Selective Photoreduction of CO2 to CH4 Triggered by Metal-Vacancy Pair Sites.

Selectively achieving the photoreduction of carbon dioxide (CO2) to methane (CH4) remains a significant challenge, which primarily arises from the complexity of the protonation process. In this work, we designed metal-vacancy pair sites in defective metal oxide semiconductors, which anchor the reactive intermediates with a bridged linkage for the selective protonation to produce CH4. As an example, oxygen-deficient Nb2O5 nanosheets are synthesized, in which the niobium-oxygen vacancy pair sites are demonstrated by X-ray photoelectron spectroscopy and electron paramagnetic resonance spectra. In situ Fourier transform infrared spectroscopy monitors the *CH3O intermediate, a key intermediate for CH4 production, during the CO2 photoreduction in oxygen-deficient Nb2O5 nanosheets. Importantly, the built metal-vacancy pair sites regulate the *CH3O formation step as a spontaneous process, making the reduction of CO2 to CH4 the preferred method. Therefore, the oxygen-deficient Nb2O5 nanosheets exhibit a CH4 formation rate of 19.14 µmol g-1 h-1, with an electron selectivity of ∼94.1%.

Nitrogen Doping-Roused Synergistic Active Sites in Perovskite Enabling Highly Selective CO2 Photoreduction into CH4.

The intricate protonation process in carbon dioxide reduction usually makes the product unpredictable. Thus, it is significant to control the reactive intermediates to manipulate the reaction steps. Here, we propose that the synergistic La-Ti active sites in the N-La2Ti2O7 nanosheets enable the highly selective carbon dioxide photoreduction into methane. In the photoreduction of CO2 over N-La2Ti2O7 nanosheets, in situ Fourier transform infrared spectra are utilized to monitor the *CH3O intermediate, pivotal for methane production, whereas such monitoring is not conducted for La2Ti2O7 nanosheets. Also, theoretical calculations testify to the increased charge densities on the Ti and La atoms and the regulated formation energy barrier of *CO and *CH3O intermediates by the constructed synergistic active sites. Accordingly, the methane formation rate of 7.97 µL h-1 exhibited by the N-La2Ti2O7 nanosheets, along with an electron selectivity of 96.6%, exceeds that of most previously reported catalysts under similar conditions.

Progress and Perspective for "Green" Strategies of Catalytic Plastics Conversion into Fuels by Regulating Half-Reactions.

Nowadays, plastic waste threatens public health and the natural ecosystems of our lives. It is highly beneficial to recycle plastic waste in order to maximize the reuse of its contained carbon sources for the development of other valuable products. Unfortunately, traditional techniques usually require significant energy consumption and result in the generation of hazardous waste. Herein, the up-to-date developments on the "green" strategies under mild conditions including electrocatalysis, photocatalysis, and photoelectrocatalysis of plastic wastes are presented. During the oxidation of plastics in these "green" strategies, corresponding reduction reactions usually exist, which affect the property of catalytic plastics conversion. Particularly, we mainly focus on how to design the corresponding half reactions, such as the water reduction, carbon dioxide reduction, and nitrate reduction. Finally, we provide forward-looking insight into the enhancement of these "green" strategies, the extension of more half reactions into other organic catalysis, a comprehensive exploration of the underlying mechanisms through in situ studies and theoretical analysis and the problems for practical applications that needs to be solved.

Fundamentals and Challenges of Engineering Charge Polarized Active Sites for CO2 Photoreduction toward C2 Products.

