Chinese Journal of Catalysis最新文献

The unique photocatalytic mechanism of S-scheme heterojunction can be used to study new and efficient photocatalysts. By carefully selecting semiconductors for S-scheme heterojunction photocatalysts, it is possible to reduce the rate of photogenerated carrier recombination and increase the conversion efficiency of light into energy. Chalcogenides are a group of compounds that include sulfides and selenides (e.g., CdS, ZnS, Bi₂S₃, MoS₂, ZnSe, CdSe, and CuSe). Chalcogenides have attracted considerable attention as heterojunction photocatalysts owing to their narrow bandgap, wide light absorption range, and excellent photoreduction properties. This paper presents a thorough analysis of S-scheme heterojunction photocatalysts based on chalcogenides. Following an introduction to the fundamental characteristics and benefits of S-scheme heterojunction photocatalysts, various chalcogenide-based S-scheme heterojunction photocatalyst synthesis techniques are summarized. These photocatalysts are used in numerous significant photocatalytic reactions, including the reduction of carbon dioxide, synthesis of hydrogen peroxide, conversion of organic matter, generation of hydrogen from water, nitrogen fixation, degradation of organic pollutants, and sterilization. In addition, cutting-edge characterization techniques, including in situ characterization techniques, are discussed to validate the steady and transient states of photocatalysts with an S-scheme heterojunction. Finally, the design and challenges of chalcogenide-based S-scheme heterojunction photocatalysts are explored and recommended in light of state-of-the-art research.

Urea and oxalic acid are critical component in various chemical manufacturing industries. However, achieving simultaneous generation of urea and oxalic acid in a continuous-flow electrolyzer is a challenge. Herein, we report a continuous-flow electrolyzer equipped with 9-square centimeter-effective area gas diffusion electrodes (GDE) which can simultaneously catalyze the glycerol oxidation reaction in the anode region and the reduction reaction of CO₂ and nitrate in the cathode region, producing oxalic acid and urea at both the anode and cathode, respectively. The current density at low cell voltage (0.9 V) remained above 18.7 mA cm^–2 for 10 consecutive electrolysis cycles (120 h in total), and the Faraday efficiency of oxalic acid (67.1%) and urea (70.9%) did not decay. Experimental and theoretical studies show that in terms of the formation of C–N bond at the cathode, Pd-sites can provide protons for the hydrogenation process of CO₂ and NO₃^–, Cu-sites can promote the generation of *COOH and Bi-sites can stabilize *COOH. In addition, in terms of glycerol oxidation, the introduction of Cu and Bi into Pd metallene promotes the oxidation of hydroxyl groups and the cleavage of C–C bond in glycerol molecules, respectively.

The electrochemical reduction of CO₂ (eCO₂R) under ambient conditions is crucial for reducing carbon emissions and achieving carbon neutrality. Despite progress with alkaline and neutral electrolytes, their efficiency is limited by (bi)carbonates formation. Acidic media have emerged as a solution, addressing the (bi)carbonates challenge but introducing the issue of the hydrogen evolution reaction (HER), which reduces CO₂ conversion efficiency in acidic environments. This review focuses on enhancing the selectivity of acidic CO₂ electrolysis. It commences with an overview of the latest advancements in acidic CO₂ electrolysis, focusing on product selectivity and electrocatalytic activity enhancements. It then delves into the critical factors shaping selectivity in acidic CO₂ electrolysis, with a special emphasis on the influence of cations and catalyst design. Finally, the research challenges and personal perspectives of acidic CO₂ electrolysis are suggested.

