Revealing the Beneficial Effects of FeVO₄ Nanoshell Layer on the BiVO₄ Inverse Opal Core Layer for Photoelectrochemical Water Oxidation

Abstract

In this paper we developed a template-assisted three-dimensionally ordered BiVO4 inverse opal (IO) film by sandwich-type infiltration through self-assembled colloidal polystyrene (PS) opal beads with a diameter of 410 nm (±20 nm) for photoelectrochemical hydrogen production. Herein, the ordered BiVO4 inverse opal structure possessed a pore diameter of ∼340 nm and wall thickness of ∼20 nm, providing a large surface area. Their photoelectrochemical behavior were assessed under 1 sun illumination (100 mW/cm2 with AM 1.5 filter) in 0.5 M Na2SO4 (pH 7) which displayed a photocurrent density (J sc) of 0.8 mA/cm2 at 1.23 V vs a normal hydrogen electrode (NHE). Low photocurrents of BiVO4 IO photoelectrodes are due to their limited photoelectrochemical ability to split water under light irradiation and their intrinsically low electronic conductivities. To overcome these problems, BiVO4 IO film was modified to deposit a nanolayer of n-type FeVO4 having a narrow band gap (E g = 2.06 eV). The bilayered BiVO4/FeVO4 core–shell film has efficient photoelectrochemical (PEC) properties compared to unmodified BiVO4, showing a photocurrent density of 2.5 mA/cm2 at 1.23 V vs NHE, probably resulting from a favorable charge transfer/transport phenomenon under beneficial band alignment as well as visible light absorption by the FeVO4 layer.

Pseudocapacitive Behavioral Testing of Iron Vanadate Nanoparticles Synthesized by Simple Co- Precipitation Method

“…The higher and lower frequency region contains the semicircle with spike which indicates the pseudocapacitive behaviour of the prepared iron vanadate nanoparticles. This is found to be in correspondence with other electrochemical results [25].…”

Elucidation of the opto-electronic and photoelectrochemical properties of FeVO4 photoanodes for solar water oxidation

“…25 It was first identified by a highthroughput screening method as a potential photoelectrode material with good absorption in the visible part of the solar spectrum. 26 The band gap of FeVO4 is reported to be ~2.0-2.1 eV; [27][28][29] while it is slightly larger than the ideal 1.7-1.9 eV, the theoretical achievable STH efficiency is still a respectable 16%. The photocurrent density of the undoped material is, however, less than 0.1 mA cm -2 at 1.23 V vs. RHE (potential relative to reversible hydrogen electrode).…”

Nanolayered CuWO4 Decoration on Fluorine-Doped SnO2 Inverse Opals for Solar Water Oxidation

“…However, the large band gap (E g ) of TiO 2 (> 3.0 eV) limits its light absorption to only 5% of solar light similar to ZnO, Nb 2 O 5 and SnO 2 . Considering the intimate relationship with photocurrent density and incident solar light absorption in PEC system, the exploration of narrower bandgap materials (e.g., WO 3 , α-Fe 2 O 3 , BiVO 4 ) as photoelectrodes is a reasonable approach to enhanced visible light capture [5][6][7]. More recently, copper tungstate (CuWO 4 , E g = 2.25 eV), which is another material showing visible light absorption to have ntype behavior, has been actively investigated because of its narrower bandgap relative to that of WO 3 (E g = 2.8 eV), the high chemical stability resulting from strong covalency associated with the copper oxygen bonds, inhibition of dissolution to form soluble tungstates by the known acid-base reaction in WO 3 at pH > 5, and high chemoselectivity even in the Clsolution [8].…”