Density Of Reactive Sites Research Articles

Salt template-assisted polymer tethering strategy to achieve high dispersed cobalt single atoms/clusters on porous carbon catalysts for effective Fenton-like reactions

The exploration of the synthesis of porous carbon-supported metal nanocatalysts with high metal loading and dispersion for the development of heterogenous catalysts is important. However, this remains a challenging subject. In this paper, a salt template-assisted polymer tethering strategy was proposed to prepare Co single atom and ultrafine cluster anchored on porous carbon (Co-NPC) with a high-loading of 16.9wt%, thereby exposing high density of reaction sites. The obtained Co-NPC catalyst exhibited excellent catalytic performance for almost 100% degradation of bisphenol A (BPA) within 20min, which is much faster than the CoSA-NPC catalyst with only single atom sites and Co-NC without salt template added. Radical quenching experiments and electron paramagnetic resonance tests verified that both the nonradical oxidation pathway by 1O2, the electron transfer and radical oxidation pathway by •OH, SO4•- appeared during the degradation process. After 3 cycles, the removal rate of BPA did not decrease significantly. The fixed bed experiment revealed that Co-NPC could realize the continuous degradation of methylene blue (MB) with almost 100% degradation efficiency. This research indicated that the strategy by pyrolyzing metal coordinated polymer is a potential method for the synthesis of high metal loading catalyst at gram scale, meeting the requirement of practical applications.

A novel naturally aspirated cathode for efficient electrosynthesis of hydrogen peroxide and wastewater purification in electro-Fenton systems

Electrochemical synthesis of hydrogen peroxide (H2O2) has developed rapidly in recent years as an alternative process to the anthraquinone method. However, the low H2O2 production and high energy consumption limit its further application. In this study, we propose a simple method to fabricate a naturally aspirated cathode (NAC), which significantly reduces the mass transfer resistance of oxygen and achieves a high oxygen diffusion coefficient (7.11 × 10-6 m2 s−1) and oxygen utilization efficiency (39.6 %). Additionally, the NAC provides a high density of reaction sites to achieve efficient production of H2O2 (0–84.33 mg h−1 cm−2) at near industrial current densities (0–240 mA cm−2) without external aeration. Meanwhile, the prepared NAC can degrade over 97.5 % of dyes within 10 min during the electro-Fenton process. The NAC exhibits excellent H2O2 production performance and great stability during long-term operation, which offers huge potential for industrial-scale electrochemical H2O2 production and the advanced oxidation processes (AOP) derived from it.

Mechanisms controlling albite dissolution/precipitation kinetics as a function of chemical affinity: New insights from experiments in 29Si spiked solutions at 150 and 180 °C

Knowledge of the rates of dissolution of rock-forming minerals close to equilibrium and their dependence on ΔGr, the Gibbs free energy of reaction, is essential for describing the temporal and spatial evolution of many environmental and engineering processes involving solid/fluid interactions. In the present study we used the isotope-doping method to quantify albite forward and net dissolution rates. Batch experiments were performed at 150, 180 °C and pH = 9 at near equilibrium and equilibrium conditions (-25 ≤ ΔGr ≤ + 8.2 kJ/mol) in 29Si spiked solutions which were undersaturated with the secondary Al-Si solid phases likely to precipitate.The forward dissolution rates normalized to the initial BET surface area were found to decrease continuously and monotonically with increasing time and ΔGr, achieving values 1.3 to 2.4 orders of magnitude lower at chemical equilibrium than initial far from equilibrium values, with the highest rate decrease for the highest solid to fluid ratio. These rate drops were accompanied by an increase in BET specific surface areas associated with the formation of widespread dissolution features. A decrease of albite forward dissolution rate together with an increase of its BET surface area was also observed as a function of reaction time at far from equilibrium conditions (ΔGr ≤ − 65 kJ/mol). These observations are consistent with a continuous decrease with time and increasing ΔGr of albite effective surface area linked to the formation of unreactive negative crystal facets, in addition to etch pits stopping nucleating above a critical value of ΔGr. Thus, the observed decrease in albite dissolution rate as equilibrium is approached is not linked primarily to the increase in the contribution of the backward reaction but rather to the decrease of the forward reaction rate in conjunction with the decrease in the density of reactive sites at the mineral surface.The results of this study show that the characterization of the effective surface area and its evolution with reaction time and chemical affinity is crucial to deriving robust dissolution rates of well-crystallized minerals like feldspars. Dissolution experiments in 29Si spiked solutions of samples with different history and well-characterized effective surface area and surface morphology should help to better quantify the rate laws controlling silicate minerals weathering.

