Developing active, robust, and nonprecious electrocatalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is highly crucial and ...challenging. In this work, a facile strategy is developed for scalable fabrication of dicobalt phosphide (Co2P)–cobalt nitride (CoN) core–shell nanoparticles with double active sites encapsulated in nitrogen‐doped carbon nanotubes (Co2P/CoN‐in‐NCNTs) by straight forward pyrolysis method. Both density functional theory calculation and experimental results reveal that pyrrole nitrogen coupled with Co2P is the most active one for HER, while Co–N–C active sites existing on the interfaces between CoN and N‐doped carbon shells are responsible for the ORR and OER activity in this catalyst. Furthermore, liquid‐state and all‐solid‐state Zn–air batteries are equipped. Co2P/CoN‐in‐NCNTs show high power density as high as 194.6 mW cm−2, high gravimetric energy density of 844.5 W h kg−1, very low charge–discharge polarization, and excellent reversibility of 96 h at 5 mA cm−2 in liquid system. Moreover, the Co2P/CoN‐in‐NCNTs profiles confirm excellent activity for water splitting.
Dicobalt phosphide–cobalt nitride core–shell particles act as double active centers and are encapsulated into the channel of N‐doped carbon nanotubes by an in situ one‐step self‐assembly and confined pyrolysis approach, which is demonstrated to afford trifunctional performance in catalyzing hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction for Zn–air batteries and water splitting.
Lithium-ion batteries (LIBs) are being intensively studied and universally used as power sources for electric vehicle applications. Despite the staggering growth in sales of LIBs worldwide, thermal ...safety issues still turn out to be the most intolerable pain point, and remain the focus of research for technological improvements. This paper presents a comprehensive overview on thermal safety issues of LIBs, in terms of thermal behavior and thermal runaway modeling and tests for battery cells, and safety management strategies for battery packs. Considering heat generation mechanism and thermal characteristics of LIBs, heat generation, dissipation and accumulation inside a cell are elaborated. The triggering factors leading to thermal runaway are also summarized. Finally, thermal runaway detection and prevention strategies for both cell- and pack-levels are introduced. Different engineering approaches from material refinement and additive adoption to thermal, electrical, and mechanical design are presented for thermal runaway prevention.
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•We reported a novel polymer adsorbent which can be facilely synthesized.•The adsorbent was an efficient and specific adsorbent for the removal of MB.•The equilibrium adsorption data ...fitted the Langmuir isotherm well.•The pseudo-second-order model could be better to describe the adsorption of MB.•The adsorption of MB onto the polymer adsorbent was endothermic and spontaneous.
Polydopamine (PDA) microspheres were synthesized by a facile oxidative polymerization method and used as a high-efficiency adsorbent for the removal of a cationic dye (methylene blue, MB) from aqueous solution. Characterizations of the as-synthesized PDA microspheres and PDA microspheres-MB (MB absorbed PDA microspheres) systems were performed using several techniques such as SEM, TEM, FTIR, N2 adsorption/desorption isotherms, particle size and zeta potential analysis. The effects of initial solution pH, temperature, initial concentration, and contact time were systematically investigated. Results showed the adsorption capacity at 25°C could reach up to 90.7mg/g. Besides, adsorption kinetics showed that the adsorption behavior followed the pseudo-second-order kinetic model. The equilibrium adsorption data fitted the Langmuir isotherm well. Thermodynamic analyses showed that the adsorption was endothermic and spontaneous, and it was also a physisorption process. In addition, the possible adsorption mechanism was also proposed based on the experimental results.
