Efficient Artificial Photosynthesis Research Articles

Hollow SrTiO3 photocatalyst with spatially separated OER and HER cocatalysts for photocatalytic overall water splitting

Overcoming the challenge of sluggish charge separation and the concurrent occurrence of overall water splitting (OWS) half reactions at the same catalytic sites is crucial for achieving efficient photocatalysis. This issue often leads to a high recombination rate and the back reaction of OWS. In this study, we addressed this challenge by enhancing interfacial spatial charge separation. Specifically, we designed hollow SrTiO3 spheres and spatially segregated the hydrogen and oxygen evolution sites on the outer and inner surfaces, respectively, for OWS. The spatially distributed Pt/SrTiO3/CoOx catalysts exhibited exceptional separation of photogenerated charges, resulting in 3-times higher stoichiometric OWS compared to Pt/SrTiO3. This work underscores the effectiveness of a well-tailored spatially distributed structure in promoting charge separation in photocatalysis, thereby opening avenues for the development of efficient artificial photosynthesis systems.

A halide perovskite based ternary heterojunction with multi-shell hollow structure for stable and efficient artificial photosynthesis

Low-cost halide perovskite materials hold great promise as photocatalysts for CO2 reduction. However, their inferior water-tolerance will lead to a substantial decline in activity during prolonged photocatalytic CO2 reduction with water as the electron source. Herein, we integrate a lead-free halide perovskite Cs3Bi2I9 as photoactive layer with TiO2 as water oxidation catalyst and g-C3N4 as CO2 reduction catalyst to construct a ternary heterojunction (TiO2/Cs3Bi2I9/g-C3N4) with a multi-shell hollow structure. The formation of heterojunction endows TiO2/Cs3Bi2I9/g-C3N4 composite with enhanced photocatalytic activity for CO2 reduction due to the improved photogenerated carrier separation. TiO2/Cs3Bi2I9/g-C3N4 achieves a CO yield of 120.6 μmol g−1 h−1 for photocatalytic CO2 reduction, which is 3.1 times higher than that of individual Cs3Bi2I9. More importantly, benefitting from the double-sided protection of g-C3N4 and TiO2, the photocatalytic CO2 reduction activity of TiO2/Cs3Bi2I9/g-C3N4 remains undiminished even over 100 h of continuous light irradiation, demonstrating significantly improved stability in water-contained reaction system.

Perovskite and layered perovskite oxynitrides for efficient sunlight-driven artificial synthesis

Perovskite and layered perovskite oxynitrides are regarded as promising visible-light-responsive semiconductors for efficient artificial photosynthesis to produce renewable value-added energy resources, including H2, formic acid, and ammonia.

Stacking Engineering of Heterojunctions in Half-Metallic Carbon Nitride for Efficient CO2 Photoreduction.

Enhancing charge separation in semiconductor photocatalysts is a major challenge for efficient artificial photosynthesis. Herein, a compact heterojunction is designed by embedding half-metallic C(CN)3 (hm-CN) hydrothermally in BiOBr (BOB) as the backbone. The interface between hm-CN and BOB is seamless and formed by covalent bonding to facilitate the transmission of photoinduced electrons from BOB to hm-CN. The transient photocurrents and electrochemical impedance spectra reveal that the modified composite catalyst exhibits a larger electron transfer rate. The photocatalytic activity of hm-CN/BOB increases significantly as indicated by a CO yield that is about four times higher than that of individual components. Density-functional theory calculations verify that the heterojunction improves electron transport and decreases the reaction energy barrier, thus promoting the overall photocatalytic CO2 conversion efficiency. The half-metal nitride coupled semiconductor heterojunctions might have large potential in artificial photosynthesis and related applications.

Oxygen defect modulating the charge behavior in titanium dioxide for boosting photocatalytic nitrogen fixation performance

Extremely high-temperature and high-pressure requirement of Haber-Bosch process motivates the search for a sustainable ammonia synthesis approach under mild conditions. Photocatalytic technology is a potential solution to convert N2 to ammonia. However, the poor light absorption and low charge carrier separation efficiency in conventional semiconductors are bottlenecks for the application of this technology. Herein, a facile synthesis of anatase TiO2 nanosheets with an abundance of surface oxygen vacancies (TiO2-OV) via the calcination treatment was reported. Photocatalytic experiments of the prepared anatase TiO2 samples showed that TiO2-OV nanosheets exhibited remarkably increased ammonia yield for solar-driven N2 fixation in pure water, without adding any sacrificial agents. EPR, XPS, XRD, UV-Vis DRS, TEM, Raman, and PL techniques were employed to systematically explore the possible enhanced mechanism. Studies revealed that the introduced surface oxygen vacancies significantly extended the light absorption capability in the visible region, decreased the adsorption and activation barriers of inert N2, and improved the separation and transfer efficiency of the photogenerated electron-hole pairs. Thus, a high rate of ammonia evolution in TiO2-OV was realized. This work offers a promising and sustainable approach for the efficient artificial photosynthesis of ammonia.

