Electrospun Fe-Al-O Nanobelts for Selective CO2 Hydrogenation to Light Olefins

Composite Indium Tin Oxide Nanofibers with Embedded Hematite Nanoparticles for Photoelectrochemical Water Splitting

Hematite is a classical photoanode material for photoelectrochemical water splitting due to its stability, performance, and low cost. However, the effect of particle size is still a question due to the charge transfer to the electrodes. In this work, we addressed this subject by the fabrication of a photoelectrode with hematite nanoparticles embedded in close contact with the electrode substrate. The nanoparticles were synthesized by a solvothermal method and colloidal stabilization with charged hydroxide molecules, and we were able to further use them to prepare electrodes for water photo-oxidation. Hematite nanoparticles were embedded within electrospun tin-doped indium oxide nanofibers. The fibrous layer acted as a current collector scaffold for the nanoparticles, supporting the effective transport of charge carriers. This method allows better contact of the nanoparticles with the substrate, and also, the fibrous scaffold increases the optical density of the photoelectrode. Electrodes based on nanofibers with embedded nanoparticles display significantly enhanced photoelectrochemical performance compared to their flat nanoparticle-based layer counterparts. This nanofiber architecture increases the photocurrent density and photon-to-current internal conversion efficiency by factors of 2 and 10, respectively.

Modified fischer-tropsch synthesis: A review of highly selective catalysts for yielding olefins and higher hydrocarbons

Global warming, fossil fuel depletion, climate change, as well as a sudden increase in fuel price have motivated scientists to search for methods of storage and reduction of greenhouse gases, especially CO2. Therefore, the conversion of CO2 by hydrogenation into higher hydrocarbons through the modified Fischer–Tropsch Synthesis (FTS) has become an important topic of current research and will be discussed in this review. In this process, CO2 is converted into carbon monoxide by the reverse water-gas-shift reaction, which subsequently follows the regular FTS pathway for hydrocarbon formation. Generally, the nature of the catalyst is the main factor significantly influencing product selectivity and activity. Thus, a detailed discussion will focus on recent developments in Fe-based, Co-based, and bimetallic catalysts in this review. Moreover, the effects of adding promoters such as K, Na, or Mn on the performance of catalysts concerning the selectivity of olefins and higher hydrocarbons are assessed.

Mechanistic Insight into Hydrocarbon Synthesis via CO2 Hydrogenation on χ-Fe5C2 Catalysts

Converting CO₂ into value-added chemicals and fuels is one of the promising approaches to alleviate CO₂ emissions, reduce the dependence on nonrenewable energy resources, and minimize the negative environmental effect of fossil fuels. This work used density functional theory (DFT) calculations combined with microkinetic modeling to provide fundamental insight into the mechanisms of CO₂ hydrogenation to hydrocarbons over the iron carbide catalyst, with a focus on understanding the energetically favorable pathways and kinetic controlling factors for selective hydrocarbon production. The crystal orbital Hamiltonian population analysis demonstrated that the transition states associated with O-H bond formation steps within the path are less stable than those of C-H bond formation, accounting for the observed higher barriers in O-H bond formation from DFT. Energetically favorable pathways for CO₂ hydrogenation to CH₄ and C₂H₄ products were identified which go through an HCOO intermediate, while the CH* species was found to be the key C₁ intermediate over χ-Fe₅C₂(510). The microkinetic modeling results showed that the relative selectivity to CH₄ is higher than C₂H₄ in CO₂ hydrogenation, but the trend is opposite under CO hydrogenation conditions. The major impact on C₂ hydrocarbon production is attributed to the high surface coverage of O* from CO₂ conversion, which occupies crucial active sites and impedes C-C couplings to C₂ species over χ-Fe₅C₂(510). The coexistence of iron oxide and carbide phases was proposed and the interfacial sites created between the two phases impact CO₂ surface chemistry. Adding potassium into the Fe₅C₂ catalyst accelerates O* removal from the carbide surface, enhances the stability of the iron carbide catalyst, thus, promotes C-C couplings to hydrocarbons.

Thermal-Switchable, Trifunctional Ceramic-Hydrogel Nanocomposites Enable Full-Lifecycle Security in Practical Battery Systems

Thermal runaway (TR) failures of large-format lithium-ion battery systems related to fires and explosions have become a growing concern. Here, we design a smart ceramic-hydrogel nanocomposite that provides integrated thermal management, cooling, and fire insulation functionalities and enables full-lifecycle security. The glass-ceramic nanobelt sponges exhibit high mechanical flexibility with 80% reversible compressibility and high fatigue resistance, which can firmly couple with the polymer-nanoparticle hydrogels and form thermal-switchable nanocomposites. In the operating mode, the high enthalpy of the nanocomposites enables efficient thermal management, thereby preventing local temperature spikes and overheating under extremely fast charging conditions. In the case of mechanical or thermal abuse, the stored water can be immediately released, leaving behind a highly flexible ceramic matrix with low thermal conductivity (42 mW m^-1 K^-1 at 200 °C) and high-temperature resistance (up to 1300 °C), thus effectively cooling the TR battery and alleviating the devastating TR propagation. The versatility, self-adaptivity, environmental friendliness, and manufacturing scalability make this material highly attractive for practical safety assurance applications.

