Conformally Coupling CoAl-Layered Double Hydroxides on Fluorine-Doped Hematite: Surface and Bulk Co-Modification for Enhanced Photoelectrochemical Water Oxidation

Abstract

Earth-abundant hematite is an attractive photoanode for photoelectrochemical water splitting, whereas the intrinsic properties of inferior charge transfer and slow water oxidation kinetics still hinder its application. In response, an integrated photoanode has been constructed with hematite nanorod arrays modified by fluorine anion doping and further decorated with amorphous CoAl-layered double hydroxides (CoAl-LDH). This novel CoAl-LDH/F–Fe2O3 photoanode exhibited an excellent photocurrent density of 2.46 mA cm–2 at 1.23 V versus reversible hydrogen electrode (V RHE), five times enhanced than that of pristine α-Fe2O3. Systematic investigations reveal that fluorine anion serving as a donor dopant dramatically enhances the density of charge carrier and reduces the resistance of hematite for rapid charge transfer. Furthermore, the cocatalyst of CoAl-LDH could effectively passivate the surface defects of F–Fe2O3 and facilitate the water oxidation kinetics through an alternative pathway of holes trapped by Co species. As a consequence, the charge separation efficiencies of the bulk and surface were improved to 32.6 and 81.8%, respectively, compared with those of α-Fe2O3 (9.7 and 31.7%). Our results demonstrate that the dual modification of the bulk and surface is an attractive maneuver to ameliorate the water oxidation activity of hematite.

Hybrid photoanodes for water oxidation combining a molecular photosensitizer with a metal oxide oxygen-evolving catalyst

“…Intense researches are devoted to the development of photoelectrodes solely based on inorganic semiconductor (SC) materials, 2,7,11,15 but they face the difficulty of having a SC that can both effectively absorb visible light and display conduction and valence bands (denoted CB and VB, respectively) with adequate energy levels to catalyze OER for photoanodes and HER for photocathodes. Some PECs using SCs based on metal oxides (WO 3 , BiVO 4 , Fe 2 O 3 and CuBi 2 O 4 ) 4,7,[20][21][22][23][24] or oxynitrides (TaON, LaTiO 2 N and SrNbO 2 N) [25][26][27][28] for the photoanodes, and on p-type chalcogenides (CdTe, CuIn 1-x Ga x Se 2 ) 29,30 or metal oxides (p-Cu 2 O) [31][32][33][34] for the photocathodes, do operate under visible light. Nevertheless their STH conversion efficiency remains below 10%, the threshold for commercial applications.…”

Self‐Assembled Urchin‐Like CuWO4/WO3 Heterojunction Nanoarrays as Photoanodes for Photoelectrochemical Water Splitting

“…For instance, TiO 2 and ZnO suffer from large band gap energy and inadequate light absorption [13,14] . As for the α‐Fe 2 O 3 , the extremely short hole diffusion length (2‐4 nm) still severely restricted its photocurrent density [15–18] . Up to now, none of the single metal oxide could meet the demand for practice applications.…”

“…[13,14] As for the α-Fe 2 O 3 , the extremely short hole diffusion length (2-4 nm) still severely restricted its photocurrent density. [15][16][17][18] Up to now, none of the single metal oxide could meet the demand for practice applications.…”

Heteroatom Doping Strategy for Establishing Hematite Homojunction as Efficient Photocatalyst for Accelerating Water Splitting

“…[1][2][3] To improve the photocatalytic ability of hematite on water oxidation, it is necessary to solve the low electrical conductivity and slow oxygen evolution kinetics problems. Several strategies have been applied in past decades, such as design well-defined structure, [4][5][6] doping heteroatoms [5][6][7][8][9][10][11] as well as establishing heterojunction [12][13][14] and homojunction [15][16][17][18] to enhance the electrical conductivity and increase the carrier density. Li et al reported a regrowth strategy to fabricate Mg-doped α-Fe 2 O 3 (Mg-α-Fe 2 O 3 ) on the nonmetallic P-doped α-Fe 2 O 3 for forming the homojunction, which is able to achieve the high charge separation efficiency, favorable band alignment, and 4.7-fold photocurrent density of that for the pristine Fe 2 O 3 .…”

“…To improve the photocatalytic ability of hematite on water oxidation, it is necessary to solve the low electrical conductivity and slow oxygen evolution kinetics problems. Several strategies have been applied in past decades, such as design well‐defined structure, [4–6] doping heteroatoms [5–11] as well as establishing heterojunction [12–14] and homojunction [15–18] to enhance the electrical conductivity and increase the carrier density. Li et al .…”