Carbon Dioxide Dimer Radical Anion as Surface Intermediate of Photoinduced CO2 Reduction at Aqueous Cu and CdSe Nanoparticle Catalysts by Rapid-Scan FT-IR Spectroscopy

Activation of Bi2MoO6/Zn0.5Cd0.5S charge transfer through interface chemical bonds and surface defects for photothermal catalytic CO2 reduction

The photocatalytic reduction of CO2 to high-value fuels has been proposed as a solution to the energy crisis caused by the depletion of energy resources. Despite significant advancements in photocatalytic CO2 reduction catalyst development, there are still limitations such as poor CO2 adsorption/activation and low charge transfer efficiency. In this study, we employed a defect-induced heterojunction strategy to construct atomic-level interface Cd-O bonds and form Bi2MoO6/Zn0.5Cd0.5S heterojunctions. The sulfur vacancies (VS) formed in Bi2MoO6/Zn0.5Cd0.5S acted as activation sites for CO2 adsorption. While the interfacial stability provided by the Cd-O bonds served as an electron transfer channel that facilitated the movement of electrons from the interface to the catalytic site. The VS and Cd-O bonds simultaneously influence the distribution of charge, inducing the creation of an interface electric field that facilitates the upward displacement of the center of the d-band. This enhances the adsorption of reaction intermediates. The optimized Bi2MoO6/Zn0.5Cd0.5S heterostructure exhibited high selectivity and stability of photoelectrochemical properties for CO, generating 42.97 μmol⋅g-1⋅h-1 of CO, which was 16.65-fold higher than Zn0.5Cd0.5S under visible light drive. This research provides valuable insights for designing photocatalyst interfaces with improved CO2 adsorption conversion efficiency.

Regulating Spin Density using TEMPOL Molecules for Enhanced CO2-to-Ethylene Conversion by HKUST-1 Framework Derived Electrocatalysts

The selectivity of multicarbon products in the CO2 reduction reaction (CO2RR) depends on the spin alignment of neighboring active sites, which requires a spin catalyst that facilitates electron transfer with antiparallel spins for enhanced C-C coupling. Here, we design a radical-contained spin catalyst (TEMPOL@HKUST-1) to enhance CO2-to-ethylene conversion, in which spin-disordered (SDO) and spin-ordered (SO) phases co-exist to construct an asymmetric spin configuration of neighboring active sites. The replacement of axially coordinated H2O molecules with TEMPOL radicals introduces spin-spin interactions among the Cu(II) centers to form localized SO phases within the original H2O-mediated SDO phases. Therefore, TEMPOL@HKUST-1 derived catalyst exhibited an approximately two-fold enhancement in ethylene selectivity during the CO2RR at -1.8 V versus Ag/AgCl compared to pristine HKUST-1. In situ ATR-SEIRAS spectra indicate that the spin configuration at asymmetric SO/SDO sites significantly reduces the kinetic barrier for *CO intermediate dimerization toward the ethylene product. The performance of the spin catalyst is further improved by spin alignment under a magnetic field, resulting in a maximum ethylene selectivity of more than 50 %. The exploration of the spin-polarized kinetics of the CO2RR provides a promising path for the development of novel spin electrocatalysts with superior performance.

Accelerating the Reaction Kinetics of CO2 Reduction to Multi-Carbon Products by Synergistic Effect between Cation and Aprotic Solvent on Copper Electrodes

Improving the selectivity of electrochemical CO2 reduction to multi-carbon products (C2+ ) is an important and highly challenging topic. In this work, we propose and validate an effective strategy to improve C2+ selectivity on Cu electrodes, by introducing a synergistic effect between cation (Na+ ) and aprotic solvent (DMSO) to the electrolyte. Based on constant potential ab initio molecular dynamics simulations, we first revealed that Na+ facilitates C-C coupling while inhibits CH3 OH/CH4 products via reducing the water network connectivity near the electrode. Furthermore, the water network connectivity was further decreased by introducing an aprotic solvent DMSO, leading to suppression of both C1 production and hydrogen evolution reaction with minimal effect on *OCCO* hydrogenation. The synergistic effect enhancing C2 selectivity was also experimentally verified through electrochemical measurements. The results showed that the Faradaic efficiency of C2 increases from 9.3 % to 57 % at 50 mA/cm2 under a mixed electrolyte of NaHCO3 and DMSO compared to a pure NaHCO3 , which can significantly enhance the selectivity of the C2 product. Therefore, our discovery provides an effective electrolyte-based strategy for tuning CO2 RR selectivity through modulating the microenvironment at the electrode-electrolyte interface.