Effect of heterogenous dopant and high temperature pulse excitation on ozone sensing behavior of In2O3 nanostructures and an image recognition method coupled to ozone sensing array

Ground-level ozone (O3) is a primary air pollutant with potential adverse impacts on human health and ecosystems. Aiming to detect O3 concentration and develop efficient O3 sensing materials, sensing behavior of heterogenous cation (Fe3+, Sn4+ and Sb5+) doped In2O3 nanostructures was investigated. The incorporation of these cations modulated the electronic structure of semiconductor oxides, affecting the density of chemisorbed oxygen species and reactive sites. From O3 sensing results, Fe3+ doped In2O3 based sensors featuring saturated resistance curves in O3 gas, demonstrated fast sensing speed and qualified detection threshold (20 ppb). In contrast, Sn4+ and Sb5+ doped counterparts exhibited non-saturated sensing curves, resulting in slower response/recovery speed. As a proof-of-concept, these optimized sensors were integrated as the sensor array. Coupled to the image recognition technique, this sensor array could successfully discriminate O3 and NOx. That is, through the tailored combination of material modulation and sensor array, this study paves a novel approach for highly sensitive and selective O3 detection.

Regulating the reactive site density of two-dimensional N self-doped carbon for boosted Fenton-like catalytic ability

The mediocre catalytic ability of metal-free carbon-based catalysts limits its practical application in wastewater treatment. Herein, a facile “steam-etching” method is utilized to boost the catalytic ability of N self-doped carbon (NSDC) catalysts. Compared to the original NSDC catalyst (NSDC-N2), the NSDC-H2O-50 catalyst modified with the water vapor content of 50 % exhibits much better catalytic performance. The pseudo-first-order kinetic rate constant k of NSDC-H2O-50 is 4.88 times that of NSDC-N2. The presence of water vapor can cause a massive vacancy-like defects in the carbon structure, which is conducive to form more edge reactive groups. Pyrrolic N and CN groups are proved to be the reactive sites for the catalytic reaction. Reactive site density can be easily adjusted by changing the water vapor content. The prepared NSDC-H2O catalysts can effectively activate peroxydisulfate (PDS) to degrade various organic pollutants with high efficiency in the pH range of 2.02–10.28. In addition, the NSDC-H2O/PDS system exhibits strong anti-interference ability to common anions and humic acid. The catalytic ability has not been affected in actual water sources. By a simple calcination treatment, most of the catalytic ability can be restored. Therefore, the prepared NSDC-H2O catalysts show strong application potential in organic wastewater treatment. Furthermore, singlet oxygen is proved to be the main active species in the NSDC-H2O/PDS system, and sulfate radical and superoxide radical play an auxiliary role.

Porous block polymer composite membranes for uranium uptake

Adsorptive membranes are an effective solution to capture uranium from seawater and contaminated water supplies. Current fibrous membrane-based sorbents suffer from a low density of binding ligands at the solid–liquid interface and broad pore size distributions. These issues lead to problems such as low binding capacity and gradual breakthrough curves during flow-through adsorption. We sought to address these challenges by developing highly permeable (i.e., ∼3.5×104 L m−2 h−1 bar−1) amidoxime-functionalized polysulfone(Psf)/polystyrene-b-poly(acrylic acid) (PS-PAA) composite membranes. A surface-segregation and vapor-induced phase separation (SVIPS) method was used to fabricate membranes that have an interconnected pore structure with PAA-lined pore walls. The PAA brushes offer a high density of reactive carboxyl sites that enable the surface chemistry to be modified with nitrile groups and then converted to amidoxime (AO) ligands for high-capacity uranium adsorption. The functionalized Psf/PS-PAO membrane removes uranium from dilute solution with a capacity of 150 mg g−1. Flow-through experiments demonstrate rapid mass transfer of the membranes, which adsorb over 90% of the uranyl ions from flowing solutions at feed concentrations of 0.1 and 1.0 mg L−1. Batch sorption–desorption experiments also indicate reusability of membranes over several cycles. Therefore, this membrane-based sorbents offers a chemically tailored platform for high-efficient uranium capture under trace concentrations.

