Graphynes and Graphdiynes for Energy Storage and Catalytic Utilization: Theoretical Insights into Recent Advances.

Carbon allotropes have contributed to all aspects of people's lives throughout human history. As emerging carbon-based low-dimensional materials, graphyne family members (GYF), represented by graphdiyne, have a wide range potential applications due to their superior physical and chemical properties. In particular, graphdiyne (GDY), as the leader of the graphyne family, has been practically applied to various research fields since it was first successfully synthesized. GYF have a large surface area, both sp and sp2 hybridization, and a certain band gap, which was considered to originate from the overlap of carbon 2pz orbitals and the inhomogeneous π-bonds of carbon atoms in different hybridization forms. These properties mean GYF-based materials still have many potential applications to be developed, especially in energy storage and catalytic utilization. Since most of the GYF have yet to be synthesized and applications of successfully synthesized GYF have not been developed for a long time, theoretical results in various application fields should be shared to experimentalists to attract more intentions. In this Review, we summarized and discussed the synthesis, structural properties, and applications of GYF-based materials from the theoretical insights, hoping to provide different viewpoints and comments.

Encapsulated ruthenium nanoparticles activated few-layer carbon frameworks as high robust oxygen evolution electrocatalysts in acidic media.

Noble metals have been extensively employed as high active catalysts for oxygen evolution reaction (OER), are usually subjected to serious surface transformation and poor structural stability, especially in acid media, which need imperatively remedied. Herein, the interfacial engineering of Ru via few-layer carbon (Ru@FLC) was carried out, in which FLC can significantly suppress the corrosion of Ru in acid media, ensuring the efficient interfacial charge transport between Ru and FLC. As a result, a low overpotentials@10 mA cm-2 of 258 mV and small Tafel slopes of 53.1 mV dec-1 for oxygen evolution OER were achieved in acid media. DFT calculations disclose that outer FLC could induce charge redistribution and effectively optimize intermediates free energy adsorption, resulting in greatly reduce the energy barrier for OER. Our work may offer a new avenue to produce progressive OER electrocatalysts for energy-related applications in acid solution.

C6N3: A novel 2D carbon nitride with sp-N as support for efficient hydrogen production.

Two-dimensional (2D) carbon nitrides (CxNy) have great potential in advanced fields such as energy harvest and storage. We report a novel 2D CxNy, C6N3, comprising sp-N and sp2-C atoms. Density functional theory calculations indicate that electronically, thermally, and dynamically stable C6N3 is metallic even when cut into very narrow nanoribbons. C6N3 adsorbed single atoms of 3d, 4d, and 5d transition metals to fabricate single-atom catalysts (SACs) for an electrocatalytic hydrogen evolution reaction (HER). Among all SACs studied, Ti-, Cr-, Zr-, and Hf-embedded C6N3 had excellent overall performance including promising stability, moderate binding strength of H and H2, and good electrical conductivity. Our results suggest a novel C6N3 with an sp-N skeleton that has great potential for HER. More investigations are needed to further understand the properties and applications of C6N3 in other fields.

A simple general descriptor for rational design of graphyne-based bifunctional electrocatalysts toward hydrogen evolution and oxygen reduction reactions.

The high cost and relative scarcity of platinum (Pt) restrict large-scale commercialization of fuel cells, which has spurred researchers to develop low-cost alternatives integrating with high hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) catalytic activity. Herein, we performed density functional theory (DFT) calculations to explore the electrocatalytic activity of graphyne nanotubes (GyNTs). Several GyNTs were found to be potential metal-free electrocatalysts, with both HER and ORR activity superior to Pt. Moreover, we revealed a linear relationship between the Gibbs free energy change of O2 adsorption (ΔGOOH) and binding energy of H adsorption (ΔEH), which could be attributed to the fact that both the CO bond of OOH adsorption and the CH bond of H adsorption are single bonds. Therefore, ΔEH is proposed as a general descriptor for the rational design of bifunctional graphyne materials toward HERs and ORRs. Our findings provide a simple strategy for the rational design of bifunctional materials.

Porous CoSe2@N-doped carbon nanowires: an ultra-high stable and large-current-density oxygen evolution electrocatalyst.