Nanostructured Black Silicon as a Stable and Surface-Sensitive Platform for Time-Resolved In Situ Electrochemical Infrared Absorption Spectroscopy

Attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is a powerful method for probing interfacial chemical processes. However, SEIRAS-active nanostructured metallic thin films for the in situ analysis of electrochemical phenomena are often unstable under biased aqueous conditions. In this work, we present a surface-enhancing structure based on etched black Si internal reflection elements with Au-coatings for in situ electrochemical ATR-SEIRAS. Using electrochemical potential-dependent adsorption and desorption of 4-methoxypyridine on Au, we demonstrate that black Si-based substrates offer advantages over commonly used structures, such as electroless-deposited Au on Si and electrodeposited Au on ITO-coated Si, due to the combination of high stability, sensitivity, and conductivity. These characteristics are especially valuable for time-resolved measurements where stable substrates are required over extended times. Furthermore, the low sheet resistance of Au layers on black Si reduces the RC time constant of the electrochemical cell, enabling a significantly higher time resolution compared to that of traditional substrates. Thus, we employ black Si-based substrates in conjunction with rapid- and step-scan Fourier transform infrared (FTIR) spectroscopy to investigate the adsorption and desorption kinetics of 4-methoxypyridine during in situ electrochemical potential steps. Adsorption is shown to be diffusion-limited, which allows for the determination of the mean molecular area in a fully established monolayer. Moreover, no significant changes in the peak ratios of vibrational modes with different orientations relative to the molecular axis are observed, suggesting a single adsorption mode and no alteration of the average molecular orientation during the adsorption process. Overall, this study highlights the enhanced performance of black Si-based substrates for both steady-state and time-resolved in situ electrochemical ATR-SEIRAS, providing a powerful platform for kinetic and mechanistic investigations of electrochemical interfaces.

Direct time-resolved observation of surface-bound carbon dioxide radical anions on metallic nanocatalysts

Time-resolved identification of surface-bound intermediates on metallic nanocatalysts is imperative to develop an accurate understanding of the elementary steps of CO2 reduction. Direct observation on initial electron transfer to CO2 to form surface-bound CO2•- radicals is lacking due to the technical challenges. Here, we use picosecond pulse radiolysis to generate CO2•- via aqueous electron attachment and observe the stabilization processes toward well-defined nanoscale metallic sites. The time-resolved method combined with molecular simulations identifies surface-bound intermediates with characteristic transient absorption bands and distinct kinetics from nanosecond to the second timescale for three typical metallic nanocatalysts: Cu, Au, and Ni. The interfacial interactions are further investigated by varying the important factors, such as catalyst size and the presence of cation in the electrolyte. This work highlights fundamental ultrafast spectroscopy to clarify the critical initial step in the CO2 catalytic reduction mechanism.

Less-Coordinated Atomic Copper-Dimer Boosted Carbon-Carbon Coupling During Electrochemical CO2 Reduction

This work reports a metal-organic framework (MOF) with less-coordinated copper dimers, which displays excellent electrochemical CO2 reduction (eCO2 RR) performance with an advantageous current density of 0.9 A cm-2 and a high Faradaic efficiency of 71% to C2 products. In comparison with MOF with Cu monomers that are present as Cu1 O4 with a coordination number of 3.8 ± 0.2, Cu dimers exist as O3 Cu1 ···Cu2 O2 with a coordination number of 2.8 ± 0.1. In situ characterizations together with theoretical calculations reveal that two *CO intermediates are stably adsorbed on each site of less-coordinated Cu dimers, which favors later dimerization via a key intermediate of *CH2 CHO. The highly unsaturated dual-atomic Cu provides large-quantity and high-quality actives sites for carbon-carbon coupling, achieving the optimal trade-off between activity and selectivity of eCO2 RR to C2 products.

Construction adsorption and photocatalytic interfaces between C, O co-doped BN and Pd-Cu alloy nanocrystals for effective conversion of CO2 to CO

Photocatalytic reduction of carbon dioxide (CO₂) into fuels is an auspicious route to alleviate the energy and environmental crisis brought by the continuous depletion of fossil fuels. The CO₂ adsorption state on the surface of photocatalytic materials plays a significant role in its efficient conversion. The limited CO₂ adsorption capacity of conventional semiconductor materials inhibit their photocatalytic performances. In this work, a bifunctional material for CO₂ capture and photocatalytic reduction was fabricated by introducing palladium (Pd)-copper (Cu) alloy nanocrystals onto the surface of carbon, oxygen co-doped boron nitride (BN). The elemental doped BN with abundant ultra-micropores had high CO₂ capture ability, and CO₂ was adsorbed in the form of bicarbonate on its surface with the presence of water vapor. The Pd/Cu molar ratio had great impact on the grain size of Pd-Cu alloy and their distribution on BN. The CO₂ molecules tended to be converted to carbon monoxide (CO) at interfaces of BN and Pd-Cu alloys due to their bidirectional interactions to the adsorbed intermediate species while methane (CH₄) evolution might occur on the surface of Pd-Cu alloys. Owing to the uniform distribution of smaller Pd-Cu nanocrystals on BN, more effective interfaces were created in the Pd₅Cu₁/BN sample and it gave a CO production rate of 7.74 μmolg^-1h^-1 under simulated solar light irradiation, higher than the other PdCu/BN composites. This work can pave a new way for constructing effective bifunctional photo-catalysts with high selectivity to convert CO₂ to CO.