ConspectusGlobal warming and climatic deterioration are partly caused by carbon dioxide (CO2) emission. Given this, CO2 reduction into valuable carbonaceous fuels is a win-win route to simultaneously alleviate the greenhouse effect and the energy crisis, where CO2 reduction into hydrocarbon fuels by solar energy may be a potential strategy. Up to now, most of the current photocatalysts photoconvert CO2 to C1 products. It is extremely difficult to achieve production of C2 products, which have higher economic value and energy density, due to the kinetic challenge of C-C coupling of the C1 intermediates. Therefore, to realize CO2 photoreduction to C2 fuels, design of high-activity photocatalysts to expedite the C-C coupling is significant. Besides, the current mechanism for CO2 photoreduction toward C2 fuels is usually uncertain, which is possibly attributed to the following two reasons: (1) It is arduous to determine the actual catalytic sites for the C-C coupling step. (2) It is hard to monitor the low-concentration active intermediates during the multielectron transfer step.Most traditional metal-based photocatalysts usually possess charge balanced active sites that have the same charge density. In this aspect, the neighboring C1 intermediates may also show the same charge distribution, which would lead to dipole-dipole repulsion, thus preventing C-C coupling for producing C2 fuels. By contrast, photocatalysts with charge polarized active sites possess obviously different charge distributions in the adjacent C1 intermediates, which can effectively suppress the electrostatic repulsion to steer the C-C coupling. Based on this analysis, higher asymmetric charge density on the active sites would be more beneficial to anchoring between the adjacent intermediates and active atoms in catalysts, which can boost C-C coupling.In this Account, we summarize various strategies, including vacancy engineering, doping engineering, loading engineering, and heterojunction engineering, for tailoring charge polarized active sites to boost the C-C coupling for the first time. Also, we overview diverse in situ characterization technologies, such as in situ X-ray photoelectron spectroscopy, in situ Raman spectroscopy, and in situ Fourier transform infrared spectroscopy, for determining charge polarized active sites and monitoring reaction intermediates, helping to reveal the internal catalytic mechanism of CO2 photoreduction toward C2 products. We hope this Account may help readers to understand the crucial function of charge polarized active sites during CO2 photoreduction toward C2 products and provide guidance for designing and preparing highly active catalysts for photocatalytic CO2 reduction.

Progress and perspective for conversion of plastic wastes into valuable chemicals.

Today, discarded plastics in nature have caused serious "white pollution", however these plastic wastes contain abundant carbon resources that could serve as the feedstock to produce commodities. Because of this, it is requisite to convert these plastic wastes into valuable chemicals. Herein, the state-of-the-art techniques for plastic conversion are divided into two categories, those performed under violent conditions and mild conditions, in which the conversion mechanisms are discussed. The strategies under violent conditions are closer to practical application thanks to their excellent conversion efficiencies, while the strategies under mild conditions are more environmentally friendly, showing enormous development potential in the future. We summarize in detail the pyrolysis, hydropyrolysis, solvolysis and microwave-initiated catalysis for bond cleavage in plastic wastes at temperatures ranging from 448 to 973 K. Also, we overview the photocatalysis, electrocatalysis and biocatalysis for bond cleavage in plastic wastes at near and even normal temperature and pressure. Finally, we present some suggestions and outlooks concerning the improvement of current techniques and in-depth mechanisms of investigation for conversion of plastics into valuable chemicals.

Light-Driven C-C Coupling for Targeted Synthesis of CH3 COOH with Nearly 100 % Selectivity from CO2.

Targeted synthesis of acetic acid (CH3 COOH) from CO2 photoreduction under mild conditions mainly limits by the kinetic challenge of the C-C coupling. Herein, we utilized doping engineering to build charge-asymmetrical metal pair sites for boosted C-C coupling, enhancing the activity and selectivity of CO2 photoreduction towards CH3 COOH. As a prototype, the Pd doped Co3 O4 atomic layers are synthesized, where the established charge-asymmetrical cobalt pair sites are verified by X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy spectra. Theoretical calculations not only reveal the charge-asymmetrical cobalt pair sites caused by Pd atom doping, but also manifest the promoted C-C coupling of double *COOH intermediates through shortening of the coupled C-C bond distance from 1.54 to 1.52 Å and lowering their formation energy barrier from 0.77 to 0.33 eV. Importantly, the decreased reaction energy barrier from the protonation of two*COOH into *CO intermediates for the Pd-Co3 O4 atomic layer slab is 0.49 eV, higher than that of the Co3 O4 atomic layer slab (0.41 eV). Therefore, the Pd-Co3 O4 atomic layers exhibit the CH3 COOH evolution rate of ca. 13.8 µmol g-1 h-1 with near 100% selectivity, both of which outperform all previously reported single photocatalysts for CO2 photoreduction towards CH3 COOH under similar conditions.

Direct Polyethylene Photoreforming into Exclusive Liquid Fuel over Charge-Asymmetrical Dual Sites under Mild Conditions.

