Calculated Activation Energy Research Articles

Masks thermal degradation as an alternative of waste valorization on the COVID-19 pandemic: A kinetic study

The COVID-19 pandemic generated a new dynamic around waste management. Personal protective equipment such as masks, gloves, and face shields were essential to prevent the spread of the disease. However, despite the increase in waste, no technical alternatives were foreseen for the recovery of these wastes, which are made up of materials that can be valued for energy recovery.It is essential to design processes such as waste to energy to promote the circular economy. Therefore, techniques such as pyrolysis and thermal oxidative decomposition of waste materials need to be studied and scaled up, for which kinetic models and thermodynamic parameters are required to allow the design of this reaction equipment. This work develops kinetic models of the thermal degradation process by pyrolysis as an alternative for energy recovery of used masks generated by the COVID-19 pandemic.The wasted masks were isolated for 72 h for virus inactivation and characterized by FTIR-ATR spectroscopy, elemental analysis, and determinate the higher calorific value (HCV). The composition of the wasted masks included polypropylene, polyethylene terephthalate, nylon, and spandex, with higher calorific values than traditional fuels. For this reason, they are susceptible to value as an energetic material.Thermal degradation was performed by thermogravimetric analysis at different heating rates in N2 atmosphere. The gases produced were characterized by gas chromatography and mass spectrometry. The kinetic model was based on the mass loss of the masks on the thermal degradation, then calculated activation energies, reaction orders, pre-exponential factors, and thermodynamic parameters. Kinetics models such as Coats and Redfern, Horowitz and Metzger, Kissinger-Akahira-Sunose were studied to find the best-fit models between the experimental and calculated data.The kinetic and thermodynamic parameters of the thermal degradation processes demonstrated the feasibility and high potential of recovery of these residues with conversions higher than 89.26% and obtaining long-chain branched hydrocarbons, cyclic hydrocarbons, and CO2 as products.

Thermal decomposition kinetics of synthesized poly(N-isopropylacrylamide) and Fe3O4 coated nanocomposite: Evaluation of calculated activation energy by RSM

In this study, poly(n-isopropylacrylamide) (PNIPA) has been synthesized by the free-radical polymerization method using azobisisobutyronitrile the initiator. Then, nanoparticle-PNIPA composite is prepared with magnetic iron oxide (Fe3O4) nanoparticles synthesized by co-precipitation. The thermal decomposition kinetics of synthesized PNIPA and nanocoated PNIPA have been investigated. It has been observed that nanocoated PNIPA has a more stable structure at high temperatures than synthesized PNIPA. In the newly improved model equations relate to thermal decomposition kinetics, a special solution has been made with the new approach. Moreover, the calculated activation energies of the samples have been evaluated with response surface methodology (RSM). The ratios required to synthesize nanocoated-PNIPA under the optimum conditions have been determined by RSM. The activation energy of the nanocomposite obtains when 0.3170 g PNIPA is coated with 0.048 g Fe3O4 nanoparticle is determined as 127.757 kJ/mol. In other words, nanocoating has been increased the thermal stability of the synthesized composite.

Efficient removal of antibiotic ciprofloxacin by catalytic wet air oxidation using sewage sludge-based catalysts: Degradation mechanism by DFT studies

In this work, the sewage sludge-derived activated carbon (SAC) loaded with iron nanoparticles (FeSAC) showed a highly effective catalytic activity in the degradation of the antibiotic ciprofloxacin by the CWAO reaction. The properties of FeSAC catalyst were studied by using N2 adsorption-desorption measurements at 77 K, scanning electron microscopy, X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. The CWAO reaction was evaluated at different temperatures (120–140 ºC), total pressure (10–30 bar) and catalyst doses (0.1–0.7 g/L) in a batch reactor. In this regard, temperature and catalyst dosage showed a significant impact on the removal of the tested antibiotic. By using a catalyst dose of 0.7 g/L, ciprofloxacin degradation and CO2 selectivity were higher than 99 % and 60 %, respectively, and were achieved within two hours at 140 °C and 20 bar. The loss of the active phase (Fe) of the catalyst in the reaction medium was measured, obtaining negligible values (less than 24 ppb). This catalyst showed high stability under the tested reaction conditions. In addition, a potential equation was proposed to correctly describe the evolution of ciprofloxacin degradation. The calculated activation energy of the CWAO process was 53.8 kJ/mol. Additionally, Density Functional Theory (DFT) calculations were performed to illustrate the degradation mechanism of ciprofloxacin, where the electronic energies indicated the compounds that are most difficult to degrade by CWAO. Finally, a proof of concept using an environmentally-relevant matrix was carried out, verifying the technical feasibility of the synthesized catalyst for its application with more complex matrices, consecutive reaction cycles and at a low treatment cost.