Efficient, Selective CO2 Photoreduction Enabled by Facet-Resolved Redox-Active Sites on Colloidal CdS Nanosheets

Advances in nanotechnology have enabled precise design of catalytic sites for CO₂ photoreduction, pushing product selectivity to near unity. However, activity of most nanostructured photocatalysts remains underwhelming due to fast recombination of photogenerated electron-hole pairs and sluggish hole transfer. To address these issues, we construct colloidal CdS nanosheets (NSs) with the large basal planes terminated by S^2- atomic layers as intrinsic photocatalysts (CdS-S^2- NSs). Experimental investigation reveals that the S^2- termination endows ultrathin CdS-S^2- NSs with facet-resolved redox-catalytic sites: oxidation occurs on S^2--terminated large basal facets and reduction happens on side facets. Such an allocation of redox sites not only promotes spatial separation of photoinduced electrons and holes but also facilitates balanced extraction of holes and electrons by shortening the hole diffusion distance along the (001) direction of the ultrathin NSs. Consequently, the CdS-S^2- NSs exhibit superb performance for photocatalytic CO₂-to-CO conversion, which was verified by the isotope-labeled experiments to be a record-breaking performance: a CO selectivity of 99%, a CO formation rate of 2.13 mol g^-1 h^-1, and an effective apparent quantum efficiency of 42.1% under the irradiation (340 to 450 nm) of a solar simulator (AM 1.5G). The breakthrough performance achieved in this work provides novel insights into the precise design of nanostructures for selective and efficient CO₂ photoreduction.

In situ and Operando Spectroscopies in Photocatalysis: Powerful Techniques for a Better Understanding of the Performance and the Reaction Mechanism

In photocatalysis, a set of elemental steps are involved together at different timescales to govern the overall efficiency of the process. These steps are divided as follow: (1) photon absorption and excitation (in femtoseconds), (2) charge separation (femto- to picoseconds), (3) charge carrier diffusion/transport (nano- to microseconds), and (4 and 5) reactant activation/conversion and mass transfer (micro- to milliseconds). The identification and quantification of these steps, using the appropriate tool/technique, can provide the guidelines to emphasize the most influential key parameter that improve the overall efficiency and to develop the "photocatalyst by design" concept. In this review, the identification/quantification of reactant activation/conversion and mass transfer (steps 4 and 5) is discussed in details using the in situ/operando techniques, especially the infrared (IR), Raman, and X-ray absorption spectroscopy (XAS). The use of these techniques in photocatalysis was highlighted by the most recent and conclusive case studies which allow a better characterization of the active site and reveal the reaction pathways in order to establish a structure-performance relationship. In each case study, the reaction conditions and the reactor design for photocatalysis (pressure, temperature, concentration, etc.) were thoroughly discussed. In the last part, some examples in the use of time-resolved techniques (time-resolved FTIR, photoluminescence, and transient absorption) are also presented as an author's guideline to study the elemental steps in photocatalysis at shorter timescale (ps, ns, and µs).

Bicarbonate Rebalances the *COOH/*OCO- Dual Pathways in CO2 Electrocatalytic Reduction: In Situ Surface-Enhanced Raman Spectroscopic Evidence

Understanding the reactive site/CO₂/electrolyte interfacial behaviors is very crucial for the design of an advantageous CO₂ electrocatalytic reduction (CO₂ER) system. One important but unrevealed question is how the CO₂ER process is influenced by the high concentration of HCO₃^-, which is deliberately added as electrolyte or from the inevitable reaction between dissolved CO₂ and OH^-. Here, we provide unambiguous in situ spectroscopic evidence that on Ag-based catalysts, HCO₃^- is apt to facilitate *OCO^- generation and therefore rebalances CO₂ER pathways. By employing an alternative acid electrolyte to restrict the exchange between CO₂ and HCO₃^- and eliminating the effect of solution pH, we reveal that HCO₃^- can decrease the onset potential of *OCO^- and promote further formate production. Theoretical calculations indicate HCO₃^- can stabilize the adsorption of *OCO^- instead of *COOH. The renewed understanding of the role of HCO₃^- could facilitate the judicious selection of electrolytes to regulate the CO₂ER pathway and product distribution.

