Ag Foams Research Articles

Pretreatment-free SERS sensing of microplastics using a self-attention-based neural network on hierarchically porous Ag foams

Low-cost detection systems are needed for the identification of microplastics (MPs) in environmental samples. However, their rapid identification is hindered by the need for complex isolation and pre-treatment methods. This study describes a comprehensive sensing platform to identify MPs in environmental samples without requiring independent separation or pre-treatment protocols. It leverages the physicochemical properties of macroporous-mesoporous silver (Ag) substrates templated with self-assembled polymeric micelles to concurrently separate and analyze multiple MP targets using surface-enhanced Raman spectroscopy (SERS). The hydrophobic layer on Ag aids in stabilizing the nanostructures in the environment and mitigates biofouling. To monitor complex samples with multiple MPs and to demultiplex numerous overlapping patterns, we develop a neural network (NN) algorithm called SpecATNet that employs a self-attention mechanism to resolve the complex dependencies and patterns in SERS data to identify six common types of MPs: polystyrene, polyethylene, polymethylmethacrylate, polytetrafluoroethylene, nylon, and polyethylene terephthalate. SpecATNet uses multi-label classification to analyze multi-component mixtures even in the presence of various interference agents. The combination of macroporous-mesoporous Ag substrates and self-attention-based NN technology holds potential to enable field monitoring of MPs by generating rich datasets that machines can interpret and analyze.

Supercooling degree decrease of barium hydroxide octahydrate employing 3D porous silver foam as supporting material

Inorganic hydrated salts possess high latent heat of phase transition and are promising phase change materials (PCMs). However, the issues of supercooling, low thermal conductivity, susceptibility to leakage, and phase separation significantly impediment the practical applications of inorganic hydrated salts. In this study, it is proposed to decrease the inorganic hydrated salt supercooling degree by increasing the surface roughness of the porous material and to load the nucleating agent silver (Ag) onto polydopamine (PDA) modified melamine foam (MF) by electroless plating to obtain 3D porous Ag foams, which are then utilized as support materials. The results demonstrated that the 3D porous Ag foam compounded with barium hydroxide octahydrate (BHO) can ameliorate the shortcomings of leakage and reduce the supercooling degree in the cooling process. The composite not only exhibits high enthalpy of over 248.5 J/g and high thermal conductivity of 1.82 W·m−1·K−1 but also has a low supercooling degree of 0.21 ℃. Furthermore, the composites exhibited superior shape stability and thermal cycling stability. This study provides an effective method for reducing the supercooling degree of inorganic hydration salts.

Porifera-Inspired Lightweight, Thin, Wrinkle-Resistance, and Multifunctional MXene Foam.

Transition metal carbides/nitrides (MXenes) demonstrate a massive potential in constructing lightweight, multifunctional wearable electromagnetic interference (EMI) shields for application in various fields. Nevertheless, it remains challenging to develop a facile, scalable approach to prepare the MXene-based macrostructures characterized by low density, low thickness, high mechanical flexibility, and high EMI SE at the same time. Herein, the ultrathin MXene/reduced graphene oxide (rGO)/Ag foams with a porifera-inspired hierarchically porous microstructure are prepared by combining Zn2+ diffusion induction and hard template methods. The hierarchical porosity, which includes a mesoporous skeleton and a microporous MXene network within the skeleton, not only exerts a regulatory effect on stress distribution during compression, making the foams rubber-like resistant to wrinkling but also provides more channels for multiple reflections of electromagnetic waves. Due to the interaction between Ag nanosheets, MXene/rGO, and porous structure, it is possible to produce an outstanding EMI shielding performance with the specific surface shielding effectiveness reaching 109152.4dBcm2 g-1 . Furthermore, the foams exhibit multifunctionalities, such as transverse Joule heating, longitudinal heat insulation, self-cleaning, fire resistance, and motion detection. These discoveries open up a novel pathway for the development of lightweight MXene-based materials with considerable application potential in wearable electromagnetic anti-interference devices.

CO2 Electroreduction on Silver Foams Modified by Ionic Liquids with Different Cation Side Chain Length.

