Surface Kinetics Research Articles

Tailoring Carrier Dynamics of BiVO4 Photoanode via Dual Incorporation of Au and Co(OH)x Cooperative Modification for Photoelectrochemical Water Splitting

AbstractPhotoelectrochemical solar to hydrogen production is a promising way to achieve carbon neutrality, but severe charge recombination in photoanodes limits the conversion efficiency. Herein, Au nanoparticles and Co(OH)x co‐sensitized bismuth vanadate (BiVO4) to construct AuCo(OH)x/BiVO4 photoanode for significantly enhancing the performance of photoelectrochemical water splitting. This process significantly improves the bulk charge carrier separation efficiency, the surface kinetics of water oxidation, and the electron density of BiVO4 photoanode through Au surface plasmon resonance (SPR) and Co(OH)x oxygen evolution catalysts effect. Additionally, the enhancement of the *O and the *OOH generation accelerate the oxygen evolution reaction kinetics. Consequently, the constructed AuCo(OH)x/BiVO4 photoanode demonstrates an excellent photocurrent of 6.2 mA cm−2 at 1.23 V versus reversible hydrogen electrode and a stable continuous output within 42 h. This work contributes to developing high‐efficiency and high‐stability photoanodes for solar H2 production through SPR effect and oxygen evolution catalysts.

Crystal violet removal from waste water by sulfonated poly (glycidyl methacrylate) nano-adsorbent: optimization by response surface methodology, isotherms, kinetics, and thermodynamics studies

Crystal violet removal from waste water by sulfonated poly (glycidyl methacrylate) nano-adsorbent: optimization by response surface methodology, isotherms, kinetics, and thermodynamics studies

Effect of As4 beam equivalent pressure on the growth dynamics of InAs films grown at low temperature on graphene layers

The present study investigates the growth of InAs films at low temperature on graphene synthesized via molecular beam epitaxy, emphasizing the effect of As4 beam equivalent pressure (5.0 × 10⁻6 Torr (low) and 4.5 × 10⁻⁵ (high)) on the growth dynamics. X-ray diffraction, scanning electron microscopy, and atomic force microscopy, along with correlation functions, revealed that monitoring the As4 beam equivalent pressure affects the structural properties of polycrystalline InAs films grown on the graphene/Si layer. The film thickness (particle size) was found to be 172 ± 10 nm and 216 ± 10 nm (40 ± 2 nm and 42 ± 2 nm) for the InAs layers grown at low and high As4 beam equivalent pressure. The increase in the film thickness and particle size with increasing the As4 beam equivalent pressure is attributed to improved material availability and surface kinetics due to the large migration energy of As compared to In and hence the larger diffusion length of In. Conversely, decreasing As4 beam equivalent pressure raises the roughness scaling exponent and enlarges interface width (0.17 µm and 0.31 µm for films grown at high and low As4 beam equivalent pressure) and lateral correlation length, implying smoother surfaces due to larger particles. These insights are pivotal for fabricating advanced semiconductors, underscoring As4 beam equivalent pressure's role in optimizing InAs films for electronic and optoelectronic applications.

A Zwitterionic Hydrogel-Based Heterogeneous Fenton Catalyst for Water Treatment.

