Abstract
This study explores the possibility of incorporating carbon fibers (CFs), basalt fibers, glass fibers, and p-aramid reinforcement fibers into carbon fiber–reinforced composites for light use ...applications. Hybrid composites can overcome the weakness of CFs and provide flexibility to design materials with the desired properties. The mechanical properties (tensile, flexural, and puncture impact properties) of the prepared hybrid composite were evaluated according to the standards ASTM D3039, ASTM D790, and ISO 6603-2, respectively. The inherent properties of reinforcement fibers, weaving density, and impregnation of a thermoplastic matrix into the composite considerably impact the mechanical performance of the hybrid composite materials.
Non-precious metal catalysts for oxygen reduction reaction (ORR) are promising alternatives to Pt/C in fuel cells, thus, demand for advanced catalysts is arising. Herein, we prepared and ...characterized mesoporous Fe and Cu anchored in N-, S-, and P-doped carbon (FeCu x NC) catalysts, revealing the presence of ordered mesoporous grain-shaped particles and demonstrating that the electronic state of the active sites (Fe–N x ) is controlled by their environments, which can affect ORR kinetics. Half-cell measurements revealed that FeCu x NC promoted ORRs more effectively (0.92 V at 3 mA cm −2 ) than Pt/C (0.87 V at 3 mA cm −2 ) in alkaline conditions, while a current density of 490 mA cm −2 was achieved at 0.6 V in a single-cell level. Multi-heteroatom doping modulated the energy of OOH* and OH − adsorption on the active sites, and the lowest overpotential (according to density functional theory calculations) was obtained for the Fe–Cu–N 3 –C–P–S model.
This work explores the efficacy of silica/organic hybrid catalysts, where the organic component is built from linear aminopolymers appended to the silica support within the support mesopores. ...Specifically, the role of molecular weight and polymer chain composition in amine-bearing atom transfer radical polymerization-synthesized poly(styrene-co-2-(4-vinylbenzyl)isoindoline-1,3-dione) copolymers is probed in the aldol condensation of 4-nitrobenzaldehyde and acetone. Controlled polymerization produces protected amine-containing poly(styrene) chains of controlled molecular weight and dispersity, and a grafting-to thiol–ene coupling approach followed by a phthalimide deprotection step are used to covalently tether and activate the polymer hybrid catalysts prior to the catalytic reactions. Site-normalized batch kinetics are used to assess the role of polymer molecular weight and chain composition in the cooperative catalysis. Lower-molecular-weight copolymers are demonstrated to be more active than catalysts built from only molecular organic components or from higher-molecular-weight chains. Molecular dynamics simulations are used to probe the role of polymer flexibility and morphology, whereby it is determined that higher-molecular-weight hybrid structures result in congested pores that inhibit active site cooperativity and the diffusivity of reagents, thus resulting in lower rates during the reaction.
Electrochemical hydrogen peroxide (H
2
O
2
) production by the direct two-electron (2e
−
) oxygen reduction reaction (ORR) has received much attention as a promising alternative to the industrially ...developed anthraquinone fabrication process. Transition metal (M) and nitrogen doped carbon (M-N-C, M = Fe or Co) catalysts are known to be active for four electron ORR pathways
via
two + two electron transfer, where the former is for the ORR and the latter for the peroxide reduction reaction (PRR). Here, we report mesoporous N-doped carbon/manganese hybrid electrocatalysts composed of MnO and Mn-N
x
coupled with N-doped carbons (Mn-O/N@NCs), which have led to the development of electrocatalysis towards the 2e
−
ORR route. Based on the structural and electrochemical characterization, the number of transferred electrons during the ORR on the Mn-O/N@NCs was found to be close to the theoretical value of the 2e
−
process, indicating their high activity toward H
2
O
2
. The favored ORR process arose due to the increased number of Mn-N
x
sites within the mesoporous N-doped carbon materials. Furthermore, there was a strong indication that the PRR is significantly suppressed by adjacent MnO species, demonstrating its highly selective production of H
2
O
2
(>80%) from the oxygen electrochemical process. The results of a real fuel cell device test demonstrated that an Mn-O/N@NC catalyst sustains a very stable current, and we attributed its outstanding activity to a combination of site-dependent facilitation of 2e
−
transfer and a favorable porosity for mass transport.