Armoring of MgO by a Passivation Layer Impedes Direct Air Capture of CO2.

It has been proposed to use magnesium oxide (MgO) to separate carbon dioxide directly from the atmosphere at the gigaton level. We show experimental results on MgO single crystals reacting with the atmosphere for longer (decades) and shorter (days to months) periods with the goal of gauging reaction rates. Here, we find a substantial slowdown of an initially fast reaction as a result of mineral armoring by reaction products (surface passivation). In short-term experiments, we observe fast hydroxylation, carbonation, and formation of amorphous hydrated magnesium carbonate at early stages, leading to the formation of crystalline hydrated Mg carbonates. The preferential location of Mg carbonates along the atomic steps on the crystal surface of MgO indicates the importance of the reactive site density for carbonation kinetics. The analysis of 27-year-old single-crystal MgO samples demonstrates that the thickness of the reacted layer is limited to ∼1.5 μm on average, which is thinner than expected and indicates surface passivation. Thus, if MgO is to be employed for direct air capture of CO2, surface passivation must be circumvented.

Oxidation kinetics and non-Marcusian charge transfer in dimensionally confined semiconductors

Electrochemical reactions represent essential processes in fundamental chemistry that foster a wide range of applications. Although most electrochemical reactions in bulk substances can be well described by the classical Marcus-Gerischer charge transfer theory, the realistic reaction character and mechanism in dimensionally confined systems remain unknown. Here, we report the multiparametric survey on the kinetics of lateral photooxidation in structurally identical WS2 and MoS2 monolayers, where electrochemical oxidation occurs at the atomically thin monolayer edges. The oxidation rate is correlated quantitatively with various crystallographic and environmental parameters, including the density of reactive sites, humidity, temperature, and illumination fluence. In particular, we observe distinctive reaction barriers of 1.4 and 0.9 eV for the two structurally identical semiconductors and uncover an unusual non-Marcusian charge transfer mechanism in these dimensionally confined monolayers due to the limit in reactant supplies. A scenario of band bending is proposed to explain the discrepancy in reaction barriers. These results add important knowledge into the fundamental electrochemical reaction theory in low-dimensional systems.

Towards building a unified adsorption model for goethite based on direct measurements of crystal face compositions: I. Acidity behavior and As(V) adsorption

We have determined the proton, electrolyte (NaNO3) and arsenate affinity constants on the corresponding surface sites of goethite. An empirical optimization approach was applied using the Charge Distribution Multisite Complexation (CD-MUSIC) model, initially, by simulating an extensive proton adsorption data set obtained from four goethites of specific surface areas (SSAs) spanning from 43 to 89 m2/g. Each goethite showed different crystal face compositions, which were measured previously from independent high resolution electron microscopy observations. Only the capacitance value was left as an additional optimizing parameter. For arsenate adsorption, with the above optimized values fixed, the contributing surface arsenate complexes and their respective affinity constants and charge distributions (CD) were also optimized. A unified set of affinity and CD parameters was obtained, where the only resulting variables among goethites were the capacitance 1, the specific surface area and the crystal face contributions (and thus their reactive surface site densities).It was found that the site density parameter is decisive when data show adsorption maxima, such as in the arsenate adsorption isotherms. The self-consistent modeling approach yielded pKa values of singly-coordinated sites of 8.82, and of triply-coordinated sites of 9.65. Three surface arsenate complexes bound only to singly-coordinated sites were found to describe all experimental data, although only two of them were predominant across the pH and As(V) concentration ranges investigated: a bidentate non protonated (BD) complex, and a protonated monodentate (HMD) one. Charge distribution of surface arsenate complexes was found to significantly influence the optimizations, but increased values of optimized capacitance 1 were found to compensate for previously underestimated surface site density values, to yield almost identical surface affinity and CD parameters.Finally, correlations found between surface site density and capacitance-1 parameters with SSA expanded the applicability of the modeling approach presented, to other goethites with different SSAs than the ones investigated here.