Electrocatalytic CO2-to-C2+ with Ampere-Level Current on Heteroatom-Engineered Copper via Tuning *CO Intermediate Coverage

An ampere-level current density of CO₂ electrolysis is critical to realize the industrial production of multicarbon (C₂₊) fuels. However, under such a large current density, the poor CO intermediate (*CO) coverage on the catalyst surface induces the competitive hydrogen evolution reaction, which hinders CO₂ reduction reaction (CO₂RR). Herein, we report reliable ampere-level CO₂-to-C₂₊ electrolysis by heteroatom engineering on Cu catalysts. The Cu-based compounds with heteroatom (N, P, S, O) are electrochemically reduced to heteroatom-derived Cu with significant structural reconstruction under CO₂RR conditions. It is found that N-engineered Cu (N-Cu) catalyst exhibits the best CO₂-to-C₂₊ productivity with a remarkable Faradaic efficiency of 73.7% under -1100 mA cm^-2 and an energy efficiency of 37.2% under -900 mA cm^-2. Particularly, it achieves a C₂₊ partial current density of -909 mA cm^-2 at -1.15 V versus reversible hydrogen electrode, which outperforms most reported Cu-based catalysts. In situ spectroscopy indicates that heteroatom engineering adjusts *CO adsorption on Cu surface and alters the local H proton consumption in solution. Density functional theory studies confirm that the high adsorption strength of *CO on N-Cu results from the depressed HER and promoted *CO adsorption on both bridge and atop sites of Cu, which greatly reduces the energy barrier for C-C coupling.

Reductive Carbon-Carbon Coupling on Metal Sites Regulates Photocatalytic CO2 Reduction in Water Using ZnSe Quantum Dots

Colloidal quantum dots (QDs) consisting of precious-metal-free elements show attractive potentials towards solar-driven CO₂ reduction. However, the inhibition of hydrogen (H₂ ) production in aqueous solution remains a challenge. Here, we describe the first example of a carbon-carbon (C-C) coupling reaction to block the competing H₂ evolution in photocatalytic CO₂ reduction in water. In a specific system taking ZnSe QDs as photocatalysts, the introduction of furfural can significantly suppress H₂ evolution leading to CO evolution with a rate of ≈5.3 mmol g^-1  h^-1 and a turnover number (TON) of >7500 under 24 h visible light. Meanwhile, furfural is upgraded to the self-coupling product with a yield of 99.8 % based on the consumption of furfural. Mechanistic insights show that the reductive furfural coupling reaction occurs on surface Zn-sites to consume electrons and protons originally used for H₂ production, while the CO formation pathway at surface anion vacancies from CO₂ remains.

Assembling CdSe Quantum Dots into Polymeric Micelles Formed by a Polyethylenimine-Based Amphiphilic Polymer to Enhance Efficiency and Selectivity of CO2-to-CO Photoreduction in Water

Colloidal quantum dots (QDs) as photocatalysts enable catalysis of CO₂-to-CO conversion in the presence of electron donors. The surface and/or interfacial chemical environment of the QDs is essential for the activity and selectivity of the CO₂ photoreduction. Various strategies, including exposing active metal sites or anchoring functional organic ligands, have been applied to tune the QDs' surface chemical environment and thus to improve both activity and selectivity of CO₂ photoreduction, which occurs at surface of the QDs. However, the efficient and selective photocatalytic CO₂ reduction with QD photocatalysts in water is still a challenging task due to low CO₂ solubility and robust competing reaction of proton reduction in water. Different from state-of-the-art QDs' surface manipulation, we proposed to ameliorate the interfacial chemical environment of CdSe QDs via assembling the QDs into functional polymeric micelles in water. Herein, CdSe@PEI-LA assemblies were constructed by loading CdSe QDs into polymeric micelles formed by PEI-LA, a polyethylenimine (PEI)-based functional amphiphilic polymer. Due to self-assembly and high CO₂ adsorption capacity of PEI-LA in water, the photocatalytic CO₂-to-CO conversion efficiency and selectivity of the CdSe@PEI-LA assemblies in water were dramatically improved to 28.0 mmol g^-1 and 87.5%, respectively. These two values increased 57 times and 1.5 times, respectively, compared with those of the pristine CdSe QDs. Mechanism studies revealed that CdSe QDs locate in polymeric micelles of high CO₂ local concentration and the photoinduced electron transfer from the conduction band of CdSe QDs to Cd-CO₂* species is thermodynamically and kinetically improved in the presence of PEI-LA. The CdSe@PEI-LA system represents a successful example of using a functionalized amphiphilic polymer to ameliorate interfacial microenvironments of nanocrystal photocatalysts and realizing efficient and selective CO₂ photoreduction in water.

Copper-mediated pentafluoroethylation of organoboronates and terminal alkynes with TMSCF3

The TMSCF₃-derived CuCF₂CF₃ species has been successfully applied in pentafluoroethylation of organoboronates and terminal alkynes. By using 1,10-phenanthroline as a ligand, a broad range of (hetero)arylboronates and alkenylboronates were smoothly pentafluoroethylated under aerobic conditions. Furthermore, terminal alkynes can undergo aerobic cross-coupling with the TMSCF₃-derived CuCF₂CF₃ species in the absence of additional ligands.

