Protoelectrochemical properties of the single-crystal SrTiO3 doped in the surface region

The photoelectrochemical properties of the single crystal SrTiO₃, doped in the surface region are studied. It is found that the doped SrTiO₃ with Cr, Co, Pt and Rh give a relatively large photoresponse to visible light. The dark anodic currents which will be due to the resonance tunnelling or hopping mechanism are observed at the doped electrodes with the above metal cations. Therefore, it is concluded that the visible light response is mainly attributable to the formed impurity levels and/or structure defetcs by the doping metal cations near the conduction band of SrTiO₃. The above doped electrodes also bring the large cathodic photocurrent or the dark cathodic current due to the O₂ reduction, except for the Co doped electrode. This will show that the impurity levels act as the active site of O₂ reduction.     

Co doped ZnO nanowires as visible light photocatalysts

High aspect ratio cobalt doped ZnO nanowires showing strong photocatalytic activity and moderate ferromagnetic behaviour were successfully synthesized using a solvothermal method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), vibrating sample magnetometry (VSM) and UV–visible absorption spectroscopy. The photocatalytic activities evaluated for visible light driven degradation of an aqueous methylene orange (MO) solution were higher than for Co doped ZnO nanoparticles at the same doping level and synthesized by the same synthesis route. The rate constant for MO visible light photocatalytic degradation was 1.9·10⁻³ min⁻¹ in case of nanoparticles and 4.2·10⁻³ min⁻¹ in case of nanowires. We observe strongly enhanced visible light photocatalytic activity for moderate Co doping levels, with an optimum at a composition of Zn_0.95Co_0.05O. The enhanced photocatalytic activities of Co doped ZnO nanowires were attributed to the combined effects of enhanced visible light absorption at the Co sites in ZnO nanowires, and improved separation efficiency of photogenerated charge carriers at optimal Co doping.     

Site‐Selected Doping of Upconversion Luminescent Er3+ into SrTiO3 for Visible‐Light‐Driven Photocatalytic H2 or O2 Evolution

A series of upconversion luminescent erbium‐doped SrTiO₃ (ABO₃‐type) photocatalysts with different initial molar ratios of Sr/Ti have been prepared by a facile polymerized complex method. Er³⁺ ions, which were gradually transferred from the A to the B site with increasing Sr/Ti, enabled the absorption of visible light and the generation of high‐energy excited states populated by upconversion processes. The local internal fields arising from the dipole moments of the distorted BO₆ octahedra promoted energy transfer from the high‐energy excited states of Er³⁺ with B‐site occupancy to the host SrTiO₃ and thus enhanced the band‐to‐band transition of the host SrTiO₃. Consequently, the erbium‐doped SrTiO₃ species with B‐site occupancy showed higher photocatalytic activity than those with A‐site occupancy for visible‐light‐driven H₂ or O₂ evolution in the presence of the corresponding sacrificial reagents. The results generally suggest that the introduction of upconversion luminescent agents into host semiconductors is a promising approach to simultaneously harnessing low‐energy photons and maintaining redox ability for photocatalytic H₂ and O₂ evolution and that the site occupancy of doped elements in ABO₃‐type perovskite oxides greatly determines the photocatalytic activity.     

Z-scheme heterojunction of SnS2-decorated 3DOM-SrTiO3 for selectively photocatalytic CO2 reduction into CH4

The rapid recombination of photoinduced electron-hole pairs as well as the deficiency of high-energy carriers restricted the redox ability and products selectivity. Herein, the heterojunction of SnS₂-decorated three-dimensional ordered macropores (3DOM)-SrTiO₃ catalysts were in-situ constructed to provide transmit channel for high-energy electron transmission. The suitable band edges of SnS₂ and SrTiO₃ contribute to the Z-scheme transfer of photogenerated carrier. The 3DOM structure of SrTiO₃-based catalyst possesses the slow light effect for enhancing light adsorption efficiency, and the surface alkalis strontium is benefit to the boosting adsorption for CO₂. The in-situ introduced SnS₂ decorated on the macroporous wall surface of 3DOM-SrTiO₃ altered the primary product from CO to CH₄. The Z-scheme electron transfer from SnS₂ combining with the holes in SrTiO₃ occurred under full spectrum photoexcitation, which improved the excitation and utilization of photogenerated electrons for CO₂ multi-electrons reduction. As a result, (SnS₂)₃/3DOM-SrTiO₃ catalyst exhibits higher activity for photocatalytic CO₂ reduction to CH₄ compared with single SnS₂ or 3DOM-SrTiO₃, i.e., its yield and selectivity of CH₄ are 12.5 μmol g^-1 h^-1 and 74.9%, respectively. The present work proposed the theoretical foundation of Z-scheme heterojunction construction for enhancing photocatalytic activity and selectivity for CO₂ conversion.     

