Fast Charge Separation Research Articles

Impact of Imine Bond Orientations and Acceptor Groups on Photocatalytic Hydrogen Generation of Donor-Acceptor Covalent Organic Frameworks.

Covalent organic frameworks (COFs) have emerged as one of the most studied photocatalysts owing to their adjustable structure and bandgaps. However, there is limited research on regulating the light-harvesting capabilities of acceptor building blocks in donor-acceptor (D-A) isomer COFs with different bond orientations. This investigation is crucial for elucidating the structure-property-performance relationship of COF photocatalysts. Herein, a series of D-A isostructural COFs are synthesized with different imine bond orientations using benzothiadiazole and its derivatives-based organic building units. Extended light absorption is achieved in COFs with acceptor groups that have strong electron-withdrawing capacities, although this resulted a decreased hydrogen generation efficiency. Photocatalytic experiments indicated that dialdehyde benzothiadiazole-based COFs, HIAM-0015, exhibit the highest hydrogen generation rate (17.99mmol g-1 h-1), which is 15 times higher than its isomer. The excellent photocatalytic performance of HIAM-0015 can be attributed to its fast charge separation and migration. This work provides insights into the rational design and synthesis of D-A COFs to achieve efficient photocatalytic activity.

Novel MoS2-In2O3-WS2 (2D/3D/2D) ternary heterostructure nanocomposite material: Efficient photocatalytic degradation of antimicrobial agents under visible-light

Fabrication of ternary composited photocatalytic nanomaterials with strong interaction is vital to deriving the fast charge separation for efficient photodegradation of organic contaminants in wastewater under visible light. In this work, novel ternary 2D/3D/2D MoS2-In2O3-WS2 multi-nanostructures were synthesized using facile hydrothermal processes. XRD, FTIR, and XPS results confirmed the phase, functional groups, and element composition of pure MoS2, MoS2-In2O3, and MoS2-In2O3-WS2 hybrids. UV-DRS spectra of the MoS2-In2O3-WS2 ternary hybrid indicate maximum absorption in the visible light range with a band-gap energy value of 2.4 eV. The surface of the 2D WS2 nanosheet structure tightly blends and densely disperses 2D MoS2 nanosheets and 3D In2O3 nanocubes. This confirmed the formation of the MoS2-In2O3-WS2 ternary hybrid in the form of 2D/3D/2D multi-nanostructures, which is also indicated from SEM and HR-TEM images. The synthesized MoS2-In2O3-WS2 ternary hybrid showed maximum photocatalytic activity under visible-light for antimicrobial agents such as triclosan (TCS) and trichlorocarban (TCC). The photocatalytic activity of TCS was revealed to be 95% at 90 min, while that of TCC was 93% at 100 min. The reusability and stability tests of the prepared MoS2-In2O3-WS2 ternary hybrid after four consecutive photocatalytic cycles were analyzed by FTIR and SEM, which indicated that the prepared ternary hybrid was very stable. Overall results suggested that the developed MoS2-In2O3-WS2 (2D/3D/2D) multi-nanostructures are environmentally friendly and low-cost nanocomposites as a potential photocatalyst for the removal of antimicrobial agents from wastewater.

Aggregation promotes charge separation in fullerene-indacenodithiophene dyad

Fast photoinduced charge separation (CS) and long-lived charge-separated state (CSS) in small-molecules facilitate light-energy conversion, while simultaneous attainment of both remains challenging. Here we accomplish this through aggregation based on fullerene-indacenodithiophene dyads. Transient absorption spectroscopy reveals that, compared to solution, the CS time in aggregates is accelerated from 41.5 ps to 0.4 ps, and the CSS lifetime is prolonged from 311.4 ps to 40 μs, indicating that aggregation concomitantly promotes fast CS and long-lived CSS. Fast CS arises from the hot charge-transfer states dissociation, opening up additional resonant channels to free carriers (FCs); subsequently, charge recombination into intramolecular triplet CSS becomes favorable mediated by spin-uncorrelated FCs. Different from fullerene/indacenodithiophene blends, the unique CS mechanism in dyad aggregates reduces the long-lived CSS dependence on molecular order, resulting in a CSS lifetime 200 times longer than blends. This endows the dyad aggregates to exhibit both photoelectronic switch properties and superior photocatalytic capabilities.

Hollow g-C3N4@Ag3PO4 Core-Shell Nanoreactor Loaded with Au Nanoparticles: Boosting Photothermal Catalysis in Confined Space.

