Reactive Surface Area Research Articles

Improved Volume-Of-Solid Formulations for Micro-Continuum Simulation of Mineral Dissolution at the Pore-Scale

We present two novel Volume-of-Solid (VoS) formulations for micro-continuum simulation of mineral dissolution at the pore-scale. The traditional VoS formulation (VoS-ψ) uses a diffuse interface localization function ψ to ensure stability and limit diffusion of the reactive surface. The main limitation of this formulation is that accuracy is strongly dependent on the choice of the localization function. Our first novel improved formulation (iVoS) uses the divergence of a reactive flux to localize the reaction at the fluid-solid interface, so no localization function is required. Our second novel formulation (VoS-ψ′) uses a localization function with a parameter that is fitted to ensure that the reactive surface area is conserved globally. Both novel methods are validated by comparison with experiments, numerical simulations using an interface tracking method based on the Arbitrary Eulerian Lagrangian (ALE) framework, and numerical simulations using the VoS-ψ. All numerical methods are implemented in GeoChemFoam, our reactive transport toolbox and three benchmark test cases in both synthetic and real pore geometries are considered: 1) dissolution of a calcite post by acid injection in a microchannel and experimental comparison, 2) dissolution in a 2D polydisperse disc micromodel at different dissolution regimes and 3) dissolution in a Ketton carbonate rock sample and comparison to in-situ micro-CT experiments. We find that the iVoS results match accurately experimental results and simulation results obtained with the ALE method, while the VoS-ψ method leads to inaccuracies that are mostly corrected by the VoS-ψ’ formulation. In addition, the VoS methods are significantly faster than the ALE method, with a speed-up factor of between 2 and 12.

Copper ferrite and cobalt oxide two-layer coated macroporous SiC substrate for efficient CO2-splitting and thermochemical energy conversion

CO2-splitting and thermochemical energy conversion effectiveness are still challenged by the selectivity of metal/metal oxide-based redox materials and associated chemical reaction constraints. This study proposed an interface/substrate engineering approach for improving CO2-splitting and thermochemical energy conversion through CuFe2O4 and Co3O4 two-layer coating SiC. The newly prepared material reactive surface area available for gas–solid reactions is characterized by micro-pores CuFe2O4 alloy easing inter-layer oxygen micro mass exchanges across a highly stable SiC-Co3O4 layer. Through a thermogravimetry analysis, oxidation of the thermally activated oxygen carriers exhibited remarkably CO2-splitting capacities with a total CO yield of 1919.33 µmol/g at 1300 °C. The further analysis of the material CO2-splitting performance at the reactor scale resulted in 919.04 mL (788.94 µmol/g) of CO yield with an instantaneous CO production rate of 22.52 mL/min and chemical energy density of 223.37 kJ/kg at 1000 °C isothermal redox cycles. The reaction kinetic behavior indicated activation energy of 30.65 kJ/mol, which suggested faster CO2 activation and oxidation kinetic on SiC-Co3O4-CuFe2O4 O-deficit surfaces. The underlying mechanism for the remarkable thermochemical performances was analyzed by combining experiment and density functional theory (DFT) calculations. The significance of exploiting the synergy between CuFe2O4 and Co3O4 layers and stoichiometric reaction characteristics provided fundamental insights useful for the theoretical modeling and practical application of the solar thermochemical process.

Pore-scale study of effects of relative humidity on reactive transport processes in catalyst layers in PEMFC

High surface area carbon (HSC) particles can be adopted to increase the specific surface area of catalyst layer (CL) in proton exchange membrane fuel cells. Relative humidity (RH) has a significant effect on the Pt activity inside HSC particles, and the underlying mechanisms need to be further investigated. In this study, a pore-scale model considering the effects of RH on the reactive transport processes inside the CLs is developed. Two kinds of liquid water distributions affected by the RH, including capillary condensation in pores and ultra-thin liquid film on Pt surface, are considered. The liquid water distribution, Pt activity and local oxygen transport resistance (Rlocal) under different RH are studied in detail. It is found that as RH increases from 0.3 to 1.0, the condensed water in micropores of HSC particles increases, resulting in an increase in reactive surface area by about 43 %. Combined effect of the RH, Pt loading, I/C ratio and different kinds of carbon particles is investigated. It is found that due to the lack of sufficient reaction sites, compared with that under a high Pt loading, Rlocal under a low Pt loading is more sensitive to the RH. Besides, since the Pt activity inside HSC particles depends on the condensed water, the Rlocal of HSC particles is more sensitive to the RH than solid carbon particles. Finally, the Rlocal at low ionomer content is more sensitive to RH due to low ionomer coverage on Pt particles. The present study provides a pore-scale model for investigating the coupled effects of RH and CL porous structures on local transport processes, and can facilitate the optimization of CL nanoscale structures for better cell performance.