High proton conduction in two highly stable phenyl imidazole dicarboxylate-based Cd(II)-MOFs

In recent years, carboxylic acid-based MOFs have gathered a lot of attention because of their high stability and excellent proton conductivity, and are likely to be promising candidates as proton-exchange membranes. In this work, we synthesized two MOFs by reference method, namely [Cd4(μ3-PhIDC)2(μ4-PhIDC)2(H2O)]n (1) (H2PhIDC ​= ​2-phenyl-4,5-imidazole dicarboxylic acid), [Cd2(μ2-PhIDC)2(phen)2]n (2) (phen ​= ​1,10-phenanthroline), which have high water stability. Therefore, this work focuses on their intrinsic proton conductivity. The results showed that under the conditions of 98% RH/100 ​°C, the proton conductivities of 1 and 2 can achieve 2.71 ​× ​10−3 and 2.67 ​× ​10−3 ​S ​cm−1, respectively. Finally, based on the structural analysis and calculations of activation energies, the principle of proton transfer is inferred, which will afford new inspiration for the design of the proton conduction crystalline materials.

Collectively exhaustive electrochemical hydrogen evolution reaction of polymorphic cobalt selenides derived from organic surfactants modified Co-MOFs

Finding and exploring non-noble metal-based electrocatalysts for the promising power-to-hydrogen fuel technology through water splitting reactions is highly emerging. Herein, we report the preparation of cobalt-based metal-organic frameworks (Co-MOFs) using an oleylamine (OLA) and 1-dodecanethiol (DDT)-modified trimesic acid (TMA), and cobalt precursor. Then, the electrocatalytically active cobalt selenides were derived from the Co-MOFs by a water-organic solvent mixture-assisted single-step selenization process. Interestingly, the cobalt selenide obtained from the DDT-modified Co-MOF shows collectively exhaustive hydrogen evolution reaction (HER) performance with very small overpotentials of ∼161 and ∼206 mV to achieve 10 and 50 mA cm−2, respectively, due to the phase mixing characteristics of cobalt selenide and the synergistic interaction. The fast reaction kinetics were identified at the DDT-Co selenide electrode surface as confirmed by observing the lower charge-transport/interfacial resistance and Tafel slope value due to the high surface coverage of adsorbed hydrogen (Hads) atoms, evidenced by high interfacial chemical capacitance value, as a result of the high electrical conductivity and large electrochemically accessible active sites. The calculated activation energy (Ea) of HER further reveals a low kinetic energy barrier in the HER on the DDT-Co selenide, indicating high intrinsic catalytic activity due to the fast surface diffusion rate of Hads. Furthermore, the obtained cathodic transfer coefficient (αc) value strongly suggested that the HER on the surface of DDT-Co selenide (αc = 2) proceeds in the Langmuir-Hinshelwood reaction mechanism and follows the Volmer-Tafel pathway. The present work provides valuable insights into the modification of Co-MOFs and their impact on HER catalytic activity of cobalt selenide, and also the mechanistic investigation of HER based on electrochemical impedance spectroscopy analysis.

Is the doped MoS2 basal plane an efficient hydrogen evolution catalyst? Calculations of voltage-dependent activation energy.