A selective and efficient electrocatalyst composed of MnO and Mn-N
x
co-doped carbon nanostructures is developed for electrochemical hydrogen peroxide generation.
The critical role of the ligand effect and ensemble effect in enhancing formic acid (FA) dehydrogenation over PdAu catalysts was highlighted by both experimental and theoretical studies. FA ...dehydrogenation energy was calculated by DFT on PdAu model catalysts of different surface atomic arrangements. The Pd3Au1 surface exhibited the lowest reaction energy and kinetic barrier for FA dehydrogenation among four different PdAu surfaces. The Pd trimer played a critical role in stabilizing reaction intermediates. The experimental FA dehydrogenation activity of three different PdAu catalysts supported the theoretical results. In addition, the electronic interaction between the surface and subsurface layers also proved to contribute to the improved catalytic activity of PdAu catalysts via modification of Pd d states.
Catalysts that are highly selective and active for H2 production from HCOOH decomposition are indispensable to realize HCOOH-based hydrogen storage and distribution. In this study, we identify two ...effective routes to promoting the Pd catalyst for selective H2 production from HCOOH by investigating the effects of early transition metals (Sc, Ti, V, and Cr) incorporated into the Pd core using density functional theory calculations. First, the asymmetric modification of the Pd surface electronic structure (d z 2 vs d yz + d zx ) can be an effective route to accelerating the H2 production rate. Significant charge transfer from the subsurface Sc atom to the surface Pd atom and subsequent extremely low level of d band occupancy (<0.1) around the Sc atoms are identified as a key factor in deriving the asymmetric modification of the Pd surface electronic structure. Second, in-plane lattice contraction of the Pd surface can be an effective route to suppressing the CO production. Compressive strain of the Pd surface is maximized as a result of alloying with V and induces subsequent changes in adsorption site preference of the key intermediates for the CO production path, resulting in a significant increase in the activation energy barrier for the CO production path. The unraveled atomic-scale factors underlying the promotion of the Pd surface catalytic properties provide useful insights into the efforts to overcome limitations of current catalyst technologies in making the HCOOH-based H2 storage and distribution economically feasible.
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PdIr nanoparticles supported on carbon support are synthesized and their oxygen reduction reaction (ORR) activity and durability in a half cell or membrane-electrode assembly (MEA) ...configuration for polymer electrolyte membrane fuel cell are examined. A synergistic effect of the combination of Pd possessing the effective ORR catalytic activity and Ir as one of the most stable elements in acidic media leads to a decrease in particle size, a higher particle dispersion, and a better ORR activity than Pd monometallic catalysts. It is expected that PdIr alloys would form phase-separated nanoalloys that have Pd-rich surface owing to the higher surface energy of Ir. The addition of Ir to Pd in PdIr/C increases the metallic Pd portion. Meanwhile, the Pd5Ir/C is the most durable compared to Pd/C and Pt/C over 3000h of MEA operation. The ORR activity of PdIr alloy is expected to increase by reducing the oxygen binding energy of Pd in the presence of Ir from the first-principle calculation, and each contribution of compressive strain and ligand effects is quantified. The cohesive energy and the kinetic segregation energy are also calculated to support the improved stability of PdIr compared to Pd and Pt in the ORR condition.