Low solar energy utilization efficiency and serious charge recombination remain major challenges for photocatalytic systems. Herein, a hollow core-shell Au/g-C3N4@Ag3PO4 photothermal nanoreactor is successfully prepared by a two-step deposition method. Benefit from efficient spectral utilization and fast charge separation induced by the unique hollow core-shell heterostructure, the H2 evolution rate of Au/g-C3N4@Ag3PO4 is 16.9 times that of the pristine g-C3N4, and the degradation efficiency of tetracycline is increased by 88.1%. The enhanced catalytic performance can be attributed to the ordered charge movement on the hollow core-shell structure and a local high-temperature environment, which effectively accelerates the carrier separation and chemical reaction kinetics. This work highlights the important role of the space confinement effect in photothermal catalysis and provides a promising strategy for the development of the next generation of highly efficient photothermal catalysts.

Efficient Charge Transfer of p-n Heterojunction UiO-66-NH2/CuFe2O4 Composite for Photocatalytic Hydrogen Production

Using a p-n heterojunction is one of the efficient methods to increase charge transfer in photocatalysis applications. So, herein, p-type UiO-66 (NH2) and n-type CuFe2O4 (CFO) are used to form an effective p-n heterojunction. Due to their poor charge separation in their pristine form, both UiO-66 (NH2) and CFO materials cannot produce hydrogen; however, the composite p-n heterojunction formed between these materials makes fast charge separation and so hydrogen is efficiently produced. The optimized catalyst UCFO 25% produces a maximum of 62.5 µmol/g/h hydrogen in an aqueous methanol solution. The formation of a p-n heterojunction is confirmed by Mott–Schottky analysis and optical properties, crystallinity and the local atomic environment of the material was analyzed by various analytical tools like UV-Vis spectroscopy, XRD, and XANES.

Asymmetric aggregation enables red-light CO2 reduction with tunable activity and selectivity by intermolecular electronic coupling

Photocatalytic CO2 reduction to value-added chemicals is a promising way to simultaneously mitigate environmental and energy issues. Integrating low-energy red light harvesting, fast charge separation, and robust CO2 activation in a photosystem is a crucial prerequisite for highly efficient CO2 photoreduction but remains a huge challenge. Herein, we constructed an aggregated [Ru(2, 2'-bipyridine)3]Cl2 (denoted as Ru(bpy)3Cl2) photosystem. Various characterizations combining molecular dynamic simulations and theoretical calculations confirm that the electronic coupling between adjacent Ru(bpy)3Cl2 molecules can induce orbital hybridization, thus broadening the light absorption edge to the red light region. Meanwhile, the asymmetric aggregation of Ru(bpy)3Cl2 enables exciton dissociation and charge transfer through a dipole polarization effect. Significantly, this dipole polarization can also upshift the d-orbital of Ni catalytic centers, greatly strengthening the activation of CO2 and lowering the formation energy barrier of COOH* intermediates. Consequently, the apparent quantum yield (AQY) of aggregates for CO2-to-CO reduction reaches 4.2% at 610 nm, significantly higher than the AQYs of other reported photosystems at wavelengths ≥ 600 nm. More importantly, the catalytic efficiency and selectivity of CO2 reduction can be rationally tuned by controlling the aggregated degrees of Ru(bpy)3Cl2. This work highlights the key role of Ru(bpy)3Cl2 aggregation in prompting red-light harvesting and CO2 activation, which may help boost CO2 photoreduction efficiency from a fresh perspective.

An organic/inorganic Z-scheme heterojunction Yb-MOF/BiOBr for efficient photocatalytic removal of NO

The advantages of visible light-driven catalysts with good light absorption, fast charge separation rate and high redox capacity are compelling. However, conventional inorganic semiconductor, such as pure BiOBr (BOB), showed a rapid photogenerated carriers recombination rate and low solar energy utilization ability, which limited the practical application of its photocatalytic performance. In this work, a novel organic/inorganic interleaved (Z-scheme) heterojunction Yb-MOF/BiOBr (Yb-MOF/BOB) photocatalyst was successfully synthesized. Compared with a single component, the Yb-MOF/BOB heterojunction exhibited significantly enhanced performance in photocatalytic oxidation of NO under visible light. Among them, Yb-MOF/BOB-20 had the best photocatalytic NO removal effect, up to 6424 ppb/g, which was 2.8 times and 4.2 times that of BOB and Yb-MOF, respectively. Photoelectrochemical characterization confirmed that the formation of heterojunctions broadened the absorption sidebands and increased the charge transfer at the interfacial junction of Yb-MOF/BOB. Combined with UPS, ESR and in-situ DRIFTS analysis, possible photocatalytic mechanisms were revealed, in which the formation of the Yb-MOF/BOB heterostructure endowed its high charge mobility and strong redox ability. Therefore, this work provided an effective way for photocatalytic removal of NO, and offered new ideas for developing heterogeneous photocatalysts.