Nitrogen doped carbon functionalized CoSe2 nanowires (CoSe2@N-C NWs), which act as potential oxygen evolution reaction (OER) catalysts with a large current density and high stability have been reported. Owing to the collaborative optimization of electrical conductivity, free adsorption energy and binding strength of OER intermediates, the prepared CoSe2@N-C NWs exhibit an enhanced 6.61-fold catalytic activity compared to the pristine CoSe2 NW electrode in 1.0 M KOH solution at the overpotential of 340 mV.

Ce-Mn coordination polymer derived hierarchical/porous structured CeO2-MnOx for enhanced catalytic properties.

Catalytic performance is largely dependent on how the structures/compositions of materials are designed. Herein, CeO2-MnOx binary oxide catalysts with a hierarchical/porous structure are prepared by a facile and efficient method, which involves the preparation of the hierarchical Ce-Mn coordination polymer (CPs) precursor, followed by a thermal treatment step. The obtained CeO2-MnOx catalysts not only well inherit the hierarchical structure of Ce-Mn CPs, but also possess porous and hollow features due to the removal of organic ligands and heterogeneous contraction during the calcination process. In addition, the effect of the Mn/Ce ratio is also studied to optimize catalytic performance. Specifically, the as-prepared CeO2-MnOx (5 : 5) catalyst exhibits excellent catalytic performance toward CO oxidation and selective catalytic reduction (SCR) of NO with NH3 at low temperatures. Based on the characterization results, we propose that the special hierarchical structure, high surface area, strong synergistic interaction between CeO2 and MnOx, and high content of active Ce3+, Mn4+ and Osurf are collectively responsible for its remarkable catalytic performance.

γ-Graphyne nanotubes as defect-free catalysts of the oxygen reduction reaction: a DFT investigation.

Graphyne materials are potential candidates to fabricate low-cost but efficient metal-free oxygen reduction reaction (ORR) electrocatalysts. However, due to the coexistence of sp and sp2 carbon atoms in graphyne, some factors playing important roles in determining the ORR activity have received little attention. In the present paper, we carried out thorough density functional theory (DFT) calculations to study the curvature effect on the ORR activity of γ-graphyne. Our results suggest that the (5, 0)-γGyNT would be an excellent metal-free ORR catalyst. Its limiting potential was computed to be 0.80 V and the corresponding active sites occupy up to 16.7% in content, much better than previously reported CACs. Moreover, it is revealed that the curvature can tune the degree of exposure of p electrons of active sites, thus tuning the ORR activity. Our findings are beneficial for further understanding catalytic behavior on graphyne related materials and we suggest a new strategy to design high performance metal-free ORR catalysts.

Graphyne-anchored single Fe atoms as efficient CO oxidation catalysts as predicted by DFT calculations.

By performing first-principles calculations, CO oxidation catalyzed by Fe-embedded defective α-graphyne was systematically investigated. It was found that Fe atoms were strongly anchored at the sp-C vacancy site of α-graphyne with a large binding energy of -5.28 eV and effectively adsorbed and activated O2 molecules. Then, we systematically compared CO oxidation by activated O2via Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. The calculated potential energy surfaces show that the Fe-doped α-graphyne can efficiently oxidize CO via the ER mechanism, in which the threshold of the rate determining step is 0.77 eV. Furthermore, Fe doping shows little effect on the diffusivities of CO, O2, and CO2, which can further enhance its catalytic performance.

Tandem Catalysis of Ammonia Borane Dehydrogenation and Phenylacetylene Hydrogenation Catalyzed by CeO2 Nanotube/Pd@MIL-53(Al).

Heterogeneously catalyzed, selective hydrogenation in the liquid phase is widely used in industry for the synthesis of chemicals. However, it can be a challenge to prevent active nanoparticles (e.g., palladium) from aggregation/leaching and meanwhile achieve high conversion as well as selectivity, especially under mild conditions. To address these issues, a CeO2 nanotube/Pd@MIL-53(Al) sandwich-structured catalyst has been prepared in which the MIL-53(Al) porous shell can efficiently stabilize the palladium nanoparticles. When this catalyst was used in a tandem catalytic reaction involving the dehydrogenation of ammonia borane and the hydrogenation of phenylacetylene, remarkably, the hydrogen released from the dehydrogenation of ammonia borane boosted the catalytic process, with 100 % conversion of phenylacetylene and a selectivity of 96.2 % for styrene, even at room temperature and atmospheric pressure, within 1 min. This work therefore provides an alternative strategy for balancing the conversion and selectivity of liquid-phase hydrogenation reactions.