Transition metal dichalcogenides are cheap and earth-abundant candidates for the replacement of precious metals as catalyst materials. Experimental measurements of the hydrogen evolution reaction (HER), for example, have demonstrated significant electrocatalytic activity of MoS2 but there is large variation depending on the preparation method. In order to gain information about the mechanism and active sites for the HER, we have carried out calculations of the reaction and activation energy for HER at the transition metal doped basal plane of MoS2 under electrochemical conditions, i.e. including applied electrode potential and solvent effects. The calculations are based on identifying the relevant saddle points on the energy surface obtained from density functional theory within the generalized gradient approximation, and the information on energetics is used to construct voltage-dependent volcano plots. Doping with 3d-metal atoms as well as Pt is found to enhance hydrogen adsorption onto the basal plane by introducing electronic states within the band gap, and in some cases (Co, Ni, Cu, Pt) significant local symmetry breaking. The Volmer-Heyrovsky mechanism is found to be most likely and the associated energetics show considerable dopant and voltage-dependence. While the binding free energy of hydrogen can be tuned to be seemingly favorable for HER, the calculated activation energy turns out to be significant, at least 0.7 eV at a voltage of -0.5 V vs. SHE, indicating low catalytic activity of the doped basal plane. This suggests that other sites are responsible for the experimental activity, possibly edges or basal plane defects.

Kinetic Modeling of Light Naphtha Hydroisomerization in an Industrial Universal Oil Products Penex™ Unit

Recently, the isomerization of light naphtha has been increasingly significant in assisting refiners in meeting sternness specifications for gasoline. Isomerization process provides refiners with the advantage of reducing sulfur, olefin, and benzene in the gasoline basin without significantly victimizing the octane. The mathematical modeling of a chemical reaction is a critical tool due to it can used to optimize the experimental data to estimate the optimum operating conditions for industrial reactors. This paper describes light naphtha isomerization reactions over a Pt/Al₂O₃-Cl catalyst at the Al-Dura Oil Refinery (Baghdad, Iraq) using a newly developed universal mathematical model. The proposed kinetic model involves 117 isomerization reactions and 90 cracking reactions to describe 52 real components graded from methane to n-octane. A Genetic Algorithm stochastic optimization technique applied in MATLAB R2020a software was employed to estimate the optimal set of kinetic parameters. The calculated activation energies for hydrocracking reactions was found to be higher than the other reactions because of hydrocracking reactions occur at higher range of temperatures. By benchmarking between the experimental and theoretical results for all 117 data sets, the mean absolute error was obtained to be 0.00360 for all 52 components. Also, a positive effect of increasing reaction temperatures was recognized on enhancing the research octane number (RON).

Kinetic mechanism of FeCr2O4 reduction in carbon-containing iron melt

Direct alloying of chromium by chromite attracts a lot of interest for its superiority in energy-saving and process simplification. The knowledge of chromium alloying by reduction of FeCr2O4, the main component of chromite, is a key to understanding the mechanism of chromium alloying from chromite. The effect of melt composition (carbon and chromium addition) and temperature on the reduction of FeCr2O4 by carbon-containing iron melt was studied. The higher the carbon content was in the melt, the higher chromium recovery was obtained. Similarly, the higher temperature is favorable for the reduction of FeCr2O4. The reduction of FeCr2O4 was impeded by chromium addition due to the lower activity of carbon resulting from the strong attraction between carbon and chromium. The kinetics of FeCr2O4 reduction by carbon dissolving in iron melt was investigated, and the results indicated that the controlling step was the chemical reaction at the FeCr2O4/melt interface at 1823K. The calculated activation energy for the chemical reaction was 392.82 kJ/mol.

Zn[B3O4(OH)3] composites fabrication based on PVC pipes scrap via comparing melt mixing and casting procedures under the effect of electron beam irradiation

In several works, scientific researchers targeted the development of polymeric materials with good mechanical and thermal properties and resist heat and fire propagation. In a new approach, this article goals to the usage of waste polyvinyl chloride (WPVC) based polymer composites derived from PVC pipes scrap filled with fixed percent of zinc borate particles (ZnB), which were prepared via two different techniques named melt mixing WPVC/ZnB (M) and casting WPVC/ZnB (C). The fabricated composites by the two methods were irradiated in an electron beam accelerator (EB) at 30 kGy. A comparative study of the thermal and mechanical properties based on stress-strain curves, tensile strength (TS), elongation at break (E %), and tear strength were evaluated. Furthermore, the rate of heat burning (%) for the two methods has been performed. Moreover, differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), Infrared spectroscopy analysis (FTIR), X-ray diffraction (XRD), and the activation energy (Ea) calculation of the prepared samples have been considered. The observed improvements in the mechanical, thermal, and flammability behavior of WPVC were succeeded by incorporating ZnB particles. The irradiated WPVC loaded with zinc borate presented a superior flame propagation fraction when matched with their corresponding unirradiated composites. Also, WPVC composite films prepared via the melt mixing method reveal more excellent properties than those equipped by the casting process for the most investigated factors.