Slow Auger Recombination of Trapped Excitons Enables Efficient Multiple Electron Transfer in CdS-Pt Nanorod Heterostructures

Solar-to-fuel conversion reaction often requires multiple proton-coupled electron transfer (PCET) processes powered by the energetic electrons and/or holes generated by the absorption of multiple photons. The effective coupling of multiple electron transfer from the light absorber with the multiple PCET reactions at the catalytic center is one of the key challenges in efficient and selective conversion of solar energy to chemical fuels. In this paper, we examine the dynamics of multiple electron transfer in quantum confined CdS nanorods with a Pt tip, in which the CdS rod functions as the light absorber and the Pt tip the catalytic center. By excitation-fluence-dependent transient absorption spectroscopic measurements, we show that the multiexciton Auger recombination rate in CdS rods follows a carrier-collision model, k_n^A = n²(n - 1)/4k₂^A, with a biexciton lifetime (1/k₂^A) of 2.0 ± 0.2 ns. In CdS-Pt nanorods, electron transfer kinetics from the CdS conduction band edge to the Pt show negligible dependence on the excitation fluence, occurring with a half-life time of 5.6 ± 0.6 ps. The efficiency of multiple exciton dissociation by multiple electron transfer to Pt decreases from 100% in biexciton states to ∼41% at 22 exciton state due to the competition with Auger recombination. The half-lifetime of the n-charge separated state recombination (with n electrons in the Pt and n holes in the CdS) decreases from 10 μs in the single charge separated state to 42 ns in nine charge separated states. Our findings suggest the possibility of driving multielectron photocatalytic reactions under intense illumination and controlling product selectivity through multielectron transfer.

Resonance Raman Vibrational Mode Enhancement of Adsorbed Benzenethiols on CdSe Is Predominantly Franck-Condon in Nature and Governed by Symmetry

Here, we report mode-specific resonance Raman enhancements of ligands covalently bound to the surface of colloidal CdSe nanocrystals (NCs). By the systematic comparison of a set of structural derivatives, the extent of resonance Raman enhancement is shown to be directly related to the molecular symmetry of the bound ligands. The enhancement dependence on molecular symmetry is further discussed in terms of Franck-Condon and Herzberg-Teller contributions and their associated selection rules. We further show that resonance Raman may be used to distinguish between possible surface binding motifs of bidentate ligands under continuous wave excitation. More generally, this work demonstrates the usefulness of resonance Raman as a characterization tool when characterizing adsorbed molecular species on semiconductor NC surfaces.

Radiolytic Approach for Efficient, Selective and Catalyst-free CO2 Conversion at Room Temperature

The present study proposes a new approach for direct CO₂ conversion using primary radicals from water irradiation. In order to ensure reduction of CO₂ into CO₂ ^-. by all the primary radiation-induced water radicals, we use formate ions to scavenge simultaneously the parent oxidizing radicals H^. and OH^. producing the same transient CO₂ ^-. radicals. Conditions are optimized to obtain the highest conversion yield of CO₂ . The goal is achieved under mild conditions of room temperature, neutral pH and 1 atm of CO₂ pressure. All the available radicals are exploited for selectively converting CO₂ into oxalate that is accompanied by H₂ evolution. The mechanism presented accounts for the results and also sheds light on the data in the literature. The radiolytic approach is a mild and scalable route of direct CO₂ capture at the source in industry and the products, oxalate salt and H₂ , can be easily separated.

Sub-Second Time-Resolved Surface-Enhanced Raman Spectroscopy Reveals Dynamic CO Intermediates during Electrochemical CO2 Reduction on Copper

The electrocatalytic carbon dioxide (CO₂ ) reduction reaction (CO₂ RR) into hydrocarbons is a promising approach for greenhouse gas mitigation, but many details of this dynamic reaction remain elusive. Here, time-resolved surface-enhanced Raman spectroscopy (TR-SERS) is employed to successfully monitor the dynamics of CO₂ RR intermediates and Cu surfaces with sub-second time resolution. Anodic treatment at 1.55 V vs. RHE and subsequent surface oxide reduction (below -0.4 V vs. RHE) induced roughening of the Cu electrode surface, which resulted in hotspots for TR-SERS, enhanced time resolution (down to ≈0.7 s) and fourfold improved CO₂ RR efficiency toward ethylene. With TR-SERS, the initial restructuring of the Cu surface was followed (<7 s), after which a stable surface surrounded by increased local alkalinity was formed. Our measurements revealed that a highly dynamic CO intermediate, with a characteristic vibration below 2060 cm^-1 , is related to C-C coupling and ethylene production (-0.9 V vs. RHE), whereas lower cathodic bias (-0.7 V vs. RHE) resulted in gaseous CO production from isolated and static CO surface species with a distinct vibration at 2092 cm^-1 .