Direct polyethylene photoreforming to high-energy-density C2 fuels under mild conditions is of great significance and still faces a huge challenge, which is partly attributed to the extreme instability of *CH2CH2 adsorbed on the traditional catalysts with single catalytic sites. Herein, charge-asymmetrical dual sites are designed to boost the adsorption of *CH2CH2 for direct polyethylene photoreforming into C2 fuels under normal temperature and pressure. As a prototype, the synthetic Zr-doped CoFe2O4 quantum dots with charge-asymmetrical dual metal sites realize direct polyethylene photoreforming into acetic acid, with 100% selectivity of liquid fuel and the evolution rate of 1.10 mmol g-1 h-1, outperforming those of most previously reported photocatalysts under similar conditions. In situ X-ray photoelectron spectra, density-functional-theory calculations, and control experiments reveal the charge-asymmetrical Zr-Fe dual sites may act as the predominate catalytic sites, which can simultaneously bond with the *CH2CH2 intermediates for the following stepwise oxidation to form C2 products.

Selective CO2 -to-C2 H4 Photoconversion Enabled by Oxygen-Mediated Triatomic Sites in Partially Oxidized Bimetallic Sulfide.

Selective CO2 photoreduction into C2 fuels under mild conditions suffers from low product yield and poor selectivity owing to the kinetic challenge of C-C coupling. Here, triatomic sites are introduced into bimetallic sulfide to promote C-C coupling for selectively forming C2 products. As an example, FeCoS2 atomic layers with different oxidation degrees are first synthesized, demonstrated by X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy spectra. Both experiment and theoretical calculation verify more charges aggregate around the introduced oxygen atom, which enables the original Co-Fe dual sites to turn into Co-O-Fe triatomic sites, thus promoting C-C coupling of double *COOH intermediates. Accordingly, the mildly oxidized FeCoS2 atomic layers exhibit C2 H4 formation rate of 20.1 µmol g-1 h-1 , with the product selectivity and electron selectivity of 82.9 % and 96.7 %, outperforming most previously reported photocatalysts under similar conditions.

Room-Temperature Photooxidation of CH4 to CH3OH with Nearly 100% Selectivity over Hetero-ZnO/Fe2O3 Porous Nanosheets.

The huge challenge for CH4 photooxidation into CH3OH lies in the activation of the inert C-H bond and the inhibition of CH3OH overoxidation. Herein, we design two-dimensional in-plane Z-scheme heterostructures composed of two different metal oxides, with efforts to polarize the symmetrical CH4 molecules and strengthen the O-H bond in CH3OH. As a prototype, we first fabricate ZnO/Fe2O3 porous nanosheets, where high-resolution transmission electron microscopy and in situ X-ray photoelectron spectroscopy affirm their in-plane Z-scheme heterostructure. In situ Fourier transform infrared spectra and in situ electron paramagnetic resonance spectra demonstrate their higher amount of ·CH3 radicals relative to the pristine ZnO porous nanosheets, in which density functional theory calculations validate that the high local charge accumulation on Fe sites lowers the CH4 adsorption energy from 0.14 to 0.06 eV. Moreover, the charge-accumulated Fe sites strengthen the polarity of the O-H bond in CH3OH through transferring electrons to the O atoms, confirmed by the increased barrier from 0.30 to 2.63 eV for *CH3O formation, which inhibits the homolytic O-H bond cleavage and thus suppresses CH3OH overoxidation. Accordingly, the CH3OH selectivity over ZnO/Fe2O3 porous nanosheets reaches up to nearly 100% with an activity of 178.3 µmol-1 gcat-1, outperforming previously reported photocatalysts without adding any oxidants under room temperature and ambient pressure.

Partially oxidized atomic cobalt layers for carbon dioxide electroreduction to liquid fuel.

Electroreduction of CO2 into useful fuels, especially if driven by renewable energy, represents a potentially 'clean' strategy for replacing fossil feedstocks and dealing with increasing CO2 emissions and their adverse effects on climate. The critical bottleneck lies in activating CO2 into the CO2(•-) radical anion or other intermediates that can be converted further, as the activation usually requires impractically high overpotentials. Recently, electrocatalysts based on oxide-derived metal nanostructures have been shown to enable CO2 reduction at low overpotentials. However, it remains unclear how the electrocatalytic activity of these metals is influenced by their native oxides, mainly because microstructural features such as interfaces and defects influence CO2 reduction activity yet are difficult to control. To evaluate the role of the two different catalytic sites, here we fabricate two kinds of four-atom-thick layers: pure cobalt metal, and co-existing domains of cobalt metal and cobalt oxide. Cobalt mainly produces formate (HCOO(-)) during CO2 electroreduction; we find that surface cobalt atoms of the atomically thin layers have higher intrinsic activity and selectivity towards formate production, at lower overpotentials, than do surface cobalt atoms on bulk samples. Partial oxidation of the atomic layers further increases their intrinsic activity, allowing us to realize stable current densities of about 10 milliamperes per square centimetre over 40 hours, with approximately 90 per cent formate selectivity at an overpotential of only 0.24 volts, which outperforms previously reported metal or metal oxide electrodes evaluated under comparable conditions. The correct morphology and oxidation state can thus transform a material from one considered nearly non-catalytic for the CO2 electroreduction reaction into an active catalyst. These findings point to new opportunities for manipulating and improving the CO2 electroreduction properties of metal systems, especially once the influence of both the atomic-scale structure and the presence of oxide are mechanistically better understood.