The development of an efficient artificial H₂O₂ photosynthesis system is a challenging work using H₂O and O₂ as starting materials. Herein, 3D In_2.77S₄ nanoflower precursor was in-situ deposited on K⁺-doped g-C₃N₄ (KCN) nanosheets using a solvothermal method, then In_2.77S₄/KCN (IS/KCN) heterojunction with an intimate interface was obtained after a calcination process. The investigation shows that the photocatalytic H₂O₂ production rate of 50IS/KCN can reach up to 1.36 mmol g⁻¹ h⁻¹ without any sacrificial reagents under visible light irradiation, which is 9.2 times and 4.1 times higher than that of KCN and In_2.77S₄, respectively. The enhanced activity of the above composite can be mainly attributed to the S-scheme charge transfer route between KCN and In_2.77S₄ according to density functional theory calculations, electron paramagnetic resonance and free radical capture tests, leading to an expanded light response range and rapid charge separation at their interface, as well as preserving the active electrons and holes for H₂O₂ production. Besides, the unique 3D nanostructure and surface hydrophobicity of IS/KCN facilitate the diffusion and transportation of O₂ around the active centers, the energy barriers of O₂ protonation and H₂O₂ desorption steps are effectively reduced over the composite. In addition, this system also exhibits excellent light harvesting ability and stability. This work provides a potential strategy to explore a sustainable H₂O₂ photosynthesis pathway through the design of heterojunctions with intimate interfaces and desired reaction thermodynamics and kinetics.

The polarization switching plays a crucial role in controlling the final products in the catalytic process. The effect of polarization orientation on nitrogen reduction was investigated by anchoring transition metal atoms to form active centers on ferroelectric material In₂Se₃. During the polarization switching process, the difference in surface electrostatic potential leads to a redistribution of electronic states. This affects the interaction strength between the adsorbed small molecules and the catalyst substrate, thereby altering the reaction barrier. In addition, the surface states must be considered to prevent the adsorption of other small molecules (such as *O, *OH, and *H). Furthermore, the V@?-In₂Se₃ possesses excellent catalytic properties, high electrochemical and thermodynamic stability, which facilitates the catalytic process. Machine learning also helps us further explore the underlying mechanisms. The systematic investigation provides novel insights into the design and application of two-dimensional switchable ferroelectric catalysts for various chemical processes.

The photoreduction of greenhouse gas CO₂ using photocatalytic technologies not only benefits environmental remediation but also facilitates the production of raw materials for chemicals. However, the efficiency of CO₂ photoreduction remains generally low due to the challenging activation of CO₂ and the limited light absorption and separation of charge. Defect engineering of catalysts represents a pivotal strategy to enhance the photocatalytic activity for CO₂, with most research on metal oxide catalysts focusing on the creation of anionic vacancies. The exploration of metal vacancies and their effects, however, is still underexplored. In this study, we prepared an In₂O₃ catalyst with indium vacancies (V_In) through defect engineering for CO₂ photoreduction. Experimental and theoretical calculations results demonstrate that V_In not only facilitate light absorption and charge separation in the catalyst but also enhance CO₂ adsorption and reduce the energy barrier for the formation of the key intermediate *COOH during CO₂ reduction. Through metal vacancy engineering, the activity of the catalyst was 7.4 times, reaching an outstanding rate of 841.32 µmol g^‒1 h^‒1. This work unveils the mechanism of metal vacancies in CO₂ photoreduction and provides theoretical guidance for the development of novel CO₂ photoreduction catalysts.

The electrolysis of water powered by renewable energy sources offers a promising method of “green hydrogen” production, which is considered to be at the heart of future carbon-neutral energy systems. In the past decades, researchers have reported a number of hydrogen evolution reaction (HER) electrocatalysts with activity comparable to that of commercial Pt/C, but most of them are tested within a small current density range, typically no more than 500 mA cm^–2. To realize the industrial application of hydrogen production from water electrolysis, it is essential to develop high-efficiency HER electrocatalysts at high current density (HCD ≥ 500 mA cm^–2). Nevertheless, it remains challenging and significant to rational design HCD electrocatalysts for HER. In this paper, the design strategy of HCD electrocatalysts is discussed, and some HCD electrocatalysts for HER are reviewed in seven categories (alloy, metal oxide, metal hydroxide, metal sulfide/selenide, metal nitride, metal phosphide and other derived electrocatalysts). At the end of this article, we also propose some viewpoints and prospects for the future development and research directions of HCD electrocatalysts for HER.