Tunable Band Engineering Management on Perovskite MAPbBr3 /COFs Nano-Heterostructures for Efficient S-S Coupling Reactions.

Efficient artificial photosynthesis of disulfide bonds holds promises to facilitate reverse decoding of genetic codes and deciphering the secrets of protein multilevel folding, as well as the development of life science and advanced functional materials. However, the incumbent synthesis strategies encounter separation challenges arising from leaving groups in the ─S─S─ coupling reaction. In this study, according to the reaction mechanism of free-radical-triggered ─S─S─ coupling, light-driven heterojunction functional photocatalysts are tailored and constructed, enabling them to efficiently generate free radicals and trigger the coupling reaction. Specifically, perovskites and covalent organic frameworks (COFs) are screened out as target materials due to their superior light-harvesting and photoelectronic properties, as well as flexible and tunable band structure. The in situ assembled Z-scheme heterojunction MAPB-M-COF (MAPbBr3 = MAPB, MA+ = CH3 NH2 + ) demonstrates a perfect trade-off between quantum efficiency and redox chemical potential via band engineering management. The MAPB-M-COF achieves a 100% ─S─S─ coupling yield with a record photoquantum efficiency of 11.50% and outstanding cycling stability, rivaling all the incumbent similar reaction systems. It highlights the effectiveness and superiority of application-oriented band engineering management in designing efficient multifunctional photocatalysts. This study demonstrates a concept-to-proof research methodology for the development of various integrated heterojunction semiconductors for light-driven chemical reaction and energy conversion.

Synergistic Trimetallic Nanocomposites as Visible-NIR-Sunlight-Driven Photocatalysts for Efficient Artificial Photosynthesis.

Here, we report monodispersed tricomponent MnNSs-SnO2@Pt and MnNFs-SnO2@Pt nanocomposites prepared by simultaneous SnO2 and Pt nanodot coating on Mn nanospheres (MnNSs) and Mn nanoflowers (MnNFs) for highly efficient CO2 photoreduction in visible-NIR-sunlight irradiation. MnNFs-SnO2@Pt showed higher efficiency with a quantum yield of 3.21% and a chemical yield of 5.45% for CO2 conversion under visible light irradiation for HCOOH formation with 94% selectivity. Similarly, MnNFs-SnO2@Pt displayed significant photocatalytic efficiency in NIR and sunlight irradiation for HCOOH yield. MnNFs-SnO2@Pt nanocomposites also showed robust morphology and sustained structural stability with shelf-life for at least 1 year and were utilized for at least 10 reaction cycles without losing significant photocatalytic efficiency. The high surface area (94.98 m2/g), efficient electron-hole separation, and Pt-nanodot support in MnNFs--SnO2@Pt contributed to a higher photocatalytic efficacy toward CO2 reduction.

Loaded Cu-Er metal iso-atoms on graphdiyne for artificial photosynthesis

Herein we report a bimetal atomic catalyst that features atomically dispersed Cu and Er atoms anchored on all crystalline graphdiyne (CuEr-GDY) for efficient artificial photosynthesis converting CO2 into sustainable fuel at the gas–solid interfaces with water as reducing medium instead of organic reagent. The CuEr-GDY can promote the efficient separation of photogenerated electron-hole pairs to drive water oxidation and CO2 activation/reduction, together with Cu/Er promoted CO2/H2O adsorption and CO desorption. This result indicates that bimetallic atoms on the high-crystalline GDY surface have high activity. This heteroatomic catalyst of CuEr-GDY demonstrates high catalytic activity with the reaction selectivity up to 97.6%, and the competitive hydrogen evolution reaction is almost completely suppressed. The CO2 conversion achieves the CO yield of 181.04 μmol g−1 h−1 under ambient conditions.

