A bifunctional lead-iron oxyfluoride, PbFeO2F, that functions as a visible-light-responsive photoanode and an electrocatalyst for water oxidation.

Ryusuke Mizuochi,Kazuhiko Maeda,Kazunari Izumi,Yoshiyuki Inaguma

doi:10.1039/d1ra04793k

Abstract

The oxyfluoride PbFeO2F was investigated as a photoanode material and as an electrocatalyst for water oxidation. PbFeO2F powder, which was synthesized by a high-pressure method and had an estimated bandgap of 2.1 eV, was deposited onto a fluorine-doped tin oxide (FTO) substrate. Mott–Schottky plot measurements for the PbFeO2F/FTO electrode showed n-type semiconductivity of PbFeO2F, with a flat-band potential of +0.53 ± 0.05 V vs. reversible hydrogen electrode (RHE). The PbFeO2F/FTO electrode, which was modified with a conductive TiO2 layer and a cobalt phosphate water-oxidation cocatalyst, showed a clear anodic photocurrent in aqueous K3PO4 solution under visible-light irradiation (λ < 600 nm). The PbFeO2F/FTO electrode without any modification functioned as a stable water-oxidation electrocatalyst to form O2 with a faradaic efficiency of close to unity. This study demonstrates that PbFeO2F is a bifunctional material, serving as a water-oxidation photoanode under a wide range of visible-light wavelengths and as an electrocatalyst that operates at a relatively low overpotential for water oxidation.

Highlights

Hydrogen is expected to be used as a renewable energy carrier
Scanning electron microscopy (SEM) observations show that the synthesized PbFeO2F consisted of 0.1–10 mm particles (Fig. S2†)
PbFeO2F synthesized by a high-pressure method had grain sizes ranging from 0.1 to 10 mm and an estimated bandgap of 2.1 eV

Summary

Introduction

Hydrogen is expected to be used as a renewable energy carrier. Water splitting using semiconductor photoelectrodes or photocatalysts has attracted attention as a method of generating clean hydrogen using solar energy.[1,2,3,4,5,6] Titanium-based metal oxides (e.g., TiO2 (ref. 7) and SrTiO3 (ref. 8)) have been developed as stable photoanode materials for solar water oxidation but are not capable of efficiently utilizing visible light, which represents the majority of solar energy, because of their wide bandgaps (>3 eV). The PbFeO2F/FTO electrode, which was modified with a conductive TiO2 layer and a cobalt phosphate water-oxidation cocatalyst, showed a clear anodic photocurrent in aqueous K3PO4 solution under visible-light irradiation (l < 600 nm).

Results

Conclusion