Exsolution of phase-separated nanoparticles via trigger effect toward reversible solid oxide cell

The electrocatalytic characteristics of heterostructure nanoparticles have attracted attention for use in devices addressing energy and environmental issues. Among the various features, exsolved alloy or core–shell nanoparticles display high reactive surface area and strong interaction between the metal and substrate oxide. Herein, we report multifunctional heterostructure nanoparticles, namely Fe/Cu Janus nanoparticles (JN) and verify an exsolution trigger effect using Cu as a seed in the La0.43Sr0.37Fe0.09Cu0.03Ti0.88O3-δ (Fe75) perovskite substrate. During the exsolution process, the exsolved Cu particles played a key role in triggering the Fe exsolution by contributing additional surface energy. These Fe/Cu JNs exhibited outstanding catalytic activity in a reversible solid oxide cell fed with H2O/H2 and CO/CO2 fuels. A single cell with Fe75 showed an impressive current density of − 1.11 A cm−2 at 1.3 V and 900 °C. Our study experimentally elucidated the mechanism of the triggering of co-exsolution and demonstrated a multifunctional catalyst using Fe/Cu JNs.

(Invited, Digital Presentation) Infiltrated Electrodes for High Temperature Energy Conversion, Electrolysis, and Chemical Synthesis

Solid oxide cell (SOC) infiltrated electrodes typically consist of a ceramic or cermet porous scaffold with the pore walls coated with catalyst particles. The pore size of the scaffold is 1 to 50 mm, whereas the catalyst particles are 10 to 300 nm. This scaffold provides a stable and durable mechanical structure, and the fine catalyst particles provide high surface area for electrochemical and heterogeneous reactions. The scaffold is sintered and bonded to the other layers of the complete cell. After this high temperature processing is finished, catalyst precursor solution is flooded into the scaffold and fired at moderate temperature to form the desired catalyst composition and phase. Because the scaffold is sintered in the absence of catalysts, re-optimization of the fabrication process, ink formulation, deposition process, and sintering protocol is not needed when a new catalyst is introduced to the cell design. Instead, a new precursor solution can be prepared from a stoichiometric mixture of metal salts, with minimal change in processing. This approach makes it straightforward to screen many catalyst compositions in a short period of time, and adapt an existing cell structure for a wide variety of applications.The Lawrence Berkeley National Laboratory metal-supported solid oxide cell (MS-SOC) design has a thin electrode scaffold of zirconia ceramic co-sintered on a thick porous stainless steel support layer. Both layers are coated with infiltrated catalysts. The catalyst precursor solution is an aqueous mixture of metal nitrate salts. After the solution is flooded into the pores of the scaffold, it is dried and heated in air to convert the nitrate salts to mixed metal oxides. The oxides can then be reduced to metals by firing in reducing atmosphere, if desired. The drying rate, heating rate, conversion temperature, and other processing parameters can have a dramatic impact on the catalyst particle morphology and ultimately on the performance and durability of the electrochemical device.Depending on the choice of catalyst composition, the MS-SOCs can be configured as fuel cells, electrolysis cells, or chemical conversion reactors. Several examples will be highlighted, including: fuel cell operation with hydrogen, ethanol, and natural gas; steam electrolysis for hydrogen production; and oxidative coupling of methane for valuable chemical synthesis. In each case, technical progress will be presented with a focus on catalyst development and device performance. Figure 1

Rational construction of reduced NiCo2S4@CuCo2S4 composites with sulfur vacancies as high-performance supercapacitor electrode for enhancing electrochemical energy storage