Persistent organic pollutants (POPs), including xenoestrogens and polyfluoroalkyl substances (PFAS), demand urgent global intervention. Fenton oxidation, catalyzed by iron ions, offers a cost-effective means to degrade POPs. However, numerous challenges like acid dependency, catalyst loss, and toxic waste generation hinder practical application. Efforts to create long-lasting heterogeneous Fenton catalysts, capable of simultaneously eliminating acid requirements, sustaining rapid kinetics, and retaining iron efficiently, have been unsuccessful. This study introduces an innovative heterogeneous zwitterionic hydrogel-based Fenton catalyst, surmounting these challenges in a cost-effective and scalable manner. The hydrogel, hosting individually complexed iron ions in a porous scaffold, exhibits substantial effective surface area and kinetics akin to homogeneous Fenton reactions. Complexed ions within the hydrogel can initiate Fenton degradation at neutral pH, eliminating acid additions. Simultaneously, the zwitterionic hydrogel scaffold, chosen for its resistance to Fenton oxidation, forms strong bonds with iron ions, enabling prolonged reuse. Diverging from existing designs, the catalyst proves compatible with UV-Fenton processes and achieves rapid self-regeneration during operation, offering a promising solution for the efficient and scalable degradation of POPs. The study underscores the efficacy of the approach by demonstrating the swift degradation of three significant contaminants-xenoestrogens, pesticides, and PFAS-across multiple cycles at traceconcentrations.

Nanoparticulated Vanadium Oxide on BiVO4 for Boosting Photoelectrochemical Glycerol Oxidation

Hydrogen (H2) has been spotlighted as ideal energy carrier due to its relatively higher energy density compared to fossil fuel and no carbon emissions during the energy generation. However, most of current produced H2 comes from as byproducts in fossil fuel reforming processes. To reduce dependence on fossil fuel in the H2 production process, photoelectrochemical (PEC) water splitting is considered as promising strategy for producing H2 using sustainable resources. Nevertheless, the insufficient efficiency in PEC water oxidation oxygen evolution reaction (OER) has limited overall PEC water splitting system efficiency due to its relatively high oxidation potential and sluggish catalytic kinetics. Furthermore, the low value of generated oxygen has been pointed out as obstacle from an economic perspective. To overcome these challenges, glycerol, byproduct of biodiesel, has been attracted numerous attentions as PEC oxidation resource since it has three hydroxyl groups and relatively lower oxidation potential than OER. Furthermore, glycerol oxygenated value-added products like dihydroxyacetone (DHA) can improve economics of PEC hydrogen production system. Upon these strengths, PEC glycerol oxidation reaction (GOR) provides improved strategy that generates value-added products in anodic part and green energy source (H2) in cathodic part simultaneously, which can replace PEC water splitting. Bismuth vanadate (BiVO4) is one of the most promising transition metal oxide based catalyst for PEC GOR due to its relatively narrow bandgap, high theoretical photocurrent density and deep positive valence band maximum (VBM) position. Additionally, although the surface kinetics of BiVO4 for OER has been sluggish, it potentially would be advantage for GOR with high production rate. However, the relatively instability of BiVO4 in acidic electrolyte during operation and lower selectivity of oxygenated products has hindered their practical application in PEC GOR. To solve these problems, introduction of nanoparticles as cocatalysts has been much studied for ameliorating surface kinetics and passivation the surface of photoanode. However, the interface between nanoparticles and photoanode with poor chemical interaction can induce the higher interfacial resistance and slow charge transfer efficiency rather. In this study, we present in-situ vanadium oxide (VOx) nanoparticle decoration on the surface of BiVO4 (VOx/BiVO4) via selective etching process using alkaline treatment for enhancing PEC GOR and we report the world best photocurrent density based on BiVO4 photoanode for GOR with high selective DHA production. VOx nanoparticles with an average size of 5 nm by selective etching process using alkaline treatment is decorated on the surface of BiVO4. The VOx promotes the surface reaction kinetics via modulating the fermi level and enhanced photovoltage of BiVO4 and improves long-term stability for GOR by compensation of V5+ and Bi3+, which combines both efficiency and stability. Furthermore, the surface decorated photoanode presents a 6.82 mA/cm2 (1.34-fold improvement) photocurrent density at 1.23 V versus the reversible hydrogen electrode (RHE) under 1 sun illumination, which has been attributed enhanced catalytic kinetics with upshifted fermi level and photovoltage of BiVO4. Moreover, the long-term stability of VOx/BiVO4 has been exhibited over 10 hours and the high selectivity for DHA is achieved. This study presents insight into the role vanadium of selective etched VOx on the surface of BiVO4 with low valence state than that of BiVO4 and improving the potential of BiVO4 based catalyst as GOR photoanode for high selective value-added DHA production using solar energy.