Microenvironment regulation of Ru(bda)L2 catalyst incorporated in metal-organic framework for effective photo-driven water oxidation

A Ru(bda)L2 molecular catalyst (H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid, L represents ligands) was incorporated into a UiO-66 metal-organic framework (MOF) as isolating sites for chemical- and photo-driven water oxidation with the water nucleophilic attack mechanism. An impressive turn-over number of 566 was obtained for photo-driven water oxidation in the phosphate buffer saline, which was nearly 20 times that of the homogenous counterpart in the presence of ruthenium tris(bipyridine) and sodium persulfate. Infrared spectroscopy, X-ray diffraction and X-ray spectroscopy techniques were used to characterize the composition and structure of the catalysts. Kinetic isotope effect (KIE), proton inventory experiment and proton nuclear magnetic resonance were conducted to understand the photo-driven O2 evolution mechanism. It was observed that the protons participated in O2 evolution with a normal KIE value, and the uptake of phosphates by UiO-66 matrix improved the affinity towards H2O via hydrogen bonding. The high O2 output and the limited photosensitizer oxidative decomposition in PBS suggest that the phosphate acted as a proton mediator to assist proton and/or proton-couple electron transfer through a hydrogen-bonded network of water molecules. This study uses a heterogenous matrix to emulate an enzyme-like microenvironment capable of achieving efficient artificial photosynthesis.

In situ constructing atomic interface in ruthenium-based amorphous hybrid-structure towards solar hydrogen evolution

The rational steering and construction of efficient and stable atomic interfaces is highly desirable but rather challenging in solar energy conversion. Here, we report an in-situ oxygen impregnation strategy to build abundant atomic interfaces composed of homogeneous Ru and RuOx amorphous hybrid-mixture with ultrafast charge transfer, for solar hydrogen evolution with sacrificial agent free. Via in-situ synchrotron X-ray absorption and photoelectron spectroscopies, we can precisely track and identify the gradual formation of atomic interfaces towards homogeneous Ru-RuOx hybrid-structure at the atomic level. Benefiting from the abundant interfaces, the amorphous RuOx sites can intrinsically trap the photoexcited hole within an ultrafast process (<100 fs), and the amorphous Ru sites enable subsequent electron transfer (~1.73 ps). Hence, this hybrid-structure triggers long-lived charge-separated states, and results in a high hydrogen evolution rate of 60.8 μmol·h−1. This design integrating the two sites fulfilled each half-reaction in a single hybrid-structure suggests potential guidelines towards efficient artificial photosynthesis.

Cu-Based Materials as Photocatalysts for Solar Light Artificial Photosynthesis: Aspects of Engineering Performance, Stability, Selectivity

Cu-oxide nanophases (CuO, Cu2O, Cu0) constitute highly potent nanoplatforms for the development of efficient Artificial Photosynthesis catalysts. The highly reducing conduction band edge of the d-electrons in Cu2O dictates its efficiency towards CO2 reduction under sunlight excitation. In the present review, we discuss aspects interlinking the stability under photocorrosion of the (CuO/Cu2O/Cu0) nanophase equilibria, and performance in H2-production/CO2-reduction. Converging literature evidence shows that, because of photocorrosion, single-phase Cu-oxides would not be favorable to be used as a standalone cathodic catalyst/electrode; however, their heterojunctions and the coupling with proper partner materials is an encouraging approach. Distinction between the role of various factors is required to protect the material from photocorrosion, e.g., use of hole scavengers/electron acceptors, band-gap engineering, nano-facet engineering, and selectivity of CO2-reduction pathways, to name a few possible solutions. In this context, herein we discuss examples and synthesis efforts that aim to clarify the role of interfaces, faces, and phase stability under photocatalytic conditions.

Designing mixed-metal electrocatalyst systems for photoelectrochemical dinitrogen activation.

Efficient artificial photosynthesis systems are currently realized as catalyst- and surface-functionalized photovoltaic tandem-and triple-junction devices, enabling photoelectrochemical (PEC) water oxidation while simultaneously recycling CO2 and generating hydrogen as a solar fuel for storable renewable energy. Although PEC systems also bear advantages for the activation of dinitrogen - such as a high system tunability with respect to the electrocatalyst integration and a directly controllable electron flux to the anchoring catalyst through the adjustability of incoming irradiation - only a few PEC devices have been developed and investigated for this purpose. We have developed a series of photoelectrodeposition procedures to deposit mixed-metal electrocatalyst nanostructures directly on the semiconductor surface for light-assisted dinitrogen activation. These electrocatalyst compositions containing Co, Mo and Ru in different atomic ratios follow previously made recommendations of metal compositions for dinitrogen reduction and exhibit different physical properties. XPS studies of the photoelectrode surfaces reveal that our electrocatalyst films are to a large degree nitrogen-free after their fabrication, which is generally difficult to achieve with traditional magnetron sputtering or e-beam evaporation techniques. Initial chronoamperometric measurements of the p-InP photoelectrode coated with the Co-Mo alloy electrocatalyst show higher photocurrent densities in the presence of N2(g) than in the presence of Ar at -0.09 V vs. RHE. Indications of successful dinitrogen activation have also been found in consecutive XPS studies, where both N 1s and Mo 3d spectra reveal evidence of nitrogen-metal interactions.