High temperature phenylethynyl-terminated imide oligomers derived from asymmetric diphenyl ether diamines for resin transfer molding

Resin transfer molding (RTM) require phenylethynyl-terminated imide oligomers (PETIs) to exhibit low melt temperatures and better melt stability. To decrease the melt temperatures of PETIs and improve their resin transfer moldable processability, asymmetric 4,4′-diaminodiphenyl ether substituted by fluorine (F-ODA), trifluoromethyl group (3F-ODA) or phenyl group (p-ODA) were introduced. Asymmetric molecular structure and substituent groups decrease the melt temperatures of PETIs, endowing PETIs with the wider processing temperature windows and low minimum melt viscosity (<1 Pa s). These polyimides show pot lives of 30–60 min at 260–280 °C. Furthermore, the effects of backbone structure on melt fluidity of imide oligomers were discussed by the calculation of viscous activation energy (Ea,η) and analysis of Molecular Dynamics. PETI-3F and PETI-P based on 3F-ODA and p-ODA exhibit low and stable melt viscosities (<1 Pa s) at 250–270 °C and 260–270 °C for 4 h respectively, enabling the successful fabrication of carbon fiber reinforced polyimide composites via RTM process. After cured at 380 °C, the thermosets of PETI-3 and PETI-4 show high Tg of 412 °C and 402 °C and good thermal stability (Td5>550 °C). Cured PETI-3 and PETI-4 also show good mechanical properties (tensile strength >50 MPa). In comparison with p-ODA, 3F-ODA could provide PETIs with superior resin transfer moldable processability and higher heat-resistance and is more suitable to synthesize PETIs for RTM application, because of better balance between polymer segmental mobility and polymer chain packing.

Multi-component sorption of Pb2+, Cu2+ and Ni2+ on PEI modified chitosan-based hybrid membranes

Novel poly(ethylene imine) (PEI) modified chitosan-based hybrid membranes (PMCHMs) were created via a soft chemistry method, in which unmodified chitosan (CS) firstly reacted with PEI to produce a CS-PEI precursor. Later, such CS-PEI precursor was blended with silicone to create the membrane solution of PMCHMs. Finally, PMCHMs could be obtained via phase-inversion process. Multi-component sorption of Pb2+, Cu2+ and Ni2+ on PMCHMs in metal mixed solutions, such as, Pb2+&Cu2+ and Pb2+&Ni2+ binary, Pb2+, Cu2+ and Ni2+ ternary, as well as Pb2+, Cu2+, Ni2+, Cd 2+ and Cr3+ quintuple mixed solutions, was inspected. The calculation of effective diffusion coefficients, distribution coefficients and selectivity coefficients showed that Pb2+ sorption on PMCHMs had excellent selectivity in these mixed multi-metal solutions. While, the calculation of activation energy proved that Pb2+, Cu2+ and Ni2+ sorption on PMCHMs was a physic-sorption process Also, mechanism insight reveals that Pb2+ sorption on PMCHMs could be depicted via Lagergren pseudo-2nd-order kinetic model and Langmuir or Freundlich isotherm equation. Exclusively, intra-particle diffusion process was discussed in detail. Desorption testing verified that HCl is a good desorbent for metals sorption on PMCHMs and the cycle time of membranes can arrive at 6 times. These results demonstrate that PMCHMs can be used to preferentially eradicate Pb2+ from metal mixture solutions, showing prospective applications in the treatment of metal mixture wastewater from waste vehicle power-battery and other various metal-bearing polluted water.