Origin and significance of ultra-slow calcite dissolution rates in deep sea sediments

Prediction of mineral-fluid reaction rates in geologic materials is subject to large uncertainties even though the rates are critical for many applications, from studies of past climate change to the engineering of carbon removal and storage. Deep sea carbonate sediments, which have been extensively cored and characterized at dozens of sites by ocean drilling programs, provide unique opportunities to examine how minerals and fluids react over multi-million-year timescales in natural conditions at low temperature. It has already been established that the calcite-fluid reaction in these systems is extremely slow, but the explanation for the ultra-slow rates, and the fact that non-zero rates persist for tens of millions of years, remains elusive. We extend the analysis of pore fluid Sr and Ca concentration data in the literature from ocean drilling archives to 21 drill sites in sediment sections where the fraction of carbonate is larger than 80% to systematically estimate the rates at which calcite dissolves and precipitates as a function of depth and sediment age. Pore fluid Sr/Ca used in this study, and Sr and Ca isotopes in other published analyses, provide estimates of the gross calcite dissolution rates, which are mostly balanced by secondary calcite precipitation. Pore fluid Ca concentration data provide key, previously underappreciated, information on the net calcite dissolution rates. Using these data we evaluate simple models for calcite reaction kinetics and pore fluid sediment evolution and conclude that (1) reaction rates are extremely slow because the reactive site density of the bulk sediment decreases continuously and systematically approximately as age−1, and (2) reaction persists to hundreds of meters burial depth and tens of millions of years because pore fluids never become closed due to diffusive communication with the oceans, and hence remain slightly undersaturated with respect to calcite. The systematic decrease in bulk reactive site density begins immediately upon deposition, greatly slowing the rate of dissolution and hence affecting models of calcite dissolution on the seafloor. The failure to reach equilibrium after millions of years and hundreds of meters of burial, is a consequence of extremely slow net reaction rates that cannot drive the pore fluids to equilibrium against the diffusive loss of Ca and DIC to the ocean. The existence of two or more calcite phases of different solubility is a likely source of a long-lived, but small, driving force for reaction, but its effect decreases with continued recrystallization and pore fluid evolution.

Sulfate-Decorated Amorphous–Crystalline Cobalt-Iron Oxide Nanosheets to Enhance O–O Coupling in the Oxygen Evolution Reaction

The electrochemical oxygen evolution reaction (OER) plays a fundamental role in several energy technologies, which performance and cost-effectiveness are in large part related to the used OER electrocatalyst. Herein, we detail the synthesis of cobalt-iron oxide nanosheets containing controlled amounts of well-anchored SO42- anionic groups (CoFexOy-SO4). We use a cobalt-based zeolitic imidazolate framework (ZIF-67) as the structural template and a cobalt source and Mohr's salt ((NH4)2Fe(SO4)2·6H2O) as the source of iron and sulfate. When combining the ZIF-67 with ammonium iron sulfate, the protons produced by the ammonium ion hydrolysis (NH4+ + H2O = NH3·H2O + H+) etch the ZIF-67, dissociating its polyhedron structure, and form porous assemblies of two-dimensional nanostructures through a diffusion-controlled process. At the same time, iron ions partially replace cobalt within the structure, and SO42- ions are anchored on the material surface by exchange with organic ligands. As a result, ultrathin CoFexOy-SO4 nanosheets are obtained. The proposed synthetic procedure enables controlling the amount of Fe and SO4 ions and analyzing the effect of each element on the electrocatalytic activity. The optimized CoFexOy-SO4 material displays outstanding OER activity with a 10 mA cm-2 overpotential of 268 mV, a Tafel slope of 46.5 mV dec-1, and excellent stability during 62 h. This excellent performance is correlated to the material's structural and chemical parameters. The assembled nanosheet structure is characterized by a large electrochemically active surface area, a high density of reaction sites, and fast electron transportation. Meanwhile, the introduction of iron increases the electrical conductivity of the catalysts and provides fast reaction sites with optimum bond energy and spin state for the adsorption of OER intermediates. The presence of sulfate ions at the catalyst surface modifies the electronic energy level of active sites, regulates the adsorption of intermediates to reduce the OER overpotential, and promotes the surface charge transfer, which accelerates the formation of oxygenated intermediates. Overall, the present work details the synthesis of a high-efficiency OER electrocatalyst and demonstrates the introduction of nonmetallic anionic groups as an excellent strategy to promote electrocatalytic activity in energy conversion technologies.

