Tds 2012c

TAS measurements were carried out using the third harmonic of a Nd:YAG laser (EKSPLA, NT 342B, 355 nm, 5 ns pulse width, 0.9 Hz) as the excitation source. A liquid light guide transmitted the laser pulse to the sample resulting in an incident pump intensity of ca. 177 μJ cm⁻² (355 nm). A 100 W tungsten lamp (Bentham, IL 1) coupled to a monochromator (Zolix, Omni - λ 300) was used as the probe light. Variation in optical density (∆OD) of the sample was calculated by measuring the transmitted light using a Si photodiode (Hamamatsu) and an amplification system coupled to both an oscilloscope (Tektronix, TDS 2012C) and data acquisition card (National Instruments NI-6221). The data were averaged over 400 laser shots. OCP measurements were conducted in 1 M NaOH solution with or without 0.5 M Na₂SO₃. The operando TAS experiments were implemented by three-electrode setup controlled by a CHI 760C potentiostat in 1M NaOH solution (pH = 13.7), with the photoanode, Pt, and Ag/AgCl as working, counter and reference electrodes, respectively. During TAS measurements, a constant potential was maintained by chronoamperometry.

The setup of transient absorption spectrometer (μs–s) has been described previously.²⁰ Briefly, a Nd:YAG laser (Big Sky Laser Technologies, Ultra CFR Nd:YAG laser system) was used as the excitation source (355 nm, 3^rd harmonic, pulsed laser, 6 ns band width). The laser flash rate was 0.33 Hz; the laser excitation intensity was set at 100 μJ cm^–2, unless otherwise stated; the probe light source was a 100 W Bentham IL1 tungsten lamp equipped with a monochromator (OBB-2001, Photon Technology International); the transmitted light was filtered using long pass filters and a band pass filter (Comar Optics) to block the scattered laser light into the detector (Si photodiode, Hamamatsu S3071). The signal collected by the detector was sent to an amplifier (Costronics) and recorded by an oscilloscope (Tektronics TDS 2012c) on μs–ms timescales and a DAQ card (National Instruments, NI USB-6211) on ms–s timescales. Each decay was averaged by 300–500 times. All data were acquired by home-programmed software based on the LabVIEW software.

We used this technique to estimate the extinction coefficient of the doubly oxidised species. This technique uses an electrochemical pump and an optical probe. The electrochemical pump (step-potential) is carried out by applying a squared (ON/OFF) voltage (potential difference) until steady-state conditions are reached. The effect of the applied potential on the electrocatalyst was monitored using light from a 100 W tungsten lamp (Bentham IL1), equipped with an Oriel cornerstone 130 monochromator. The transmitted probe light was filtered by several band pass and long pass filters (Comar Optics) and detected by a silicon photodiode (Hamamatsu S3071). Collected photons were converted to a voltage signal, sent to an amplifier (Costronics) and recorded by an oscilloscope (Tektronics TDS 2012c) and with a DAQ card (National Instruments, NI USB-6211) on the timescale of ms–s. Simultaneously, the extracted current was monitored using a Palmsens3 potentiostat. All data were acquired on home-built LabView software.