Dual-vacancies modulation of 1T/2H heterostructured MoS2-CdS nanoflowers via radiolytic radical chemistry for efficient photocatalytic H2 evolution

Precise defect engineering of photocatalysts is highly demanding but remains a challenge. Here, we developed a facile and controllable γ-ray radiation strategy to assemble dual-vacancies confined MoS2-CdS-γ nanocomposite photocatalyst. We showed the solvated electron induced homogeneous growth of defects-rich CdS nanoparticles, while the symbiotic •OH radicals etched flower-like 1T/2H MoS2 substrate surfaces. The optimal MoS2-CdS-γ exhibited a H2 evolution rate of up to 37.80 mmol/h/g under visible light irradiation, which was 36.7 times higher than that of bare CdS-γ, and far superior to those synthesized by hydrothermal method. The microscopic characterizations and theoretical calculations revealed the formation of such unprecedented dual-sulfur-vacancies ensured the tight interfacial contact for fast charge separation. Besides, the existence of 1T-MoS2 phase further improved the conductivity and strengthened the adsorption interaction with H+ intermediate. Therefore, the radiolytic radical chemistry offered a facile, ambient and effective synthetic strategy to improve the catalytic performances of photocatalytic materials.

Constructing oxygen defect-rich Bi2WO6/CeO2 S-scheme heterojunction for boosted photocatalytic antibiotic removal

Efficient photocatalytic eradication of antibiotic contaminant from water is of significance for the sustainability of the aquatic environment. Oxygen defective Bi2WO6/CeO2 S-scheme heterojunctions were obtained by two-step hydrothermal processes. The optimal Bi2WO6/CeO2 heterostructure (BC-10) delivered degradation efficiencies of 86.6 % and 87.1 % for tetracycline (TC) and ciprofloxacin (CIP), respectively. The boosted photocatalytic performance of BC-10 was attributed to the increased specific surface area, S-scheme construction and the formed oxygen-defect energy level which promoted the fast charge transfer and separation of photoinduced h+/e– pairs. In addition, experiments confirmed that BC-10 possessed a good catalytic performance for other organic pollutants. The toxic behavior of the TC-removal solution was verified via the Ecological Structure-Activity Relationship (ECOSAR) model and hemp-pea growth experiment, and the possible photocatalytic degradation mechanism of TC and CIP on BC-10 was proposed. This work offers an applicable construction concept of advanced photocatalysts with high redox capacity for wastewater remediation.

Piezo-enhanced near infrared photocatalytic nanoheterojunction integrated injectable biopolymer hydrogel for anti-osteosarcoma and osteogenesis combination therapy

Preventing local tumor recurrence while promoting bone tissue regeneration is an urgent need for osteosarcoma treatment. However, the therapeutic efficacy of traditional photosensitizers is limited, and they lack the ability to regenerate bone. Here, a piezo-photo nanoheterostructure is developed based on ultrasmall bismuth/strontium titanate nanocubes (denoted as Bi/SrTiO3), which achieve piezoelectric field-driven fast charge separation coupling with surface plasmon resonance to efficiently generate reactive oxygen species. These hybrid nanotherapeutics are integrated into injectable biopolymer hydrogels, which exhibit outstanding anticancer effects under the combined irradiation of NIR and ultrasound. In vivo studies using patient-derived xenograft models and tibial osteosarcoma models demonstrate that the hydrogels achieve tumor suppression with efficacy rates of 98.6 % and 67.6 % in the respective models. Furthermore, the hydrogel had good filling and retention capabilities in the bone defect region, which exerted bone repair therapeutic efficacy by polarizing and conveying electrical stimuli to the cells under mild ultrasound radiation. This study provides a comprehensive and clinically feasible strategy for the overall treatment and tissue regeneration of osteosarcoma.

Structure-enabled long-lived charge separation in single crystals of an asymmetric donor-acceptor perylenediimide cyclophane.