Pyrolysis mechanism of composite binder composed of coal tar pitch and phenolic resin for carbon materials

The composite binder consisting of coal tar pitch (CTP) and phenolic resin (PR) has both low viscosity and high char yield, and it has great potential in the preparation of advanced carbon materials. However, the lack of understanding of its synergetic behavior and mechanism hinders the optimization of the preparation process. In this work, the co-pyrolysis of CTP and PR was systematically investigated. The char yield of the composite binder was confirmed to be remarkably higher than the weighted average of the two single binders. Furthermore, the calculated activation energy for the pyrolysis of the composite binder was higher than that of CTP and PR after 400 °C. The interaction and structure evolution mechanisms of composite binder were clarified. Specifically, the ortho-position of the phenoxy carbon in CTP cross-link with the para-position of the phenoxy carbon in PR by the methylene bridge, and the free polycyclic aromatic hydrocarbons stack onto the as-crosslinked polycyclic aromatics driven by the pancake bonds.

Rare metals recycling from spent NCM cathode materials and simultaneous dehydrofluorination of polyvinylidene fluoride (PVDF) in subcritical water

Several studies have examined the recovery of lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn) from used lithium-ion batteries (LIBs). However, the environmentally friendly and cost-effective leaching and efficient separation of rare metals from the active cathode material of LIBs remains a challenge. In this study, we present a novel route for the extraction of high-value metals from the NCM cathode material of spent LIBs using subcritical water-containing polyvinylidene fluoride (PVDF). The experimental parameters such as reaction temperature, time, liquid–solid and mass ratios, were carefully investigated. The raw cathode material and the solid residues before and after leaching were characterized using ICP-OES, XRD, FT-IR and SEM-EDS analyses. Results showed that the maximum extraction efficiencies of Li, Ni, Co, and Mn of (98.69, 98.24, 97.52, and 99.04) %, respectively, were achieved under the optimized conditions of 350 °C, 2 h, 1:3 mass ratio, and 60:1 mL/g liquid–solid ratio. Meanwhile, the experimental results of leaching kinetics revealed that the reaction in the system was controlled by the surface chemical reaction model with the linear fitting degree of (R2 = 0.97–0.99) and the calculated activation energies of 63.72 kJ/mol (for Li), 73.55 kJ/mol (for Ni), 74.99 kJ/mol (for Co), and 71.88 kJ/mol (for Mn). The overall findings of this research concluded that the PVDF-assisted subcritical water extraction process is a beneficial and a promising alternative to other existing methods.

Characteristics and mechanism of modified hydrotalcite for coal spontaneous combustion preventing

Hydrotalcite is a new fire-fighting material with a sound effect of preventing the spontaneous combustion of coal. In this paper, hydrotalcite (Zn–Mg–Al-LDHs) and rare earth element Ce-modified hydrotalcite (Zn–Mg–Al–Ce-LDHs) inhibitor samples were prepared by the co-precipitation method, respectively. The surface morphology, dispersibility, and pyrolysis properties of the inhibitor were characterized by thermogravimetric experiments. Based on thermogravimetric experiments, the effects of hydrotalcite and modified hydrotalcite containing rare earth element Ce on the spontaneous combustion characteristics of coal were studied. Combined with thermodynamic parameters, the inhibition mechanism of coal spontaneous combustion was analyzed. The results showed that Zn–Mg–Al-LDHs and Zn–Mg–Al–Ce-LDHs inhibitors were successfully prepared. Adding the two to coal can inhibit both coal samples, and the inhibition effect of Zn–Mg–Al–Ce-LDHs is more significant. The Zn–Mg–Al–Ce-LDHs inhibitor can effectively reduce the weight loss rate of coal, delay the critical temperature, and maximum weight loss rate temperature of coal samples by 6 °C and 31.5 °C, respectively, and increase the residual heat by 2.3%. The calculation of apparent activation energy shows that the average activation energies of Zn–Mg–Al–Ce-LDHs for inhibiting coal samples in the stages of water evaporation and gas desorption and thermal decomposition and combustion are 30935.256 J/mol and 76962.582 J/mol, respectively; 464.878 J/mol and 31914.233 J/mol higher than raw coal, respectively.