Layered β‐ZrNBr Nitro‐Halide as Multifunctional Photocatalyst for Water Splitting and CO2 Reduction

AbstractDeveloping mixed‐anion semiconductors for solar fuel production has inspired extensive interest, but the nitrohalide‐based photocatalyst is still in shortage. Here we report a layered nitro‐halide β‐ZrNBr with a narrow band gap of ca. 2.3 eV and low defect density to exhibit multifunctionalities for photocatalytic water reduction, water oxidation and CO2 reduction under visible‐light irradiation. As confirmed by the results of electron paramagnetic resonance (EPR) and density functional theory (DFT) calculations, the formation of anion vacancies in the nitro‐halide photocatalyst was inhibited due to its relatively high formation energy. Furthermore, performance of β‐ZrNBr can be effectively promoted by a simple exfoliation into nanosheets to shorten the carrier transfer distance as well as to promote charge separation. Our work extends the territory of functional photocatalysts into the nitro‐halide, which opens a new avenue for fabricating efficient artificial photosynthesis.

Layered β-ZrNBr Nitro-Halide as Multifunctional Photocatalyst for Water Splitting and CO2 Reduction.

Developing mixed-anion semiconductors for solar fuel production has inspired extensive interest, but the nitrohalide-based photocatalyst is still in shortage. Here we report a layered nitro-halide β-ZrNBr with a narrow band gap of ca. 2.3 eV and low defect density to exhibit multifunctionalities for photocatalytic water reduction, water oxidation and CO2 reduction under visible-light irradiation. As confirmed by the results of electron paramagnetic resonance (EPR) and density functional theory (DFT) calculations, the formation of anion vacancies in the nitro-halide photocatalyst was inhibited due to its relatively high formation energy. Furthermore, performance of β-ZrNBr can be effectively promoted by a simple exfoliation into nanosheets to shorten the carrier transfer distance as well as to promote charge separation. Our work extends the territory of functional photocatalysts into the nitro-halide, which opens a new avenue for fabricating efficient artificial photosynthesis.

Ligand-free CsPbBr3 with calliandra-like nanostructure for efficient artificial photosynthesis

The low-efficiency CO2 uptake capacity and insufficient photogenerated exciton dissociation of current metal halide perovskite (MHP) nanocrystals with end-capping ligands extremely restrict their application in the field of artificial photosynthesis. Herein, we demonstrate that ligand-free CsPbBr3 with calliandra-like nanostructure (LF-CPB CL) can be synthesized easily through a ligand-free seed-assisted dissolution-recrystallization growth process, exhibiting significantly enhanced CO2 uptake capacity. More specifically, the abundant surface bromine (Br) vacancies in ligand-free MHP materials are demonstrated to be beneficial to photogenerated carrier separation. The electron consumption rate of LF-CPB CL for photocatalytic CO2 reduction increases 7 and 20 times over those of traditional ligand-capping CsPbBr3 nanocrystal (L-CPB NC) and bulk CsPbBr3, respectively. Moreover, the absence of ligand hindrance can facilitate the interfacial electronic coupling between LF-CPB CL and tetra(4-carboxyphenyl)porphyrin iron(III) chloride (Fe-TCPP) cocatalyst, bringing forth significantly accelerated interfacial charge separation. The LF-CPB CL/Fe-TCPP exhibits a total electron consumption rate of 145.6 μmol g−1 h−1 for CO2 photoreduction coupled with water oxidation, which is over 14 times higher than that of L-CPB NC/Fe-TCPP.

Nb–O–C Charge Transfer Bridge in 2D/2D Nb2O5/g‐C3N4 S‐Scheme Heterojunction for Boosting Solar‐Driven CO2 Reduction: In Situ Illuminated X‐Ray Photoelectron Spectroscopy Investigation and Mechanism Insight

Although the construction of heterojunction photocatalysts is a promising way to achieve outstanding photocatalytic activities, a 2D heterojunction which possesses strong chemical bonding and appropriate interfacial contact toward efficient artificial photosynthesis is still a challenge. Herein, 2D/2D Nb2O5/g‐C3N4 S‐scheme heterojunction photocatalysts are successfully fabricated by a convenient in situ calcination route derived from niobic acid/urea precursor for the gas–solid CO2 reduction reaction. Under simulated solar irradiation, the total yield of C1 products (CH4 and CO) obtained on the optimized sample NOCN‐5 are 6.7 times and 5.3 times that over pristine Nb2O5 and g–C3N4 nanosheets, respectively, without sacrificial agent or cocatalysts. The enhanced performances of CO2 photoreduction might be attributed to the unique Nb─O─C chemical bonds induced charge transfer bridge, face‐to‐face contact, and the efficient S‐scheme transfer path of photoinduced electron–hole pairs, which is confirmed by in situ illuminated X‐ray photoelectron spectroscopy and density functional theory calculation. This work will provide a promising strategy for constructing S‐scheme heterojunction systems for efficient artificial photosynthesis reactions toward carbon neutrality.