Modulating electron density of vacancy site by single Au atom for effective CO2 photoreduction

The surface electron density significantly affects the photocatalytic efficiency, especially the photocatalytic CO₂ reduction reaction, which involves multi-electron participation in the conversion process. Herein, we propose a conceptually different mechanism for surface electron density modulation based on the model of Au anchored CdS. We firstly manipulate the direction of electron transfer by regulating the vacancy types of CdS. When electrons accumulate on vacancies instead of single Au atoms, the adsorption types of CO₂ change from physical adsorption to chemical adsorption. More importantly, the surface electron density is manipulated by controlling the size of Au nanostructures. When Au nanoclusters downsize to single Au atoms, the strong hybridization of Au 5d and S 2p orbits accelerates the photo-electrons transfer onto the surface, resulting in more electrons available for CO₂ reduction. As a result, the product generation rate of Au_SA/Cd_1−xS manifests a remarkable at least 113-fold enhancement compared with pristine Cd_1−xS.

The electron density of reactive sites significantly affects catalytic performances. Here, authors demonstrate the electron density of different reactive sites can be modulated by regulating the type of vacancy and the size of Au, leading to effective CO₂ photoreduction.

Photocatalytic C-C Coupling from Carbon Dioxide Reduction on Copper Oxide with Mixed-Valence Copper(I)/Copper(II)

To realize the evolution of C₂₊ hydrocarbons like C₂H₄ from CO₂ reduction in photocatalytic systems remains a great challenge, owing to the gap between the relatively lower efficiency of multielectron transfer in photocatalysis and the sluggish kinetics of C-C coupling. Herein, with Cu-doped zeolitic imidazolate framework-8 (ZIF-8) as a precursor, a hybrid photocatalyst (CuO_X@p-ZnO) with CuO_X uniformly dispersed among polycrystalline ZnO was synthesized. Upon illumination, the catalyst exhibited the ability to reduce CO₂ to C₂H₄ with a 32.9% selectivity, and the evolution rate was 2.7 μmol·g^-1·h^-1 with water as a hole scavenger and as high as 22.3 μmol·g^-1·h^-1 in the presence of triethylamine as a sacrificial agent, all of which have rarely been achieved in photocatalytic systems. The X-ray absorption fine structure spectra coupled with in situ FT-IR studies reveal that, in the original catalyst, Cu mainly existed in the form of CuO, while a unique Cu⁺ surface layer upon the CuO matrix was formed during the photocatalytic reaction, and this surface Cu⁺ site is the active site to anchor the in situ generated CO and further perform C-C coupling to form C₂H₄. The C-C coupling intermediate *OC-COH was experimentally identified by in situ FT-IR studies for the first time during photocatalytic CO₂ reduction. Moreover, theoretical calculations further showed the critical role of such Cu⁺ sites in strengthening the binding of *CO and stabilizing the C-C coupling intermediate. This work uncovers a new paradigm to achieve the reduction of CO₂ to C₂₊ hydrocarbons in a photocatalytic system.

Ultrafast Dynamics of Electronic Resonances in Molecules Adsorbed on Metal Surfaces: A Wave Packet Propagation Approach

We present a wave packet propagation-based method to study the electron dynamics in molecular species in the gas phase and adsorbed on metal surfaces. It is a very general method that can be employed to any system where the electron dynamics is dominated by an active electron and the coupling between the discrete and continuum electronic states is of importance. As an example, one can consider resonant molecule-surface electron transfer or molecular photoionization. Our approach is based on a computational strategy allowing incorporating ab initio inputs from quantum chemistry methods, such as density functional theory, Hartree-Fock, and coupled cluster. Thus, the electronic structure of the molecule is fully taken into account. The electron wave function is represented on a three-dimensional grid in spatial coordinates, and its temporal evolution is obtained from the solution of the time-dependent Schrödinger equation. We illustrate our method with an example of the electron dynamics of anionic states localized on organic molecules adsorbed on metal surfaces. In particular, we study resonant charge transfer from the π* orbitals of three vinyl derivatives (acrylamide, acrylonitrile, and acrolein) adsorbed on a Cu(100) surface. Electron transfer between these lowest unoccupied molecular orbitals and the metal surface is extremely fast, leading to a decay of the population of the molecular anion on the femtosecond timescale. We detail how to analyze the time-dependent electronic wave function in order to obtain the relevant information on the system: the energies and lifetimes of the molecule-localized quasistationary states, their resonant wavefunctions, and the population decay channels. In particular, we demonstrate the effect of the electronic structure of the substrate on the energy and momentum distribution of the hot electrons injected into the metal by the decaying molecular resonance.

Visible-Light Photocatalysts and Their Perspectives for Building Photocatalytic Membrane Reactors for Various Liquid Phase Chemical Conversions

Photocatalytic organic synthesis/conversions and water treatment under visible light are a challenging task to use renewable energy in chemical transformations. In this review a brief overview on the mainly employed visible light photocatalysts and a discussion on the problems and advantages of Vis-light versus UV-light irradiation is reported. Visible light photocatalysts in the photocatalytic conversion of CO2, conversion of acetophenone to phenylethanol, hydrogenation of nitro compounds, oxidation of cyclohexane, synthesis of vanillin and phenol, as well as hydrogen production and water treatment are discussed. Some applications of these photocatalysts in photocatalytic membrane reactors (PMRs) for carrying out organic synthesis, conversion and/or degradation of organic pollutants are reported. The described cases show that PMRs represent a promising green technology that could shift on applications of industrial interest using visible light (from Sun) active photocatalysts.