Engineering of the d-Band Center of Perovskite Cobaltite for Enhanced Electrocatalytic Oxygen Evolution.

Great efforts have been made to understand and upgrade the kinetically sluggish oxygen evolution reaction (OER). In this study, a series of V-doped LaCoO3 (V-LCO) OER electrocatalysts with optimized d-band centers are fabricated. When utilized as an electrode for the OER, as-formed LaCo0.8 V0.2 O3 (V-LCO-II) requires an overpotential of only 306 mV to drive a geometrical catalytic current density of 10 mA cm-2 . Furthermore, at a given overpotential of 350 mV, the OER current density of V-LCO-II is about 22 times that of pure LaCoO3 (LCO) nanoparticles. Tailoring of the d-band center by V doping facilitates the adsorption of OER intermediates and promotes the formation of amorphous active species on the surface of LCO through the exchange interaction between high-spin V4+ and low-spin Co2+ . This work may create new opportunities for developing other highly active OER catalysts through d-band center engineering.

Novel Disassembly Mechanisms of Sigmoid Aß42 Protofibrils by Introduced Neutral and Charged Drug Molecules.

Alzheimer's disease (AD) is characterized by fibrillar deposits of amyloid-ß (Aß) peptides and neurofibrillary tangles of Tau proteins. Aß peptides are composed of 37-49 residues, among which the Aß42 isoform is particularly toxic and aggregation-prone and is enriched in the plaques of AD brains and thus considered central to the development of AD. Therefore, disaggregation and disruption provide potential therapeutic approaches to reduce, inhibit, and even reverse Aß aggregation. Here we capture the atomic-level details of the interactions between sigmoid Aß42 fibril 2MXU or 5KK3 and either natural tanshinone compounds TS1 or TS0 or negatively charged ER, proposing two unprecedented disassembly mechanisms. Natural TS1 or TS0 prefers to insert into the cavity together with part at the surface of the 2MXU to open up the mouth and twist the conformation, destroying the ordered growth of subsequent monomers along the fibril axis. For the more compact two-fold 5KK3 , attachment of TS1 or TS0 at the surface including some inserted in cavity results in the separation of the two folds. In the two sigmoid fibril systems, it is no longer applicable for the routine criteria to assess Aß42 fibril disassembly by introduction of these drugs, such as either reduced H-bond number, decreased ß-sheet contents, or both. ER, like-charged to Aß42 fibril, is especially exceptional, and departs utterly from the neutral ones to disassemble Aß42 fibril. Besides the inapplicable routine criteria, positive binding energy between ER and Aß42 fibril also deviates from the hypotheses of "ligands exhibiting greater affinity for the ß-amyloid peptide are effective at altering its aggregation and inhibiting cell toxicity" ( Cairo et al. , Biochemistry 2002 , 41 , 8620 - 8629 ) but results in stronger disassembly effect on the two kinds of sigmoid Aß42 fibrils than neutral TS0 or TS1. The disassembly power of charged ER molecules derives from its stronger deformation ability to the conformation of Aß42 fibril than the neutral ones, twisting the one-fold 2MXU into tapered-shape and separating two-fold 5KK3 in two parts further, which is in great agreement with experimental observations ( Irwin et al. Biomacromolecules 2013 , 14 ( 1 ), 264 - 274 ). The unusual disassembly mechanisms fill the gaps and offer an alternative direction in engineering new inhibitors to treat AD.

Synergy of sp-N and sp2-N codoping endows graphdiyne with comparable oxygen reduction reaction performance to Pt.

Nitrogen doped graphdiyne (NGDY) has been reported to have comparable oxygen reduction reaction (ORR) performance to Pt-based catalysts. However, the source of this enhanced ORR performance is not clearly understood. Herein, density functional theory calculations were performed to study the detailed ORR process on NGDY. The theoretically predicted overpotential (η) of GDY materials was 0.442 V, which is comparable to that of Pt-based catalysts, suggesting that GDY is a candidate for non-expensive metal-free ORR catalyst. Our results revealed that the good ORR performance of NGDY originates from the synergy of sp-N and sp2-N, which rules out the experimental proposal that sp-N doping is the dominating factor. Our results further suggest that local positive charge is not a definite descriptor to predict the ORR performance of GDY; instead ΔGO shows a better correlation with performance. Furthermore, it was revealed that the adsorption site is crucial for determining ORR performance, which should not be ignored to fully understand the catalytic activity of GDY-based materials.