Ionic liquids (ILs) are capable of tuning the kinetics of electroreduction processes by modifying a catalyst interface. In this work, a group of hydrophobic imidazolium-based ILs were immobilized on Ag foams by using a procedure known as "solid catalyst with ionic liquid layer" (SCILL). The derived electrocatalysts demonstrated altered selectivity and CO production rates for the electrochemical reduction of CO2 compared to the unmodified Ag foam. The activity change caused by the IL was dependent on the length of the N-alkyl substituent. The rate of CO production is optimized at moderate chain length and IL loadings. The observed trends are attributed to a local enrichment of CO2-based species in the proximity of the catalyst and a modification of the environment of its active sites. On the contrary, high loadings or long IL chains render the surface inaccessible and favor the hydrogen evolution reaction.

AgCu Bimetallic Electrocatalysts for the Reduction of Biomass-Derived Compounds.

The electrochemical transformation of biomass-derived compounds (e.g., aldehyde electroreduction to alcohols) is gaining increasing interest due to the sustainability of this process that can be exploited to produce value-added products from biowastes and renewable electricity. In this framework, the electrochemical conversion of 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydroxymethyl)furan (BHMF) is studied. Nanostructured Ag deposited on Cu is an active and selective electrocatalyst for the formation of BHMF in basic media. However, this catalyst deserves further research to elucidate the role of the morphology and size of the coated particles in its performance as well as the actual catalyst surface composition and its stability. Herein, Ag is coated on Cu open-cell foams by electrodeposition and galvanic displacement to generate different catalyst morphologies, deepening on the particle growth mechanism, and the samples are compared with bare Ag and Cu foams. The chemical–physical and electrochemical properties of the as-prepared and spent catalysts are correlated to the electroactivity in the HMF conversion and its selectivity toward the formation of BHMF during electroreduction. AgCu bimetallic nanoparticles or dendrites are formed on electrodeposited and displaced catalysts, respectively, whose surface is Cu-enriched along with electrochemical tests. Both types of bimetallic AgCu particles evidence a superior electroactive surface area as well as an enhanced charge and mass transfer in comparison with the bare Ag and Cu foams. These features together with a synergistic role between Ag and Cu superficial active sites could be related to the twofold enhanced selectivity of the Ag/Cu catalysts for the selective conversion of HMF to BHMF, that is, >80% selectivity and ∼ 100% conversion, and BHMF productivity values (0.206 and 0.280 mmol cm–2 h–1) ca. 1.5–3 times higher than those previously reported.

(Invited) Power-to-Value: Metal Foam Catalysts for the Electrochemical Conversion of CO2

The electrochemical conversion of CO2 (denoted as CO2RR) has attained significant interest in the catalysis research worldwide over the recent years as it provides means of transforming an environmentally harmful molecule back into products of higher value (e.g. high energy density fuels, chemical feedstock and useful commodity chemicals such as carbon monoxide). This process becomes particularly sustainable when using the surplus of electric power produced from renewable hydro, wind or solar sources (power-to-value concept). Substantial progresses have already been made during the last decade in the tailored design of novel catalyst materials needed to increase the energy efficiency of the CO2/water co-electrolysis and to guide the product distribution reaction into the desired direction. These progresses remained, however, restricted to the fundamental research whereas no technologically and economically feasible process could be established on an industrial scale so far. One key challenge left is related to the particular stability of the catalyst materials, a crucial pre-requisite for any industrial application of catalytic processes.In this contribution, concepts for the design of monometallic and bimetallic CO2RR catalysts will be discussed that are based on the additive-assisted electroplating of high-surface area metal foams. Main target products of the CO2RR addressed herein are formate (Bi foams), syngas (Ag foams; see Figure below) as valuable chemical feedstock for a subsequent non-electrochemical conversion process (Fischer-Tropsch, Rheticus process/Siemens-Evonik), and high energy density fuels (e.g. ethanol, n-propanol; bimetallic AgCu foams and co-alloed PdCu foams). Advanced operando Raman spectroscopy will be demonstrated to be highly useful for the identification of active catalyst species under CO2 electrolysis conditions. Figure 1

Preparation of Ag foam catalyst based on in-situ thermally induced redox reaction between polyvinyl alcohol and silver nitrate with supercritical CO2 foaming technology