Photoassisted Selective Steam and Dry Reforming of Methane to Syngas Catalyzed by Rhodium–Vanadium Bimetallic Oxide Cluster Anions at Room Temperature

Photoassisted steam reforming and dry (CO₂) reforming of methane (SRM and DRM) at room temperature with high syngas selectivity have been achieved in the gas-phase catalysis for the first time. The catalysts used are bimetallic rhodium–vanadium oxide cluster anions of Rh₂VO_1–3⁻. Both the oxidation of methane and reduction of H₂O/CO₂ can take place efficiently in the dark while the pivotal step to govern syngas selectivity is photo-excitation of the reaction intermediates Rh₂VO_2,3CH₂⁻ to specific electronically excited states that can selectively produce CO and H₂. Electronic excitation over Rh₂VO_2,3CH₂⁻ to control the syngas selectivity is further confirmed from the comparison with the thermal excitation of Rh₂VO_2,3CH₂⁻, which leads to diversity of products. The atomic-level mechanism obtained from the well-controlled cluster reactions provides insight into the process of selective syngas production from the photocatalytic SRM and DRM reactions over supported metal oxide catalysts.     

Metal-Free Photocatalytic CO2 Reduction to CH4 and H2O2 under Non-sacrificial Ambient Conditions

Photocatalytic CO₂ reduction to CH₄ requires photosensitizers and sacrificial agents to provide sufficient electrons and protons through metal-based photocatalysts, and the separation of CH₄ from by-product O₂ has poor applications. Herein, we successfully synthesize a metal-free photocatalyst of a novel electron-acceptor 4,5,9,10-pyrenetetrone (PT), to our best knowledge, this is the first time that metal-free catalyst achieves non-sacrificial photocatalytic CO₂ to CH₄ and easily separable H₂O₂. This photocatalyst offers CH₄ product of 10.6 μmol ⋅ g⁻¹ ⋅ h⁻¹ under non-sacrificial ambient conditions (room temperature, and only water), which is two orders of magnitude higher than that of the reported metal-free photocatalysts. Comprehensive in situ characterizations and calculations reveal a multi-step reaction mechanism, in which the long-lived oxygen-centered radical in the excited PT provides as a site for CO₂ activation, resulting in a stabilized cyclic carbonate intermediate with a lower formation energy. This key intermediate is thermodynamically crucial for the subsequent reduction to CH₄ product with the electronic selectivity of up to 90 %. The work provides fresh insights on the economic viability of photocatalytic CO₂ reduction to easily separable CH₄ in non-sacrificial and metal-free conditions.     

Photo-Induced Switching of CO2 Hydrogenation Pathway towards CH3OH Production over Pt@UiO-66-NH2(Co)

It is highly desired to achieve controllable product selectivity in CO₂ hydrogenation. Herein, we report light-induced switching of reaction pathways of CO₂ hydrogenation towards CH₃OH production over actomically dispersed Co decorated Pt@UiO-66-NH₂. CO, being the main product in the reverse water gas shift (RWGS) pathway under thermocatalysis condition, is switched to CH₃OH via the formate pathway with the assistance of light irradiation. Impressively, the space-time yield of CH₃OH in photo-assisted thermocatalysis (1916.3 μmol g_cat⁻¹ h⁻¹) is about 7.8 times higher than that without light at 240 °C and 1.5 MPa. Mechanism investigation indicates that upon light irradiation, excited UiO-66-NH₂ can transfer electrons to Pt nanoparticles and Co sites, which can efficiently catalyze the critical elementary steps (i.e., CO₂-to-*HCOO conversion), thus suppressing the RWGS pathway to achieve a high CH₃OH selectivity.     