Enhanced proton conductivity of viscose-based membranes via ionic modification and dyeing processes for fuel cell applications

Proton exchange membranes (PEMs), which are crucial fuel cell parts, play an important role in the field of energy science. However, the further development of conventional PEMs based on synthetic polymers is greatly limited by high energy consumption and difficult degradation. In this work, we reported the fabrication of a novel viscose-based PEM via cationic modification and dyeing treatment with the reactive dyes KE-7B1. High-efficiency proton transmission channels can be constructed due to the formation of the complex internal three-dimensional network of the as-prepared viscose-based PEM. H+ conductivity (σH+) and water uptake are intensively investigated by changing the cationic agents and KE-7B1, and the maximum σH+ reaches 44.19 mS/cm at 80 °C and 98% relative humidity (RH). Furthermore, the prepared membrane shows the lowest calculated activation energy value (12.25 kJ/mol), indicating that both Grotthuss and Vehicle mechanisms play an important role in ionic transport. The membrane chemical structure and micromorphology are analyzed and the proton transmission modes are explored in detail, supplemented with research on the hydrophilic/hydrophobic characteristics and crystallinity of the membranes. The application stability of the membranes is also evaluated analyzing the thermal, mechanical, and oxygen resistance properties, and the results show that all the prepared membranes can maintain good thermal stability within 200 °C. The maximum tensile strength reaches 42.12 MPa, and the mass losses of the membranes soaked in 30% (in mass, same below) H2O2 solution for 120 h can be restricted to 10%. Therefore, as a novel PEM, the obtained dye viscose-based membranes show great potential for application in fuel cells.

Boronic ester-based vitrimeric methylvinyl silicone elastomer with “solid-liquid” feature and rate-dependent mechanical performance

Vitrimer chemistry can integrate reprocessability, recyclability, self-healing and good creep-resistance into polymers through covalent adaptive network structure. In particular, reactive processing shows great potential to convert commercial polymers into vitrimers in industrial scale. In this work, vitrimeric silicone elastomer was successfully prepared in a one-step peroxide-induced thiol-ene click reaction between thiol-terminated boronic ester and vinyl groups of commercial methylvinyl silicone rubber (MVQ) via reactive processing. It was found that MVQ vitrimer elastomer shows good reprocessability, self-healing property, excellent elasticity and a similar gel content to that of traditional peroxide-crosslinked MVQ rubbers. Based on classical Arrhenius theory, the calculated activation energy (Ea) of B–O dynamic bond in MVQ vitrimer is 28.5 kJ/mol along with a topology-freezing transition temperature (Tv) of 6.4 °C. Intriguingly, the fabricated MVQ vitrimer shows a strongly rate-dependent mechanical response, i.e., larger mechanical strength at higher deformation rate, which is mainly due to fast bond-exchange rate of the B–O bonds even at room temperature. MVQ vitrimer shows a “solid-liquid” feature, that is, exhibiting liquid-like behavior at longer obeservation time or when stretched at low strain rate while acting as solid elastomer at high strain rate. Notably, the tensile toughness (@500% strain) can obtain nearly 1.6-fold increase to 47.59 MJ/m3 from 18.58 MJ/m3 when increasing tensile speed, indicating an excellent energy-dissipative behavior especially at high deformation rate. Therefore, our work can provide guidance for molecular design and reactive processing of high-performance vitrimeric silicone elastomers toward industrial applications.

Caution! Static Supercell Calculations of Defect Migration in Higher Symmetry ABX3 Perovskite Halides May Be Unreliable: A Case Study of Methylammonium Lead Iodide.

Activation energies of defect migration in ABX3 perovskite halides are widely obtained through static supercell calculations with the nudged-elastic-band method. Taking methylammonium lead iodide (CH3NH3PbI3, MAPbI3) as an example, we demonstrate that such calculations are unreliable for the higher symmetry structures adopted by the material at temperatures relevant to device operation (tetragonal and cubic MAPbI3) because, in addition to ion relaxation around the point defects, local structural modifications characteristic of the ground-state (orthorhombic) structure occur. In this way, we offer a simple explanation of why calculated activation energies of defect migration in MAPbI3 suffer from surprisingly large scatter. We propose a robust test to determine whether static supercell calculations of point-defect processes in ABX3 perovskite systems are reliable.