High-Quality Ge-Rich Nanosheets on Silicon on Insulator Substrates Based on Ultra-Low Temperature Epitaxy

Ge and Ge-rich SiGe channel materials are expected to enhance performance in next-generation electronic devices, such as e.g. reconfigurable field effect transistors [1]. However, an inherent lattice mismatch exists between Ge and Si of about 4%. Ge layers on Si grow under compressive in-plane strain, drastically limiting the thickness of high-quality Ge layers on Si to a few monolayers, i.e., far too thin for practical device applications.In principle, vertically grown nanowires grown by vapor-liquid-solid growth (VLS) can be used to overcome these limitations as their small footprint can mitigate the strain. That is why, to date, basically all Ge-rich nanoelectronics device concepts are based on VLS nanowires.However, for device fabrication, the nanowires grown on untypical (111) substrates need to be picked and placed onto Si(001) substrates, which is a serial process and, thus, barely scalable.Thus, whenever two-dimensional nanosheets of a material are available, they provide distinct advantages with respect to device integration. In this context, pure Ge and SiGe alloyed nanowires formed from through top-down lithography from nanosheets would enable extended device functionalities.The problem is that for high Ge contents, the achievable thickness of pseudomorphic, defect-free (Si)Ge epilayers is just a couple of monolayers if grown directly on Si(001) substrates [2] as the inherent strain between the layer and substrate leads to harmful plastic or elastic relaxation under common growth conditions. Thus, using conventional epitaxy, the attainable defect-free SiGe/Si layer thicknesses are typically far from usable in electronic transport devices.Therefore, we depart from established (Si)Ge epitaxy temperatures of ≥500°C and employ molecular beam epitaxy (MBE) growth at ultra-low temperatures (ULT), ranging from 100°C to 350°C.[3] We show that the lowered surface kinetics leads to a pronounced layer supersaturation, allowing us to access layer thicknesses that are more than an order of magnitude larger than previously reported values. We highlight that pristine growth pressures deep in the ultra-high vacuum range ( ≤10-10 mbar) are crucial to keep the density of unwanted impurities in the (Si)Ge layers to a minimum and, thus, enable excellent electrical and optical properties of the grown heterostructures. These low growth pressures are particularly important in ULT growth since the low thermal budget impedes the efficient desorption of residual gas molecules from the substrate.We show that such fully strained, defect-free (Si)Ge epilayers grown directly on SOI substrates form high-quality nanosheets [4] for which properties like thickness, SiGe(Sn) content, and barrier material, doping can be conveniently tuned during the epitaxy process beyond past limitations. These nanosheets are the highly scalable base for advanced transport devices, such as reconfigurable transistors with excellent performance characteristics [4,5,6].

(Invited) Boosted Photoelectrochemical Water Splitting Performance by Plasmonic Assisted Ternary Heterostructures

Traditional semiconducting metal oxide-based photoelectrodes have been extensively explored for energy and environmental applications. However, their performance is hindered by poor light absorption, high charge recombination rates, and low surface kinetics. Some of the recent results will be presented to discuss the rational design of ternary materials systems, which incorporating of metal-organic framework and plasmonic structures into semiconducting metal oxides, as one of the most promising strategies to achieve performances beyond those of bare MOF and/or conventional semiconductors. The application examples of this new generation of composite photoelectrodes in water splitting, CO2 reduction and pollution degradation will be discussed, together with the challenges and prospects.

