Crystallinity Engineering of Hematite Nanorods for High‐Efficiency Photoelectrochemical Water Splitting

Abstract

An effective strategy to overcome the morphology evolution of hematite nanorods under high‐temperature activation is presented, via tuning the crystallinity and sintering temperature by substrate modification. It is demonstrated that the as‐prepared doping‐free hematite nanorods with fine nanostructures obtain a significantly higher photocurrent density of 2.12 mA cm−2 at 1.23 V versus RHE, due to effective charge separation and transfer.

Flat band potential determination: avoiding the pitfalls

“…Similar to the manner in which the Mott-Schottky equation is being applied, the Helmholtz layer is usually disregarded and eqn (10) is written as eqn (11), leading to an overestimation of photocurrent, as shown in Fig. 7.…”

“…[1][2][3][4] Material modication techniques are being employed in attempts to enhance solar-to-fuel conversion efficiencies. One set of such techniques can be described collectively as 'nanostructuring', [5][6][7] a term that broadly encompasses: modications of bulk material structures to improve charge transport properties, 8,9 nanotexturing of surfaces to enhance photon absorption 7,[10][11][12][13] and decoration of surfaces with catalyst particles to improve reaction kinetics via plasmonic effects. [14][15][16] While nanostructuring is proving to be benecial to the improvement of energy conversion efficiencies, it also complicates the characterization of the fundamental properties of the modied materials.…”

Enhanced Solar Water Splitting by Swift Charge Separation in Au/FeOOH Sandwiched Single‐Crystalline Fe2O3 Nanoflake Photoelectrodes

“…Moreover, Fe 2 O 3 photoanodes composed of nanoparticles usually suffer from charge migration and recombination problems at or in grain boundaries. Recently, photoanodes comprised of one‐dimensional (1D) nanoarrays (e.g., nanorods and nanotubes) grown perpendicularly to the conductive substrate [e.g., fluorine‐doped tin oxide (FTO)] have become of particular interest because of a direct electron‐transport pathway and short hole‐diffusion length to the interface, which result in improved PEC properties compared to traditional particles or porous films . More recently, vertically aligned nanosheet arrays with specifically designed different crystal facets were reported .…”

“…Recently,photoanodes comprised of one-dimensional (1D) nanoarrays (e.g.,n anorods and nanotubes) grown perpendicularly to the conductive substrate [e.g.,f luorine-doped tin oxide (FTO)] have become of particulari nterest because of ad irecte lectron-transport pathway and short hole-diffusion lengtht ot he interface, which result in improved PEC properties comparedt ot raditional particles or porousf ilms. [7][8][9][10][11] More recently,v ertically aligned nanosheet arrays with specifically designed different crystal facets were reported. [12] Owing to the different relative energies of different facets, photoexcited electrons and holes can be driven to different crystal facets, and thus certain facets of as emiconductor effect reduction whereas others facilitate oxidation.…”

Enhancing Solar‐Driven Water Splitting with Surface‐Engineered Nanostructures

“…It was proposed that these corundum‐structured oxide overlayers decreased both the lattice strain of α‐Fe 2 O 3 and the density of surface states, thereby partially suppressing surface charge recombination . Recent efforts have trended toward low‐dimensional nanostructures, as structures of this type are likely to utilize the benefits afforded by designed surface overlayers, and thus show functional behavior relating to the engineered surface and/or interfacial region . Kronawitter et al fabricated a novel one‐dimensional α‐Fe 2 O 3 /WO 3 core/shell nanorod array, and demonstrated that visible light PEC activity performed by hole extraction from the α‐Fe 2 O 3 core should be directly related to the unique features of the core/shell nanoscale architecture, such as interfacial electronic structure reconstruction via p‐d orbital hybridization .…”