Photoelectrochemical Hydrogen Production on α‐Fe₂O₃ (0001): Insights from Theory and Experiments

Abstract

The photoelectrochemical (PEC) decomposition of organic compounds in wastewater is investigated by using quantum chemical (DFT) methods to evaluate alternatives to water splitting for the production of renewable and sustainable hydrogen. Methanol is used as a model organic species for the theoretical evaluations of electrolysis on the surface of the widely available semiconductor hematite, α-Fe2 O3 , a widely studied photocatalyst. Three different α-Fe2 O3 surface terminations were investigated, including the predominant surface found in aqueous electrolytes, (OH)3 R. The PEC oxidation of methanol is energetically downhill, producing CO2 and protons. The protons are reduced to hydrogen on the cathode. Experimental PEC measurements were also performed for several polyalcoholic compounds, glycerol, erythritol, and xylitol, on α-Fe2 O3 as the photocatalyst and showed high incident-photon-to-current-efficiencies (IPCE) that were much greater than those of water splitting. Interestingly, high IPCEs were observed for hydrogen production from polyalcohols in the absence of any applied bias, which was not thought to be possible on hematite. These results support the potential application of PEC for hydrogen production by using widely available hematite for the PEC oxidation of selected components of organic wastewater present in large quantities from anthropogenic and industrial sources.

Iron oxide surfaces

“…A CTR study [416] was performed on a natural single crystal prepared by annealing in 1x10 -5 mbar O 2 . On exposure to a highly watersaturated atmosphere, evidence was found for a hydroxylated oxygen termination (HO) 3 -Fe-Fe-R, and a multiple coordination (HO) 3 -Fe-H 3 O 3 -termination (the Fe-(OH) 3 species is thought to occur in aqueous solution [421]). Interestingly, α-Fe 2 O 3 (0001) single crystals have also been cleaved, and prepared by a wet-chemical method (etching in Nitric acid, washing in doubly deionized water).…”

Graphene‐Supported Pyrene‐Modified Cobalt Corrole with Axial Triphenylphosphine for Enhanced Hydrogen Evolution in pH 0–14 Aqueous Solutions

“…The growing global energy demand and environmental concerns have forced people to find clean, sustainable, and environmentally benign energy carriers to replace fossil fuels . Hydrogen is an ideal energy carrier and its generation by water splitting is a key component in artificial photosynthesis for the solar‐to‐chemical energy conversion . Pt is highly active for hydrogen evolution but its scarcity and high cost restrict its widespread application .…”

One-pot synthesis and Nb4N5 surface modification of Nb4+ self-doped KNbO3 nanorods for enhanced visible-light-driven hydrogen production

“…[1][2][3][4] Theoretical calculations indicate that an effective visible light responsive photocatalyst should possess a direct band gap of around 2.0 eV. However, most of the semiconductor photocatalysts mainly harvest UV light (only 4% in the solar spectrum) because of their big band gaps (E g 4 3 eV), such as un-modified TiO 2 .…”

“…However, most of the semiconductor photocatalysts mainly harvest UV light (only 4% in the solar spectrum) because of their big band gaps (E g 4 3 eV), such as un-modified TiO 2 . [1][2][3][4] Theoretical calculations indicate that an effective visible light responsive photocatalyst should possess a direct band gap of around 2.0 eV. 5,6 Hence, various kinds of efforts have been made to extend the cut-off wavelength of wide band catalysts, including doping with the small size atomic elements (C, N, F, and S) or designing heterostructures.…”