Enhancing Zn-MnO2 Battery Performance with Hydrogen-Bonded MnO2 Interfaces in Wet Nonaqueous Electrolytes

The quest for sustainable and high-performing battery technologies has directed attention towards Zinc (Zn)-manganese dioxide (MnO2) based rechargeable batteries. These batteries emerge as a viable alternative to lithium-ion systems, particularly due to their advantageous raw material supply, cost, and performance parameters. Despite their potential, Zn-MnO2 batteries face operational challenges, including gas evolution, Zn self-corrosion, and dissolution of the host material when utilized in mild acid aqueous electrolytes. Addressing these issues, our research explores the efficacy of wet nonaqueous electrolytes as a solution. Previously, we demonstrated a substantial enhancement in battery performance (~200 mAh/g of MnO2) by incorporating a specific proportion of water into the nonaqueous electrolyte. Building on this foundation, our current study investigates the role of hydrogen-bonded pillars, particularly proton and ammonium cations, in augmenting the interfacial properties of MnO2. This modification aims to bolster surface kinetics, thereby elevating battery performance closer to that of aqueous systems. Employing a suite of material characterization techniques, including in-situ X-ray absorption spectroscopy (XAS), Raman spectroscopy, and synchrotron X-ray diffraction (XRD), we observed a notable performance improvement (~270 mAh/g), while maintaining stability. These findings hold significant promise for advancing the practical application of MnO2-based hosts in Zn-MnO2 batteries, marking a stride towards next-generation energy storage solutions.

Deconvoluting Surface Modification Effects on Flow Battery Electrode Performance by Impedance Spectroscopy

Flow batteries have proliferated over the past decade, both in installed capacity and in the diversity of systems being developed for grid storage applications. As a long duration energy storage technology, flow batteries offer the distinct advantage of independent scaling of energy capacity through their liquid electrolytes, and of power capacity through stack design. Across flow battery systems, improving the design of reactor stacks to achieve high power densities at acceptable energy conversion efficiencies remains an important lever for lowering overall levelized costs of storage. In pursuit of this aim, understanding the reaction kinetics on the surfaces of porous carbon electrodes is key [1]. However, traditional techniques such as voltammetry, impedance spectroscopy, and cell performance must be utilised with caution to avoid convoluting observations of surface kinetics with other effects.Previous studies on vanadium flow batteries have used impedance spectroscopy to circumvent this issue, utilising the shared dependence of double layer capacitance and charge transfer conductance [2]. In recent years, DRT analysis of impedance spectra has also been used to further study electrode treatments for vanadium systems [3]. Building on these works, we use impedance spectroscopy combined with other techniques to deconvolute the effects of electrode treatments ex-situ before demonstrating the modified electrode performance in flow cells. The accompanying abstract image illustrates how different electrode modifications can manifest comparative differences in identified faradaic features in impedance spectra. As the most well studied system, we first apply our analysis to electrodes for vanadium electrolytes, validating our method and previous studies on electrode modifications. Following this, we apply our approach to capture a range of behaviours by studying redox active species with faster kinetics, such as recently developed organic species [4].The results of this work aim to improve the evaluation of reaction kinetics for different redox active species and electrode treatments. By doing so, we seek to further understand surface reaction mechanisms and how they can be harnessed to improve stack and electrolyte performance.[1] T. V. Sawant, C. S. Yim, T. J. Henry, D. M. Miller, and J. R. McKone, ‘Harnessing Interfacial Electron Transfer in Redox Flow Batteries’, Joule, vol. 5, no. 2, pp. 360–378, Feb. 2021, doi: 10.1016/j.joule.2020.11.022.[2] H. Fink, J. Friedl, and U. Stimming, ‘Composition of the Electrode Determines Which Half-Cell’s Rate Constant is Higher in a Vanadium Flow Battery’, J. Phys. Chem. C, vol. 120, no. 29, pp. 15893–15901, Jul. 2016, doi: 10.1021/acs.jpcc.5b12098.[3] K. Köble et al., ‘Revealing the Multifaceted Impacts of Electrode Modifications for Vanadium Redox Flow Battery Electrodes’, ACS Appl. Mater. Interfaces, vol. 15, no. 40, pp. 46775–46789, Oct. 2023, doi: 10.1021/acsami.3c07940.[4] J.-M. Fontmorin, S. Guiheneuf, T. Godet-Bar, D. Floner, and F. Geneste, ‘How anthraquinones can enable aqueous organic redox flow batteries to meet the needs of industrialization’, Current Opinion in Colloid & Interface Science, vol. 61, p. 101624, Oct. 2022, doi: 10.1016/j.cocis.2022.101624. Figure 1