An Original Monomer Sampling from a Ready-Made Aß42 NMR Fibril Suggests a Turn-ß-Strand Synergetic Seeding Mechanism.

Aggregation of amyloid beta (Aß) is a central step of Alzheimer's disease. Aß42 monomers are building blocks in the formation of both "on pathway" intermediate structures and "off pathway" oligomers. How to sample an Aß monomer becomes a problem however due to the instinct of Aß high flexibility and diversity as well as aggregation propensity. Currently, (1) most samplings focus on either the ready-made helix-rich 1Z0Q/1IYT NMR structure, or the completely extended conformation, but (2) few on a ready-made Aß NMR fibril (i. e., 2BEG). Here we compare the simulation results from sampling in scheme (1) with that in scheme (2), and find that the coil and ß-sheet contents in the 1Z0Q-sampled system are comparable to the counterparts in the 2BEG-sampled system, but with a large difference in simulation time and dynamics character. 1Z0Q-sampled system not only takes several times longer than the 2BEG-sampled one, and only ß1-seeding dynamics characteristic is observed probably due to far insufficient conformation transition in the limited simulation time. Two dynamics characteristics of Aß42 folding observed experimentally, that either ß1 region or ß2 region aggregates first, reproduce in the present simulations for 2BEG-sampled system however, suggesting a preferential sampling in the future simulation. In addition, a turn-ß-strand synergetic seeding mechanism of aggregation is first proposed based on the trajectory analyses on the four regions of Aß42 chain.

Tautomerization Effect of Histidines on Oligomer Aggregation of ß-Amyloid(1-40/42) during the Early Stage: Tautomerism Hypothesis for Misfolding Protein Aggregation.

As the intrinsic origin of the hypothesis for ß-amyloid (Aß) from Alzheimer's disease, histidine behaviors were found to play a crucial role in Aß aggregation. To investigate the histidine behaviors during the early stage of aggregation, Aß40/42 pentamers with different histidine isomer states were simulated at the atomic level. Results show that five Aß40 (δδδ) and Aß42 (εδδ) monomers can rapidly decrease the aggregation threshold, promote stable pentamer formation, and increase pentamer contents by 51.8% and 56.7%, respectively, as compared with the values of their wild-type (εεε) counterparts. Additionally, pentamers of Aß40 (δδδ) and Aß42 (εδδ) have different aggregation pathways and disassembly species, Tr+D and Te+M, during the growth of the pentamer. This work discloses the significance of histidine tautomerization in Aß aggregation, implying a potential way to control Aß aggregation and develop the assembly inhibitors.

Chiral γ-graphyne nanotubes with almost equivalent bandgaps.

Analogous to conventional carbon nanotubes, single-walled, chiral, γ-graphyne nanotubes (C-γGyNTs) are modeled based on the synthesized 2D γ-graphyne motif, and their electronic properties are investigated via density-functional tight-binding calculations for the first time. The resulting γGyNTs are predicted to be excellent semiconductors with moderate bandgaps ranging from 1.291 eV to 1.928 eV. In addition, the bandgaps of zigzag γGyNTs and armchair γGyNTs show damped oscillatory behaviour, while those of C-γGyNTs do not show any chirality- or diameter-dependent oscillatory behaviour. Interestingly, it is revealed that the (2a, m)-γGyNTs, where a is a positive integer, have nearly identical bandgap values, which provides a fresh method of bandgap manipulation for semiconductor devices that has not yet been reported.

A highly specific and ultrasensitive p-aminophenylether-based fluorescent probe for imaging native HOCl in live cells and zebrafish.