The preparation process of a traditional metal foam catalyst is cumbersome, energy-intensive, and difficult to scale production, which restricts its development. In this work, the potential of polyvinyl alcohol (PVA) as a polyhydroxy reductant was explored. We used the thermally induced redox reaction between PVA and silver nitrate (AgNO3), combining with supercritical carbon dioxide (ScCO2) foaming technology, proposing an innovative idea for preparing the micron-sized Ag foam catalyst. Firstly, through the compound plasticizing effect of H2O and AgNO3, using CO2 as foam agent, the PVA/AgNO3 composite foams with uniform structure could be prepared below 100 °C. The maximum cell density could reach 5.39*109 cells/cm3 and the average cell size could reach 8.27 μm. Then, using the PVA matrix as a reductant and self-sacrifice template, silver ions could be quickly in-situ reduced at lower temperature (160–210 °C), the resulting silver particles could self-assemble into a foam-like skeleton structure. The Ag foams have an adjustable porous structure with a cell size of 4.01–16.30 μm and a ligament size of 1.08–2.82 μm. Applying it as a catalyst to promote the reduction of 4-nitrophenol (4-NP), the catalytic reaction rate constant is 10 times that of existing commercial Ag foam. The prepared Ag foam catalyst has the advantages of less dosage, easy recovery and good stability. Also, it has great application potential in the sensing, biomedicine, heat conduction and other fields.

Ag Electrodeposited on Cu Open‐Cell Foams for the Selective Electroreduction of 5‐Hydroxymethylfurfural

AbstractThe electrocatalytic conversion of 5‐hydroxymethylfurfural (HMF), a biomass platform molecule, to 2,5‐bis(hydroxymethyl)furan (BHMF), a polymer precursor, is a fully sustainable route that operates at room temperature and pressure, using water as source of hydrogen, and avoids high H2 pressures. In this work, we investigate the use of 3D electrocatalysts, made by Ag0 electrodeposited on Cu open‐cell foams (Ag/Cu), to improve the efficiency in the electrochemical conversion of HMF to BHMF in basic media at different HMF concentrations. For comparison purposes, Ag and Cu bulk foams as well as Ag, Cu and Ag/Cu foil counterparts are investigated. For diluted 0.02 M HMF solutions, BHMF is selectively produced at high HMF conversion and FE over Ag/Cu foams. The large surface area of 3D Ag/Cu foams, compared to their 2D counterparts, does not affect selectivity, but increases the rate of conversion and in turn the productivity. However, it would appear that the increase in the surface area is not enough to increase the efficiency in the conversion of more concentrated HMF electrolytes (0.05–0.50 M). The productivity of Ag/Cu is modified with electrocatalytic cycles.

Multi-stage pore development in Ag foams by the reduction of Ag2O and CuO mixtures

Pore expansion in solid metals is typically driven by an entrapped gas phase, such that temperature directly determines both the pressure within the pores and the ability of the matrix to plastically deform. This approach fundamentally limits the total porosity, as all pores are active simultaneously, which quickly results in coalescence and percolation. The method introduced here converts dispersed oxide particles to a gaseous reactant using reduction, such that independent stages of pore formation and expansion can be achieved by using more than one oxide chemistry. This is demonstrated using silver and copper oxides distributed within a silver matrix. As the temperature is raised, the silver oxide reduces first and creates porosity. As the temperature is raised further, the copper oxide reduces and creates additional porosity. This allows the pore morphology and grain size to be uniquely controlled while still maintaining the simplicity and scalability of the process. The microstructural development is studied through a combination of isothermal annealing, optical dilatometry, and focused ion beam cross-sectioning, and implications and strategies for other alloy systems are discussed.

Enhanced Electroreduction of Carbon Dioxide to Methanol Using Zinc Dendrites Pulse-deposited on Silver Foam

The electrocatalytic CO2 reduction reaction (CO2RR) can dynamize the carbon cycle by lowering anthropogenic CO2 emissions and sustainably producing valuable fuels and chemical feedstock. Methanol is arguably the most desirable C1 product of CO2RR, although it typically forms in negligible amounts. In our search for efficient methanol-producing CO2RR catalysts, we engineer Ag-Zn catalysts by pulse-depositing Zn dendrites on Ag foams (PD-Zn/Ag foam). By themselves, Zn and Ag cannot effectively reduce CO2 to CH3OH, while their alloys gave CH3OH with Faradaic efficiencies (FE) of ~1%. Interestingly, with nanostructuring, PD-Zn/Ag foam reduces CO2 to CH3OH with FE and current densities reaching as high as 10.5% and -2.7mA/cm2, respectively. Control experiments and DFT calculations pinpoint strained undercoordinated Zn atoms as the active sites for CO2RR to CH3OH in a reaction pathway mediated by adsorbed CO and formaldehyde. Surprisingly, the stability of the *CHO intermediate does not influence the activity. https://doi.org/10.1002/anie.201810991 Figure 1

