Efficient photoelectrochemical CO2 conversion for selective acetic acid production

Novel applications of photobiocatalysts in chemical transformations

Photocatalysis has proven to be an effective approach for the production of reactive intermediates under moderate reaction conditions. The possibility for the green synthesis of high-value compounds using the synergy of photocatalysis and biocatalysis, benefiting from the selectivity of enzymes and the reactivity of photocatalysts, has drawn growing interest. Mechanistic investigations, substrate analyses, and photobiocatalytic chemical transformations will all be incorporated in this review. We seek to shed light on upcoming synthetic opportunities in the field by precisely describing mechanistically unique techniques in photobiocatalytic chemistry.

Lead-Free Halide Perovskite Cs2AgBiBr6/Bismuthene Composites for Improved CH4 Production in Photocatalytic CO2 Reduction

CO2 photocatalytic conversion into value-added fuels through solar energy is a promising way of storing renewable energy while simultaneously reducing the concentration of CO2 in the atmosphere. Lead-based halide perovskites have recently shown great potential in various applications such as solar cells, optoelectronics, and photocatalysis. Even though they show high performance, the high toxicity of Pb2+ along with poor stability under ambient conditions restrains the application of these materials in photocatalysis. In this respect, we developed an in situ assembly strategy to fabricate the lead-free double perovskite Cs2AgBiBr6 on a 2D bismuthene nanosheet prepared by a ligand-assisted reprecipitation method for a liquid-phase CO2 photocatalytic reduction reaction. The composite improved the production and selectivity of the eight-electron CH4 pathway compared with the two-electron CO pathway, storing more of the light energy harvested by the photocatalyst. The Cs2AgBiBr6/bismuthene composite shows a photocatalytic activity of 1.49(±0.16) μmol g-1 h-1 CH4, 0.67(±0.14) μmol g-1 h-1 CO, and 0.75(±0.20) μmol g-1 h-1 H2, with a CH4 selectivity of 81(±1)% on an electron basis with 1 sun. The improved performance is attributed to the enhanced charge separation and suppressed electron-hole recombination due to good interfacial contact between the perovskite and bismuthene promoted by the synthesis method.

Modulating the Cu2O Photoelectrode/Electrolyte Interface with Bilayer Surfactant Simulating Cell Membranes for Boosting Photoelectrochemical CO2 Reduction

The low solubility of CO₂ molecules and the competition of the hydrogen evolution reaction (HER) in aqueous electrolytes pose significant challenges to the current photoelectrochemical (PEC) CO₂ reduction reaction. In this study, inspired by the bilayer phospholipid molecular structure of cell membranes, we developed a Cu₂O/Sn photocathode that was modified with the bilayer surfactant DHAB for achieving high CO₂ permeability and suppressed HER. The Cu₂O/Sn/DHAB photocathode stabilizes the *OCHO intermediate and facilitates the production of HCOOH. Our findings show that the Faradaic efficiency (FE) of HCOOH by the Cu₂O/Sn/DHAB photoelectrode is 83.3%, significantly higher than that achieved with the Cu₂O photoelectrode (FE_HCOOH = 30.1%). Furthermore, the FE_H2 produced by the Cu₂O/Sn/DHAB photoelectrode is only 2.95% at -0.6 V vs RHE. The generation rate of HCOOH by the Cu₂O/Sn/DHAB photoelectrode reaches 1.52 mmol·cm^-2·h^-1·L^-1 at -0.7 V vs RHE. Our study provides a novel approach for the design of efficient photocathodes for CO₂ reduction.

