Accelerating Oxygen Evolution Reaction Kinetics by Reconstructing Layered and Defective Ni₃FeOOH/FeOOH in a Hematite Photoanode

Abstract

Surface engineering has outstanding advantages for improving the carrier exaction of photoelectrodes in the photoelectrochemical water splitting field. NiFe‐layered double hydroxides (NiFe‐LDH), as promising catalysts for water oxidation, can facilitate carrier transport. But surface collapse and structural deformation limit their applications. In this work, a hematite (α‐Fe2O3) photoanode is sequentially cumulatively modified with NiFe‐LDH (Ni3FeOOH), Ag/SiO2, and FeOOH, and exhibits a high photocurrent density, which increases from 0.92 to 4.54 mA cm−2 at 1.23 V relative to the standard hydrogen electrode (VRHE). The mechanism studies demonstrate that the introduction of FeOOH suppresses the electrochemical self‐reduction of Ni3FeOOH, remedies the obvious valley formed in the current density and voltage curve, reduces recombination, and facilitates the OH− transformation, which increases the catalytic activities of the photoanode. The Ag@SiO2 nanoparticles can reduce the interface defects between Ni3FeOOH and FeOOH. The density‐functional theory calculation reveals that the valley is caused by the direction of the internal electric field formed between Ni3FeOOH and α‐Fe2O3, which is opposite to that of solid–liquid junction, resulting in serious carrier recombination. FeOOH possesses a higher electrostatic potential than that of Ni3FeOOH and α‐Fe2O3 and forms an internal electric field directing from α‐Fe2O3/Ni3FeOOH to FeOOH, which synergistically promotes carrier separation with solid–liquid junction.

Integration of a Cu2O/ZnO heterojunction and Ag@SiO2 into a photoanode for enhanced solar water oxidation

“…S10 †) prove that there is no obvious change in chemical structure in the ZnO photoanode before and aer the stability test. 45 The variation tendencies of transient current density for FTO/ZnO/Cu 2 O, FTO/ZnO/Cu 2 O/Ag, and FTO/ZnO/Cu 2 O/ Ag@SiO 2 photoanodes are consistent with those of the J-V curves (Fig. 4b).…”

“…The transient photocurrent densities of FTO/ZnO/Cu 2 O/Ag and FTO/ZnO/Cu 2 O/Ag@SiO 2 decrease significantly because of the oxidation of Ag and Ag@SiO 2 during the photoelectrochemical process. 45 As shown in Fig. 4c, the FTO/ZnO/Cu 2 O/Ag@SiO 2 photoanode possesses the smallest arc radius, indicating that the introduction of Ag@SiO 2 catalyst can decrease the charge transfer resistance to accelerate the photogenerated carrier transfer.…”

“…S10†) prove that there is no obvious change in chemical structure in the ZnO photoanode before and after the stability test. 45…”

Investigation of in situ sulfide/nitride/phosphide treatments of hematite photoanodes for improved solar water oxidation

“…FeCl 3 (1.22 g) and UR (0.27 g) were dissolved in 50 mL of distilled water to obtain a mixed aqueous solution. 33 The FTO conductive glass was obliquely immersed in the above mixed solution in a 100-mL Teflon reactor, where the conductive side faces down. The above solution was heated to 100 °C for 12 h to obtain FTO/FeOOH.…”

Regulating a Zn/Co bimetallic catalyst in a metal–organic framework and oxyhydroxide for improved photoelectrochemical water oxidation

“…However, their synthesis methods are very different and rarely realized through simple variables. 33 Although both catalysts have been reported to exhibit excellent catalytic performance, there is a lack of a related comparative study for them (similarities and differences) existing in PEC-WS. 34 In this work, two α-Fe 2 O 3 photoanodes are modified by two bimetallic ZnCo-ZIFs (a type of MOF catalyst) and ZnCoOOH catalysts, respectively.…”