Rational design of NiCo2S4-based nanostructures supercapacitor electrodes was considered as an important route for increasing specific capacitance in the field of electrochemical energy storage. Here we reported that a novel reduced NiCo2S4@CuCo2S4 (R–NiCo2S4@CuCo2S4) core-shell heterostructure with sulfur vacancies improved electrochemical performance of supercapacitor electrode material. These composites were designed and synthesized by a combination of solvothermal, electrochemical deposition and reduction of sodium borohydride (NaBH4). Among them, NiCo2S4 nanosheets were grown on nickel foam as a core and act scaffold for the reaction by a solvothermal method, while CuCo2S4 as a shell to aggrandizement specific surface area of reaction by electrochemical deposition method and to further raise active sites and conductivity of reaction, sulfur vacancies were further constructed in NiCo2S4@CuCo2S4. The construction of sulfur vacancies shortens the reaction distance and accelerated electrons and ions transmission. Therefore, R–NiCo2S4@CuCo2S4 exhibited an excellent capacity (2922.9 F g−1 at 0.5 A g−1), superior rate capability (68% retention from 0.5 A g−1 to 10 A g−1) and extraordinary cycling stability (99.92% capacitance after 10000 cycles at 30 A g−1). This strategy successfully fabricated the R–NiCo2S4@CuCo2S4 core-shell heterostructure with excellent electrochemical performance, making it a potential candidate as supercapacitor electrode materials for enhanced electrochemical energy storage.

Evaporation of As and Sn from Liquid Iron: Experiments and a Kinetic Model during Top-Blown Oxygen Steelmaking Process.

Evaporation kinetics of tramp elements (M = As and Sn) in liquid iron were investigated by high-temperature gas–liquid reaction experiments and a phenomenological kinetic model. Residual content of As or Sn in the liquid iron ([pct M]) during the evaporation was measured in the temperature range of 1680 C to 1760 C. [pct As] and [pct Sn] decreased faster as the reaction temperature and [pct C] increased. Assuming first-order reaction kinetics, the apparent rate constants () were obtained at each reaction temperature and [pct C]. [pct M] in a liquid iron during the top-blown oxygen steelmaking process was simulated, with an emphasis on enlarging the reaction surface area by forming a large number of liquid iron droplets. The surface area and the droplet generation rate were obtained based on the oxygen-blowing condition. The whole surface area increased up to ∼163 times the initial liquid iron (bath) surface area, due to the generation of the droplets. Using the obtained in the present study, the evaporation of M during the top-blown oxygen steelmaking process for 200 tonnes of liquid iron was simulated. For a condition of [pct M] = 0.005 (M = As and Sn), As and Sn could be removed from the liquid iron, which was seen to be much improved by the consideration of the droplet generation. However, additional actions are required to improve the evaporation rate, as the evaporation rate in the BOF process was not fast enough to be practically considered.

Adopting co-metabolism strategy for optimized biotreatment of ortho-hydroxytoluene and bioelectricity generation in microbial fuel cell: Transformation products and pathways

This study investigated the effects of carbon source availability and concentrations, external loads (Rload), and cathode conditions on the overall removal rate of ortho-hydroxytoluene and bioelectricity generation characteristics in anti-gravity flow microbial fuel cell (AGF-MFC) through co-metabolism approach. Sodium acetate outperformed sucrose, glucose and carbamide, and the optimum influent acetate concentration (1000 mg L−1) significantly enhanced the o-hydroxytoluene degradation by 13.41 % (98.71 %), output voltage by 15.14 % (609.25 mV) and power generation by 30.96 % (159.44 mW m−2). The results demonstrated that there were prominent differences in MFC performances under different Rload (p < 0.05). Different external load conditions resulted in varying electron transfer reactions, and thus affecting the removal efficiency and power responses of MFC system. A complete removal of o-hydroxytoluene and highest power density of 173.10 mW m−2, with a Chemical Oxygen Demand (COD) removal of 93.56 % were obtained with the Rload of 230 Ω, where the Rload approaches the cell design point. Hysteresis phenomenon was detected in the dynamic polarization during Rload variations. Moreover, it was observed that the removal efficiency of o-hydroxytoluene was significantly enhanced with aeration rate of 50 mL min−1, and dissolved oxygen concentration of 5.4 mg L−1. Conversely, higher aeration rate (400 mL min−1) had caused a decline of 26 % in power generation, ascribed to the limited active surface area for oxygen reduction reaction. Additionally, the degradation pathway of o-hydroxytoluene was proposed based on the identified intermediates.

