Influence of Sb⁵⁺as a Double Donor on Hematite (Fe³⁺) Photoanodes for Surface-Enhanced Photoelectrochemical Water Oxidation

Abstract

To exploit the full potential of hematite (α-FeO) as an efficient photoanode for water oxidation, the redox processes occurring at the FeO/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb states in Sb-doped FeO photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 10 vs 1.3 × 10 cm) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb can activate multiple Fe ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.

Fe2O3 Blocking Layer Produced by Cyclic Voltammetry Leads to Improved Photoelectrochemical Performance of Hematite Nanorods

“…two distinct Fe 2p1/2 and Fe 2p3/2 peaks at 724.5 and 711.1 eV, respectively [52]. The satellite peak at 720 eV is characteristic of Fe 3+ in Fe2O3 [53]. Figure 5c shows the high-resolution O1s spectra: the peak at 530 eV corresponds to oxygen in the oxide structure, whereas the peak at 533 eV represents surface hydroxyl groups [54].…”

“…Electrochemical impedance spectroscopy (EIS) was employed to investigate the kinetics of charge transport of hematite photoanodes grown on the blocking layer and decorated with the co-catalyst by the Zn-Co treatment in comparison to the reference sample; Nyquist curves of EIS experiments under illumination are shown in Figure 7a. Clearly, the charge transfer resistance for the blocking layer hematite photoanode with the Zn-Co catalyst is reduced as compared to the reference sample [53,63]. IMPS test was carried out to investigate charge transport behavior.…”

Photo-electrochemical hydrogen production from neutral phosphate buffer and seawater using micro-structured p-Si photo-electrodes functionalized by solution-based methods

“…[9][10][11][12] However, enabling global-scale solarfuel generation requires the fabrication of devices, in particularly of photoelectrodes, from earth-abundant materials. To obtain the maximal device performance, the interplay between light-harvesting, charge separation and electron/proton transport, as well as water oxidation and reduction catalysis needs to be carefully optimized 2,3,[12][13][14][15][16][17][18][19][20] The intrinsic band gap (1.1 eV) of silicon photo-electrodes make them capable of absorbing a broad spectrum of the solar light. Over the past decades, they have thus gathered much attention towards photo-electrochemical (PEC) water splitting.…”

Enhancing Solar‐Driven Water Splitting with Surface‐Engineered Nanostructures

“…Other approaches have focused on improving the kinetics of the water oxidation reaction, the rate‐limiting step for PEC water splitting with α‐Fe 2 O 3 , through surface treatments like surface doping and co‐catalyst incorporation . Metal elements, such as Cr, Zn, Ni, Sn, and Sb, have been doped onto the surface of α‐Fe 2 O 3 nanostructures to enhance PEC performance by promoting charge migration and/or used as a doped overlayer to catalyze the surface water oxidation reaction. Co‐catalyst surface modification has been shown to effectively enhance the surface reaction by facilitating the four‐electron process of water oxidation, resulting in suppressed surface charge recombination .…”