X‐Shaped α‐FeOOH with Enhanced Charge Separation for Visible‐Light‐Driven Photocatalytic Overall Water Splitting

Abstract

Photocatalytic overall water splitting (POWS) is a promising route for converting solar energy into green and sustainable energy. Herein, we report a facile hydrothermal approach for the fabrication of x-shaped α-FeOOH photocatalysts containing high-index facets for POWS. The x-shaped α-FeOOH photocatalysts exhibited enhanced visible-light-driven POWS activities in comparison with that of FeOOH without x-structures, with a maximum H and O evolution rate of 9.2 and 4.7 μmol h g , respectively. The morphology and particle size of the α-FeOOH could be controlled by adjusting the NH F concentration in the precursors. The photodeposition of Pt and RuO on the x-shaped α-FeOOH revealed the specially separated reduction and oxidation centers on the surface of α-FeOOH, with the oxidation-active sites selectively located on the edges of the α-FeOOH x-structures. Electrochemical experiments further affirmed the enhanced charge separation in the x-shaped α-FeOOH. The smaller particle size and unique x-shape of the α-FeOOH photocatalyst were shown to enhance the POWS performance owing to the large specific surface area, high proportion of exposed high-index facets, high electron-transfer efficiency and effective separation of the photogenerated electron-hole pairs. The current study revealed that the x-shaped α-FeOOH products could serve as cost-effective and stable photocatalysts for POWS.

Thermally treated zeolitic imidazolate framework-8 (ZIF-8) for visible light photocatalytic degradation of gaseous formaldehyde

“…5c), the valence band (VB) maximum positions . 41 Consequently, a diagram of the band structures is established as shown in Fig. 5d.…”

Tailored Assembly of Molecular Water Oxidation Catalysts on Photoelectrodes for Artificial Photosynthesis

“…Interestingly and unfortunately, however, a limited number of electrocatalysts have been found effective upon integration. In the case of photoanodes for OER in particular, only a few heterogeneous electrocatalysts have been successfully employed, such as cobalt phosphate (CoPi), NiOOH,, and FeOOH except for highly expensive Ir‐ and Ru‐based compounds.…”

“…Such limited success can be attributed to the utilization of semiconductors, which leads to complex reaction processes and raises the following issues:, , rapid surface recombination of photogenerated charge carriers, their photocorrosion in aqueous electrolytes, and kinetic imbalance between charge transport from the bulk semiconductor to the electrode/electrolyte interface and interfacial catalytic charge transfer (on the scale of several µs vs. several ms to s) . Thus, effective electrocatalysts for artificial photosynthesis should satisfy the following conditions: (1) high catalytic activity and selectivity for a targeted reaction,, (2) protection of an underlying semiconductor, (3) rapid scavenging and effective storage of charge carriers for electrocatalysis, and (4) passivation of surface recombination centers, , , (Figure f). For PEC cells, the decoration of a photocathode and a photoanode with proper electrocatalysts might lead to an anodic and a cathodic shift of the HER and OER onset potentials, respectively, with a remarkably increased photocurrent density (Figure g).…”

“…However, even the best‐performing heterogeneous OER catalysts for PEC water oxidation, such as CoPi, NiOOH, and FeOOH, were found to only partially fulfil the above requirement. It is reported that their excellent performance is mainly due to the passivation of the surface recombination centers, albeit with their moderate or poor electrocatalytic activity (Figureàa–b) , . On the contrary, the decoration with RuO x , which is known as one of the best heterogeneous OER catalysts, could result in severe degradation of photoanode performance due to inefficient surface‐state passivation (Figure c) …”

Heterostructured MOFs photocatalysts for water splitting to produce hydrogen

“…It has been known that the recombination of photoelectrons and holes during photocatalytic processes plays a negative effect and becomes the bottleneck of improving the quantum efficiency of semiconductor photocatalyst [25,26]. Up to now, multifarious strategies have been undertaken to facilitate the separation of photoelectrons from vacancies in semiconductors, which contains doping [27,28], loading cocatalysts [29,30], interface modification [31,32], facet engineering [33,34], size and morphology control [35,36] or introducing heterostructure [37,38]. Among them, construction of the heterostructure by coupling two semiconductors with suitable band gap positions is one of the most promising ways to promote the charge separation, because the difference in the interface potential will generate a built-in electric field to achieve feasible and effective spatial separation between photo-induced electrons and holes and inhibit them recombination.…”