One-dimensional hierarchical porous carbon nanofibers with cobalt oxide in a hollow channel for electrochemical applications

One-dimensional hierarchical porous carbon nanofibers (CNFs) embedded with Co3O4 nanoparticles in a hollow channel (PPMCo) are fabricated by coaxial electrospinning followed by thermal treatment. The degree to which the CNF surface is exposed to Co3O4 nanoparticles was controlled by the cobalt(II) acetate concentration. The well-controlled structure of PPMCo with porous structure, heteroatoms, and amorphous Co3O4 nanoparticles provided fast ion transport and large reaction surface area, resulting in effective ion migration to the active site and a high rate capacity of the electrode. Benefitting from the unique structure, the PPMCo supercapacitor electrodes displays a high specific capacitance of 188 Fg−1 at 1 mAcm−2, rate capability of 82% when the current density is increased from 1 to 20 mAcm−2, and cycling stability of 93% for 10,000 cycles. The good capacitive performance of the PPMCo electrode is attributed to the synergistic effect of the hierarchical porosity, electroactive material of Co3O4, high effective surface area, and polar effects by heteroatoms.

Production and Optimization of Biodiesel in a Membrane Reactor, Using a Solid Base Catalyst.

The commercial Calcium oxide was successfully embedded on activated carbon surfaces to increase the reactive surface area of a composite catalyst material CaO/AC. The composite catalyst material was also successfully packed in the tubular titanium dioxide/Aluminum dioxide ceramic membrane reactor used to separate the biodiesel produced. Virgin soybean oil was used as precursor feedstock for the reaction. Using a central composite approach, response surface methodology (RSM) was employed to obtain the optimum conditions for producing biodiesel from soybean oil. A total of four process factors were examined (24 experimental designs). 30 experiments were derived and run to investigate the effects of temperature, reaction time, methanol to oil molar ratio, and catalyst concentration (calcium oxide attached on activated carbon). 96.9 percent of soybean oil methyl ester (SOME/biodiesel) was produced at 65 °C temperature, 90 min of reaction time, 4.2:1 molar ratio of methanol to oil, and 3.0 wt.% catalyst concentration. The measured yield and expected biodiesel production values were correlated in a linear sequence. The fuel qualities of SOME/biodiesel were tested, including kinematic viscosity, density, flash point, copper corrosion, calorific value, cloud point, pour point, ash content, and carbon residue.

The reduction in porosity of permeable reactive barriers due to bio-geochemical clogging caused by acidic groundwater flow

This study demonstrates the change in porosity of permeable reactive barrier (PRB) material when it reacts with acidic flow. The laboratory column test data obtained over 9 months prove that the porosity of a granular limestone assembly decreases significantly due to bio-geochemical clogging caused by a continuous flow of acidic groundwater. The variations in pH, the pressure measurements, ion concentrations, and the results from X-ray diffraction suggest that clogging at the outlet of the column is much less than at the inlet. About 57% of the total reduction in porosity of the column is attributed to chemical clogging, while the remainder is mainly due to biological clogging. In this paper, a mathematical approach is proposed to estimate the reduction of reactive surface area based on changes in the pore volume. These proposed equations suggest that at the end of experimentation, the dissolution of calcite and bio-geochemical clogging can reduce the total surface area of limestone aggregates by more than 70%. The rigorous approach presented in this paper to determine the dominant clogging component within a granular filter at a given time is vital in estimating the longevity of a PRB and for planning its maintenance.

Facile Electrodeposition of NiCo2O4 Nanosheets on Porous Carbonized Wood for Wood-Derived Asymmetric Supercapacitors.