We report the synthesis and characterization of a covalently linked asymmetric cyclophane comprising a 1,7-di(pyrrolidin-1'-yl)perylene-3,4,9,10-bis(dicarboximide) (pyrPDI) and 1,6,7,12-tetra(4'-t-butylphenoxy)perylene-3,4,9,10-bis(dicarboximide) (tpPDI), which absorbs light from 400-750 nm. Single crystals of pyrPDI-tpPDI were analyzed by using X-ray diffraction and transient absorption microscopy. The crystal structure contains several types of intermolecular donor-acceptor interactions (pyrPDI-pyrPDI, tpPDI-tpPDI, and pyrPDI-tpPDI) in addition to the covalently installed intramolecular interaction. Following photoexcitation of the pyrPDI-tpPDI single crystal, the transient absorption data show that charge separation occurs in τ = 21 ps, which is about nine times faster than in toluene solution, while charge recombination occurs in τ > 2 μs, which is more than 400 times longer than in solution. The faster charge separation in the single crystals results from the intermolecular donor-acceptor pyrPDI-tpPDI interactions, while the greatly enhanced charge-separated state lifetime is a consequence of charge transport through the intermolecular π-stacks. These results demonstrate the utility of pre-organizing donor-acceptor structural motifs to elicit specific crystal morphologies that can lead to enhanced photogenerated charge carrier lifetimes for solar energy conversion.

Host–guest complexes of perylene bisimide-based metallacage and fullerenes for efficient photoinduced charge separation

Fast photoinduced charge separation was predicted in non-covalent complexes of Pt6PBI3 metallacage and endohedral metallofullenes.

Ultrafast symmetry-breaking charge separation in Perylenemonoimide-embedded multichromophores: impact of regioisomerism.

Symmetry-breaking charge separation (SB-CS) has recently evolved as an emerging concept offering its potential to the latest generation of organic photovoltaics. However there are several concerns that need to be addressed to reach the state-of-the-art in SB-CS chemistry, for instance, the desirable molecular geometry, interchromophoric distance and extent of electronic coupling. To shed light on those features, it is reported herein, that ortho-functionalized perylene monoimide (PMI) constituted regioisomeric dimer and trimer derivatives with varied molecular twisting and electronic conjugation have been synthesized. In steady-state photophysical studies, all the dimers and trimer derivatives exhibit a larger bathochromic shift in the emission spectra and a significant reduction of fluorescence quantum yield in polar DMF. Among the series of multichromophores, ortho- and self-coupled dimers display the strikingly different optical feature of SB-CS with a very fast charge separation rate (τCS = 80.2 ps) upon photoexcitation in DMF, which is unveiled by femtosecond transient absorption (fs-TA) studies. The SB-CS for two dimers is well-supported by the formation of PMI˙+ and PMI˙- bands in the fs-TA spectra. Further analysis of fs-TA data revealed that, among the other multichromophores the trimer also exhibits a clear charge separation, whereas SB-CS signatures are less prominent, but can not be completely disregarded, for the meta- and para-dimers. Additionally, the charge separation dynamics of those above-mentioned PMI derivatives are devoid of a kinetically favorable excimer or triplet formation. The evidence of a profound charge transfer phenomenon in the ortho-dimer is characterized by density functional theory (DFT) calculations on excited state electronic structures. The excitonic communications in the excited state electronic arrangements unravel the key role of dihedral twisting in SB-CS. The thermodynamic feasibility of CS (ΔGCS) and activation barrier (ΔG≠) of the derivatives in DMF are established from the Rehm-Weller equation and Marcus's theory, respectively. This work is an in-depth study of the effect of mutual orientation of PMIs and regioisomerism in determining sustainable guidelines for using SB-CS.

Rational design of pyrene and thienyltriazine-based conjugated microporous polymers for high-performance energy storage and visible-light photocatalytic hydrogen evolution from water