It is very important to detect native hypochlorous acid (HOCl) in the complex biosystems owing to the important roles of HOCl in the immune defense and the pathogenesis of numerous diseases. In this paper, a new p-aminophenylether-based fluorescent probe PAPE-HA was developed for specific detection of HOCl. Probe PAPE-HA could implement the quantitative detection of HOCl ranging from 0 to 1 µM and the detection limit was obtained as low as 1.37 nM. Additionally, probe PAPE-HA could reach a rapid response for HOCl (<2 min). Importantly, probe PAPE-HA with preeminent specificity and ultrasensitivity was proven to possess powerful capability of tracking native HOCl in live cells and zebrafish, and we thus anticipate that probe PAPE-HA could be used as a novel promising tool for revealing diverse cellular functions of HOCl.

Sulfur-Doped CoO Nanoflakes with Loosely Packed Structure Realizing Enhanced Oxygen Evolution Reaction.

The development of active and inexpensive electrocatalysts for the oxygen evolution reaction (OER) to promote water splitting has always been a major challenge. Cobalt-based oxides and sulfides have been actively investigated due to their low cost and high activity. However, the lower intrinsic conductivity of cobalt oxide and the inferior stability of cobalt sulfides still limit their practical application. Herein, CoO was chosen for a proof-of-concept study in which the anion-doping strategy was used to obtain an excellent catalyst. Sulfur incorporation optimizes the charge-transfer properties and active sites of sulfur-doped CoO (S-CoO) and thus gives rise to improved catalytic activity. Besides sulfur doping, the stable framework of the cobalt oxide was well maintained, and thus high stability of S-CoO throughout the reaction process was ensured.

Effects of double-atom vacancies on the electronic properties of graphyne: a DFT investigation.

Vacancy defects are one of the key impurities that strongly affect the properties of materials. In the present study, some different double-atom vacancies were introduced into α-graphyne (Gy), ßGy, and γGy, depending on their own structural characteristics. Subsequently, density functional theory (DFT) calculations were carried out to evaluate the changes in the structural and electronic properties induced by the double-atom vacancies. The results indicated that the double-atom vacancies only lead to an in-plane structural rearrangement of all three of the Gy systems. It was further revealed that the position of the double-atom vacancies is a crucial factor in the manipulation of the electronic properties of αGy and ßGy as compared with γGy. Our work is expected to yield new Gy materials with the desired properties obtained by altering the position of induced double-atom vacancies.

Positive effect of strong acidity on the twist of Aß42 fibrils and the counteraction of Aß42 N-terminus.

pH is a crucial factor in terms of affecting the aggregation and morphology of ß-Amyloid and hence a focus of study. In this study, structural and mechanical properties of a series of models (5, 6, …, 30 layer) of one-fold Aß42 fibrils at pH 1.5, 3.0 and 7.5, have been computed by using all-atom molecular dynamics simulations. 12, 14, and 15 layers are established to be the smallest realistic models for Aß42 fibrils at pH 1.5, 3.0 and 7.5, with twist angles of 0.40°, 0.34°, 0.31° respectively, disclosing the favorable effect of strong acidity on fibril twist. However, these angles are all lower than that (0.48°) determined for the truncated Aß17-42 fibril at pH 7.5, indicating that the disordered N-terminal depresses greatly the fibril twist and the lower pH disfavors the depression. Three commonly used indices to measure the fibril properties, namely number of H-bonds, interstrand distance and ß-sheet content have imperceptible changes with the pH alternation, therefore changes in fibril twist can be taken as a probe to monitor fibril properties. By contrast, N-terminus is determined not only to inhibit the U-shaped fibril twist by hampering the stagger between ß1 and ß2 strands, but also to play a vital carrier role in feeling solution (i.e., pH, salt) changes. These results can help design the nextgeneration of amyloid materials for state-of-the-art bio-nano-med applications by changing the solution pH or modifying chain length.

Micro Galvanic Cell To Generate PtO and Extend the Triple-Phase Boundary during Self-Assembly of Pt/C and Nafion for Catalyst Layers of PEMFC.

The self-assembly powder (SAP) with varying Nafion content was synthesized and characterized by XRD, XPS, HRTEM, and mapping. It is observed that the oxygen from oxygen functional groups transfers to the surface of Pt and generate PtO during the process of self-assembly with the mechanism of micro galvanic cell, where Pt, carbon black, and Nafion act as the anode, cathode and electrolyte, respectively. The appearance of PtO on the surface of Pt leads to a turnover of Nafion structure, and therefore more hydrophilic sulfonic groups directly contact with Pt, and thus the triple-phase boundary (TPB) has been expanded.