Efficient Photooxidation of Methane to Liquid Oxygenates over ZnO Nanosheets at Atmospheric Pressure and Near Room Temperature.

Direct CH4 photoconversion into liquid oxygenates under mild conditions still represents a huge challenge. Herein, two-dimensional oxide semiconductors are designed to generate abundant active O- species for activating C-H bond of methane. Taking the synthetic ZnO nanosheets as an example, in situ electron paramagnetic resonance spectra verified their lattice oxygen atoms could capture photoexcited holes and generate active O- species, which could efficiently abstract H from CH4 to generate ·CH3 radicals. Gibbs free energy calculations and in situ Fourier-transform infrared spectroscopy corroborated the rate-limiting step was the first C-H bond activation process, whereas the exoergic oxidation of *CHO to HCOOH was easier than the endoergic overoxidation to CO, accounting for the selective production of liquid oxygenates. As a result, the formation rate of liquid oxygenates over ZnO nanosheets reached 2.21 mmol g-1 h-1 with a selectivity of 90.7% at atmospheric pressure and approximately 50 °C, outperforming previously reported photocatalysts under similar conditions.

Selective CH4 Partial Photooxidation by Positively Charged Metal Clusters Anchored on Carbon Aerogel under Mild Conditions.

Selective partial photooxidation of CH4 into value-added chemicals under mild conditions still remains a huge bottleneck. Herein, we design positively charged metal clusters anchored on a three-dimensional porous carbon aerogel. With 0.75FeCA800-4 as an example, X-ray photoelectron spectra and Raman spectra disclose that the iron sites are positively charged. In situ electron paramagnetic resonance spectra show that the Feδ+ sites could donate electrons to activate CH4 into CH4- by virtue of the excited-state carbon atoms; meanwhile, they could convert H2O2 into •OH radicals under irradiation. In addition, in situ diffuse Fourier-transform infrared spectra suggest the CH3OOH obtained is derived from CH4 oxidation by the hydroxylation of *CH3 and *CH3O intermediates. Consequently, 0.75FeCA800-4 displays a CH3OOH selectivity of near 100% and a CH3OOH evolution rate of 13.2 mmol gFe-1 h-1, higher than those of most previously reported supported catalysts under similar conditions.

Selective CO2 Photoreduction into C2 Product Enabled by Charge-Polarized Metal Pair Sites.

Selective CO2 photoreduction into a high-energy-density C2 product is still challenging. Here, charge-polarized metal pair sites are designed to trigger C-C coupling through manipulating asymmetric charge distribution on the reduction intermediates. Taking the synthetic partially reduced Co3O4 nanosheets as an example, theoretical calculations unveil the asymmetric charge distribution on surface cobalt sites. The formed charge-polarized cobalt pair sites not only donate electrons to CO2 molecules but also accelerate the coupling of asymmetric COOH* intermediates through lowering the energy barrier from 0.680 to 0.240 eV, affirmed by quasi in situ X-ray photoelectron spectroscopy and Gibbs free energy calculations. Also, the electron-rich cobalt sites strengthen their interaction with O of the HOOC-CH2O* intermediate, which favors the C-O bond cleavage and hence facilitates the rate-limiting CH3COOH desorption process. The partially reduced Co3O4 nanosheets achieve 92.5% selectivity of CH3COOH in simulated air, while the CO2-to-CH3COOH conversion ratio is 2.75%, obviously higher than that in pure CO2.

Asymmetric Triple-Atom Sites Confined in Ternary Oxide Enabling Selective CO2 Photothermal Reduction to Acetate.