Two-dimensional model in a laminar flow slit photoreactor for the determination of surface kinetic constants considering the presence of diffusion limitations

Narrow slit reactors are widely used in laboratory testing of photocatalytic materials, as well as for the determination of kinetic coefficients in surface photocatalyzed reactions. In this work, the behavior of a continuous laminar flow slit reactor was described by a two-dimensional model, addressing the advection–diffusion problem in the fluid phase, coupled with a first-order chemical reaction on the reactor walls. The concentration profile of the reactant, in the transverse and longitudinal directions of the reactor, depends on two parameters that characterize the system; the Péclet number and the Damköhler number, in addition to the geometry of the reactor. Once a short distance from the reactor’s entrance has been surpassed, the relationship between the transversally averaged reactant concentration and the concentration existing on the catalytic surface becomes essentially constant, thus defining an (external) effectiveness factor. The simulations carried out for a wide range of values of the parameters characterizing the model showed that the effectiveness factor only depends on the Damköhler number, being independent of the value of the Péclet number and of the relationship between the reactor length and the distance separating the plates. An analytical expression for the effectiveness factor as a function of the Damköhler number was proposed, which allows to determine the value of the kinetic coefficient for the surface reaction (ks), even in the presence of important limitations to mass transfer. The methodology proposed was illustrated performing experiments of photocatalytic oxidation of toluene in air (with Péclet numbers ranging from 20 to 40), employing a paint formulated with carbon-doped TiO2 in a continuous laboratory photoreactor of flat parallel plates. The observed toluene conversions were in the range of 13 to 26 %, consequently, the calculated Damköhler number was Da = 0.0307 and the surface kinetic coefficient thus determined (for 50 % of relative humidity and 42.3 W/m2 of irradiance flux) was ks = 1.262 10-4 m/s. The significance of this work lies in the development of a comprehensive model that can be used to know the surface kinetics in photocatalytic reactions, applicable to scenarios where there are considerable mass transfer limitations or not.

Towards detailed combustor wall kinetics: An experimental and kinetic modeling study of hydrogen oxidation on Inconel

Gas-phase hydrogen combustion is ubiquitous in industrial processes, and the associated surface kinetics on heat-resistant alloys plays a crucial role in designing efficient low-carbon technologies. We conducted new temperature programmed reduction experiments to determine the reducibility of materials following an oxidation cycle. These experiments were modeled using a thermoconsistent multi-site microkinetic model for H2 heterogeneous oxidation on Inconels, which was validated against literature experiments. This competitive adsorption model considers iron bulk content, hydrogen spillover and subsurface oxygen migration on hydrogen surface oxidation kinetics. New X-ray diffraction experiments confirmed the postulated crystallographic structures in the Inconel samples, suggesting their presence on the surface scale. The phenomenological model was coupled with several state-of-the-art gas-phase oxidation mechanisms to assess gas/surface reactions interaction as a function of material and temperature. The results reveal a complex interaction in which surface removes H radicals from the gas-phase, while the Bradford (H2+OH) reaction converts OH into H2O, promoting water adsorption on Inconel. This interaction was found to give rise to gas-phase thermokinetic oscillations. The model predicts a non-monotonous effect of reactor area-to-volume ratio on reactivity and emphasizes the impact of Inconel composition on product selectivity. Overall, the multi-site model provides new insight into the contrasting reactivities among active sites, bridging the gap between material science and heterogeneous combustion modeling.