Recent Advances in the Mitigation of the Catalyst Deactivation of CO2 Hydrogenation to Light Olefins

The catalytic conversion of CO2 to value-added chemicals and fuels has been long regarded as a promising approach to the mitigation of CO2 emissions if green hydrogen is used. Light olefins, particularly ethylene and propylene, as building blocks for polymers and plastics, are currently produced primarily from CO2-generating fossil resources. The identification of highly efficient catalysts with selective pathways for light olefin production from CO2 is a high-reward goal, but it has serious technical challenges, such as low selectivity and catalyst deactivation. In this review, we first provide a brief summary of the two dominant reaction pathways (CO2-Fischer-Tropsch and MeOH-mediated pathways), mechanistic insights, and catalytic materials for CO2 hydrogenation to light olefins. Then, we list the main deactivation mechanisms caused by carbon deposition, water formation, phase transformation and metal sintering/agglomeration. Finally, we detail the recent progress on catalyst development for enhanced olefin yields and catalyst stability by the following catalyst functionalities: (1) the promoter effect, (2) the support effect, (3) the bifunctional composite catalyst effect, and (4) the structure effect. The main focus of this review is to provide a useful resource for researchers to correlate catalyst deactivation and the recent research effort on catalyst development for enhanced olefin yields and catalyst stability.

Catalysts for the Conversion of CO2 to Low Molecular Weight Olefins-A Review

There is a large worldwide demand for light olefins (C₂⁼-C₄⁼), which are needed for the production of high value-added chemicals and plastics. Light olefins can be produced by petroleum processing, direct/indirect conversion of synthesis gas (CO + H₂) and hydrogenation of CO₂. Among these methods, catalytic hydrogenation of CO₂ is the most recently studied because it could contribute to alleviating CO₂ emissions into the atmosphere. However, due to thermodynamic reasons, the design of catalysts for the selective production of light olefins from CO₂ presents different challenges. In this regard, the recent progress in the synthesis of nanomaterials with well-controlled morphologies and active phase dispersion has opened new perspectives for the production of light olefins. In this review, recent advances in catalyst design are presented, with emphasis on catalysts operating through the modified Fischer-Tropsch pathway. The advantages and disadvantages of olefin production from CO₂ via CO or methanol-mediated reaction routes were analyzed, as well as the prospects for the design of a single catalyst for direct olefin production. Conclusions were drawn on the prospect of a new catalyst design for the production of light olefins from CO₂.

Electrospun nanofibers with surface oriented lamellar patterns and their potential applications

This work shows conclusively that lamellar surface patterns can be obtained with diverse ceramic compositions during electrospinning. The lamellar structure formation is governed by the creation of an outer shell during the thermal treatment of initially uniform cylindrical fibers, consisting of polymer and pre-ceramic compounds. By changing the polymer to pre-ceramic ratio in the electrospinning solution, we demonstrate for the first time a facile way to control the obtained surface structure and the orientation of the lamellas. Furthermore, the lamellar morphology was illustrated in seven different compositions. This report provides a new pathway to obtain unique surface patterns in metal-oxide nanofibers and demonstrates their utilization in different applications. Specifically, we demonstrate the prospect of utilizing Ni-Al-O fibers with lamellar structures as alternative Li-ion battery anodes. In addition, we show the potential of Fe-Al-O fibers as an effective catalyst material.

Electrospun Anion-Conducting Ionomer Fibers-Effect of Humidity on Final Properties

Anion-conducting ionomer-based nanofibers mats are prepared by electrospinning (ES) technique. Depending on the relative humidity (RH) during the ES process (RHES), ionomer nanofibers with different morphologies are obtained. The effect of relative humidity on the ionomer nanofibers morphology, ionic conductivity, and water uptake (WU) is studied. A branching effect in the ES fibers found to occur mostly at RHES < 30% is discussed. The anion conductivity and WU of the ionomer electrospun mats prepared at the lowest RHES are found to be higher than in those prepared at higher RHES. This effect can be ascribed to the large diameter of the ionomer fibers, which have a higher WU. Understanding the effect of RH during the ES process on ionomer-based fibers' properties is critical for the preparation of electrospun fiber mats for specific applications, such as electrochemical devices.