Search

Highlights: Strain induces coupling in Bi12O17Br2 and Cu porphyrin-based monoatomic layer (PML-Cu), constructing Bi–O bonding interface in PML-Cu/BOB (PBOB). Surface interface dual polarization boosts internal electric field, promoting electron transfer. PML-Cu provides high density of dispersed active Cu sites in PBOB, enhancing CO2 photoreduction. The insufficient active sites and slow interfacial charge transfer of photocatalysts restrict the efficiency of CO2 photoreduction. The synchronized modulation of the above key issues is demanding and challenging. Herein, strain-induced strategy is developed to construct the Bi–O-bonded interface in Cu porphyrin-based monoatomic layer (PML-Cu) and Bi12O17Br2 (BOB), which triggers the surface interface dual polarization of PML-Cu/BOB (PBOB). In this multi-step polarization, the built-in electric field formed between the interfaces induces the electron transfer from conduction band (CB) of BOB to CB of PML-Cu and suppresses its reverse migration. Moreover, the surface polarization of PML-Cu further promotes the electron converge in Cu atoms. The introduction of PML-Cu endows a high density of dispersed Cu active sites on the surface of PBOB, significantly promoting the adsorption and activation of CO2 and CO desorption. The conversion rate of CO2 photoreduction to CO for PBOB can reach 584.3 μmol g−1, which is 7.83 times higher than BOB and 20.01 times than PML-Cu. This work offers valuable insights into multi-step polarization regulation and active site design for catalysts. [ABSTRACT FROM AUTHOR]

The glorious charge transfer efficiency of photoanode is an important factor for efficient photoelectrochemical (PEC) water oxidation. However, it is often limited by slow kinetics of oxygen evolution reaction. Herein, a dual transition metal‐based metal–organic frameworks (MOF) cocatalyst, Fe@Ni–MOF, is introduced into a titanium‐doped hematite (Fe2O3:Ti) photoanode. The combination of Ni and Fe can optimize the filling of 3d orbitals. Moreover, the introduction of Fe donates electrons to Ni in the MOF structure, thus, suppressing the irreversible (long‐life‐time) oxidation of Ni2+ into Ni3+. The resulting Fe@Ni–MOF/Fe2O3:Ti photoanode exhibits ∼threefold enhancement in the photocurrent density at 1.23 V versus the reversible hydrogen electrode. Kinetic analysis of the PEC water oxidation processes indicates that this performance improvement is primarily due to modulating the charge transfer efficiency of hematite photoanode. Further results show that a single transition metal‐based MOF cocatalyst, Ni–MOF, exhibits slow charge transfer in spite of a reduction in surface charge recombination, resulting in a smaller charge transfer efficiency. These findings provide new insights for the development of photoelectrodes decorated with MOFs. [ABSTRACT FROM AUTHOR]

The charge separation and transfer are critical steps during the photoelectrochemical processes. In this paper, we focus on the interfacial properties within the heteropolyacid (denoted as PW 12) modified WO 3 heterojunction film synthesized by an epitaxial growth method. The characterizations show that heteropolyacid is formed on the surface of WO 3 plates with less interfacial defects between PW 12 and WO 3. The PW 12 /WO 3 photoanodes synthesized via the in-situ method display a photocurrent density of 0.65 mA/cm2 at 1.23 V vs. RHE, which exhibits 1.6 times as much as the bare WO 3. And the composite achieves the maximum value of 1.52 mA/cm2 at 1.8 V vs. RHE, while those of PW 12 /WO 3 films prepared by a dip-coating method and pristine WO 3 films are just 1.10 and 0.85 mA/cm2. The improvements in PEC performances of PW 12 /WO 3 photoanodes (in-situ) were attributed to the higher electron transmission rate and longer electron lifetime resulted from the less interfacial defects. Moreover, the PW 12 /WO 3 film was treated with TiCl 4 solution to form a TiO 2 /PW 12 /WO 3 ternary heterojunction, which exhibits a higher photocurrent density of 1.89 mA/cm2. The current research has proposed a new perspective and method for the design of highly efficient heterojunction photoelectrodes and inorganic synthesis. [ABSTRACT FROM AUTHOR]

[Display omitted] • A CuWO 4 film was constructed with gradient concentration of surficial forward Ni and interior reversed Mo. • The bidirectional gradient doping results stepwise energy bands that like continuous heterojunctions. • The continuous band bending encourages charge transfer in the film. Photoelectrochemical water splitting is an attractive approach for producing green hydrogen energy from solar energy. CuWO 4 has emerged as a promising candidate for photoanode, due to its favorable band gap and remarkable stability. However, its application is limited by poor charge transfer capability. To address this issue, we employed a simple spin coating method to introduce a gradient distribution of Mo in the bulk of CuWO 4 film, and Ni was doped in the outermost layer. The gradient concentration of surficial forward Ni and interior reversed Mo creates stepwise energy bands and continuous band bending, which facilitates the separation of photogenerated carriers and suppresses charge-carrier recombination. The CuWO-grad-MoNi photoanode exhibited a photocurrent of 0.85 mA/cm2 at 1.23 V vs. RHE with high stability, which is 2.2 times that of unmodified CuWO 4. This approach provides a means to construct stepwise energy bands and obtain photoelectrodes with enhanced charge transfer and separation. [ABSTRACT FROM AUTHOR]

