DOI: 10.25338/b83h0k
title: Data from: Contactless measurement of the photovoltage in BiVO4 photoelectrodes

description: The power output of photoelectrochemical devices for solar energy-to-fuel
 conversion is determined by the photovoltage of the junction under
 illumination. In the presence of fast redox couples, the photovoltage can
 be obtained directly from current-voltage measurements of the device.
 However, for slow redox couples (H+/H2, O2/H2O) used in solar fuel
 photoelectrodes, photovoltage measurements are not straightforward, due to
 the kinetic overpotentials during charge transfer. Here we show that the
 photovoltage of BiVO4 electrodes in contact with fast electron donors KI,
 Na2SO3 or H2O2 or K4Fe(CN)6 can be measured in a contactless way with
 vibrating Kelvin probe surface photovoltage (SPV) spectroscopy. The
 photovoltage varies with illumination wavelength and intensity and matches
 the open circuit potential of the electrodes, obtained separately from
 electrochemical measurements. Plots of the photovoltage versus irradiance
 can be used to predict the oxidizing power of each electrode under zero
 applied bias. Except for K4Fe(CN)6, which causes shunting in the BiVO4
 electrode, photovoltage values correlate well with the built-in potential
 of each junction. The ability to obtain photovoltage information through
 contactless SPV measurements will be useful in the search for solid-liquid
 junctions with superior energy conversion properties.
description: Surface photovoltage (SPV) data was obtained
 with the vibrating Kelvin probe technique, using a semi-transparent (60%)
 3.0 mm diameter gold Kelvin probe (<em>Kelvin Probe
 S,</em> <em>Delta PHI Besocke</em>) and
 a <em>Besocke Kelvin Control</em>.  Measurements were
 conducted in a custom-made chamber under vacuum (≤ 2 ×
 10<sup>-4</sup> mbar) or in
 H<sub>2</sub>O-saturated N<sub>2</sub> gas.
 Samples were coated  with 10-15 mL of liquid electrolytes using a
 micropipette and covered with a glass cover slip
 (Fisher Scientific, 0.17 to 0.25 mm
 thickness). For the
 acquisition of full spectra, n-GaP was illuminated through the Kelvin
 probe using light from a 300 W tungsten-halogen lamp filtered through an
 Oriel Cornerstone 130 monochromator (1-10 mW cm<sup>-2</sup>).
 Scans were performed from 9600 cm<sup>-1</sup> to 40000
 cm<sup>-1</sup>. The contact potential difference (CPD) data
 were corrected for drift effects by subtracting a fitted logarithmic curve
 of a dark scan from the spectral scan. Intensity-dependent measurements
 were performed with an air-cooled 400 nm LED array connected to a DC power
 supply. The voltage was regulated between 33 and 43.2 V to produce
 irradiances of 5x10<sup>-4</sup> – 60
 mW/cm<sup>2</sup> at the sample surface, as measured by a
 photometer equipped with a GaAsP UV-Vis detector (International Light
 Technologies, Inc), and after correction using a 60% transmission value
 for the Kelvin probe. Linear sweep voltammograms were recorded in an
 electrochemical cell controlled by a Gamry Reference 600 potentiostat.
 Working electrodes and electrolytes were prepared as described below. All
 electrolytes were purged with N<sub>2</sub>for 20 mins before
 and during the measurements, except for
 H<sub>2</sub>O<sub>2</sub> solutions, which were
 purged with air.   A calomel electrode (3.5 M KCl) was used as the
 reference and a platinum wire as the counter electrode. The cell was
 calibrated using the standard reduction of potential of hexacyanoferrate
 (0.358 V vs NHE) and potentials were then adjusted to the RHE scale using
 the formula V<sub>RHE</sub> =
 V<sub>NHE</sub> + 0.0592 × pH. A 400 nm LED was used for illumination.
 Measurements were taken at
 20 mV/s intervals with light chopped approximately every 3 s while
 stirring the electrolyte. Open circuit potential (OCP) measurements were
 conducted using a two-electrode system consisting of the sample as working
 electrode and a calomel electrode (3.5 M KCl) as reference and counter electrode.