Theoretical insights into the hydrogen oxidation reaction on single metal atoms anchored on the edge of MoS2 nanosheets

The application of alkaline fuel cells (AFCs) is seriously limited by the sluggish kinetics of the anodic hydrogen oxidation reaction (HOR), so it is urgent to develop efficient and stable non-noble metal HOR catalysts. In this work, we explored the HOR performance of single 3d metal atoms anchored at the edge of MoS2 nanosheets (MSA-MoS2, MSA = Fe, Co, and Ni) by the density functional theory calculations. The results suggested that the tetra-coordinated MSA and penta-coordinated meta-Mo atoms at the MoS2 edge could form the dual-active sites for the H* and OH* adsorption. The interaction between MSA and MoS2 supports can efficiently optimize the adsorption free energy of H* (ΔGH*) and OH* (ΔGOH*) by tuning the d band center of the activity sites. The calculated activation energy, rate constant, and exchange current density indicate that among the MSA-MoS2 catalysts, NiSA-MoS2 exhibits the highest activity for HOR, which is attributed to the optimal ΔGH* and ΔGOH*. Moreover, the thermodynamic and electrochemical stability of NiSA-MoS2 is confirmed by the strong formation energy and high oxidation potential. Therefore, NiSA-MoS2 can be considered as a promising candidate for HOR at the anode of AFCs.

Insight into kinetic and Thermodynamic Analysis methods for lignocellulosic biomass pyrolysis

Pyrolysis is particularly attractive because it can convert lignocellulosic biomass into bio-oil, gases and solid charcoal in an efficient and environmentally friendly way. Determining the kinetic and thermodynamic parameters is fundamental to elucidate the reaction mechanisms and optimize biomass pyrolysis processes. The applicability and accuracy of kinetic and thermodynamic methods are systematically studied by analyzing theoretically simulated processes which simulate biomass pyrolysis processes and using statistical analyses. In terms of activation energy calculation, the Friedman method is capable of providing accurate activation energies, whereas the KAS and FWO isoconversional methods lead to some systematic errors in the resultant activation energies. The accuracy of the Kissinger method for estimating the frequency factor is dependent on the variation degree of kinetic parameters with conversion. The conventional method for determining thermodynamic parameters is based on the conversion rate peak temperature, which has no theoretical basis. Therefore, the concept of effective thermodynamic parameters is proposed, which are dependent on conversion and heating rate. And the thermodynamic analysis of the simulated processes is comprehensively investigated. Results revealed that the accuracy of the resulting thermodynamic parameters from the conventional method is dependent on the variation degree of kinetic parameters with conversion. It is expected that this study will provide an analysis framework and methodological guideline for the kinetic and thermodynamic analyses of biomass pyrolysis.

High Water-Assisted Proton Conductivities of Two Cadmium(II) Complexes Constructed from Zwitterionic Ligands.

Finding more metal complexes with outstanding water stability and high proton conductivity still has important research significance for the energy field. Herein, two highly proton-conductive complexes, one hydrogen-bonded supramolecular framework (HSF) [Cd(CBIA)2(H2O)4]·2H2O (1) and one coordination polymer (CP), {[Cd2(CBIA)2(4,4'-bipy)2(H2O)2]·(CBIA)·(OH)·2H2O}n (2) (4,4'-bipy = 4,4'-bipyridine), were triumphantly assembled using a zwitterionic organic compound, 2-(1-(carboxymethyl)-1H-benzo[d]imidazol-3-ium-3-yl)acetate (HCBIA). In the structure of HSF 1, there are several coordination and lattice H2O units except for the two monodentate CBIA- anions. CP 2 with a one-dimensional (1D) cylindrical structure has free CBIA- units and free H2O units located in the cavity. Thanks to the ability of the uncoordinated carboxyl groups and coordination/lattice water molecules to construct the rich H-bonding networks, both complexes exhibit super-high proton conductivities, reaching 5.09 × 10-3 and 3.41 × 10-3 S cm-1 under 100 °C/98% relative humidity (RH), respectively. Based on the exploration of crystal structure data, combined with the calculated activation energy, and adsorption/desorption plots of nitrogen and water vapor, the causes and differences in proton conductivity of the two complexes, especially the proton-conductive mechanism, are compared and analyzed. This study again confirms that the zwitterionic ligands can exert important effects on forming organo-inorganic hybrid materials with high proton conductivity.