Multichannel-porous carbon derived from wood can serve as a conductive substrate for fast charge transfer and ion diffusion, supporting the high-theory capacitance of pseudocapacitive materials. Herein, NiCo2O4 nanosheets, which are hierarchically porous, anchored on the surface of carbonized wood via electrodeposition for free-binder high-performance supercapacitor electrode materials, were proposed. Benefiting from the effectively alleviated NiCo2O4 nanosheets accumulation and sufficient active surface area for redox reaction, a N-doped wood-derived porous carbon-NiCo2O4 nanosheet hybrid material (NCNS–NCW) electrode exhibited a specific electric capacity of 1730 F g−1 at 1 A g−1 in 1 mol L−1 KOH and splendid electrochemical firmness with 80% capacitance retention after cycles. Furthermore, an all-wood-based asymmetric supercapacitor based on NCNS–NCW//NCW was assembled and a high energy density of 56.1 Wh kg−1 at a watt density of 349 W kg−1 was achieved. Due to the great electrochemical performance of NCNS–NCW, we expect it to be used as an electrode material with great promise for energy storage equipment.

Oxygen vacancy-engineered Fe2O3 porous microspheres with large specific surface area for hydrogen evolution reaction and lithium-sulfur battery

Iron oxide (Fe2O3) with intrinsic catalytic activity and desirable theoretical capacity are expected to be promising active materials for hydrogen evolution reaction (HER) and lithium-sulfur (Li-S) batteries. Nevertheless, the sluggish electrons transfer accompanied with limited active sites impede their large-scale application. Generally, the silicon dioxide (SiO2) is employed as sacrificial template to regulate morphological structure of target products. However, selecting SiO2 as sacrificial shell may be a novel method to overcome the limitations and further optimize the performance of Fe2O3. Hence, a novel self-activation strategy along with reduction treatment is presented to prepare oxygen vacancy-engineered Fe2O3 porous microspheres featured with high specific surface area (SA-Fe2O3 (Ov)). Specifically, the simultaneously formation of rich oxygen vacancies and porous configuration could regulate electronic configuration, expose numerous active sites and enhance electrons transfer, leading to superior achievement for HER and Li-S batteries. Remarkably, the elaborately designed SA-Fe2O3 (Ov) achieves low overpotential and relatively small Tafel slopes. Furthermore, SA-Fe2O3 (Ov) holds great promise serving as sulfur host in the field of Li-S batteries with reversible capacity and impressive durability. This work contributes new insights into the self-activation strategy coupled with reduction synthesis of oxygen vacancy-engineered porous oxides with large specific surface area and raises the understanding of multifunctional energy applications.

Bio-Inspired Hierarchical Porous TiO&lt;sub&gt;2&lt;/sub&gt; for Photodegradation of Organic Pollutant under Solar Irradiation

Photo-degradation of organic pollutants is of immense importance for environmental protection. The key is low-cost photocatalysts of high efficiency. Templating approach is attractive to gain hierarchical porous photocatalysts with high surface area, while is usually stuck by the limited types of desirable templates, in particular those with sophisticated microstructures. Herein, we showed a bio-inspired templating strategy that was applied to fabricate an efficient TiO2 photocatalyst with a unique hierarchical porous structure. Taking rape-pollen grains as a typical example of bio-templates, a process combining hydrothermal treatment with calcination was developed to grow TiO2 nanoparticles of 6-14 nm on the templates and subsequently to remove the organic biotemplates. As-obtained TiO2 were micro-sized spheres or ellipsoids that were surrounded by open tubular arrays. The surface area was as large as ~175 m2/g. For photodegradation, the rape-pollen-grains-architectured TiO2 has a rate (k) of 0.150 min-1, which is 10.9 times faster than the non-templated TiO2. The superior photocatalytic activity should be ascribed to the unique hierarchical porous structures, which provided interconnected channels for efficient mass transport and a large surface area for fast reaction. Our work demonstrates an effective method, namely bioinspired templating, for the scalable synthesis of efficient photocatalysts. Considering the structural diversity of pollen grains, this work may inspire others on the research of photo-response materials that rely on morphology optimization.

