Epitaxial Bi₂FeCrO₆ Multiferroic Thin-Film Photoanodes with Ultrathin p-Type NiO Layers for Improved Solar Water Oxidation

Abstract

The photoelectric properties of multiferroic double-perovskite Bi2FeCrO6 (BFCO), such as above-band gap photovoltages, switchable photocurrents, and bulk photovoltaic effects, have recently been explored for potential applications in solar technology. Here, we report the fabrication of photoelectrodes based on n-type ferroelectric (FE) semiconductor BFCO heterojunctions coated with p-type transparent conducting oxides (TCOs) by pulsed laser deposition and their application for photoelectrochemical (PEC) water oxidation. The photocatalytic properties of the bare BFCO photoanodes can be improved by controlling the FE polarization state. However, the charge recombination as well as the limited charge transfer kinetics in the photoanode/electrolyte cause major energy loss and thus hinder the PEC performance. We show that this problem may be addressed by the deposition of an ultrathin p-type NiO layer on the photoanode to enhance the charge transport kinetics and reduce charge recombination at surface-trapped states for increased surface band bending. A fourfold enhancement of photocurrent density, up to 0.4 mA cm–2 (at +1.23 V vs RHE), a best performance of stability over 4 h, and a high incident photon-to-current efficiency (∼3.7%) were achieved under 1 sun illumination in such p-NiO/n-BFCO heterojunction photoanodes. These studies reveal the optimization of PEC performance by polarization switching of BFCO and the successful achievement of p-TCOs/n-FE heterojunction photoanodes that are able to sustain water oxidation that is stable for many hours.

High Interfacial Hole‐Transfer Efficiency at GaFeO3 Thin Film Photoanodes

“…[ 12–17 ] Ferroelectric materials such as BiFeO 3 and Bi 2 FeCrO 6 show complex PEC properties that have been linked to ferroelectric domains. [ 18,19 ] For instance, BiFeO 3 exhibits both n‐ and p‐type conductivity, including above photovoltages larger than the bandgap. [ 20–22 ]…”

Design of MOF‐Derived NiO‐Carbon Nanohybrids Photocathodes Sensitized with Quantum Dots for Solar Hydrogen Production

“…Besides its use as mesoporous layer for p‐type dye‐sensitized solar cells (DSSCs), NiO has also been used as hole transporting/electron blocking layer in perovskite solar cells, due to its inertness and intrinsically p‐type conductivity with a deep valence band (5.1–5.4 eV). [ 31 ] These characteristics are beneficial for both efficient hole extraction and device stability. In our work a back‐illuminated configuration is used, thus more holes are photogenerated at the back contact and be exposed to recombination centers.…”

Photocatalysis Within Intrinsic Spontaneous Polarization Electric Field

“…Therefore, a fourfold increase of photoirradiated current intensity (0.4 mA cm − 2 at +1.23 V versus RHE) with a high stability over 4 h and outstanding photon‐to‐current efficiency (3.7%) were achieved under sun illumination over the constructed p‐NiO/n‐Bi 2 FeCrO 6 heterojunction photoanodes. [ 38 ] Lu and coworkers designed a multiferroelectric Bi 5 CoTi 3 O 15 by in situ synthesized BiCoO 3 [36m] . Due to synergism between electronic structure optimization and ferroelectric polarization, the multiferroic electrocatalysts with ISPEFs were therefore more efficient than an IrO 2 electrocatalyst.…”