Light-induced heat is largely neglected in traditional photocatalytic systems, especially for the thermodynamically and kinetically challenging CO2 reduction to C2 fuels. Herein, we first design asymmetric Metal1-O-Metal2 triple-atom sites confined in phenakite to facilitate C-C coupling and employ photoinduced heat to increase molecular thermal vibration and accelerate CO2 reduction to C2 fuels. Using O-vacancy-rich Zn2GeO4 nanobelts as prototypes, quasi in situ Raman spectra disclose the Zn-O-Ge triatomic sites are likely the reactive sites. Density functional theory calculations reveal that the asymmetric Zn-O-Ge sites could promote C-C coupling through inducing distinct charge distributions of neighboring C1 intermediates, whereas the created O vacancies could lower the energy barrier of the rate-determining hydrogenation step from 1.46 to 0.67 eV. Catalytic performances under different testing conditions demonstrate that light initiates the CO2 reduction reaction. In situ Fourier-transform infrared spectra and D2O kinetic isotopic effect experiments disclose that light-induced heat kinetically triggers C-C coupling and accelerates OCCO* hydrogenation via providing abundant hydrogen species. Consequently, in a simulated air atmosphere under 0.1 W/cm2 illumination at 348 K, the O-vacancy-rich Zn2GeO4 nanobelts demonstrate an acetate output of 12.7 µmol g-1 h-1, a high acetate selectivity of 66.9%, a considerable CO2-to-CH3COOH conversion ratio of 29.95%, and a stability of up to 220 h.

Fundamentals and challenges of ultrathin 2D photocatalysts in boosting CO2 photoreduction.

Carbon dioxide photoreduction currently suffers from low photoconversion efficiency and poor product selectivity. Ultrathin two-dimensional materials, which possess highly active sites with high density and high uniformity, can serve as ideal models to tailor three crucial parameters that determine the carbon dioxide photoconversion efficiency and product selectivity. In this review, we summarize the extended absorption spectrum range enabled by ultrathin two-dimensional semiconductors with defect levels and intermediate bands, as well as conductors with special partially occupied bands. Moreover, we overview the boosted carrier separation efficiency aroused by ultrathin two-dimensional semiconductors with defect states, surface polarization states and built-in electric fields. We also review the accelerated redox reaction kinetics induced by ultrathin two-dimensional semiconductors with in-plane heterostructures, isolated single atoms and abundant low-coordinated dual-metal sites. Finally, we end this review with an outlook on unsolved issues concerning highly selective and efficient photo-conversion of carbon dioxide into C2+ products by ultrathin two-dimensional materials with dual or multiple active sites.

Photocatalytic Conversion of Waste Plastics into C2 Fuels under Simulated Natural Environment Conditions.

Reported here is the first highly selective conversion of various waste plastics into C2 fuels under simulated natural environment conditions by a sequential photoinduced C-C cleavage and coupling pathway, where single-use bags, disposable food containers, food wrap films, and their main components of polyethylene, polypropylene, and polyvinyl chloride can be photocatalytically transformed into CH3 COOH without using sacrificial agents. As an example, polyethylene is photodegraded 100 % into CO2 within 40 h by single-unit-cell thick Nb2 O5 layers, while the produced CO2 is further photoreduced to CH3 COOH. Various methods and experiments disclose that O2 and . OH radicals trigger the oxidative C-C cleavage of polyethylene to form CO2 , while other investigations show that the yielded CH3 COOH stems from CO2 photoreduction by C-C coupling of . COOH intermediates. This two-step plastic-to-fuel conversion may help to simultaneously address the white pollution crisis and harvest highly valuable multicarbon fuels in natural environments.

Ultrathin Conductor Enabling Efficient IR Light CO2 Reduction.

The concurrent transformation of carbon dioxide and water into hydrocarbons and oxygen by low-photonic-energy IR light still represents a huge challenge. Here, we design an ultrathin conductor system, in which the special partially occupied band serves as the mediator to simultaneously guarantee IR light harvesting and satisfy band-edge positions, while the ultrathin configuration improves charge separation rates and surface redox kinetics. Taking the low cost and earth-abundant CuS as an example, we first fabricate ultrathin CuS layers, where temperature-dependent resistivities, valence-band spectra, and theoretical calculations affirm their metallic nature. Synchrotron-radiation photoelectron and ultraviolet-visible-near-infrared spectra show that metallic CuS atomic layers could realize a new cooperative intraband-interband transition under IR light irradiation, where the generated electrons and holes could simultaneously involve the carbon dioxide reduction and water oxidation reactions. As a result, CuS atomic layers exhibit nearly 100% selective CO production with an evolution rate of 14.5 µmol g-1 h-1 under IR light irradiation, while the catalytic performance shows no obvious decay after a 96 h test. Briefly, benefiting from ultrahigh conductivity and a unique partially occupied band, abundant conductor materials such as conducting metal sulfides and metal nitrides hold great promise for applications as effective IR light responsive photocatalysts.

