Copper-Sulfur-Nitrogen Cluster Providing a Local Proton for Efficient Carbon Dioxide Photoreduction

Atomically precise Cu clusters are highly desirable as catalysts for CO2 reduction reaction (CO2 RR), and they provide an appropriate model platform for elaborating their structure-activity relationship. However, an efficient overall photocatalytic CO2 RR with H2 O using assembled Cu-cluster aggregates as single component photocatalyst has not been reported. Herein, we report a stable crystalline Cu-S-N cluster photocatalyst with local protonated N-H groups (denoted as Cu6 -NH). The catalyst exhibits suitable photocatalytic redox potentials, high structural stability, active catalytic species, and a narrow band gap, which account for its outstanding photocatalytic CO2 RR performance under visible light, with ≈100 % selectivity for CO evolution. Remarkably, systematic isostructural Cu-cluster control experiments, in situ infrared spectroscopy, and density functional theory calculations revealed that the protonated pyrimidine N atoms in the Cu6 -NH cluster act as a proton relay station, providing a local proton during the photocatalytic CO2 RR. This efficiently lowers the energy barrier for the formation of the *COOH intermediate, which is the rate-limiting step, efficiently enhancing the photocatalytic performance. This work lays the foundation for the development of atomically precise metal-cluster-based photocatalysts.

Boosting CO2 Photoreduction via Regulating Charge Transfer Ability in a One-Dimensional Covalent Organic Framework

Two-dimensional (2D) imine-based covalent organic frameworks (COFs) hold potential for photocatalytic CO2 reduction. However, high energy barrier of imine linkage impede the in-plane photoelectron transfer process, resulting in inadequate efficiency of CO2 photoreduction. Herein, we present a dimensionality induced local electronic modulation strategy through the construction of one-dimensional (1D) pyrene-based covalent organic frameworks (PyTTA-COF). The dual-chain-like edge architectures of 1D PyTTA-COF enable the stabilization of aromatic backbones, thus reducing energy loss during exciton dissociation and thermal relaxation, which provides energetic photoelectron to traverse the energy barrier of imine linkages. As a result, the 1D PyTTA-COF exhibits significantly enhanced CO2 photoreduction activity under visible-light irradiation when coordinated with metal cobalt ion, yielding a remarkable CO evolution of 1003 μmol g-1 over an 8-hour period, which surpasses that of the corresponding 2D counterpart by a factor of 59. These findings present a valuable approach to address in-plane charge transfer limitations in imine-based COFs.

Organic Polymer Dots Photocatalyze CO2 Reduction in Aqueous Solution

Developing low-cost and efficient photocatalysts to convert CO2 into valuable fuels is desirable to realize a carbon-neutral society. In this work, we report that polymer dots (Pdots) of poly[(9,9'-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-thiadiazole)] (PFBT), without adding any extra co-catalyst, can photocatalyze reduction of CO2 into CO in aqueous solution, rendering a CO production rate of 57 μmol g-1  h-1 with a detectable selectivity of up to 100 %. After 5 cycles of CO2 re-purging experiments, no distinct decline in CO amount and reaction rate was observed, indicating the promising photocatalytic stability of PFBT Pdots in the photocatalytic CO2 reduction reaction. A mechanistic study reveals that photoexcited PFBT Pdots are reduced by sacrificial donor first, then the reduced PFBT Pdots can bind CO2 and reduce it into CO via their intrinsic active sites. This work highlights the application of organic Pdots for CO2 reduction in aqueous solution, which therefore provides a strategy to develop highly efficient and environmentally friendly nanoparticulate photocatalysts for CO2 reduction.

A General Preparation of Solid Solution-Oxide Heterojunction Photocatalysts through Metal-Organic Framework Transformation Induced Pre-nucleation

Solid solution-oxide heterostructures combine the advantages of solid solution and heterojunction materials to improve electronic structure and optical properties by metal doping, and enhance charge separation and transfer in semiconductor photocatalysts by creating a built-in electric field. Nevertheless, the effective design and synthesis of these materials remains a significant challenge. Here, we develop a generally applicable strategy that leverages the transformable properties of metal-organic frameworks (MOFs) to prepare solid solution-oxide heterojunctions with controllable structural and chemical compositions. The process consists of three main steps. First, MOFs with different topological structures and metal centers are transformed, accompanied by pre-nucleation of a metal oxide. Second, solid solution is prepared through calcination of the transformed MOFs. Finally, a heterojunction is formed by combining solid solution with another metal oxide group through endogenous overflow. DFT calculations and study on carrier dynamics show that the structure of the material effectively prevents electrons from returning to the bulk phase, exhibiting superior photocatalytic reduction performance of CO₂ . This study is expected to promote the controllable synthesis and research of MOF-derived heterojunctions.

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.

Co-Dissolved Isostructural Polyoxovanadates to Construct Single-Atom-Site Catalysts for Efficient CO2 Photoreduction

We explored a co-dissolved strategy to embed mono-dispersed Pt center into V₂ O₅ support via dissolving [PtV₉ O₂₈ ]^7- into [V₁₀ O₂₈ ]^6- aqueous solution. The uniform dispersion of [PtV₉ O₂₈ ]^7- in [V₁₀ O₂₈ ]^6- solution allows [PtV₉ O₂₈ ]^7- to be surrounded by [V₁₀ O₂₈ ]^6- clusters via a freeze-drying process. The V centers in both [PtV₉ O₂₈ ]^7- and [V₁₀ O₂₈ ]^6- were converted into V₂ O₅ via a calcination process to stabilize Pt center. These double separations can effectively prevent the Pt center agglomeration during the high-temperature conversion process, and achieve 100 % utilization of Pt in [PtV₉ O₂₈ ]^7- . The resulting Pt-V₂ O₅ single-atom-site catalysts exhibit a CH₄ yield of 247.6 μmol g^-1  h^-1 , 25 times higher than that of Pt nanoparticle on the V₂ O₅ support, which was accompanied by the lactic acid photooxidation to form pyruvic acid. Systematical investigations on this unambiguous structure demonstrate an important role of Pt-O atomic pair synergy for highly efficient CO₂ photoreduction.

Phosphorus Tailors the d-Band Center of Copper Atomic Sites for Efficient CO2 Photoreduction under Visible-Light Irradiation

Photoreduction of CO₂ into solar fuels has received great interest, but suffers from low catalytic efficiency and poor selectivity. Herein, two single-Cu-atom catalysts with unique Cu configurations in phosphorus-doped carbon nitride (PCN), namely, Cu₁ N₃ @PCN and Cu₁ P₃ @PCN were fabricated via selective phosphidation, and tested in visible light-driven CO₂ reduction by H₂ O without sacrificial agents. Cu₁ N₃ @PCN was exclusively active for CO production with a rate of 49.8 μmol_CO  g_cat ^-1  h^-1 , outperforming most polymeric carbon nitride (C₃ N₄ ) based catalysts, while Cu₁ P₃ @PCN preferably yielded H₂ . Experimental and theoretical analysis suggested that doping P in C₃ N₄ by replacing a corner C atom upshifted the d-band center of Cu in Cu₁ N₃ @PCN close to the Fermi level, which boosted the adsorption and activation of CO₂ on Cu₁ N₃ , making Cu₁ N₃ @PCN efficiently convert CO₂ to CO. In contrast, Cu₁ P₃ @PCN with a much lower Cu 3d electron energy exhibited negligible CO₂ adsorption, thereby preferring H₂ formation via photocatalytic H₂ O splitting.