Visible Light Photoelectrochemical Properties of PbCrO₄, Pb₂CrO₅, and Pb₅CrO₈

Abstract

Photoactivities of lead chromates with various combinations of Pb and Cr are rapidly screened using scanning electrochemical microscopy (SECM). In the rapid screening investigation, the metal oxide spot electrode with a Pb/Cr ratio of 2:1 exhibits the highest photoactivity among the semiconductor prepared with different compositions. The photoactivity and electrochemical properties of thin-film electrodes of PbCrO 4 , Pb 2 CrO 5 , and Pb 5 CrO 8 are further studied following the combinatorial screening. In the bulk electrode measurements, the Pb 2 CrO 5 bulk electrode displays the highest photocurrent of 0.23 mA/cm 2 for SO 3 2− oxidation at 0.4 V vs Ag/AgCl under 100 mW/cm 2 UV−vis light irradiation. Pb 2 CrO 5 presents visible light activity with an absorption wavelength up to 550 nm and an incident photon to current conversion efficiency (IPCE) of 10% at the wavelength of 340 nm. The onset wavelength observed in the UV−vis absorption spectrum increases with increasing Pb contents in lead chromates. Optically obtained direct band gaps decreased from 2.38 to 2.25 to 2.07 eV for PbCrO 4 , Pb 2 CrO 5 , and Pb 5 CrO 8 , respectively. However, the onset wavelength that appeared in IPCE is 2.26 ± 0.02 eV for all three lead chromates where the photocurrent under longer wavelength light irradiation is insignificant. The results imply that more Pb 6s orbitals form interband states, increasing optical transitions in lead chromates. The band structures of PbCrO 4 , Pb 2 CrO 5 , and Pb 5 CrO 8 are also determined by electrochemical analyses and ultraviolet photoelectron spectroscopy (UPS).

Can a PbCrO4 Photoanode Perform as Well as Isoelectronic BiVO4?

“…The measured PbCrO 4 bandgap matches those reported previously in the literature. 17,18,37 The photoelectrochemical behavior of PbCrO 4 was first investigated in pH 9 borate buffer with 0.1 M Na 2 SO 3 as the hole scavenger. The rapid oxidation kinetics of a hole scavenger such as sulfite allows us to assume that the loss of surface-reaching holes to surface recombination is negligible.…”

“…There have been a few previous papers on PbCrO 4 as a photoanode, but the photocurrent densities of PbCrO 4 reported in these studies were not close to those of BiVO 4 . 17,18 For example, at 1.23 V vs RHE, the best performance achieved by PbCrO 4 for sulfite oxidation is 0.5 mA/cm 2 , while that of BiVO 4 is ∼5 mA/cm 2 . 5,6,18 However, we note that the electron−hole separation yield or any other photoelectrochemical property of a polycrystalline photoelectrode varies significantly depending on the quality of the photoelectrode because impurities, unevenness in composition, poor electrical continuity, poor quality interface with the conducting substrate, and poor crystallinity considerably affect the electron−hole recombination and charge-transport properties.…”

In Situ Analytical Techniques for the Investigation of Material Stability and Interface Dynamics in Electrocatalytic and Photoelectrochemical Applications

“…[231] The Bard group has reported many studies of spatially resolved photoelectrode activity enabled by light-coupled SECM. [232][233][234][235][236][237][238][239][240] They have pioneered the application of SECM as a screening technique for photoelectrocatalysts by imaging the illuminated activity of arrays of compositionally varied catalyst spots on a semiconductor [232] or varied doping of a photoelectrode (Figure 12f). [233] In another novel photoelectrochemistry application, Esposito et al combined SECM with scanning photocurrent microscopy (SPCM) by fixing a laser beam immediately next to the UME tip, allowing them to map the rate of local light-driven H 2 evolution at Pt catalyst islands on p-Si photocathodes.…”

Putting the Squeeze on Lead Chromate Nanorods

“…7 It is also relevant for geophysical studies and for radioactive waste management. 8 As a consequence, several studies have been performed in order to improve the characterization of PbCrO 4 at ambient, 9 high-pressure (HP), 10−13 low-temperature, 14 and high-temperature (HT) conditions, 15 as well as to develop green synthesis methods for nanoscale PbCrO 4 . 16,17 One of the most relevant achievements on the study of PbCrO 4 is the discovery of a very rich polymorphism.…”

“…It is also relevant for geophysical studies and for radioactive waste management . As a consequence, several studies have been performed in order to improve the characterization of PbCrO 4 at ambient, high-pressure (HP), − low-temperature, and high-temperature (HT) conditions, as well as to develop green synthesis methods for nanoscale PbCrO 4 . , One of the most relevant achievements on the study of PbCrO 4 is the discovery of a very rich polymorphism. An orthorhombic Barite-type polymorph (space group Pnma ) has been reported at HT, and a sequence of phase transitions has been observed under HP. , These transitions include a transformation to a tetragonal scheelite-type polymorph (space group I 4 1 / a ) and a subsequent transformation to an orthorhombic distortion of Barite (space group P 2 1 2 1 2 1 ).…”