Photo-coupled electrocatalytic CO 2 reduction is an emerging method to promote energy efficiency of electrocatalytic CO 2 reduction. However, precisely designing a precatalysts with site-selectivity for efficient photo-coupled electrocatalytic CO 2 reduction is still a challenge. Here, a photo-coupled electrocatalyst bearing aluminum (Al)-oxo chain as metal node and transition metal sites as metal center, is dedicated to reducing CO 2 for the first time. A satisfactory CO 2 -to-CO conversion is achieved for Al-PMOF(Co), showing a Faradaic efficiency as high as ∼90% and a long-term stability over 35 h under visible light. The improved performance stem from Al-oxo chain imparting high stability, atomic Co site expediting charge transfer rate (K ct) and visible light accelerating charge transfer across interface. Theoretical calculations and in situ reflection infrared spectroscopy show that the 3d z 2 orbital of atomic Co site exists a large resonance with the 2p orbital of *COOH intermediate, thus inducing CO 2 reduction though a favorable pathway. [Display omitted] • A site-selective porphyrin was used for photo-coupled electrocatalytic CO 2 reduction. • The catalyst achieves a higher CO 2 -to-CO conversion under light condition. • The atomic metal (Co) site exist a large resonance with *COOH intermediate. • Visible light accelerates charge transfer from the ligand to the active center. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Tin-rich SnWO 4 photoanode demonstrated the state-of-the-art photocurrent density of this material so far (1.05 mA cm−2 at 1.23 V vs. RHE in 0.2 M KPi). • Up-regulate the surface band-edge position of α-SnWO 4 photoanode to build an internal electric field by changing the surface tin atom content. • The increase of active sites of tin atoms on the surface reduces the potential barrier of water oxidation reaction. Achieving high-efficient photoelectrochemical (PEC) water splitting requires great charge transfer and excellent surficial reaction activity. To improve the PEC performance of α-SnWO 4 photoanode, the atomic ratio of Sn and W on the surface of the α-SnWO 4 photoanode is subtly adjusted by exposing the α-SnWO 4 photoanode to a Sn2+ or H+-rich microenvironment, which is considered to determine the coordination environment of active sites. Increasing the content of tin on the surface can shift the work function to vacuum level and up-regulate the band-edge position, and the difference between the energy band of bulk and surface facilitates transferring photo-generated carriers to the surface. Besides, the tin atom as the actives sites is in favor of the water oxidation reaction compared to the W atom as termination. Thus, the faster charge separation and enhanced hole injection ability lead to the 1st-order reaction behavior of water oxidation on the tin-rich surface, while the tin-poor surface presents 2nd-order behavior. As a result, the Tin-rich SnWO 4 photoanode (1.05 mA cm−2 at 1.23 V vs. RHE in 0.2 M KPi) shows 2 folds photocurrent of Tin-poor SnWO 4 photoanode, which is the state-of-the-art photocurrent density of the material so far. This study provides a path for understanding the effect of surface termination, and the method for engineering surface can easy to be used for other metal oxide photoelectrodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of operating temperature on the PEC performance is discussed. • An improved carrier concentration instead of increased conductance of the electrolyte is the main factor. • A suitable temperature is favor for increasing carrier concentration without notable recombination. • Electron-hole collisions increase at high temperature but have minimal effect compared to carrier density until 70 ℃. Photoelectrochemical (PEC) water splitting is a kind of strategy to produce hydrogen by using renewable energy. Copper tungstate (CuWO 4) with a suitable bandgap (∼2.3 eV) is a potential candidate, but its poor charge transfer ability limits the real performance. According to the fact that the real reaction temperature is different from the normal temperature (298 K) in the laboratory, the testing temperature was considered as a potential influence factor for the PEC performance of photoelectrodes. In this study, the effects of temperature on the PEC properties of CuWO 4 photoanode were discussed from the viewpoint of charge transfer in the photoanode, specific conductance and pH of the electrolyte, and the reaction Gibbs free energy. An increasing photocurrent is achieved by increasing the testing temperature, which is from 0.11 mA/cm2 (1.23 V vs RHE) at 5 ℃ to 0.31 mA/cm2 at 70 ℃. A similar increasing trend was seen between the carrier concentration and photocurrent, indicating the main influence factors are considered as improved carrier concentration and accelerated charge transfer ability of semiconductors. At higher temperatures, the risk of collisions of electrons and holes increases, although this negative effect is smaller than the positive effect brought on by greater carrier densities, as indicated by the smaller rise in current density compared to that of carrier density at 60/70/80/90 °C. This research suggests that a real-world factor favoring PEC water splitting is an increase in temperature. [ABSTRACT FROM AUTHOR]