Activating the surface and bulk of hematite photoanodes to improve solar water splitting

Abstract

A simple electrochemical activation treatment is proposed to improve effectively the photoelectrochemical performance of Nb,Sn co-doped hematite nanorods. The activation process involves an initial thrice cathodic scanning (reduction) and a subsequent thrice anodic scanning (oxidation), which modifies both the surface and bulk properties of the Nb,Sn:Fe 2 O 3 photoanode. First, it selectively removes the surface components to different extents endowing the hematite surface with fewer defects and richer Nb-O and Sn-O bonds and thus passivates the surface trap states. The surface passivation effect also enhances the photoelectrochemical stability of the photoanode. Finally, more Fe 2+ ions or oxygen vacancies are generated in the bulk of hematite to enhance its conductivity. As a result, the photocurrent density is increased by 62.3% from 1.88 to 3.05 mA cm À2 at 1.23 V RHE , the photocurrent onset potential shifts cathodically by $70 mV, and photoelectrochemical stability improves remarkably relative to the pristine photoanode under simulated sunlight (100 mW cm À2 ). Fig. 3 XPS spectra of the pristine and activated Nb,Sn:Fe 2 O 3 photoanode before and after surface etching ($5 nm), respectively. (a 0 and a 1 ) Fe 2p. (b 0 and b 1 ) O 1s. (c 0 and c 1 ) Nb 3d. (d 0 and d 1 ) Sn 3d.This journal is

Recent advances on interfacial engineering of hematite photoanodes for viable photo‐electrochemical water splitting

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“…Surface activation is an important alternative for excellent hematite photoanode, owing to its capability of reducing or removing the hematite surface defects, and thus enhanced PEC stability. Lee et al proposed a simple electrochemical activation treatment to enhance its conductivity by reducing the hematite surface defects, making richer NbO and SnO bonds, and generating more Fe 2+ ions or oxygen vacancies in hematite bulk 87 . The photocurrent density was increased to 3.05 mA cm −2 at 1.23 V RHE in comparison to the raw hematite photoanode.…”

The behavior of hydrothermally synthesized hematite nanorods prepared on spin coated seed layers

“…While nano-engineering of electrodes addresses some of the limiting factors for hematite performance, a multifaceted approach to address the various limitations of material performance is reported to yield better results [21]. For example, a study conducted by Sun et al used a consolidated strategy of doping, surface-etching, and seed layering to enhance the performance of hematite NRs [18].…”

Revealing the synergy of Sn insertion in hematite for next‐generation solar water splitting nanoceramics

“…The presence of natural mineral reserves and mining activity represents an advantage if hematite is used in PEC photoanodes, since the demand could be supplied by the countries that explore iron sources. To overcome well‐known intrinsic deficiencies of hematite associated with their electronic limitation that make the real response fall short of the predicted theoretical efficiency into solar to hydrogen conversion, different elements, such as: Ti, 18 V, 19 Sb, 20,21 P, 22 Cr, 23 B, 24,25 Ge, 26 and Sn, 27–32 and combinations like Nb‐Sn, 33 Ti‐Mg, 34 and Co‐Sn, 35 have been successfully employed. Sn has been highlighted as a potential modifier for this semiconductor polycrystalline ceramic, since it has been reported as able to improve the separation of photogenerated charges, achieving the highest photocurrent values among hematite photoanodes with different morphologies 36–38 .…”