Geochemical evolution of a sublacustrine hydrothermal vent system: Temporal constraints imposed by reactive transport modeling

Studies of heat and mass transport in hydrothermal systems are challenging owing to the complex feedback that exists between chemical and physical processes. Taking full advantage of the existing geochemical framework recently recognized for sublacustrine vent fluids in the Stevenson Island Deep Hole, Yellowstone Lake, here we apply a multiphase reactive transport model, coupling hydraulic and thermal effects, to simulate time series changes in mineralization associated with venting of vapor-dominated hydrothermal fluids. This distinctive region of the lake floor is characterized by a series of overlapping depressions hosting sites of active venting. Model results show that the addition of high enthalpy steam enriched in CO2 and H2S, creates acidic and reducing conditions, while heating entrained lake water and coexisting sediment to temperatures in excess of 174 °C. The diatomaceous silica-rich substrate is predicted to dissolve, being replaced largely by pyrite, quartz, and kaolinite, in good agreement with the observed vent mineralization and fluid chemistry. Data suggest that vent-related mineral dissolution and transformation processes occur rapidly, on the order of 1 ka for the spatial scale of the modeled-up flow zone considered. The accuracy of time series changes predicted however, is explicitly linked to a number of physical and chemical factors imposed on the model, including source fluid, flow rate and gas enrichment, and sediment thermal conductivity, permeability, and reactive surface area, as well as mineral reaction rate data for primary and secondary alteration phases. When combined with robust field observations, as is the case here, reactive transport models can elucidate important, if not fundamental, controls on the temporal and spatial evolution of the geochemistry of modeled system, challenging chemical, and physical conditions notwithstanding.

Low Heat Capacity 3D Hollow Microarchitected Reactors for Thermal and Fluid Applications

Lightweight reactor materials that simultaneously possess low heat capacity and large surface area are desirable for various applications such as catalytic supports, heat exchangers, and biological scaffolds. However, they are challenging to satisfy this criterion originating from their structural property in most porous cellular solids. Microlattices have great potential to resolve this issue in directing transport phenomena because of their hierarchically ordered design and controllable geometrical features such as porosity, specific surface, and tortuosity. In this study, we report hollow ceramic microlattices comprising a 10 μm thick hollow nickel oxide beam in an octet-truss architecture with low heat capacity and high specific surface area. Our microarchitected reactors exhibited a low heat capacity for a rapid thermal response with a small Biot number (Bi &lt;&lt; 1) and large intertwined surface area for homogeneous flow mixing and chemical reactions, which made them ideal candidates for various energy applications. The hollow ceramic microlattice was fabricated by digital light three-dimensional (3D) printing, composite electroless plating, polymer removal, and subsequent thermal annealing. The transient thermal response and fluidic properties of the 3D-printed microstructures were experimentally investigated using a small-scale thermal and fluid test system, and analytically interpreted using simplified models. Our findings indicate that hollow microarchitected reactors provide a promising platform for developing multifunctional materials for thermal and fluid applications.

Quantum computational, spectroscopic (FT-IR, NMR and UV–Vis) profiling, Hirshfeld surface, molecular docking and dynamics simulation studies on pyridine-2,6-dicarbonyl dichloride

PDD (pyridine-2,6-dicarbonyl dichloride) has been explored both experimentally and theoretically. Pyridines and their analogues are heterocyclic nitrogenous compounds that have a wide variety of applications in the development of anticancer medicines. These synthetic sources are utilised to treat many different types of disorders, including breast cancer, myeloid leukaemia, pancreatic cancer, liver cancer, and idiopathic pulmonary fibrosis. In this study, FT-IR, 1H, 13C NMR, and UV-Vis spectra, as well as theoretical DFT calculations, were used to explore pyridine-2,6-dicarbonyl dichloride (PDD). The most stable optimized structure was found using the B3LYP/6-311++G(d,p) basis set, which was subsequently studied using FT-IR and NMR. Hirshfeld's surface analysis were presented and discussed. Chemical reactivity investigations, MEP maps, and surface area maps were also carried out. The vibrational assignments were completed using individual vibrational modes, which were then compared to experimental data. The docking studies were used to look into how the ligand PDD interacted with specific protein targets. In order to better visualise binding locations and the influence of the ligand on 4LB4 conformation, this system was also subjected to molecular dynamic simulations.