Conjugated microporous polymers (CMPs) have found extensive applications in various fields such as optoelectronics, CO2 capture, and catalysis. However, their potential in electrochemical supercapacitors as energy storage and H2 production systems remains relatively unexplored. This limited exploration can be attributed to certain challenges, including issues related to structural and electrochemical stability, as well as the relatively modest specific capacitance. Additionally, many of the CMPs discovered thus far have exhibited lower energy densities, further contributing to this underexplored aspect of their utility. In this study, we prepared two different CMPs [TPET-TTh and PyT-TTh CMPs] containing thienyltriazine units (TTh) for the redox mechanism and constructed electrodes for supercapacitor applications. The synthesized TPET-TTh and PyT-TTh CMPs displayed exceptionally high specific surface areas of 545 and 528 m² g⁻¹, respectively. Furthermore, their pore sizes were very similar, centered at approximately 0.39 and 0.36 nm, respectively. To evaluate their electrochemical properties, the TTh-CMPs were examined using cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). The resulting CV curves exhibited rectangular shapes, indicative of the characteristic behavior of electric double-layer capacitors, across a range of potential and scan rates. These TPET-TTh and PyT-TTh CMPs delivered nominal specific capacitances of 74 and 76 F g−1 at 0.5 A g−1, respectively. In addition, they exhibited outstanding capacity retentions of 95.2 and 97.30 % even after 2000 cycles [analyzed at 10 A g−1]. The TTh-CMPs also exhibited excellent light-capture capabilities. The PyT-TTh CMP has faster charge separation and lower charge recombination rates than TPET-TTh CMP. This results in a higher hydrogen evolution rate from the water decomposition reaction. The H2 production rate of PyT-TTh CMP could be as high as 18,533 μmol g−1 h−1, which is approximately 4-fold that of TPET-TTh CMP. This study offers a strategy for the design of TTh-containing CMPs that exhibit exceptional energy storage application and photocatalytic efficiency for H2 evolution.

Construction of IO-B-TiO2/In2O3 S-scheme heterojunction with photothermal effects and its highly efficient photocatalytic reduction of CO2 under full-spectrum light

The conversion of greenhouse gases such as carbon dioxide (CO2) into fuel and high-value chemical materials using solar energy is considered as a viable solution to the environmental pollution and the alleviation of the energy crisis. Herein, a black titanium dioxide/indium oxide S-scheme heterojunction (IO-B-TiO2/In2O3) with a three-dimensional porous inverse opal structure was prepared. In the photocatalytic reduction of CO2, IO-B-TiO2/In2O3 exhibited an excellent CO production rate (251.25 μmol·g−1·h−1), being 8.62 and 1.55 times of pure IO-TiO2 and IO-B-TiO2/In2O3 under non-photothermal conditions, respectively. A series of characterizations and theoretical calculations (DFT) systematically demonstrated that the excellent photocatalytic performance results from the full spectral response of the material, fast charge separation and transport efficiency, and superior photothermal conversion efficiency of the infrared light. This work will provide a promising insight to the design of S-scheme catalysts with outstanding photocatalytic performance via photothermal assistance and the improved solar energy conversion efficiency.

Photo-driven electrochemical etching to construct porous structures with oxygen vacancies on ZnO photoanodes for efficient solar water splitting

Fast charge separation and oxidation kinetics are the key issues for photoelectrochemical (PEC) water splitting. Herein, photo-driven electrochemical etching (PEE) was applied to modify the morphology and surface properties of ZnO photoanodes to improve PEC performance. By regulating the applied potential and treatment time, the PEE generated a lotus root like porous structure with a pore diameter of 20–30 nm and depth of about 300 nm, and produced a large amount (30.1 %) of oxygen vacancies (Ov) on ZnO photoanode. PEE treated-ZnO array demonstrated a charge separation efficiency of 87 %, and achieved 1.8 times larger photocurrent (1.26 mAcm−2 at 1.23 VRHE) with a cathodic shift of onset potential of 0.12 VRHE than pristine ZnO. The introduced Ov and the shortened charge transport distance of porous microstructures by PEE treatment improved the electrode/electrolyte interface charge transfer and water oxidation kinetics. DFT calculations indicate that the construction of oxygen defects on the catalyst surface can reduce the overpotential of oxygen evolution reaction (OER) and further promote the catalytic activity of OER. Moreover, electrode surface pore structure can be tailored by adjusting illumination parameters and electrolytes. This work illustrates a novel and effective approach to tunable photo-corrodible electrode materials for solar water splitting.

Enhanced efficiency and long-term stability of all inorganic CsPbBr3 perovskite solar cells via regulation of charge separation and extraction by band engineered-Co3O4 nanocrystals as a hole transport material layer

Insertion of an inorganic HTM intermediate at the CsPbBr3/Carbon interface can significantly improve photo-generated holes extraction efficiency without sacrificing advantages in device stability. Herein, low-cost and eco-friendly Co3O4 nanocrystals were synthesized by precipitation method and utilized as efficient inorganic HTM for CsPbBr3 PSCs. By regulating the hole quasi-fermi level (Ef, HTL) of the perovskite film with Co3O4 nanocrystals possessing a lower conduction band (CB), the built-in electric field (BEF) inside the CsPbBr3 can be reinforced, for which the Co3O4-induced energy level reconstruction facilitates fast charge separation and extraction because of the intensified driving force. In addition, the charge recombination behavior can be effectively inhibited. Finally, all inorganic CsPbBr3 PSCs with an architecture of FTO/c-TiO2/m-TiO2/CsPbBr3/Co3O4/carbon PSC realizes efficiency of 8.92% with an open-circuit voltage (Voc) of 1.531 V. Furthermore, the unencapsulated Co3O4-based PSC exhibits excellent stability in ambient air, keeping 98% of its initial efficiency after 90 days in 80% high humidity condition, and 97% of initial efficiency after 40 days in a high-temperature atmosphere of ∼80 °C.

