Sn-Doped Hematite Nanostructures for Photoelectrochemical Water Splitting

Abstract

We report on the synthesis and characterization of Sn-doped hematite nanowires and nanocorals as well as their implementation as photoanodes for photoelectrochemical water splitting. The hematite nanowires were prepared on a fluorine-doped tin oxide (FTO) substrate by a hydrothermal method, followed by high temperature sintering in air to incorporate Sn, diffused from the FTO substrate, as a dopant. Sn-doped hematite nanocorals were prepared by the same method, by adding tin(IV) chloride as the Sn precursor. X-ray photoelectron spectroscopy analysis confirms Sn(4+) substitution at Fe(3+) sites in hematite, and Sn-dopant levels increase with sintering temperature. Sn dopant serves as an electron donor and increases the carrier density of hematite nanostructures. The hematite nanowires sintered at 800 °C yielded a pronounced photocurrent density of 1.24 mA/cm(2) at 1.23 V vs RHE, which is the highest value observed for hematite nanowires. In comparison to nanowires, Sn-doped hematite nanocorals exhibit smaller feature sizes and increased surface areas. Significantly, they showed a remarkable photocurrent density of 1.86 mA/cm(2) at 1.23 V vs RHE, which is approximately 1.5 times higher than that of the nanowires. Ultrafast spectroscopy studies revealed that there is significant electron-hole recombination within the first few picoseconds, while Sn doping and the change of surface morphology have no major effect on the ultrafast dynamics of the charge carriers on the picosecond time scales. The enhanced photoactivity in Sn-doped hematite nanostructures should be due to the improved electrical conductivity and increased surface area.

Dynamics of photogenerated holes in surface modified α-Fe 2 O 3 photoanodes for solar water splitting

“…The lifetime of this phase is increased under high anodic bias conditions, assigned, as pre- viously, to slower electron/hole recombination due to enhanced electron depletion in the photoelectrode at such bias conditions (36). We note here that faster recombination phases are also likely (13,37,38) although not resolved in the studies reported herein. In addition, a slow (approximately 2-s) decay phase is observed, assigned to long-lived holes, whose amplitude increases with increasingly anodic bias.…”

Fabrication of flexible and freestanding zinc chalcogenide single layers

“…3b clearly validated their highest IPCE of 42.5% at 300 nm, which was strikingly higher than that of bulk ZnSe (0.25%), (Zn 2 Se 2 )(pa) (0.4%), ZnSe-pa octuple layers (4.3%), ZnSe-pa quadruple layers (5%) and ZnSe-pa double layers (12.1%). To the best of our knowledge, the photoconversion efficiency of 42.5% is much better than that of most existing reports 22,23 . This extraordinary IPCE of the ZnSe single layers could be attributed to their several clear-cut advantages including ultraflexible, large-area, atomic thickness and high (110) orientation, which would be detailedly discussed below.…”

Achieving Highly Efficient Photoelectrochemical Water Oxidation with a TiCl4 Treated 3D Antimony‐Doped SnO2 Macropore/Branched α‐Fe2O3 Nanorod Heterojunction Photoanode

“…Introducing substitutional doping elements or forming surface passivating layer are extensively recognized as efficient strategy to enhance the photoelectrochemical performance 5, 7. Herein we realize the Ti doped hematite and TiO 2 passivating layer on the surface of hematite nanorod and mpATO by a simple hydrothermal decomposition of TiCl 4 followed a postannealing process (see the Experimental Section for details).…”

“…Although the theoretical solar‐to‐hydrogen (STH) efficiency of hematite can reach to 15% if incorporate with a proper tandem photovoltaic (PV) setup,3 the performance of the state‐of‐the‐art hematite based photoelectrode is far from the idealized model, owing to the intrinsic adverse factors such as poor electrical conducting ability, restricted hole diffusion length (<5 nm), low absorption coefficient, and low flat‐band potential in water splitting. [[qv: 1b,4]] Much efforts have been devoted to addressing this issues including elemental doping,5 morphology tailoring,[[qv: 5e,6]] and surface modification 7…”