Regulating Efficient and Selective Single-atom Catalysts for Electrocatalytic CO2 Reduction

Anchoring transition metal (TM) atoms on suitable substrates to form single-atom catalysts (SACs) is a novel approach to constructing electrocatalysts. Graphdiyne with sp−sp² hybridized carbon atoms and uniformly distributed pores have been considered as a potential carbon material for supporting metal atoms in a variety of catalytic processes. Herein, density functional theory (DFT) calculations were performed to study the single TM atom anchoring on graphdiyne (TM₁−GDY, TM=Sc, Ti, V, Cr, Mn, Co and Cu) as the catalysts for CO₂ reduction. After anchoring metal atoms on GDY, the catalytic activity of TM₁−GDY (TM=Mn, Co and Cu) for CO₂ reduction reaction (CO₂RR) are significantly improved comparing with the pristine GDY. Among the studied TM₁−GDY, Cu₁−GDY shows excellent electrocatalytic activity for CO₂ reduction for which the product is HCOOH and the limiting potential (U_L) is −0.16 V. Mn₁−GDY and Co₁−GDY exhibit superior catalytic selectivity for CO₂ reduction to CH₄ with U_L of −0.62 and −0.34 V, respectively. The hydrogen evolution reaction (HER) by TM₁−GDY (TM=Mn, Co and Cu) occurs on carbon atoms, while the active sites of CO₂RR are the transition metal atoms . The present work is expected to provide a solid theoretical basis for CO₂ conversion into valuable hydrocarbons.     

In Situ Investigation of Methane Dry Reforming on Metal/Ceria(111) Surfaces: Metal–Support Interactions and C−H Bond Activation at Low Temperature

Studies with a series of metal/ceria(111) (metal=Co, Ni, Cu; ceria=CeO₂) surfaces indicate that metal–oxide interactions can play a very important role for the activation of methane and its reforming with CO₂ at relatively low temperatures (600–700 K). Among the systems examined, Co/CeO₂(111) exhibits the best performance and Cu/CeO₂(111) has negligible activity. Experiments using ambient pressure X‐ray photoelectron spectroscopy indicate that methane dissociates on Co/CeO₂(111) at temperatures as low as 300 K—generating CH_x and CO_x species on the catalyst surface. The results of density functional calculations show a reduction in the methane activation barrier from 1.07 eV on Co(0001) to 0.87 eV on Co²⁺/CeO₂(111), and to only 0.05 eV on Co⁰/CeO_2−x (111). At 700 K, under methane dry reforming conditions, CO₂ dissociates on the oxide surface and a catalytic cycle is established without coke deposition. A significant part of the CH_x formed on the Co⁰/CeO_2−x (111) catalyst recombines to yield ethane or ethylene.     

Highly Efficient Low‐Temperature Plasma‐Assisted Modification of TiO2 Nanosheets with Exposed {001} Facets for Enhanced Visible‐Light Photocatalytic Activity

Anatase TiO₂ nanosheets with exposed {001} facets have been controllably modified under non‐thermal dielectric barrier discharge (DBD) plasma with various working gas, including Ar, H₂, and NH₃. The obtained TiO₂ nanosheets possess a unique crystalline core/amorphous shell structure (TiO₂@TiO_2?x), which exhibit the improved visible and near‐infrared light absorption. The types of dopants (oxygen vacancy/surface Ti³⁺/substituted N) in oxygen‐deficient TiO₂ can be tuned by controlling the working gases during plasma discharge. Both surface Ti³⁺ and substituted N were doped into the lattice of TiO₂ through NH₃ plasma discharge, whereas the oxygen vacancy or Ti³⁺ (along with the oxygen vacancy) was obtained after Ar or H₂ plasma treatment. The TiO₂@TiO_2?x from NH₃ plasma with a green color shows the highest photocatalytic activity under visible‐light irradiation compared with the products from Ar plasma or H₂ plasma due to the synergistic effect of reduction and simultaneous nitridation in the NH₃ plasma.     