In this paper, we report the preparation of a highly active and durable ordered intermetallic PdFe catalyst supported on carbon black for formic acid oxidation reaction (FAOR) by high-temperature ...heat treatment under a reductive atmosphere. We found that the ordered intermetallic PdFe catalyst exhibited considerably better catalytic activity and durability toward FAOR than the disordered PdFe and pure Pd catalysts because of the high alloying degree between Pd and Fe, which induced a downshift of the Pd d-band center and structural modifications that formed a superlattice crystalline structure with Pd surface segregation. We analyzed the improved catalytic properties of the ordered intermetallic PdFe catalyst through various electrochemical analyses such as cyclic voltammetry, CO oxidation methods, chronoamperometry, physicochemical analyses such as X-ray photoelectron spectroscopy, and synchrotron radiation methods such as X-ray absorption spectroscopy. Density functional theory calculation verified the improved FAOR activity of the ordered intermetallic PdFe catalyst. In addition, a single cell based on the ordered intermetallic PdFe catalyst was also fabricated and exhibited enhanced cell performance compared to those based on the other catalysts. To the best of our knowledge, this is the first study on the preparation of an ordered intermetallic PdFe catalyst for FAOR with real single-cell application in direct formic acid fuel cells (DFAFCs). We believe that our results will be helpful for the development of highly active and durable Pd alloy catalysts for FAOR and the commercialization of DFAFC.
Over the past decades, the design of active catalysts has been the subject of intense research efforts. However, there has been significantly less deliberate emphasis on rationally designing a ...catalyst system with a prolonged stability. A major obstacle comes from the ambiguity behind how catalyst degrades. Several degradation mechanisms are proposed in literature, but with a lack of systematic studies, the causal relations between degradation and those proposed mechanisms remain ambiguous. Here, a systematic study of a catalyst system comprising of small particles and single atoms of Pt sandwiched between graphene layers, GR/Pt/GR, is studied to unravel the degradation mechanism of the studied electrocatalyst for oxygen reduction reaction(ORR). Catalyst suffers from atomic dissolution under ORR harsh acidic and oxidizing operation voltages. Single atoms trapped in point defects within the top graphene layer on their way hopping through toward the surface of GR/Pt/GR architecture. Trapping mechanism renders individual Pt atoms as single atom catalyst sites catalyzing ORR for thousands of cycles before washed away in the electrolyte. The GR/Pt/GR catalysts also compare favorably to state‐of‐the‐art commercial Pt/C catalysts and demonstrates a rational design of a hybrid nanoarchitecture with a prolonged stability for thousands of operation cycles.
Catalyst protection through sandwiching between two graphene sheets enhances stability without compromising the activity to catalyze oxygen reduction reaction in acidic medium. Spectroscopic and computational analyses reveal the catalyst degradation mechanism. Under oxygen reduction reaction (ORR) conditions, evolution of point defects in graphene top layers provides a tortuous path for single atoms to reach the catalyst surface to catalyze ORR.
Multicompartment micelles (MCMs) containing acid and base sites in discrete domains are prepared from poly(norbornene)‐based amphiphilic bottlebrush copolymers in aqueous media. The acid and base ...sites are localized in different compartments of the micelle, enabling the nonorthogonal reaction sequence: deacetalization – Knoevenagel condensation – Michael addition of acetals to 2‐amino chromene derivatives. Computational simulations using dissipative particle dynamics (DPD) elucidated the bottlebrush composition required to effectively site‐isolate the nonorthogonal catalysts. This contribution presents MCMs as a new class of nanostructures for one‐pot multistep nonorthogonal cascade catalysis, laying the groundwork for the isolation of three or more incompatible catalysts to synthesize value‐added compounds in a single reaction vessel, in water.
An acid‐base bifunctional multicompartment micelle prepared from amphiphilic bottlebrush copolymers is reported for the nonorthogonal reaction sequence: deacetalization‐Knoevenagel condensation – Michael addition of acetals to 2‐amino chromene derivatives. Multicompartment micelles are promising nanostructures for compartmentalization of nonorthogonal catalysts for multistep transformations.
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