Enhanced electrocatalytic CO formation from CO2 on nanostructured silver foam electrodes in ionic liquid/water mixtures

We employ a novel type of nanostructured silver foam electrocatalyst to the electrochemical CO2 reduction reaction (CO2RR) in 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) ionic liquid. The Ag catalyst is prepared from an aqueous electroplating bath by means of an additive-assisted electrodeposition approach, yielding macro-porous Ag foams. The pore sidewalls are composed of Ag nanoneedles having diameters of ∼50–100 nm and lengths that can exceed 1 μm. We demonstrate that, when combined with the [Bmim][BF4] electrolyte, this Ag electrocatalyst significantly shifts the onset of CO2 electroreduction by ∼220 mV to less negative potentials as compared to a polished Ag foil electrode. The addition of moderate amounts of water (optimum water mole fraction of 20%) to the pure [Bmim][BF4] electrolyte leads to a further ∼120 mV decrease in the CO2RR overpotential. The combination of the Ag foam catalyst with the [Bmim][BF4]/water mixture results in a ∼300 mV wide potential window where CO is selectively produced with Faraday efficiencies >94%. The structural stability of the catalyst is supported by identical location scanning electron microscopy.

Enhanced Electroreduction of Carbon Dioxide to Methanol Using Zinc Dendrites Pulse‐Deposited on Silver Foam

AbstractThe electrocatalytic CO2 reduction reaction (CO2RR) can dynamise the carbon cycle by lowering anthropogenic CO2 emissions and sustainably producing valuable fuels and chemical feedstocks. Methanol is arguably the most desirable C1 product of CO2RR, although it typically forms in negligible amounts. In our search for efficient methanol‐producing CO2RR catalysts, we have engineered Ag‐Zn catalysts by pulse‐depositing Zn dendrites onto Ag foams (PD‐Zn/Ag foam). By themselves, Zn and Ag cannot effectively reduce CO2 to CH3OH, while their alloys produce CH3OH with Faradaic efficiencies of approximately 1 %. Interestingly, with nanostructuring PD‐Zn/Ag foam reduces CO2 to CH3OH with Faradaic efficiency and current density values reaching as high as 10.5 % and −2.7 mA cm−2, respectively. Control experiments and DFT calculations pinpoint strained undercoordinated Zn atoms as the active sites for CO2RR to CH3OH in a reaction pathway mediated by adsorbed CO and formaldehyde. Surprisingly, the stability of the *CHO intermediate does not influence the activity.

Enhanced Electroreduction of Carbon Dioxide to Methanol Using Zinc Dendrites Pulse-Deposited on Silver Foam.

The electrocatalytic CO2 reduction reaction (CO2 RR) can dynamise the carbon cycle by lowering anthropogenic CO2 emissions and sustainably producing valuable fuels and chemical feedstocks. Methanol is arguably the most desirable C1 product of CO2 RR, although it typically forms in negligible amounts. In our search for efficient methanol-producing CO2 RR catalysts, we have engineered Ag-Zn catalysts by pulse-depositing Zn dendrites onto Ag foams (PD-Zn/Ag foam). By themselves, Zn and Ag cannot effectively reduce CO2 to CH3 OH, while their alloys produce CH3 OH with Faradaic efficiencies of approximately 1 %. Interestingly, with nanostructuring PD-Zn/Ag foam reduces CO2 to CH3 OH with Faradaic efficiency and current density values reaching as high as 10.5 % and -2.7 mA cm-2 , respectively. Control experiments and DFT calculations pinpoint strained undercoordinated Zn atoms as the active sites for CO2 RR to CH3 OH in a reaction pathway mediated by adsorbed CO and formaldehyde. Surprisingly, the stability of the *CHO intermediate does not influence the activity.