Understanding the interfacial water structure in electrocatalysis

The structure of interfacial water molecules plays a crucial role in modulating the electrochemical surface kinetics. This article provides an in-depth understanding of the water molecule structure inside the double layer and its main influencing factors at the molecular scale.

Fabrication of Zn-doped Cu2O for auxiliary graphdiyne to enhance photocatalytic H2 evolution performance

Graphdiyne (GDY) is widely used in photocatalysis due to its large specific surface area, high porosity and good stability. In this study, GDY was prepared by ball-milling-assisted alkyne-negative method, and GDY/Zn-Cu2O S-scheme heterojunction catalysts were constructed by introducing Zn-doped Cu2O into it through low-temperature mixing. The modified composite catalysts showed hydrogen evolution performance reached 213.65 μmol after 5 h of visible light irradiation, which was 142.4, 82.2 and 8.1 times than that of Cu2O, Zn-Cu2O and GDY, respectively. The large specific surface area of GDY provided abundant active sites to promote surface kinetics. Zinc doping adjusted the energy band structure of Cu2O and improved the light absorption efficiency of the catalysts. The S-scheme heterojunction established between Zn-Cu2O and GDY greatly facilitated the separation and transport of photogenerated carriers, which was the dominant factor for the improvement of hydrogen evolution performance. A possible mechanism is proposed and analyzed by combining ultraviolet photoelectron spectroscopy (UPS), valence band XPS (VB-XPS), in-situ irradiated X-ray photoelectron spectroscopy (In-situ XPS) and density functional theory (DFT) results. This work provides a new insight into the doping and construction strategies of GDY-based S-scheme heterojunction.

Modeling the mechanosensitive collective migration of cells on the surface and the interior of morphing soft tissues.

Cellular contractility, migration, and extracellular matrix (ECM) mechanics are critical for a wide range of biological processes including embryonic development, wound healing, tissue morphogenesis, and regeneration. Even though the distinct response of cells near the tissue periphery has been previously observed in cell-laden microtissues, including faster kinetics and more prominent cell-ECM interactions, there are currently no models that can fully combine coupled surface and bulk mechanics and kinetics to recapitulate the morphogenic response of these constructs. Mailand et al. (Biophys J 117(5):975-986, 2019) had shown the importance of active elastocapillarity in cell-laden microtissues, but modeling the distinct mechanosensitive migration of cells on the periphery and the interior of highly deforming tissues has not been possible thus far, especially in the presence of active elastocapillary effects. This paper presents a framework for understanding the interplay between cellular contractility, migration, and ECM mechanics in dynamically morphing soft tissues accounting for distinct cellular responses in the bulk and the surface of tissues. The major novelty of this approach is that it enables modeling the distinct migratory and contractile response of cells residing on the tissue surface and the bulk, where concurrently the morphing soft tissues undergo large deformations driven by cell contractility. Additionally, the simulation results capture the changes in shape and cell concentration for wounded and intact microtissues, enabling the interpretation of experimental data. The numerical procedure that accounts for mechanosensitive stress generation, large deformations, diffusive migration in the bulk and a distinct mechanism for diffusive migration on deforming surfaces is inspired from recent work on bulk and surface poroelasticity of hydrogels involving elastocapillary effects, but in this work, a two-field weak form is proposed and is able to alleviate numerical instabilities that were observed in the original method that utilized a three-field mixed finite element formulation.