Biochar as composite of phosphate fertilizer: Characterization and agronomic effectiveness

Organomineral phosphate fertilizers (OMP) may reduce phosphate release rate and its direct contact to the soil solid phase, increasing the effectiveness of phosphorus (P) fertilization. This study aimed to evaluate the effect of granulating biochar (BC) with triple superphosphate (TSP) in two forms (blend or coated) and three proportions (5, 15 and 25%, w/w) on the P release kinetics and plant growth. A successive plant trial using two soils of contrasting P buffering capacities and five P doses (0, 20, 40, 80 and 120 mg kg^-1) was set to investigate the agronomic effectiveness of OMP that presented the slowest P release kinetic. The kinetic test showed that within the first 1.5 h, TSP, OMP blend and OMP coated fertilizers released 92, 82 and 36% of total P, respectively. Thereby, BC addition to TSP reduced the P release rate, mainly due to coating. The fertilizers coated with 15% and 25% BC (C15 and C25, respectively) presented the slowest P release rate. For the plant trial, C15 was chosen because it requires less BC when compared with C25 fertilizer. In the first crop, C15 provided more P to plants, especially in the soil with high P buffering capacity, which increased by 10% and 20% the P uptake and the P recovered by the plant when compared with TSP, respectively. In the sandy soil, fertilizers C15 and TSP showed the same performances regarding yield, P uptake and P recovery rate. At consecutive cultivation, regardless of the soil type, P sources (C15 and TSP) did not differ in yield, P uptake and P recovery. Therefore, biochar-based organomineral phosphate fertilizer can enhance P use efficiency in high P-fixing tropical soils, increasing P recovery and uptake when compared with TSP.

Direct and indirect Z-scheme heterostructure-coupled photosystem enabling cooperation of CO2 reduction and H2O oxidation

The stoichiometric photocatalytic reaction of CO2 with H2O is one of the great challenges in photocatalysis. Here, we construct a Cu2O-Pt/SiC/IrOx composite by a controlled photodeposition and then an artificial photosynthetic system with Nafion membrane as diaphragm separating reduction and oxidation half-reactions. The artificial system exhibits excellent photocatalytic performance for CO2 reduction to HCOOH and H2O oxidation to O2 under visible light irradiation. The yields of HCOOH and O2 meet almost stoichiometric ratio and are as high as 896.7 and 440.7 μmol g-1 h-1, respectively. The high efficiencies of CO2 reduction and H2O oxidation in the artificial system are attributed to both the direct Z-scheme electronic structure of Cu2O-Pt/SiC/IrOx and the indirect Z-scheme spatially separated reduction and oxidation units, which greatly prolong lifetime of photogenerated electrons and holes and prevent the backward reaction of products. This work provides an effective and feasible strategy to increase the efficiency of artificial photosynthesis.

B-O Bonds in Ultrathin Boron Nitride Nanosheets to Promote Photocatalytic Carbon Dioxide Conversion

Limited by the chemical inertness of CO₂ and the high dissociation energy of the C═O bond, photocatalytic CO₂ conversion is highly challenging. Herein, we prepare ultrathin oxygen-modified h-BN (O/BN) nanosheets containing B-O bonds. On the O/BN surface, CO₂ can be chemically captured and is bonded with the B-O bond, leading to the formation of an O-B-O bond. This new chemical bond acting as an electron-delivery channel strengthens the interaction between CO₂ and the surface. Thus, the reactants can continuously obtain electrons from the surface through this channel. Therefore, the majority of gaseous CO₂ directly converts into carbon active species that are detected by in situ DRIFTS over O/BN. Moreover, the activated energies of CO₂ conversion are significantly reduced with the introduction of the B-O bond evidenced by DFT calculations. As a result, O/BN nanosheets present an enhanced photocatalytic CO₂ conversion performance with the H₂ and CO generation rates of 3.3 and 12.5 μmol g^-1 h^-1, respectively. This work could help in realizing the effects of nonmetal chemical bonds in the CO₂ photoreduction reaction for designing efficient photocatalysts.

Highly Efficient Photocatalytic Conversion of CO2 to CO Catalyzed by Surface-Ligand-Removed and Cd-Rich CdSe Quantum Dots

Surface ligand-removed and Cd-rich CdSe quantum dots (QDs) exhibited exceptional activity as photocatalyst for the conversion of CO₂ to CO. A CO production rate up to 789 mmol g^-1  h^-1 was achieved in a triethylamine/dimethylformamide mixture under visible-light irradiation. Mechanistic studies revealed that improving the Cd/Se stoichiometric ratio and exposing more active surface Cd atoms significantly enhanced the activity of CdSe QDs for CO₂ photoreduction.