Unusual aliovalent Cd doped γ‐Bi2MoO6 nanomaterial for efficient photocatalytic degradation of sulfamethoxazole and rhodamine B under visible light irradiation

AbstractDue to γ‐Bi2MoO6 (BMO) has attracted considerable attention because of its unique layered perovskite structure and excellent electrical conductivity. However, the easy recombination of electron–hole pairs limits its practical application. To address this issue, we successfully prepared aliovalent Cd2+ doped BMO (Cd‐BMO) by using a simple hydrothermal method for the degradation of the sulfamethoxazole (SMZ) and Rhodamine B (RhB). The result found that the degradation efficiency of Cd‐BMO is significantly higher than that of BMO, despite an increase in the bandgap after the introduction of Cd2+. The superior degradation efficiency of 8% Cd‐BMO, with a smaller particle size and larger specific surface area, can be attributed to its fast charge separation efficiency, low charge transfer resistance, and low rate of electron–hole pair recombination. Repeated and ion spillover experiments prove that 8% Cd‐BMO shows good stability and environmental protection. Theoretical simulation demonstrates that Cd offers electrons to the BMO system due to the decreased binding energy of BMO. The 8% Cd‐BMO sample can provide a suitable electric band edge for generating dominant active radicals during degradation. This work not only provides a potential candidate of 8% Cd‐BMO for practical degradation but also sheds light on the design of superior photocatalysts.

Modular design of solar-powered photocathodic metal protection device

Metal corrosion leads to severe economic losses and safety hazards to human society. As an energy-efficient and sustainable anticorrosion technique, photocathodic protection (PCP) systems have received growing attention in the past two decades. However, the existing PCP devices barely meet the requirements of adequate metal protection in real-world scenarios. This perspective aims to provide some constructive insights into the rational design of PCP devices and propose “functional module integration” as a new concept for future PCP systems. Similarly to multi-layered solar cells, PCP systems may incorporate multiple modules based on the corresponding functions. These include photoabsorber module (PAM), electron transfer module (ETM), hole transfer module (HTM), hole consumption module (HCM), and electron storage module (ESM). With such a modular design, improved capture of sunlight and fast charge separation, directional transportation, and effective utilization of the photogenerated carriers might be attained. Consequently, the solar-to-electric energy conversion efficiency and operation consistency of PCP devices can be significantly boosted, paving the way for practical application of solar-powered metal protection technology.Graphical This perspective analyses the key issues of current photocathodic protection systems and proposes a unified design composed of functional modules for the next generation systems inspired by the architecture of solar cells. This modular design allows the breaking-down of all reaction steps of the solar-to-electric conversion process onto various modules, which may bring about breakthroughs for green cathodic metal protection.

Self-healing of oxygen vacancies and phase transition-induced built-in electric field regulate H2 and H2O2 production

Oxygen vacancies in photocatalysts are an important parameter for improving their catalytic activities. However, this study found that oxygen vacancies do not always help with photocatalytic properties. MXene nanosheets were annealed at different temperatures to prepare nanosheets of titanium dioxide (TiO2) with anatase or rutile phase. Photo-induced self-healing of oxygen vacancies in MXene nanosheets annealed at 400 °C promoted the efficient photocatalytic evolution of hydrogen (H2) with a ∼ 6.8 mmol/g optimized yield. In contrast, the photo-induced increase of oxygen vacancies in MXene nanosheets annealed at 500 °C corresponded to an optimized ∼ 1.8 mmol/g/h yield of hydrogen peroxide (H2O2). Spectroscopic and electrochemical methods revealed that the built-in electric field between the anatase and rutile TiO2 facilitated the fast charge separation from the anatase to rutile TiO2. The photo-induced self-healing of oxygen vacancies and the phase transition-induced built-in electric field regulated the photocatalytic selectivity of H2 and H2O2 production.