N-doped carbon dots modified Bi2MoO6 microspheres as anode materials for high performance aqueous rechargeable nickel//bismuth batteries

Aqueous rechargeable batteries, as one kind of new energy storage and conversion systems, have gradually drawn researchers’ concern. Herein, N-doped carbon dots (N-CDs) are used as conductive agents to prepare multidimensional Bi2MoO6@N-CDs anode materials. The synergistic effect between three-dimensional (3D) flowering spherical Bi2MoO6 and zero-dimensional (0D) carbon dots derived carbon depends on the spatial and compositional diversity. The anode performs excellent electrochemical properties owing to the introduction of N-CDs offering high density of reaction sites and quick charge transfer process. Similar to Bi2MoO6@N-CDs, N‑CDs modified Co0.5Ni0.5MoO4 was prepared as cathode materials, manifesting excellent specific capacity. A novel aqueous rechargeable nickel//bismuth battery with above materials delivers the energy density of 50.85 Wh/kg along with power density of 344.27 W/kg at 0.5 A/g. The present research would broaden the path for effectively structuring of electrode active materials for aqueous rechargeable Ni//Bi batteries.

Sequential Infiltration Synthesis of Al2O3 in Biodegradable Polybutylene Succinate: Characterization of the Infiltration Mechanism.

The introduction of inorganic materials into biopolymers has been envisioned as a viable option to modify the optical and structural properties of these polymers and promote their exploitation in different application fields. In this work, the growth of Al2O3 in freestanding ∼30-μm-thick poly(butylene succinate) (PBS) films by sequential infiltration (SIS) at 70 °C via trimethylaluminum (TMA) and H2O precursors was investigated for the first time. The incorporation of Al2O3 into the PBS matrix was clearly demonstrated by XPS analysis and SEM-EDX cross-sectional images showing a homogeneous Al2O3 distribution inside the PBS films. Raman measurements on infiltrated freestanding PBS show a reduction of the signal related to the ester carbonyl group as compared to pristine freestanding PBS films. Accordingly, FTIR and NMR characterization highlighted that the ester group is involved in polymer–precursor interaction, leading to the formation of an aliphatic group and the concomitant rupture of the main polymeric chain. Al2O3 mass uptake as a function of the number of SIS cycles was studied by infiltration in thin PBS films spin-coated on Si substrates ranging from 30 to 70 nm. Mass uptake in the PBS films was found to be much higher than in standard poly(methyl methacrylate) (PMMA) films, under the same process conditions. Considering that the density of reactive sites in the two polymers is roughly the same, the observed difference in Al2O3 mass uptake is explained based on the different free volume of these polymers and the specific reaction mechanism proposed for PBS. These results assessed the possibility to use SIS as a tool for the growth of metal oxides into biopolymers, paving the way to the synthesis of organic–inorganic hybrid materials with tailored characteristics.

Pt-SDC alloy anode for methanol fueled low temperature solid oxide fuel cell

Direct methanol-fueled low-temperature solid oxide fuel cells (DM LT-SOFCs) operating temperature ≤ 500 ℃ are promising candidates as portable power sources owing to the high energy density and portability of methanol. Herein, we have systematically studied the Pt-samaria-doped ceria (SDC) cermet alloy anodes with varying Pt: SDC ratios to achieve high methanol oxidation reaction activity (MOR) and resistance to CO poisoning. It is observed that the optimal composition of the Pt-SDC alloy anode is Pt0.83SDC0.17, which exhibited lower activation resistance by 63 %, better tolerance to CO poisoning by 44 %, and higher thermal stability than that of pure Pt upon direct methanol operation at 450 ℃. Such improvements were ascribed to high Pt-SDC interfacial density of reaction sites with less CO poisoning due to oxygen spill over from SDC, while thermally stable SDC also helped preserve the morphology of the Pt anode at elevated temperatures.

