Constructing Metal-Organic Framework Films with Adjustable Electronic Properties on Hematite Photoanode for Boosting Photogenerated Carrier Transport.

Hematite (α-Fe2O3) has become a research hotspot in the field of photoelectrochemical water splitting (PEC-WS), but the low photogenerated carrier separation efficiency limits further application. The electronic structure regulation, such as element doping and organic functional groups with different electrical properties, is applied to alleviate the problems of poor electrical conductivity, interface defects, and band mismatch. Herein, α-Fe2O3 photoanodes are modified to regulate their electric structures and improve photogenerated carrier transport by the bimetallic metal-organic frameworks (MOFs), which are constructed with Fe/Ni and terephthalate (BDC) with 2-substitution of different organic functional groups (─H, ─Br, ─NO2 and ─NH2). The α-Fe2O3 photoanode loaded with FeNi-NH2BDC MOF catalyst exhibits the optimal photocurrent density (2 mA cm-2) at 1.23 VRHE, which is 2.33 times that of the pure α-Fe2O3 photoanode. The detailed PEC analyses demonstrate that the bimetallic synergistic effect between Fe and Ni can improve the conductivity and inhibit the photogenerated carrier recombination of α-Fe2O3 photoanodes. The ─NH2 group as an electron-donor group can effectively regulate the electron distribution and band structure of α-Fe2O3 photoanodes to prolong the lifetime of photogenerated holes, which facilitates photogenerated carrier transport and further enhances the PEC-WS performance of α-Fe2O3 photoanode.

Integration of a Cu2O/ZnO heterojunction and Ag@SiO2 into a photoanode for enhanced solar water oxidation.

Photoelectrochemical water splitting (PEC-WS) has attracted considerable attention owing to its low energy consumption and sustainable nature. Constructing semiconductor heterojunctions with controllable band structure can effectively facilitate photogenerated carrier separation. In this study, a FTO/ZnO/Cu2O/Ag@SiO2 photoanode with a Cu2O/ZnO p-n heterojunction and Ag@SiO2 nanoparticles is constructed to investigate its PEC-WS performance. Compared with a bare ZnO photoanode, the photocurrent density of the FTO/ZnO/Cu2O/Ag@SiO2 photoanode (0.77 mA cm-2) at 1.23 VRHE exhibits an increment of 88%, and a cathodic shift of 0.1 V for the on-set potential (0.4 VRHE). Detailed photoelectrochemical analyses reveal that the Cu2O/ZnO p-n heterojunction formed between Cu2O and ZnO can effectively promote photogenerated carrier separation. The surface plasmonic effect of the Ag@SiO2 nanoparticles can further promote the photogenerated carrier transfer efficiency, which synergistically improves the PEC-WS performance.

Investigation of in situ sulfide/nitride/phosphide treatments of hematite photoanodes for improved solar water oxidation.

Surface catalyst engineering can effectively improve the photoelectrochemical water splitting (PEC-WS) performance of semiconductor photoelectrodes. In situ surface functional treatments can effectively reduce interface defects and improve photogenerated carrier transport. In this study, FTO/Sn@α-Fe2O3/FeOOH photoanodes were modified with in situ sulfide/nitride/phosphide treatments to improve their PEC-WS performance. Compared with the pure α-Fe2O3 photoanode, the photocurrent densities of FTO/Sn@α-Fe2O3/FeOOH photoanodes after sulfide/nitride/phosphide treatments increased from 0.88 to 3.38 mA cm-2 at 1.23 VRHE. The onset potential showed a cathode shift of 0.1 V. Photoelectrochemical analyses and theoretical calculation demonstrated that the surface engineering by sulfide/nitride/phosphide treatments can significantly reduce surface defects, enhance electrical conductivity and promote photogenerated carrier separation and transfer efficiency by regulating interface charge transfer, binding energy and internal electric field. The formation of an FeSx catalyst and N/P coordination complexes in the sulfide/nitride/phosphide processes on the surface of α-Fe2O3 photoanodes can effectively reduce photogenerated carrier recombination. This work provides experimental and theoretical support for surface structure design and improved photoelectric conversion performance of semiconductor photoelectrode materials.

Regulating a Zn/Co bimetallic catalyst in a metal-organic framework and oxyhydroxide for improved photoelectrochemical water oxidation.

As one of the most popular photoanode materials, hematite (α-Fe2O3) has obvious advantages in the field of photoelectrochemical water splitting (PEC-WS). However, it is difficult to achieve excellent PEC-WS performance without loading a cocatalyst serving as an electron/hole collector to promote photogenerated carrier separation. In this work, FTO/Sn@α-Fe2O3 photoanodes are modified with ZnCo-ZIF and ZnCoOOH bimetallic catalysts to obtain FTO/Sn@α-Fe2O3/Zn0.5Co0.5-ZIF and FTO/Sn@α-Fe2O3/Zn0.46Co0.54OOH photoanodes. Their photocurrent densities reach 2.6 mA cm-2 and 2.3 mA cm-2 at 1.23 VRHE, respectively. The detailed mechanism studies demonstrate that both ZnCoOOH and ZnCo-ZIF can effectively decrease the transfer resistance, increase the Fe2+/Fe3+ ratio and reduce the charge recombination of the α-Fe2O3 film, which synergistically improves the PEC-WS performance. Compared with ZnCoOOH, the ZnCo-ZIF exhibits better photogenerated carrier transfer efficiency and catalytic performance, which mainly can be attributed to the improved binding energy between the ZnCo-ZIF catalyst and the α-Fe2O3 film. This work provides a simple and feasible strategy for constructing bimetallic catalysts and deepens the understanding of different types of bimetallic catalysts for high-performance PEC-WS systems.