With the continuous improvement of solar energy production capacity, how to effectively use the electricity generated by renewable solar energy for electrochemical conversion of biomass is a hot topic. Electrochemical conversion of 5-hydroxymethylfurfural (HMF) to biofuels and value-added oxygenated commodity chemicals provides a promising and alternative pathway to convert renewable electricity into chemicals. Although nickel-based eletrocatalysts are well-known for HMF oxidation, their relatively low intrinsic activity, poor conductivity and stability still limit the potential applications. Here, we report the fabrication of a freestanding nickel-based electrode, in which Ni(OH)₂ species were in-situ constructed on Ni foam (NF) support using a facile acid-corrosion-induced strategy. The Ni(OH)₂/NF electrocatalyst exhibits stable and efficient electrochemical HMF oxidation into 2,5-furandicarboxylic acid (FDCA) with HMF conversion close to 100% with high Faraday efficiency. In-situ formation strategy results in a compact interface between Ni(OH)₂ and NF, which contributes to good conductivity and stability during electrochemical reactions. The superior performance benefits from dynamic cyclic evolution of Ni(OH)₂ to NiOOH, which acts as the reactive species for HMF oxidation to FDCA. A scaled-up device based on a continuous-flow electrolytic cell was also established, giving stable operation with a high FDCA production rate of 27 mg h⁻¹ cm⁻². This job offers a straightforward, economical, and scalable design strategy to design efficient and durable catalysts for electrochemical conversion of valuable chemicals.

Photocatalytic decomposition of sugars is a promising way of providing H₂, CO, and HCOOH as sustainable energy vectors. However, the production of C₁ chemicals requires the cleavage of robust C−C bonds in sugars with concurrent production of H₂, which remains challenging. Here, the photocatalytic activity for glucose decomposition to HCOOH, CO (C₁ chemicals), and H₂ on Cu/TiO₂ was enhanced by nitrogen doping. Owing to nitrogen doping, atomically dispersed and stable Cu sites resistant to light irradiation are formed on Cu/TiO₂. The electronic interaction between Cu and nitrogen ions originates valence band structure and defect levels composed of N 2p orbit, distinct from undoped Cu/TiO₂. Therefore, the lifetime of charge carriers is prolonged, resulting in the production of C₁ chemicals and H₂ with productivities 1.7 and 2.1 folds that of Cu/TiO₂. This work provides a strategy to design coordinatively stable Cu ions for photocatalytic biomass conversion.

Weak redox ability and severe charge recombination pose significant obstacles to the advancement of CO₂ photoreduction. To tackle this challenge and enhance the CO₂ photoconversion efficiency, fabricating well-matched S-scheme heterostructure and establishing a robust built-in electric field emerge as pivotal strategies. In pursuit of this goal, a core-shell structured CuInS₂@CoS₂ S-scheme heterojunction was meticulously engineered through a two-step molten salt method. This approach over the CuInS₂-based composites produced an internal electric field owing to the disparity between the Fermi levels of CoS₂ and CuInS₂ at their interface. Consequently, the electric field facilitated the directed migration of charges and the proficient separation of photoinduced carriers. The resulting CuInS₂@CoS₂ heterostructure exhibited remarkable CO₂ photoreduction performance, which was 21.7 and 26.5 times that of pure CuInS₂ and CoS₂, respectively. The S-scheme heterojunction photogenerated charge transfer mechanism was validated through a series of rigorous analyses, including in situ irradiation X-ray photoelectron spectroscopy, work function calculations, and differential charge density examinations. Furthermore, in situ infrared spectroscopy and density functional theory calculations corroborated the fact that the CuInS₂@CoS₂ heterojunction substantially lowered the formation energy of *COOH and *CO. This study demonstrates the application potential of S-scheme heterojunctions fabricated via the molten salt method in the realm of addressing carbon-related environmental issues.