During the preparation of atomically dispersed Fe–N–C catalysts, it is difficult to avoid the formation of iron‐carbide‐containing iron clusters (“FexC/Fe”), along with the desired carbon matrix ...containing dispersed FeNx sites. As a result, an uncertain amount of the oxygen reduction reaction (ORR) occurs, making it difficult to maximize the catalytic efficiency. Herein, sulfuration is used to boost the activity of FexC/Fe, forming an improved system, “FeNC–S–FexC/Fe”, for catalysis involving oxygen. Various spectroscopic techniques are used to define the composition of the active sites, which include Fe–S bonds at the interface of the now‐S‐doped carbon matrix and the FexC/Fe clusters. In addition to outstanding activity in basic media, FeNC–S–FexC/Fe exhibits improved ORR activity and durability in acidic media; its half‐wave potential of 0.821 V outperforms the commercial Pt/C catalyst (20%), and its activity does not decay even after 10 000 cycles. Interestingly, the catalytic activity for the oxygen evolution reaction (OER) simultaneously improves. Thus, FeNC–S–FexC/Fe can be used as a high‐performance bifunctional catalyst in Zn–air batteries. Theoretical calculations and control experiments show that the original FeNx active centers are enhanced by the FexC/Fe clusters and the Fe–S and C–S–C bonds.
An “FeNC–S–FexC/Fe” bifunctional catalyst for the oxygen reduction and oxygen evolution reactions is successfully incorporated in liquid and flexible solid‐state zinc–air batteries. Based on an atomically dispersed Fe–N–C catalyst where the FeNx sites are distributed throughout a carbon framework and iron carbide cluster impurities are unavoidable, sulfuration is used to incorporate S bonds that enhance the activity of the catalytic centers in an acidic medium.
Metal–organic frameworks（MOFs） are of great interest as potential electrochemically active materials.However, few studies have been conducted into understanding whether control of the shape and ...components of MOFs can optimize their electrochemical performances due to the rational realization of their shapes. Component control of MOFs remains a significant challenge. Herein, we demonstrate a solvothermal method to realize nanostructure engineering of 2D nanoflake MOFs. The hollow structures withNi/Co-and Ni-MOF（denoted as Ni/Co-MOF nanoflakes and Ni-MOF nanoflakes） were assembled for their electrochemical performance optimizations in supercapacitors and in the oxygen reduction reaction（ORR）. As a result, the Ni/CoMOF nanoflakes exhibited remarkably enhanced performance with a specific capacitance of 530.4 F g-1at 0.5 A g-1in1 M LiO H aqueous solution, much higher than that of NiMOF(306.8 F g-1) and ZIF-67(168.3 F g-1), a good rate capability, and a robust cycling performance with no capacity fading after 2000 cycles. Ni/Co-MOF nanoflakes also showed improved electrocatalytic performance for the ORR compared to Ni-MOF and ZIF-67. The present work highlights the significant role of tuning 2D nanoflake ensembles of Ni/Co-MOF in accelerating electron and charge transportation for optimizing energy storage and conversion devices.
Enhancing Network Robustness via Shielding Jianan Zhang; Modiano, Eytan; Hay, David
IEEE/ACM transactions on networking,
2017-Aug., 2017-8-00, 20170801, Letnik:
25, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We consider shielding critical links to enhance the robustness of a network, in which shielded links are resilient to failures. We first study the problem of increasing network connectivity by ...shielding links that belong to small cuts of a network, which improves the network reliability under random link failures. We then focus on the problem of shielding links to guarantee network connectivity under geographical and general failure models. We develop a mixed integer linear program (MILP) to obtain the minimum cost shielding to guarantee the connectivity of a single source-destination pair under a general failure model, and exploit geometric properties to decompose the shielding problem under a geographical failure model. We extend our MILP formulation to guarantee the connectivity of the entire network, and use Benders decomposition to significantly reduce the running time. We also apply simulated annealing to obtain near-optimal solutions in much shorter time. Finally, we extend the algorithms to guarantee partial network connectivity, and observe significant reduction in the shielding cost, especially when the geographical failure region is small.
A photoinduced atom transfer radical polymerization (ATRP) of methacrylate with a Fe-based catalytic system was studied in the absence of additional ligands, reducing agents, and radical initiators. ...Linear semilogarithmic polymerization kinetics and narrow molecular weight distributions were obtained in the presence but also absence of conventional ATRP initiators. The proposed mechanism involves monomer-mediated photoreduction of Fe(III) to Fe(II) but also photoactivation of Fe(II) species. The polymerization was studied with different radiation sources for several methacrylates. The technique was successfully used to synthesize block copolymers, confirming the living nature of ATRP.