Development of Core-Shell Rh@Pt and Rh@Ir Nanoparticle Thin Film Using Atomic Layer Deposition for HER Electrocatalysis Applications

The efficiency of hydrogen gas generation via electrochemical water splitting has been mostly limited by the availability of electrocatalyst materials that require lower overpotentials during the redox reaction. Noble metals have been used extensively as electrocatalysts due to their high activity and low overpotentials. However, the use of single noble metal electrocatalyst is limited due to atomic aggregation caused by its inherent high surface energy, which results in poor structural stability, and, hence, poor electrocatalytic performance and long-term stability. In addition, using noble metals as electrocatalysts also causes the cost to be unnecessarily high. These limitations in noble metal electrocatalysts could be enhanced by combining two noble metals in a core-shell structure (e.g., Rh@Ir) as a thin film over a base substrate. This could significantly enhance electrocatalytic activity due to the following: (1) the modification of the electronic structure, which increases electrical conductivity; (2) the optimization of the adsorption energy; and (3) the introduction of new active sites in the core-shell noble metal structure. The current state-of-the-art employs physical vapor deposition (PVD) or other deposition techniques to fabricate core-shell noble metals on flat 2D substrates. This method does not allow 3D substrates with high surface areas to be used. In the present work, atomic layer deposition (ALD) was used to fabricate nanoparticle thin films of Rh@Ir and Rh@Pt in a core-shell structure on glassy carbon electrodes. ALD enables the fabrication of nanoparticle thin film on three-dimensional substrates (a 2D functional film on a 3D substrate), resulting in a significantly increased surface area for a catalytic reaction to take place; hence, improving the performance of electrocatalysis. The Rh@Pt (with an overpotential of 139 mV and a Tafel slope of 84.8 mV/dec) and Rh@Ir (with an overpotential of 169 mV and a Tafel slope of 112 mV/dec) core-shell electrocatalyst exhibited a better electrocatalytic performances compared to the single metal Rh electrocatalyst (with an overpotential of 300 mV and a Tafel slope of 190 mV/dec). These represented a 54% and a 44% improvement in performance, respectively, illustrating the advantages of core-shell thin film nanostructures in enhancing the catalytic performance of an electrocatalyst. Both electrocatalysts also exhibited good long-term stability in the harsh acidic electrolyte conditions when subjected to chronopotentiometry studies.

Polyoxometalate‐Based Metal Organic Frameworks: Recent Advances and Challenges

AbstractPolyoxometalates (POMs) are stable metal anion clusters formed by pre‐transition metal elements in their highest oxidation state, with rich chemical composition and diverse structures. However, the highly dispersed structure makes it difficult to perform catalytic activity in a stable manner. Metal‐organic frameworks (MOF) with high specific surface and topological structure are a unique class of solid porous materials based on metal ions or metal clusters and organic ligands. In recent years, numerous studies have combined these two as POMOF composite nanoplatform, which not only retains the advantages of them but also ameliorates the shortcomings. With active reactivity, high stability and large specific surface area, this synergistic and complementary combination makes it a promising composite nanomaterial. This mini‐review presents the applications of POMOFs in different fields, including combating environmental problems and energy crises, catalyzing organic reactions, biosensors and supercapacitors, and presents the prospect of future work of POMOFs.

Sustainable desalination device capable of producing freshwater and electricity

Freshwater shortage and the growing demand for electricity are the most common issues on the path toward achieving global sustainability. Therefore, finding creative solutions involving the use of renewable energy sources presents the main challenge. Herein, we developed a cost-effective and highly efficient 2-in-1 integrated conical device consisting of multi-walled carbon nanotubes deposited filter paper, and iron wire, capable of simultaneously generating not only freshwater but also electricity from seawater. The 3D multi-walled carbon nanotubes/paper conical structure is an interconnecting link between steam and electricity generation, providing spacious surface area for both interfacial evaporation and oxygen reduction reaction (as a cathode of metal-air battery). The use of multi-walled carbon nanotubes not only secure high broadband light absorptance (~97% in UV–Vis-NIR) but also its conductivity is vital for efficient electricity generation. The device is capable of generating a power density of 13.50 W·m−2 while maintaining an evaporation rate of 1.53 kg·m-2·h−1 under 1 kW·m−2 solar illumination. In the current implementation, the energy density and built-in characteristics of the device, along with desalination capabilities can be a modest but invaluable solution for freshwater and energy needs in off-grid areas.