TiO2 Nanotube Arrays Modified with Cr‐Doped SrTiO3 Nanocubes for Highly Efficient Hydrogen Evolution under Visible Light

In recent decades, solar‐driven hydrogen production over semiconductors has attracted tremendous interest owing to the global energy and environmental crisis. Among various semiconductor materials, TiO₂ exhibits outstanding photocatalytic properties and has been extensively applied in diverse photocatalytic and photoelectric systems. However, two major drawbacks limit practical applications, namely, high charge‐recombination rate and poor visible‐light utilization. In this work, heterostructured TiO₂ nanotube arrays grafted with Cr‐doped SrTiO₃ nanocubes were fabricated by simply controlling the kinetics of hydrothermal reactions. It was found that coupling TiO₂ nanotube arrays with regular SrTiO₃ nanocubes can significantly improve the charge separation. Meanwhile, doping Cr cations into SrTiO₃ nanocubes proved to be an effective and feasible approach to enhance remarkably the visible‐light response, which was also confirmed by theoretical calculations. As a result, the rate of photoelectrochemical hydrogen evolution of these novel heteronanostructures is an order of magnitude larger than those of TiO₂ nanotube arrays and other previously reported SrTiO₃/TiO₂ nanocomposites under visible‐light irradiation. Furthermore, the as‐prepared Cr‐doped SrTiO₃/TiO₂ heterostructures exhibit excellent durability and stability, which are favorable for practical hydrogen production and photoelectric nanodevices.     

Lattice-matched in-situ construction of 2D/2D T-SrTiO3/CsPbBr3 heterostructure for efficient photocatalysis of CO2 reduction

The elaborate regulation of heterostructure interface to accelerate the interfacial charge separation is one of practicable approaches to improve the photocatalytic CO₂ reduction performance of halide perovskite (HP) materials. Herein, we report an in-situ growth strategy for the construction of 2D CsPbBr₃ based heterostructure with perovskite oxide (SrTiO₃) nanosheet as substrate (CsPbBr₃/SrTiO₃). Lattice matching and matchable energy band structures between CsPbBr₃ and SrTiO₃ endow CsPbBr₃/SrTiO₃ heterostructure with an efficient interfacial charge separation. Moreover, the interfacial charge transfer rate can be further accelerated by etching SrTiO₃ with NH₄F to form flat surface capped with Ti?O bonds. The resultant 2D/2D T-SrTiO₃/CsPbBr₃ heterostructure exhibits an impressive photocatalytic activity for CO₂ conversion with a CO yield of 120.2 ± 4.9 μmol g^?1 h^?1 at the light intensity of 100 mW/cm² and water as electron source, which is about 10 and 7 times higher than those of the pristine SrTiO₃ and CsPbBr₃ nanosheets, surpassing the reported halide perovskite-based photocatalysts under the same conditions.     

Highly Efficient Electroreduction of CO2 to C2+ Alcohols on Heterogeneous Dual Active Sites

Electroreduction of CO₂ to liquid fuels such as ethanol and n‐propanol, powered by renewable electricity, offers a promising strategy for controlling the global carbon balance and addressing the need for the storage of intermittent renewable energy. In this work, we discovered that the composite composed of nitrogen‐doped graphene quantum dots (NGQ) on CuO‐derived Cu nanorods (NGQ/Cu‐nr) was an outstanding electrocatalyst for the reduction of CO₂ to ethanol and n‐propanol. The Faradaic efficiency (FE) of C2+ alcohols could reach 52.4 % with a total current density of 282.1 mA cm^?2. This is the highest FE for C2+ alcohols with a commercial current density to date. Control experiments and DFT studies show that the NGQ/Cu‐nr could provide dual catalytic active sites and could stabilize the CH₂CHO intermediate to enhance the FE of alcohols significantly through further carbon protonation. The NGQ and Cu‐nr had excellent synergistic effects for accelerating the reduction of CO₂ to alcohols.     

