Enhanced Surface and Bulk Recombination Kinetics by Virtue of Sequential Metal and Nonmetal Incorporation in Hematite-Based Photoanode for Superior Photoelectrochemical Water Oxidation

Abstract

Harvesting clean energy from sunlight is a promising and desirable path to resolve the energy challenge through photoelectrochemical (PEC) water splitting. Herein, we report the design and synthesis of a stable hematite photoanode with sequential metal and nonmetal incorporation to resolve the limiting factors such as low carrier density and high charge recombination for its practical applications. Comprehensive morphological, optical, and photoelectrochemical properties of the doped hematite photoanodes are presented to understand the mechanisms by which the dopant incorporation impacts the photoelectrode performance. It is found that with controlled calcination temperature metal and nonmetal incorporation not only increases the carrier density but also facilitates faster charge transfer. The charge carrier density of the photoanode derived from Mott–Schottky plot shows an increase by an order of magnitude, i.e., from 5.1 × 1019 to 5.7 × 1020 cm–3, with dual modification. The dual modified hematite photoanode shows a photocurrent density of 2.56 mA/cm2 at 1.23 V vs RHE, which is ∼5-fold higher as compared to that of the bare hematite photoanode. We believe that the present method of designing and fabricating the hematite photoanode by sequential incorporation of metal and nonmetal will provide an economical and efficient strategy for better solar energy conversion.

Tuning the Electronic Structure of Monoclinic Tungsten Oxide Nanoblocks by Indium Doping for Boosted Photoelectrochemical Performance

“…In the circuit model, R s is the series resistance, R trap is the resistance due to surface state trapping and R ct is the resistance at the interfacial position between semiconductor and electrolyte due to charge transfer among them. [37] The Nyquist plots of both doped and undoped WO 3 photoanodes are the fusion of two semicircles with different frequency regions, i. e., higher and lower frequencies. The semicircles at higher and lower frequency regions correspond to charge transfer resistance at bulk of photoanode and semiconductor electrolyte interfacial region, respectively.…”

“…For clarification, we have proposed an equivalent circuit model for fitting the impedance measurement data, as shown inside Figure 6a. In the circuit model, R s is the series resistance, R trap is the resistance due to surface state trapping and R ct is the resistance at the interfacial position between semiconductor and electrolyte due to charge transfer among them [37] . The Nyquist plots of both doped and undoped WO 3 photoanodes are the fusion of two semicircles with different frequency regions, i. e., higher and lower frequencies.…”

Facile Fabrication of a Highly Crystalline and Well-Interconnected Hematite Nanoparticle Photoanode for Efficient Visible-Light-Driven Water Oxidation

“…We demonstrate the efficient performance for PEC water oxidation of the w-α-Fe 2 O 3 photoanode prepared from the precursor solutions containing iron nitrate and EIm compared with w/o-α-Fe 2 O 3 prepared without EIm. The w-α-Fe 2 O 3 photoanode provided the highest η sep value of 27% among the state-of-the-art pristine α-Fe 2 O 3 photoanodes (Table S1), − providing IPCE 420 of 13% at 1.23 V vs RHE.…”

“…This is believed to be mainly due to inherent characters, for example, short hole diffusion length (2–4 nm), low absorption coefficient (∼10 5 cm –1 at 566 nm), , and inefficient water oxidation competed by the rapid capture of holes by the Fe 3+ e g 2 level, which lies above the top of the O 2p 6 band . The issues on these inherent characters of α-Fe 2 O 3 would be broken through by doping of another element to the lattice of α-Fe 2 O 3 to enhance the hole diffusion length, nanostructure control, and heterojunction formation to enhance the charge separation efficiency and modifying with a catalyst to improve the water oxidation reaction at the surface. − Nevertheless, there is still room to improve the performance of the state-of-the-art pristine α-Fe 2 O 3 photoanodes for PEC water oxidation, as indicated in Table S1, − including the highest IPCE (IPCE 420 ) of 36% at 420 nm for cauliflower α-Fe 2 O 3 prepared by the atmospheric pressure chemical vapor deposition (APCVD) technique . Although α-Fe 2 O 3 -based photoanodes have been fabricated via various physical and chemical techniques such as chemical vapor deposition, − ultrasonic spray pyrolysis, atomic layer deposition, dense solution-based regrown, e-beam evaporation, electrodeposition, and hydrothermal, a facile way available for mass production of α-Fe 2 O 3 photoanodes is mandatory for practical systems of solar-driven water splitting.…”

Fabrication of tin‐doped hematite modified with NiFe‐LDH nanoflakes for highly efficient solar water splitting

“…Moreover, the electron-hole pairs in hematite generally suffer from bulk and surface recombination. 7 The photogenerated charge carriers within the space charge layer or those that can diffuse into this layer are separated. However, the remaining electron-hole pairs recombine in the bulk.…”