 A monochromatic 400 nm LED with an intensity range of 0.0009 − 305
 mW/cm<sup>2</sup> at the working electrode was employed for
 illumination.  Chronoamperometry was performed in a 2-electrode
 set-up, with the sample as the working electrode and a Pt wire as both the
 counter and reference electrode. A 0 V bias was applied and a 400 nm LED
 (250 mW/cm<sup>2</sup>) was used as the light
 source.
description: # Contactless Measurement of Photovoltage in BiVO4 Photoelectrodes Access
 this dataset on Dryad(DOI:10.25338/B83H0K) This set contains surface
 photovoltage spectra (Figs 3a-d), transient surface photovoltage data
 (Figs 3e-h, S3), Open circuit potential data (Fig 4, S5), Fermi level data
 (Fig. 5), short circuit current data (Fig S6). All data is organized in
 the same order as in the Figures in the source publication. ## Description
 of the data and file structure The data is organized in csv format, as
 follows: Surface photovoltage spectra of n-BiVO4 Fig3aVacuum Column A:
 Photon energy / eV Column B: Delta CPD signal / V Fig3a005MI3 Column A:
 Photon energy / eV Column B: Delta CPD signal / V Fig3a0005MI3 Column A:
 Photon energy / eV Column B: Delta CPD signal / V Fig3bNa2SO3 Column A:
 Photon energy / eV Column B: Delta CPD signal / V Fig3cH2O2 Column A:
 Photon energy / eV Column B: Delta CPD signal / V Fig3dHCF Column A:
 Photon energy / eV Column B: Delta CPD signal / V Transient SPV repeat
 scans Fig3eI3 Column A: Time / s Column B: CPD signal / V Fig3fNa2SO3
 Column A: Time / s Column B: CPD signal / V Fig3gH2O2 Column A: Time / s
 Column B: CPD signal / V Fig3hHCF Column A: Time / s Column B: CPD signal
 / V Open circuit potentials / V and DeltaCPD / V Fig4aI3 Column A: Light
 power / mW cm-2 Column B: CPD / V Column C: Light power / mW cm-2 Column
 D: VOC/ V Fig4bNa2SO3 Column A: Light power / mW cm-2 Column B: CPD / V
 Column C: Light power / mW cm-2 Column D: VOC/ V Fig4cH2O2 Column A: Light
 power / mW cm-2 Column B: CPD / V Column C: Light power / mW cm-2 Column
 D: VOC/ V Fig4dHCF Column A: Light power / mW cm-2 Column B: CPD / V
 Column C: Light power / mW cm-2 Column D: VOC/ V Fermi Levels EFf and EFb
 / v Fig5aI3 Column A: Light power / mW cm-2 Column B: EFb/ V Column C:
 EFf/ V Fig5bNa2SO3 Column A: Light power / mW cm-2 Column B: EFb/ V Column
 C: EFf/ V Fig5cH2O2 Column A: Light power / mW cm-2 Column B: EFb/ V
 Column C: EFf/ V Fig5dHCF Column A: Light power / mW cm-2 Column B: EFb/ V
 Column C: EFf/ V Transient SPV repeat scans FigS3aI3 Column A: Photon
 energy / eV Column B: Delta CPD signal / V Column C: Photon energy / eV
 Column D: Delta CPD signal / V FigS3bNa2SO3 Column A: Photon energy / eV
 Column B: Delta CPD signal / V Column C: Photon energy / eV Column D:
 Delta CPD signal / V FigS3cH2O2 Column A: Photon energy / eV Column B:
 Delta CPD signal / V Column C: Photon energy / eV Column D: Delta CPD
 signal / V FigS3dHCF Column A: Photon energy / eV Column B: Delta CPD
 signal / V Column C: Photon energy / eV Column D: Delta CPD signal / V
 Open circuit potential measurements FigS5aI3 Column A: time / s Column B:
 E vs 3.5MSCE / V Column C: E vs RHE / V FigS5bNa2SO3 Column A: time / s
 Column B: E vs 3.5MSCE / V Column C: E vs RHE / V FigS5cH2O2 Column A:
 time / s Column B: E vs 3.5MSCE / V Column C: E vs RHE / V FigS5dHCF
 Column A: time / s Column B: E vs 3.5MSCE / V Column C: E vs RHE / V Short
 Circuit Current / mA cm-2 FigS6aI3 Column A: time / s Column B: I / microA
 cm-2 FigS6bNa2SO3 Column A: time / s Column B: I / microA cm-2 FigS6cH2O2
 Column A: time / s Column B: I / microA cm-2 FigS6dHCF Column A: time / s
 Column B: I / microA cm-2 ## Sharing/Access information Daemi, S., et al.,
 Contactless Measurement of Photovoltage in BiVO4 Photoelectrodes. Energy
 Environ. Sci., 2023. https://doi.org/10.1039/D3EE02087H.