A novel method for the quantitative morphometric characterization of soluble salts on volcanic ash

Formation of soluble sulfate and halide salts on volcanic ash particles via syn-eruptive interactions between ash surfaces and magmatic gases is a ubiquitous phenomenon in explosive eruptions. Surficial salts may be rapidly mobilized into their depositional environment undermining the quality of drinking water, harming aquatic life, and damaging soil and vegetation. Assessment of the potential for salt formation on ash and related environmental impacts have been based almost exclusively on bulk mineralogical or chemical analyses of ash; similarly, quantification of surficial salts has been made via leachate analysis only. However, it is the ash surface state and salt crystal properties that exert the predominant control on its reactivity, thus in determining their immediate environmental impact. Here, using scanning electron microscope (SEM) images, we present a novel image analysis protocol for the quantitative characterization of surficial salts, together with chemical analyses of resulting leachates. As volcanic ash proxies, we used synthetic rhyolitic glass particles (with systematic variations in FeOT and CaO content) and a crushed obsidian. Using an ash-gas reactor, we artificially surface-loaded samples with CaSO4 and NaCl crystals, the most common crystal phases found on volcanic ash surfaces. Analogous variations were found using both methods: for CaSO4 crystals, higher temperature treatments or increasing FeOT content at the same temperature led to higher concentrations of salt leachate and higher salt volumes; unexpectedly, increasing the CaO content caused only a minor increase in salt formation. In addition to bulk salt formation, morphometric results provided insight into formation processes, nucleation and growth rates, and limiting factors for salt formation. Higher temperatures increased CaSO4 crystal size and surface coverage which we infer to result from higher element mobility in the glasses driving crystal growth. Increasing FeOT content of the glasses yielded increased salt surface coverage and leachate concentrations, but decreased crystal size (i.e., the salt number density increased). This latter effect likely relates to the role of iron as an electron-donor to charge balance salt-forming cation migration to the ash surface, indicating the importance of iron in determining surface reaction site density and, consequently, environmental reactivity. The controlling roles of ash composition and temperature on salt formation observed here can improve estimations for surface salt formation, volatile scavenging, and environmental impact for eruptions producing glass-rich ash. Our characterization protocol can therefore become a useful tool for the investigation of solid–gas reactions for terrestrial and planetary processes, and it also appears to be a powerful complement to research into atmospheric processes mediated by ash surfaces, such as ash aggregation and nucleation of water or ice on ash.

New insights into the exploitation of oxidized carbon nitrides as heterogeneous base catalysts

In this work, the development of a novel efficient heterogeneous catalytic system capable of driving Knoevenagel condensation reactions between benzaldehydes and malononitrile was reported. Specifically, we explored a post-synthetic modification of graphitic carbon nitride (g-CN) through a strong oxidation treatment by acid mixture (HNO3/H2SO4). The as-prepared oxidized CN material (CNO) shows a large number of surface acidic moieties, that can be easily deprotonated through an aqueous alkaline wash with different bases (NaOH, K2CO3, t-BuOK), to introduce a high density of reactive basic sites. The best catalyst is obtained with NaOH as the base (CNO-NaOH), and displays high reactivity and good tolerance towards functional group variations of the reagents, thus emerging as a potential new recyclable carbon nitride-based structure for organic base catalysis.

Heterogeneous Sorption of Radionuclides Predicted by Crystal Surface Nanoroughness.

Reactive transport modeling (RTM) is an essential tool for the prediction of contaminants' behavior in the bio- and geosphere. However, RTM of sorption reactions is constrained by the reactive surface site assessment. The reactive site density variability of the crystal surface nanotopography provides an "energetic landscape", responsible for heterogeneous sorption efficiency, not covered in current RTM approaches. Here, we study the spatially heterogeneous sorption behavior of Eu(III), as an analogue to trivalent actinides, on a polycrystalline nanotopographic calcite surface and quantify the sorption efficiency as a function of surface nanoroughness. Based on experimental data from micro-focus time-resolved laser-induced luminescence spectroscopy (μTRLFS), vertical scanning interferometry, and electron back-scattering diffraction (EBSD), we parameterize a surface complexation model (SCM) using surface nanotopography data. The validation of the quantitatively predicted spatial sorption heterogeneity suggests that retention reactions can be considerably influenced by nanotopographic surface features. Our study presents a way to implement heterogeneous surface reactivity into a SCM for enhanced prediction of radionuclide retention.