Valorization of Bambusa striata shavings into functional superparamagnetic material and its application in biodiesel production: Response surface optimization, kinetics, thermodynamics and economic assessment

Herein, a novel highly porous biomass-based (Bambusa vulgaris striata) magnetic solid acid catalyst was developed for the first time via simultaneous activation and magnetization followed by acid functionalization. The sulfonated magnetic porous carbon was utilized as a catalyst for transesterifying Jatropha curcas oil (JCO) to biodiesel under microwave irradiation. The synthesized catalyst was extensively characterized using VSM, XRD, FTIR, SEM, EDS, TGA, XPS, Raman spectroscopy, and AFM techniques. Through Response Surface Methodology (RSM), a maximal biodiesel yield of 98.8 % was achieved over optimal optimal parametric states (catalyst loading 8 wt%, MOMR 24:1, 50 min, 80 °C). NMR confirmed JCO biodiesel formation with a FAME content of 98.04 %, and GCMS provided insight into its chemical composition. A pseudo-first-order kinetic study revealed an activation energy (Ea) of 28.734 kJ mol1. Thermodynamic analysis showed endothermic and non-spontaneous behavior with ΔH#, ΔS#, and ΔG# values of 25.928 kJ mol1, −0.193 kJ mol1 K1, and 94.251 kJ mol1, respectively. The catalyst displayed good reusability, easy recoverability, and stability, maintaining 75.4 % oil conversion even after ten consecutive cycles. Life cycle cost analysis (LCCA) estimates biodiesel production cost of $0.60 per liter, emphasizing high commercial viability.

Response surface optimization, kinetics, thermodynamics, and life cycle cost analysis of biodiesel production from Jatropha curcas oil using biomass-based functional activated carbon catalyst

A highly efficient activated porous catalyst, BPAC-500-S, derived from waste banana peels through a novel synthesis involving pyrolysis; and functionalization with 4-benzene diazonium sulphonate, has been developed. For comparison of catalytic activity, the material was also functionalized with sulphuric acid (BPAC-500-SX). The (BPAC-500-S) catalyst underwent impregnation and activation with ZnCl2, and its properties were extensively characterized using BET, SEM, XPS, XRD, FT-IR, and TGA techniques. Comparative analysis of catalysts obtained at different pyrolysis temperatures (400, 500, and 600 °C) revealed that BPAC-500-S pyrolyzed at 500 °C, exhibited maximum surface area (840.83 m2g-1) and sulphur density (4.7 %). Utilizing BPAC-500-S as a catalyst, an efficient process for biodiesel synthesis from Jatropha curcas oil (JCO) was developed, achieving a remarkable 98.91 % conversion, as confirmed by 1H NMR spectroscopy. Notably, life cycle cost analysis demonstrated a low biodiesel production cost of $ 0.70/L. The BPAC-500-S catalyst exhibited exceptional reusability maintaining more than 80 % biodiesel yield over seven reaction cycles. This study presents a sustainable and cost-effective approach to biodiesel production, emphasizing the potential of waste-derived catalysts in green and economically viable processes.

Nitrogen adsorption induced surface kinetics changes of diamond growth by microwave plasma CVD

The strong temperature dependence of the contribution of nitrogen to diamond growth enhancement by microwave plasma chemical vapor deposition (MPCVD) have been firstly reported and systematically studied. Generally, an enhanced hydrogen desorption from the growing surface induced by the incorporated nitrogen atoms in diamond sublayer has been successfully used to explain the weak temperature depended growth enhancement of diamond by nitrogen addition, but cannot be employed to explain the observed strong temperature dependence of nitrogen contribution to diamond growth enhancement observed in this work. This indicates a significant change of surface kinetics of diamond growth induced by nitrogen addition should be occurred around 700 °C where a maximum value achieved. At this relative low temperature, the growing surface sites should be almost fully covered with hydrogen atoms with relative low nitrogen incorporated in the diamond. The adsorbed nitrogen may then make a contribution to promote hydrogen desorption, which is believed to play a dominant role in affecting the contribution of nitrogen. Experimental and calculation results do show that both the nitrogen adsorbed on the growing surface and incorporated in the sublayer may have different contribution to the growth rate enhancement, resulting in strong and weak temperature dependence, respectively.

Investigation of Water Impacts on Surface Properties and Performance of Air-Electrode in Reversible Protonic Ceramic Cells.

