Simultaneously Enhanced Charge Separation and Transfer in Cocatalyst-Free Hematite Photoanode by Mo/Sn Codoping

Abstract

It is well-known that sluggish surface charge transfer on a cocatalyst-free hematite photoanode limits its solar conversion efficiency in photoelectrochemical (PEC) water splitting. Here, Mo is used as a codopant synergistically with Sn in α-Fe2O3 to solve this problem. Besides causing a slight narrowing of bandgap, morphological change, and even sublimation loss of α-Fe2O3, Mo doping also imports low-valent Fe due to charge compensation with MoV/VI as indicated by X-ray photoelectron spectroscopy and Bader charge computation, which increases the densities of donor and surfaces states. Although rate law analysis demonstrates slight retardation of surface reaction kinetics, strongly inhibited charge recombination in surface states by Mo doping still contributes to improving the photocurrent density and reducing the onset potential of α-Fe2O3 and Sn–Fe2O3 photoanodes. An optimized Mo/Sn–Fe2O3 photoanode can realize a low onset potential of 0.68 V vs a reversible hydrogen electrode (VRHE) and a photocurrent density of 1.97 mA cm–2 at 1.23 VRHE, enhanced by 58% and 20 times compared to Sn–Fe2O3 and α-Fe2O3, respectively. It is demonstrated that Mo doping promotes charge transfer which differs from most traditional n-type dopants that facilitate charge separation but inhibit charge transfer. This report expands the n-type dopant family of α-Fe2O3 for efficient PEC water splitting.

Molybdenum-doped iron oxide nanostructures synthesized via a chemical co-precipitation route for efficient dye degradation and antimicrobial performance: in silico molecular docking studies

“…3b and c . Subsequently, the 6% Mo-doped Fe 3 O 4 sample exhibited a completely different morphology, where the nanorods disappeared and an excess of surface floccules of Mo emerged on the surface of the nanoparticles, 47 as presented in Fig. 3d .…”

“…Upon doping, slight peak shis with a signicant decrease in peak intensity were manifested due to the enhanced structural disorder and amorphous nature of the high concentration of occules on the Mo-doped samples. 47 The crystallite size (D) of the prepared materials was measured using the Debye-Scherrer equation. The difference in crystalline size basically depends on the angles of diffraction and the effect of peak broadening.…”

“…Upon doping, slight peak shifts with a significant decrease in peak intensity were manifested due to the enhanced structural disorder and amorphous nature of the high concentration of floccules on the Mo-doped samples. 47 …”

Exploring the effect of partial B-site Al3+–Mg2+ dual substitution on optoelectronic, surface, and photocatalytic properties of BaTaO2N

“…4 A photocurrent density of 1.97 mA cm −2 at 1.23 V RHE and a relatively low onset potential of 0.68 V RHE were obtained by a simultaneous introduction of Sn and Mo in α-Fe 2 O 3 , where the former accelerated charge separation by improving conductivity and the latter induced high density of surface trapping states, leading to the inhibition of charge recombination kinetics in surface states. 5 A significant increase in the concentration of (co)doped ions decreases the efficiency. By applying a computational method, Smart et al 6 recently found a doping clustering, which traps free-electron polarons and severely lowers the carrier concentration with respect to the doping concentration, to be responsible for the doping bottleneck in α-Fe 2 O 3 , and proposed a codoping with dopants having low binding energies for clustering, such as Sn–Ti, as a solution.…”

Lanthanide-Based Dual Modulation in Hematite Nanospindles for Enhancing the Photocatalytic Performance

“…Photocatalysis has received extensive attention for the direct utilization of solar energy to deal with environmental and energy problems. − As one of the most important photocatalysts, hematite (Fe 2 O 3 ) has attracted much attention because of its low cost, suitable band gap (absorption of visible light), and thermodynamic stability. − However, its photocatalytic efficiency is still limited by some shortcomings such as short-holes diffusion length, fast photoelectron pair recombination, and poor electron conductivity. , Currently, many strategies, including elemental doping, heterojunction formation, and defect engineering, have been used to modulate the properties of Fe 2 O 3 so as to improve the separation of photoelectron–hole pairs and finally achieve enhanced photocatalytic activity. − …”