Plasmon-Driven Interfacial Catalytic Reactions in Plasmonic MOF Nanoparticles.

Benefiting from the noble metal nanoparticle core and organic porous nanoshell, plasmonic metal-organic frameworks (MOFs) become a nanostructure with great enhancement of the electromagnetic field and a high density of reaction sites, which has fantastic optical properties in surface plasmon-related fields. In this work, the plasmon-driven interfacial catalytic reactions involving p-aminothiophenol to 4,4'-dimercaptoazobenzene (trans-DMAB) in both the liquid and gaseous phases are studied in plasmonic MOF nanoparticles, which consist of a Ag nanoparticle core and an organic shell (ZIF-8). The surface-enhanced Raman spectroscopy (SERS) spectra recorded at the plasmonic MOF in an aqueous environment demonstrate that the reversible plasmon-driven interfacial catalytic reactions could be modulated by a reductant (NaBH4) or oxidant (H2O2). Also, the situ SERS spectra also point out that plasmonic MOF (AgNP@ZIF-8) nanoparticles exhibit much better catalytic performance in the H2O2 solution compared to pure Ag nanoparticles for the anti-oxidation caused by the MOF shell. It is surprising that although there is greater SERS enhancement obtained at pure Ag nanoparticles, the plasmon-driven interfacial catalytic reactions only occur at plasmonic AgNP@ZIF-8 nanoparticles in the gaseous phase. This interesting phenomenon is further confirmed and analyzed by simulated electromagnetic field distributions, which could be understood by the effective capture of gaseous molecules by the organic porous nanoshell. Our work not only explores the plasmonic MOF nanoparticles with unique optical properties but also strengthens the understanding of plasmon-driven interfacial catalytic reactions.

Quantifying the Effect of Temperature and Humidity on Infiltrated Cell Performance Using Electrochemical Impedance Spectroscopy and Distribution of Relaxation Times Analysis

Infiltrating nanoparticle electrocatalysts into solid oxide fuel cells (SOFCs) has been shown to improve their intermediate-temperature performance by increasing the density of reaction sites, known as triple phase boundaries (TPBs), in the electrode. By increasing TPB density with infiltration, anode activation polarization is mitigated and cell performance improves relative to an uninfiltrated cell, especially at low temperatures. In this study, electrochemical impedance spectroscopy and distribution of relaxation times analyses were performed on baseline and Ni-infiltrated NiYSZ anode symmetric cells. A transmission line model (TLM) was used to deconvolute the electrode processes. The effects of temperature and humidity on TLM parameters, and the relative polarization contributions of various charge transfer processes will be discussed.

Quantitative Analysis of Solid-State Energy Devices Via 3D Reconstruction Using a FIB/SEM Dual Beam System

To lower the carbon emission from the rising consumption of fossil fuels, electrochemical devices such as fuel cells and batteries, which can produce or store electricity from renewable resources, are attracting attention. Both systems require an electronically insulating solid membrane, which separates the cathode and anode to prevent short-circuiting. To improve the performance of porous electrodes, researchers have focused on tuning the electrode microstructure. The addition of highly ionic conducting materials to the electrode is commonly used to maximize the reaction site density. However, microstructural features, such as particle size distribution, electrochemically active site density and connectivity of each phase, are difficult to quantify only using conventionally used characterization methods such as scanning electron microscopy (SEM).One well-established method for obtaining three-dimensionally interconnected microstructural information is serial sectioning using a FIB/SEM dual beam system. Using this technique, more reliable and accurate quantification of the SOFC and ASSLIB electrodes microstructure are available. Also, the quantified features will be reflected in the responses of electrochemical impedance spectroscopy (EIS) measurements. These results can provide a link between them. Therefore, the aim of this study is to three-dimensionally reconstruct the microstructure of solid-state energy devices via FIB/SEM dual beam system and to quantify their microstructural features. Also, these results will be combined with the electrochemically analyzed properties to further understanding their relationship with microstructural properties.