Hydrophobic surface efficiently boosting Cu2O nanowires photoelectrochemical CO2 reduction activity

The limited mass transfer of CO₂ and the competitive hydrogen evolution reaction (HER) during photoelectrochemical (PEC) CO₂ reduction usually result in low CO₂ reduction activity. Here, we constructed a Cu₂O/Sn/PTFE photocathode with a hydrophobic surface based on Cu₂O by physical vapor deposition and a dipping method. The CO faradaic efficiency (FE) increased from 34.5% (Cu₂O) to 95.1% (Cu₂O/Sn/PTFE) at -0.7 V vs. RHE, and the FE_H2 decreased from 27.9% (Cu₂O) to 3.8% (Cu₂O/Sn/PTFE). The introduction of the hydrophobic layer enhances the local CO₂ concentration on the electrode surface and effectively isolates H⁺ from the aqueous electrolyte, thereby enhancing the CO₂ reduction activity.

Selective CO2 Photoreduction to Acetate at Asymmetric Ternary Bridging Sites

Photoreduction of CO₂ is a promising strategy to synthesize value-added fuels or chemicals and realize carbon neutralization. Noncopper catalysts are seldom reported to generate C₂ products, and the selectivity over these catalysts is low. Here, we design rich-interface, heterostructured In₂O₃/InP (r-In₂O₃/InP) for highly competitive photocatalytic CO₂-to-CH₃COOH conversion with a productivity of 96.7 μmol g^-1 and selectivity > 96% along with water oxidation to O₂ in pure water (no sacrificial agent) under visible light irradiation. The hard X-ray absorption near-edge structure (XANES) shows that the formation of r-In₂O₃/InP with the isogenesis cation adjusts the coordination environment via interface engineering and forms O-In-P polarized sites at the interface. In situ FT-IR and Raman spectra identify the key intermediates of OCCO* for acetate production with high selectivity. Density functional theory (DFT) calculations reveal that r-In₂O₃/InP with rich O-In-P polarized sites promotes C-C coupling to form C₂ products because of the imbalanced adsorption energies of two carbon atoms. This work reports an interesting indium-based photocatalyst for selective CO₂ photoreduction to acetate under strict solution and irradiation conditions and provides significant insights into fabricating interfacial polarization sites to promote the process.

A Novel POP-Ni Catalyst Derived from PBTP for Ambient Fixation of CO2 into Cyclic Carbonates

The immobilization of homogeneous catalysts has always been a hot issue in the field of catalysis. In this paper, in an attempt to immobilize the homogeneous [Ni(Me₆Tren)X]X (X = I, Br, Cl)-type catalyst with porous organic polymer (POP), the heterogeneous catalyst PBTP-Me₆Tren(Ni) (POP-Ni) was designed and constructed by quaternization of the porous bromomethyl benzene polymer (PBTP) with tri[2-(dimethylamino)ethyl]amine (Me₆Tren) followed by coordination of the Ni(II) Lewis acidic center. Evaluation of the performance of the POP-Ni catalyst found it was able to catalyze the CO₂ cycloaddition with epichlorohydrin in N,N-dimethylformamide (DMF), affording 97.5% yield with 99% selectivity of chloropropylene carbonate under ambient conditions (80 °C, CO₂ balloon). The excellent catalytic performance of POP-Ni could be attributed to its porous properties, the intramolecular synergy between Lewis acid Ni(II) and nucleophilic Br anion, and the efficient adsorption of CO₂ by the multiamines Me₆Tren. In addition, POP-Ni can be conveniently recovered through simple centrifugation, and up to 91.8% yield can be obtained on the sixth run. This research provided a facile approach to multifunctional POP-supported Ni(II) catalysts and may find promising application for sustainable and green synthesis of cyclic carbonates.

Correlating Oxidation State and Surface Ligand Motifs with the Selectivity of CO2 Photoreduction to C2 Products

The design for non-Cu-based catalysts with the function of producing C₂₊ products requires systematic knowledge of the intrinsic connection between the surface state as well as the catalytic activity and selectivity. In this work, photochemical in situ spectral surface characterization techniques combined with the first principle calculations (DFT) were applied to investigate the relationships between the composition of surface states, coordinated motifs, and catalytic selectivity of a titanium oxynitride catalyst. When the catalyst mediates CO₂ photoreduction, C₂ product selectivity is positively correlated with the surface Ti²⁺ /Ti³⁺ ratio and the surface oxidation state is regulated and controlled by coordinated motifs of N-Ti-O/V[O], which can reduce the potential dimerization energy barriers of *CO-CO* and promote spontaneous formation of the subsequent *CO-CH₂ * intermediate. This phenomenon provides a new perspective for the design of heterogeneous catalysts for photoreduction of CO₂ into useful products.