Water, being abundant and readily accessible, gains widespread usage as proton source in many catalysis and energy conversion technologies, including applications like reversible protonic ceramic cells (R-PCCs). Revealing the influence of water on the electrode surface and reaction kinetics is critical for further improving their electrochemical performance. Herein, a hydrophilic air-electrode PrBa0.875Cs0.125Co2O5+δ is developed for R-PCC, which demonstrates a remarkable peak power density of 1058mWcm-2 in fuel cell mode and a current density of 1354mAcm-2 under 1.3V in electrolyzing steam at 650°C. For the first time on R-PCC, surface protons' behavior in response to external voltages is captured using in situ FTIR characterizations. Further, it is shown that contrary to the bulk proton uptake process that is thought to follow hydrogenation reactions and lead to cation reductions. The air-electrode presents enriched surface protons occurring through oxidizing surface cations, as confirmed by depth-profiling XPS results. H/D isotope exchange experiments and subsequent electrochemical characterization analyses reveal that the presence of protons enhances surface reactions. This study fills the knowledge gap between water-containing atmospheres and electrochemical performance by providing insights into the surface properties of the material. These new findings provide guidance for future electrode design and optimization.

Exploring the combustion mechanism of single micron-sized aluminum particles with a numerical model

In this work, we explore the combustion mechanism of single micron-sized aluminum particles using a numerical model. The Burcat database and Catoire mechanism is considered as the thermodynamic data and the kinetic mechanism for our numerical model of aluminum combustion. Two independent experiments, including particle temperature profiles, ignition delay and burning time, are selected to evaluate the performance of the numerical model. The model shows great agreement for all considered properties. A parametric study is further conducted to identify the effect of involved physical parameters on the combustion process. The diffusion coefficient (D) of oxidizers and the activation energy of surface kinetics (Esurf) and evaporation coefficient (α) of aluminum impact the particle temperature the most. Burning time is most sensitive to the activation energy of surface kinetics (Esurf). The optical measurement in a solid propellant combustion indicates that the contact angle of the oxide cap on Al particle is between 10° and 20°. It is found that the selection of contact angle of the oxide cap significantly impacts the prediction of combustion time and residual of active aluminum. The current work highlights the importance of physical properties on the prediction of Al combustion, suggesting that more detailed evaluation from experiments and theory is encouraged.

Accelerating Surface Reaction Kinetics and Enhancing Bulk as well as Surface Charge Carrier Dynamics in Al/ Al2O3‐Coated BiVO4Photoanode

AbstractPhotoelectrochemical (PEC) hydrogen evolution from water splitting of semiconductor photoanodes is intricately linked to their light‐absorbing capacity, surface reaction kinetics, bulk charge carrier separation efficiency, and surface charge carrier injection efficiency. Harnessing the surface plasmon resonance effect of metals emerges as a promising approach to enhance PEC performance of semiconductor photoanodes. This work presents the first application of non‐noble metal Al nanoparticles to sensitize a BiVO4nanoporous film (NPF) photoanode. This process significantly expedites the surface kinetics of water oxidation, and improves both bulk charge carrier separation and surface carrier injection efficiencies of BiVO4NPF photoanode. Additionally, the surface‐formed Al2O3film effectively preserves the stability of photoanode, leading to a substantial improvement in PEC hydrogen evolution of BiVO4NPF photoanode in a three‐electrode PEC cell with sulfite scavenger. The constructed BiVO4/Al NPF heterojunction photoanode exhibits a hydrogen evolution rate of 73.9 µmol cm⁻2h⁻¹ at 1.23 V versus reversible hydrogen electrode, 1.68 times of BiVO4photoanode. Additionally, BiVO4/Al NPF photoanode exhibits excellent stability under long‐time light irradiation of 8 h. This study provides valuable insights into the design of nonnoble‐metal‐based plasmonic photoanodes for efficient hydrogen generation through PEC cell from the perspectives of surface reaction kinetics, charge carrier injection, and separation.