Ultrathin Amorphous Ni(OH)₂ Nanosheets on Ultrathin α‐Fe₂O₃ Films for Improved Photoelectrochemical Water Oxidation

Abstract

Hematite (α‐Fe2O3) is a promising photoanode material for photoelectrochemical (PEC) water splitting, however, its performance is largely limited by the short hole diffusion length that requires the thin active layer and efficient catalysts. In this work, ultrathin α‐Fe2O3 films are fabricated using atomic layer deposition technology, and then ultrathin amorphous Ni(OH)2 nanosheets are decorated on α‐Fe2O3 films through a hydrothermal method. The microscopic morphology, phase, and composition are characterized by scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectra, and high resolution transmission electron microscopy. The quantity of Ni(OH)2 is adjusted by controlling the growth time. The results show that the onset potential of the optimum thick Ni(OH)2/Fe2O3 films demonstrate a cathodical shift by 400 mV, and the photocurrent density at 1.23 V is enhanced from 0.21 to 0.37 mA cm−2 compared with the pristine ultrathin α‐Fe2O3 films. The Ni(OH)2/Fe2O3 films show the superior stability up to 20 h. The enhanced PEC performances are attributed to the amorphous Ni(OH)2 nanosheets that do not affect obviously the light utilization, maintain large specific area to the electrolyte, and store holes produced in Fe2O3 for oxidizing water efficiently in situ with fast regeneration of Ni2+.

Visible‐Light‐Driven Plasmonic Photocatalysis Enhanced by Charge Accumulation

“…We coated the TiO 2 /AuNP electrode with Ni(OH) 2 or CrO x to obtain n‐M‐p type electrodes, namely TiO 2 /AuNP/Ni(OH) 2 and TiO 2 /AuNP/CrO x electrodes. In the former, AuNPs were rather loosely covered with Ni(OH) 2 nanosheets with a thickness of 10.4±2.3 nm (Figure c, d) . In the latter, AuNPs were tightly coated with a dense CrO x layer of 30.3±3.5 nm thick (Figure e, f) …”

“…Since ohmic contact is formed at the Au‐Ni(OH) 2 interface (Figure b), smooth charge transfer to Ni(OH) 2 is expected. In addition, Ni(OH) 2 is reported to be an electrocatalyst for oxygen evolution from water without noble metal co‐catalysts …”

“…In addition, Ni(OH) 2 is reported to be an electrocatalyst for oxygen evolution from water without noble metal co-catalysts. [25][26][27] Cr 2 O 3 is a p-type semiconductor that is used as an energy storage material in supercapacitors, [28,29] so that it could be suitable for positive charge accumulation. Because the ionization energy of Cr 2 O 3 is~5.7 eV [30] and work function of Au is 5.1 eV, [31] Schottky junction with the barrier height of~0.6 eV is expected for the Au-Cr 2 O 3 interface ( Figure 1c).…”

A Dual Plasmonic Photoelectrode System for Visible‐Light Photocatalysis

“…The Faradaic efficiency for this photoanode was estimated to be ∼40% at +0.2 V vs. Ag|AgCl in a three‐electrode system with a Pt counter electrode and a N 2 ‐saturated 0.1 M KOH electrolyte. Ni(OH) 2 is known to be a good catalyst for oxygen evolution . It can also store positive charges, and therefore has been applied to photocatalysts with the oxidative energy storage ability and a photoanode for multi‐electron oxidation .…”

Synthesis of Host‐Guest Hematite Photoelectrodes for Solar Water Splitting

“…This combination should result in higher photocurrents, including better charge extraction efficiencies. Additionally, the required overpotential for water oxidation reactions can be reduced employing surface treatments, such as co‐catalyst coatings, which enhance the photopotential and decrease the electron‐hole recombination . To reach the maximum performance of a α‐Fe 2 O 3 photoelectrode, nanostructuring and surface passivation strategies should be combined …”