Plasmonic Ag-decorated Cu2O nanowires for boosting photoelectrochemical CO2 reduction to multi-carbon products

The generation of multi-carbon products on the Cu₂O photocathode remains a great challenge. Herein, effective charge separation and surface catalytic reaction are achieved for photoelectrochemical CO₂ reduction through plasmon metal (Ag) decoration on Cu₂O nanowires. The Cu₂O/Ag composite photocathode achieves a 47.7% faradaic efficiency for CH₃COOH and the generation rate is 212.7 μmol cm^-2 h^-1 under illumination, which is about five times that in dark (44.4 μmol cm^-2 h^-1) at -0.7 V vs. RHE.

Synergy between plasmonic and sites on gold nanoparticle-modified bismuth-rich bismuth oxybromide nanotubes for the efficient photocatalytic CC coupling synthesis of ethane

The photocatalytic reduction of carbon dioxide (CO₂) to fossil fuels has attracted widespread attention. However, obtaining the high value-added hydrocarbons, especially C₂₊ products, remains a considerable challenge. Herein, gold (Au) nanoparticle-modified bismuth-rich bismuth oxybromide Bi₁₂O₁₇Br₂ nanotube composites were designed and tested. Au nanoparticles act as electron traps and thermal electron donors that promote the efficient separation and migration of carriers to form the C₂₊ product. As a result, compared with the pure Bi₁₂O₁₇Br₂ nanotubes, Au@Bi₁₂O₁₇Br₂ composites can not only produce the carbon monoxide (CO) and methane (CH₄), but also covert CO₂ into ethane (C₂H₆). In this study, Au@Bi₁₂O₁₇Br₂-700 was used to obtain a C₂H₆ production rate of 29.26 μmol h^-1 g^-1. The selectivities during a 5-hour test reached 94.86% for hydrocarbons and 90.81% for C₂H₆. The proposed approach could be used to design high-performance photocatalysts to convert CO₂ into high value-added hydrocarbon products.

Nanostructured Copper-Based Electrodes Electrochemically Synthesized on a Carbonaceous Gas Diffusion Membrane with Catalytic Activity for the Electroreduction of CO2

In this work, four different 4 cm2-sized nanostructured Cu-based electrocatalysts have been designed by a one-step electrodeposition process of Cu metal on a three-dimensional carbonaceous membrane. One consisted of Cu0, and the other three were obtained by further simple oxidative treatments. Morphological, structural, and electrochemical investigations on the four materials were carried out by scanning electron microscopy, Raman spectroscopy, X-ray diffraction, linear sweep voltammetry, and potential-controlled electrolysis. All the electrocatalysts showed promising catalytic activities toward CO2 electroreduction in liquid phase, with a remarkable selectivity toward acetic acid achieved when using the oxidized materials. In particular, the best electrocatalytic activity was observed for the Cu2O-Cu0 catalyst, working at a relatively low potential (-0.4 V vs RHE), which exhibited a stable and low current density of 0.46 mA cm-2 and a productivity of 308 μmol gcat-1 h-1. These results were attributed to the nanostructured morphology that is characterized by many void spaces and by a high surface area, which should guarantee a large number of CuI and Cu0 catalytic active sites. Moreover, kinetic analyses and preliminary studies about catalyst regeneration highlighted the stability of the best-performing catalyst.

Efficient electrocatalytic CO2 conversion into formate with AlxBiyOz nanorods in a wide potential window

Novel kinds of AlxBiyOz nanorods have been developed for the CO2RR for the first time, which show high selectivity to formate under a wide potential window and exhibit a maximum faradaic efficiency to formate of 97.5% at −1.19 V vs. RHE.