Visible-Light-Driven Overall Water Splitting Boosted by Tetrahedrally Coordinated Blende Cobalt(II) Oxide Atomic Layers.

Directly splitting water into H2 and O2 with solar light is extremely important; however, the overall efficiency of water splitting still remains extremely low. Two types of ultrathin semiconductor layers with the same elements and the same thicknesses were designed to uncover how different atomic arrangements influence water-splitting efficiency thermodynamically and kinetically. As an example, tetrahedrally coordinated blende and octahedrally coordinated rocksalt CoO atomic layers with nearly the same thicknesses were synthesized for the first time. The blende CoO atomic layers have a smaller Eg and abundant d-d internal transition features relative to the rocksalt CoO atomic layers, which ensure enhanced visible-light harvesting ability. Density functional theory calculations reveal that the Bader charge for Co atoms in blende CoO atomic layers is larger than that of the rocksalt CoO atomic layers, which facilitates photocarrier transfer kinetics, as verified by photoluminescence spectra and time-resolved fluorescence emission decay spectra. In situ FTIR spectra and energy calculations reveal that the *OOH dissociation step is the rate-limiting step, where the blende CoO atomic layers possess a smaller *OOH dissociation energy thanks to their higher Bader charge and stronger steric effect, as confirmed by the elongated Co-OOH bonds. The blende CoO atomic layers exhibit visible-light-driven H2 and O2 formation rates of 4.43 and 2.63 µmol g-1 h-1 , roughly 3.7 times higher than those of the rocksalt CoO atomic layers.

Efficient Visible-Light-Driven CO2 Reduction Mediated by Defect-Engineered BiOBr Atomic Layers.

Solar CO2 reduction efficiency is largely limited by poor photoabsorption, sluggish electron-hole separation, and a high CO2 activation barrier. Defect engineering was employed to optimize these crucial processes. As a prototype, BiOBr atomic layers were fabricated and abundant oxygen vacancies were deliberately created on their surfaces. X-ray absorption near-edge structure and electron paramagnetic resonance spectra confirm the formation of oxygen vacancies. Theoretical calculations reveal the creation of new defect levels resulting from the oxygen vacancies, which extends the photoresponse into the visible-light region. The charge delocalization around the oxygen vacancies contributes to CO2 conversion into COOH* intermediate, which was confirmed by in situ Fourier-transform infrared spectroscopy. Surface photovoltage spectra and time-resolved fluorescence emission decay spectra indicate that the introduced oxygen vacancies promote the separation of carriers. As a result, the oxygen-deficient BiOBr atomic layers achieve visible-light-driven CO2 reduction with a CO formation rate of 87.4 µmol g-1 h-1 , which was not only 20 and 24 times higher than that of BiOBr atomic layers and bulk BiOBr, respectively, but also outperformed most previously reported single photocatalysts under comparable conditions.

Highly Efficient and Exceptionally Durable CO2 Photoreduction to Methanol over Freestanding Defective Single-Unit-Cell Bismuth Vanadate Layers.

Unearthing an ideal model for disclosing the role of defect sites in solar CO2 reduction remains a great challenge. Here, freestanding gram-scale single-unit-cell o-BiVO4 layers are successfully synthesized for the first time. Positron annihilation spectrometry and X-ray fluorescence unveil their distinct vanadium vacancy concentrations. Density functional calculations reveal that the introduction of vanadium vacancies brings a new defect level and higher hole concentration near Fermi level, resulting in increased photoabsorption and superior electronic conductivity. The higher surface photovoltage intensity of single-unit-cell o-BiVO4 layers with rich vanadium vacancies ensures their higher carriers separation efficiency, further confirmed by the increased carriers lifetime from 74.5 to 143.6 ns revealed by time-resolved fluorescence emission decay spectra. As a result, single-unit-cell o-BiVO4 layers with rich vanadium vacancies exhibit a high methanol formation rate up to 398.3 µmol g-1 h-1 and an apparent quantum efficiency of 5.96% at 350 nm, much larger than that of single-unit-cell o-BiVO4 layers with poor vanadium vacancies, and also the former's catalytic activity proceeds without deactivation even after 96 h. This highly efficient and spectrally stable CO2 photoconversion performances hold great promise for practical implementation of solar fuel production.