具有分级多孔结构和光催化性质的核-壳纳米球(HP-Fe2O3@TiO2)

通过溶剂热和溶胶-凝胶涂层法, 设计并制备了具有分级多孔结构和光催化性质的核-壳纳米球(HP-Fe₂O₃@TiO₂). 透射电子显微镜(TEM)照片证明所得HP-Fe₂O₃@TiO₂样品具备分级多孔结构, 这是因为HP-Fe₂O₃@TiO₂的内核-Fe₂O₃具有大孔空隙, 同时外壳-TiO₂具有介孔空隙. 此外, 通过X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、X射线光电子能谱(XPS)以及氮气吸附-脱附曲线深入研究了HP-Fe₂O₃@TiO₂的结构及其性质. 分别在可见及紫外光照下, 研究了样品在H₂O₂体系下的光催化降解亚甲基蓝(MB)的性质. 所观察到的HP-Fe₂O₃@TiO₂纳米球的光催化性能, 可归因于核-壳结构的协同作用, 这进一步表明, TiO₂外壳对α-Fe₂O₃的光催化活性有重要影响作用. 在可见光照射下, HP-Fe₂O₃@TiO₂ (1 mL Ti(OC₄H₉)₄ (TBT))具有较优异的光催化活性. 同时, HP-Fe₂O₃@TiO₂ (4mL TBT)具备优异的单分散形貌, 并在紫外光照射下, 表现出最优的光催化活性.     

Experimental Evidence of CO2 Photoreduction Activity of SnO2 Nanoparticles

Tin dioxide (SnO₂) has intrinsic characteristics that do not favor its photocatalytic activity. However, we evidenced that surface modification can positively influence its performance for CO₂ photoreduction in the gas phase. The hydroxylation of the SnO₂ surface played a role in the CO₂ affinity decreasing its reduction potential. The results showed that a certain selectivity for methane (CH₄), carbon monoxide (CO), and ethylene (C₂H₄) is related to different SnO₂ hydrothermal annealing. The best performance was seen for SnO₂ annealed at 150 °C, with a production of 20.4 μmol g⁻¹ for CH₄ and 16.45 μmol g⁻¹ for CO, while for SnO₂ at 200 °C the system produced more C₂H₄, probably due to a decrease of surface −OH groups.     

Promotion of photocatalytic steam reforming of methane over Ag~0/Ag~+-SrTiO_3

Methane(CH_4) is not only used as a fuel but also as a promising clean energy source for hydrogen generation.The steam reforming of CH4(SRM) using photocatalysts can realize the production of syngas(CO+H_2) with low energy consumption.In this work,Ag~0/Ag~+-loaded SrTi03 nanocomposites were successfully prepared through a photodeposition method.When the loading amount of Ag is 0.5 mol%,the atom ratio of Ag~+ to Ag~0 was found to be 51:49.In this case,a synergistic effect of Ago and Ag~+ was observed,in which Ago was proposed to improve the adsorption of H_2 O to produce hydroxyl radicals and enhance the utilization of light energy as well as the separation of charge carriers.Meanwhile,Ag~0 was regarded as the reduction reaction site with the function of an electron trapping agent.In addition,Ag~+adsorbed the CH4 molecules and acted as the oxidation reaction sites in the process of photocatalytic SRM to further promote electron-hole separation.As a result,0.5 mol% Ag-SrTi03 exhibited enhancement of photocatalytic activity for SRM with the highest CO production rate of 4.3 μmol g~(-1) h~(-1),which is ca.5 times higher than that of pure SrTi03.This work provides a facile route to fabricate nanocomposite with cocatalyst featuring different functions in promoting photocatalytic activity for SRM.     

A Dinuclear Cobalt Cryptate as a Homogeneous Photocatalyst for Highly Selective and Efficient Visible-Light Driven CO2 Reduction to CO in CH3CN/H2O Solution

A dinuclear cobalt complex [Co₂(OH)L¹](ClO₄)₃ ( 1 , L¹=N[(CH₂)₂NHCH₂(m-C₆H₄)CH₂NH(CH₂)₂]₃N) displays high selectivity and efficiency for the photocatalytic reduction of CO₂ to CO in CH₃CN/H₂O (v/v=4:1) under a 450 nm LED light irradiation, with a light intensity of 100 mW cm⁻². The selectivity reaches as high as 98 %, and the turnover numbers (TON) and turnover frequencies (TOF) reach as high as 16896 and 0.47 s⁻¹, respectively, with the calculated quantum yield of 0.04 %. Such high activity can be attributed to the synergistic catalysis effect between two Co^II ions within 1 , which is strongly supported by the results of control experiments and DFT calculations.     