Semiconductor Quantum Dots: An Emerging Candidate for CO2 Photoreduction

As one of the most critical approaches to resolve the energy crisis and environmental concerns, carbon dioxide (CO₂ ) photoreduction into value-added chemicals and solar fuels (for example, CO, HCOOH, CH₃ OH, CH₄ ) has attracted more and more attention. In nature, photosynthetic organisms effectively convert CO₂ and H₂ O to carbohydrates and oxygen (O₂ ) using sunlight, which has inspired the development of low-cost, stable, and effective artificial photocatalysts for CO₂ photoreduction. Due to their low cost, facile synthesis, excellent light harvesting, multiple exciton generation, feasible charge-carrier regulation, and abundant surface sites, semiconductor quantum dots (QDs) have recently been identified as one of the most promising materials for establishing highly efficient artificial photosystems. Recent advances in CO₂ photoreduction using semiconductor QDs are highlighted. First, the unique photophysical and structural properties of semiconductor QDs, which enable their versatile applications in solar energy conversion, are analyzed. Recent applications of QDs in photocatalytic CO₂ reduction are then introduced in three categories: binary II-VI semiconductor QDs (e.g., CdSe, CdS, and ZnSe), ternary I-III-VI semiconductor QDs (e.g., CuInS₂ and CuAlS₂ ), and perovskite-type QDs (e.g., CsPbBr₃ , CH₃ NH₃ PbBr₃ , and Cs₂ AgBiBr₆ ). Finally, the challenges and prospects in solar CO₂ reduction with QDs in the future are discussed.

Probing CO2 Conversion Chemistry on Nanostructured Surfaces with Operando Vibrational Spectroscopy

With the rising emphasis on renewable energy research, the field of electrocatalytic CO₂ conversion to fuels has grown tremendously in recent years. Advances in nanomaterial synthesis and characterization have enabled researchers to screen effects of elemental composition, size, and surface chemistry on catalyst performance. However, direct links from structure and active state to catalytic function are difficult to establish. To this end, operando spectroscopic techniques, those conducted simultaneously as catalysts operate, can provide key complementary information by investigating electrocatalysis under turnover conditions. In particular, Raman and infrared spectroscopy have the potential to reveal the identity of surface-bound intermediates, catalyst active state, and possible reaction sites to supplement the insights extracted from conventional electrochemistry. Such research aims to work in tandem synthetic and catalytic efforts to guide the development of next-generation CO₂ electrocatalytic systems through rational design. In this Mini Review, we examine the latest developments in the operando probing of electrochemical CO₂ reduction on nanostructured electrocatalysts and detail how this research accelerates the advancement of this field.

Emerging Carbon-Based Heterogeneous Catalysts for Electrochemical Reduction of Carbon Dioxide into Value-Added Chemicals

The electrocatalytic reduction of CO₂ provides a sustainable way to mitigate CO₂ emissions, as well as store intermittent electrical energy into chemicals. However, its slow kinetics and the lack of ability to control the products of the reaction inhibit its industrial applications. In addition, the immature mechanistic understanding of the reduction process makes it difficult to develop a selective, scalable, and stable electrocatalyst. Carbon-based materials are widely considered as a stable and abundant alternative to metals for catalyzing some of the key electrochemical reactions, including the CO₂ reduction reaction. In this context, recent research advances in the development of heterogeneous nanostructured carbon-based catalysts for electrochemical reduction of CO₂ are summarized. The leading factors for consideration in carbon-based catalyst research are discussed by analyzing the main challenges faced by electrochemical reduction of CO₂ . Then the emerging metal-free doped carbon and aromatic N-heterocycle catalysts for electrochemical reduction of CO₂ with an emphasis on the formation of multicarbon hydrocarbons and oxygenates are discussed. Following that, the recent progress in metal-nitrogen-carbon structures as an extension of carbon-based catalysts is scrutinized. Finally, an outlook for the future development of catalysts as well as the whole electrochemical system for CO₂ reduction is provided.

Enhanced catalytic activity of Au core Pd shell Pt cluster trimetallic nanorods for CO2 reduction

Au@Pd@Pt nanorods greatly enhance the catalytic activities for CO₂ reduction because of Pd–Pt edge active sites as investigated by SERS.

On the origin of the elusive first intermediate of CO2 electroreduction

We resolve the long-standing controversy about the first step of the CO₂ electroreduction to fuels in aqueous electrolytes by providing direct spectroscopic evidence that the first intermediate of the CO₂ conversion to formate on copper is a carboxylate anion *CO₂ ^- coordinated to the surface through one of its C-O bonds. We identify this intermediate and gain insight into its formation, its chemical and electronic properties, as well as its dependence on the electrode potential by taking advantage of a cutting-edge methodology that includes operando surface-enhanced Raman scattering (SERS) empowered by isotope exchange and electrochemical Stark effects, reaction kinetics (Tafel) analysis, and density functional theory (DFT) simulations. The SERS spectra are measured on an operating Cu surface. These results advance the mechanistic understanding of CO₂ electroreduction and its selectivity to carbon monoxide and formate.