAs or Si is lower in nonaqueous media than in aqueous solvents.…”

Pulsed Laser Depassivation of Metallic Electrodes in Aqueous Corrosive Media

“…In presence of a corroding media Laser pulses of higher power density (10GWlcm2) allowed to initiate pitting corrosion on metallic targets (7). At relatively lower density of energy the radiation of a Nd-YAG laser has been used to perform photoelectrochemistry (Laser-induced transient open circuit photovoltages) on semi-conductor electrodes (8).…”