Constructing crystalline redox catalyst to achieve efficient CO2 photoreduction reaction in water vapor

Artificial photosynthesis, coupling CO2 photoreduction and water photooxidation reactions, is an important and green means to convert CO2. Compared with traditional multiphasic heterojunctions, monophasic photocatalysts for artificial photosynthesis are still very rare. Here we construct a crystalline overall reaction catalyst, RO-4, by connecting reductive {CuI8} and oxidative {PMo8V6O42} clusters with bridging oxygen atoms, which allow the photogenerated electrons to transfer easily between the redox clusters. Under light irradiation, RO-4 can achieve efficient artificial photosynthesis with a high CO production activity of 20.06 μmol g-1h−1 (>99.5% selectivity) along with O2 release. Furthermore, in situ DRIFTS and DFT calculations uncover the related reaction intermediates and CO2 photoreduction mechanism. This work validates a feasible strategy to engineer monophasic crystalline RO photocatalysts for efficient artificial photosynthetic overall reaction.

Pr3+-doped La1-xPrxMn0.6Ni0.4O3-δ as efficient artificial photosynthesis catalysts for solar methanol

In this study, a transition metal-based perovskite oxide catalyst with high CH3OH yield was successfully developed. The A-site substitution by Pr3+ in La1-xPrxMn0.6Ni0.4O3-δ can effectively adjust the activity of the perovskite catalysts for the direct conversion of CO2 and H2O into hydrocarbon fuels, especially CH3OH. Based on the designed photo-thermo synergetic photosynthesis strategy, the first hour CH3OH yield of La1-xPrxMn0.6Ni0.4O3-δ reached 3.97 mmol g−1, while only 0.24 μmol g−1 under normal photocatalysis mode. The synergistic photo-thermo catalysis was demonstrated to be a promising strategy for the future artificial photosynthesis development.

Bismuth Vacancy-Induced Efficient CO2 Photoreduction in BiOCl Directly from Natural Air: A Progressive Step toward Photosynthesis in Nature.

Photocatalytic CO2 conversion into carbonaceous fuels through artificial photosynthesis is beneficial to global warming mitigation and renewable resource generation. However, a high cost is always required by special CO2-capturing devices for efficient artificial photosynthesis. For achieving highly efficient photocatalytic CO2 reduction (PCR) directly from natural air, we report rose-like BiOCl that is rich in Bi vacancies (VBi) assembled by nanosheets with almost fully exposed active {001} facets. These rose-like BiOCl with VBi assemblies provide considerable adsorption and catalytic sites, which hoists the CO2 capture and reduction capabilities, and thus expedites the PCR to a superior value of 21.99 μmol·g-1·h-1 CO generation under a 300 W Xe lamp within 5 h from natural air. The novel design and construction of a photocatalyst in this work could break through the conventional PCR system requiring compression and purification for CO2, dramatically reduce expenses, and open up new possibilities for the practical application of artificial photosynthesis.

Ultrathin MOF Coupling with Molecular Cobaloxime to Construct an Efficient Hybrid Hematite Photoanode for Photocatalytic Water Splitting

It is a great challenge to develop efficient artificial photosynthesis systems by mimicking natural photosynthesis. In this present work, an organo-inorganic hybrid photoanode was fabricated by depositing ultrathin NiFe MOF nanolayers and molecular cobaloxime cocatalyst on the surface of Ti-doped porous hematite (Ti-PH). This hybrid photoanode exhibited a high photocurrent density of 2.45 mA/cm2 at 1.23 V vs the reversible hydrogen electrode (RHE) under AM 1.5 G illumination with excellent stability. Moreover, the optimal incident photon-to-current efficiency (IPCE) of the hybrid photoanode reached 83.0% at 365 nm and the surface charge injection efficiency (ηinj) was improved to 87.5% at 1.23 V vs RHE. Detailed investigations reveal that NiFe MOFs can effectively facilitate charge separation as a hole-transport layer and molecular cobaloxime cocatalyst can passivate surface trap states to increase water oxidation kinetics.