Elucidating the Mechanism of Simultaneous Activation of CH4 and CO2 Mediated by Single Group 10 Metal Anions in Gas Phase

Quantum chemistry calculations predict that besides the reported single metal anion Pt⁻, Ni⁻ can also mediate the co-conversion of CO₂ and CH₄ to form [CH₃−M(CO₂)−H]^– complex, followed by transformation to C−C coupling product [H₃CCOO−M−H]⁻ ( A ), hydrogenation products [H₃C−M−OCOH]⁻ ( B ) and [H₃C−M−COOH]⁻. For Pd⁻, a fourth product channel leading to PdCO₂⁻…CH₄ becomes more competitive. For Ni⁻, the feed order must be CO₂ first, as the weaker donor-acceptor interaction between Ni⁻ and CH₄ increases the C−H activation barrier, which is reduced by [Ni−CO₂]⁻. For Ni⁻/Pt⁻, the highly exothermic products A and B are similarly stable with submerged barrier that favors B . The smaller barrier difference between A and B for Ni⁻ suggests the C−C coupling product is more competitive in the presence of Ni⁻ than Pt⁻. The charge redistribution from M⁻ is the driving force for product B channel. This study adds our understanding of single atomic anions to activate CH₄ and CO₂ simultaneously.     

Non-Interacting Ni and Fe Dual-Atom Pair Sites in N-Doped Carbon Catalysts for Efficient Concentrating Solar-Driven Photothermal CO2 Reduction

Solar-to-chemical energy conversion under weak solar irradiation is generally difficult to meet the heat demand of CO₂ reduction. Herein, a new concentrated solar-driven photothermal system coupling a dual-metal single-atom catalyst (DSAC) with adjacent Ni−N₄ and Fe−N₄ pair sites is designed for boosting gas-solid CO₂ reduction with H₂O under simulated solar irradiation, even under ambient sunlight. As expected, the (Ni, Fe)−N−C DSAC exhibits a superior photothermal catalytic performance for CO₂ reduction to CO (86.16 μmol g⁻¹ h⁻¹), CH₄ (135.35 μmol g⁻¹ h⁻¹) and CH₃OH (59.81 μmol g⁻¹ h⁻¹), which are equivalent to 1.70-fold, 1.27-fold and 1.23-fold higher than those of the Fe−N−C catalyst, respectively. Based on theoretical simulations, the Fermi level and d-band center of Fe atom is efficiently regulated in non-interacting Ni and Fe dual-atom pair sites with electronic interaction through electron orbital hybridization on (Ni, Fe)−N−C DSAC. Crucially, the distance between adjacent Ni and Fe atoms of the Ni−N−N−Fe configuration means that the additional Ni atom as a new active site contributes to the main *COOH and *HCO₃ dissociation to optimize the corresponding energy barriers in the reaction process, leading to specific dual reaction pathways (COOH and HCO₃ pathways) for solar-driven photothermal CO₂ reduction to initial CO production.     

A Dinuclear Cobalt Cryptate as a Homogeneous Photocatalyst for Highly Selective and Efficient Visible‐Light Driven CO2 Reduction to CO in CH3CN/H2O Solution

A dinuclear cobalt complex [Co₂(OH)L¹](ClO₄)₃ ( 1 , L¹=N[(CH₂)₂NHCH₂(m ‐C₆H₄)CH₂NH(CH₂)₂]₃N) displays high selectivity and efficiency for the photocatalytic reduction of CO₂ to CO in CH₃CN/H₂O (v/v=4:1) under a 450 nm LED light irradiation, with a light intensity of 100 mW cm⁻². The selectivity reaches as high as 98 %, and the turnover numbers (TON) and turnover frequencies (TOF) reach as high as 16896 and 0.47 s⁻¹, respectively, with the calculated quantum yield of 0.04 %. Such high activity can be attributed to the synergistic catalysis effect between two Co^II ions within 1 , which is strongly supported by the results of control experiments and DFT calculations.