•CuFe2O4 modified activated carbon was used to remove H2S from humidified air.•Carbon with 20% CuFe2O4 is practical material with 291.66 mg/mL volumetric capacity.•An important intermediate, FeOOH, ...was formed during the H2S removal.•Sulfur is the principal product of H2S oxidation on the modified activated carbon.•Desulfurization effect reduced by 7% after two cycles of thermal regeneration.
A variety of CuFe2O4-based adsorbents with different active phase loadings were synthesized to remove H2S from humidified air at room temperature. The materials were characterized by adsorption of nitrogen, SEM-EDX, XPS, XRD, and TGA. According to the results, the activated carbon with 20 wt% CuFe2O4 exhibited the best H2S adsorption performance, reaching 292 mg/mL (667 mg/g). Furthermore, the H2S adsorption capacity reduced by 7% after two cycles of thermal regeneration. During the desulfurization process, FeOOH formed as an intermediate played a catalytic role. The products comprised sulfide, elemental sulfur, and sulfates. Elemental sulfur was the predominant product. The H2S removal involved both reactive adsorption and catalytic oxidation. In addition to the chemical properties of the active phase, structural characteristics like pore volume also determined the adsorption capacity. Pore volume of less than 6 nm pores could enhance catalyst dispersion, provide adsorption centers and store the oxidation products. This study will offer novel insights for the efficient synthesis of metal oxide-based adsorbents and the extensive application of their reactive adsorption capacity at the nanoscale level.
Structural and compositional engineering of atomic-scaled metal-N-C catalysts is important yet challenging in boosting their performance for the oxygen reduction reaction (ORR) and oxygen evolution ...reaction (OER). Here, boron (B)-doped Co-N-C active sites confined in hierarchical porous carbon sheets (denoted as Co-N,B-CSs) were obtained by a soft template self-assembly pyrolysis method. Significantly, the introduced B element gives an electron-deficient site that can activate the electron transfer around the Co-N-C sites, strengthen the interaction with oxygenated species, and thus accelerate reaction kinetics in the 4e- processed ORR and OER. As a result, the catalyst showed Pt-like ORR performance with a half-wave potential (E1/2) of 0.83 V versus (vs) RHE, a limiting current density of about 5.66 mA cm-2, and higher durability (almost no decay after 5000 cycles) than Pt/C catalysts. Moreover, a rechargeable Zn-air battery device comprising this Co-N,B-CSs catalyst shows superior performance with an open-circuit potential of ∼1.4 V, a peak power density of ∼100.4 mW cm-2, as well as excellent durability (128 cycles for 14 h of operation). DFT calculations further demonstrated that the coupling of Co-Nx active sites with B atoms prefers to adsorb an O2 molecule in side-on mode and accelerates ORR kinetics.
Nitrogen‐doped carbon materials (N‐Cmat) are emerging as low‐cost metal‐free electrocatalysts for the electrochemical CO2 reduction reaction (CO2RR), although the activities are still unsatisfactory ...and the genuine active site is still under debate. We demonstrate that the CO2RR to CO preferentially takes place on pyridinic N rather than pyrrolic N using phthalocyanine (Pc) and porphyrin with well‐defined N‐Cmat configurations as molecular model catalysts. Systematic experiments and theoretic calculations further reveal that the CO2RR performance on pyridinic N can be significantly boosted by electronic modulation from in‐situ‐generated metallic Co nanoparticles. By introducing Co nanoparticles, Co@Pc/C can achieve a Faradaic efficiency of 84 % and CO current density of 28 mA cm−2 at −0.9 V, which are 18 and 47 times higher than Pc/C without Co, respectively. These findings provide new insights into the CO2RR on N‐Cmat, which may guide the exploration of cost‐effective electrocatalysts for efficient CO2 reduction.
Nitrogen‐doped carbon catalysts are presented for application in the electrochemical CO2 reduction reaction (CO2RR). Molecular probes were designed to clarify the genuine catalytically active sites. CO2RR takes place preferentially on pyridinic rather than pyrrolic nitrogen, and metallic cobalt nanoparticles enhance the CO2RR on pyridinic nitrogen significantly.
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