Beyond Copper in CO2 Electrolysis: Effective Hydrocarbon Production on Silver-Nanofoam Catalysts

Ag-foam catalysts have been developed for the electrochemical CO2 reduction reaction (ec-CO2RR) based on a concerted additive- and template-assisted metal-deposition process. In aqueous media (CO2-saturated 0.5 M KHCO3 electrolyte), these Ag foams show high activity and selectivity toward CO production at low and moderate over-potentials. Faradaic efficiencies for CO (FECO) never fell below 90% within an extremely broad potential window of ∼900 mV, starting at −0.3 V and reaching up to −1.2 V versus a reversible hydrogen electrode (RHE). An increased adsorption energy of CO on the Ag foam is discussed as the origin of the efficient suppression of the competing hydrogen-evolution reaction (HER) in this potential range. At potentials of <−1.1 V versus RHE, the FEH2 values significantly increase at the expense of FECO. Superimposed on this anti-correlated change in the CO and H2 efficiencies is the rise in the CH4 efficiency to the maximum of FECH4 = 51% at −1.5 V versus RHE. As a minor byproduct, even C–C-c...

Electrochemical Fabrication of Ag and Au Foams for Electrochemical Conversion of CO2

In recent, huge efforts have been conducted to relieve the global warming problem by the electrochemical conversion of CO2 into useful chemicals. Particularly, it has been reported that the Ag and Au are highly active materials to produce the CO with high selectivity. However, the cost problem originated from use of noble metal catalysts limits their practical applications. In this study, the Ag and Au foam structures were electrochemically fabricated as a catalyst for CO2 reduction to produce CO. As a first step, the Cu foam was prepared on Ti foil substrate by galvanostatic pulse deposition which consisted of low current for continuous Cu film and following high current for porous Cu. The pore size (22 ~ 56 μm) and wall thickness (14 ~ 42 μm) were controlled by concentration of Cu precursor and applied deposition currents. Then, the Cu foams were immersed in the electrolyte which contained noble metal precursors and additives, in order to minimize the noble metal usage as well as to increase the electrochemical surface area. The coverage and morphology of noble metals on the surface of Cu form were affected by the precursor and additives concentrations in displacement step. The catalytic activity of fabricated noble metal foams were examined for electrochemical CO2 reduction. As a result, it was revealed that the CO Faradaic efficiency was significantly related to the morphology and composition of noble metal foams.

Enhanced CO selectivity and stability for electrocatalytic reduction of CO2 on electrodeposited nanostructured porous Ag electrode

Nanostructured electrocatalysts for CO2 reduction have attracted much attention due to their unique properties compared to their bulk counterparts. Here we report the synthesis of porous Ag foams on a polished Ag substrate via electrodeposition using the hydrogen bubble dynamic template. The as-prepared porous Ag foams has an average pore size of 10–25μm with the porous wall composed of 40–100nm Ag nanoparticles. CV tests indicate that the competing hydrogen evolution reaction remarkably slow down on porous Ag electrode and the onset potential of CO2 reduction occurs at 0.15V less than that on the Ag foil electrode. Moreover, the high current density and CO faradaic efficiency of over 90% were stable over the course of several hours, whereas Ag foil electrode exhibited the drop of CO faradaic efficiency from 74.4% to 58.6% under identical conditions. We found that the enhanced activity and stability are the result of a large electrochemical surface area (approximately 120 times larger) which can provide more active sites. The noteworthy difference between the two electrodes suggests that the nanostructured surface of porous Ag foams is likely to not only favor the formation of CO2− intermediate but also suppress the competitive reaction of hydrogen evolution.

Characterization and Functional Applications of Nanoporous Ag Foams Prepared by Chemical Dealloying

In this study, the pure Ag nanoporous foams, with open cell pore volume fractions 55 to 70 pct and pore sizes 100 to 400 nm, have been prepared by chemical dealloying. The Ag nanoporous foams possess favorable modulus (~0.7 GPa) and strength (~14 MPa), much higher than most of the polymers or ceramic foams. It is found that the Ag nanoporous foams are appropriate candidates for the catalytic and electrode applications. However, they do not exhibit efficient anti-bacterial effect, unless much smaller bacteria with cell sizes of 100 nm or less in the neighborhood are encountered.

Fabrication of metal sulfide porous foams via electrodeposition and galvanic replacement reaction

A simple and non toxic method is reported for fabrication of metal sulfide foams such as Cu2S, Ag2S and CdS. The presented method is mainly based on the electrochemical fabrication of metal foam and galvanic replacement reaction. Cu2S and Ag2S foams are synthesized by immersing as-fabricated Cu and Ag foams in aqueous sulfide solution. Furthermore, another method is used for fabrication of Ag2S foam based on immersing of as-prepared Cu2S foam in AgNO3 solution. Electrodeposition of CdS on as-fabricated Cu foam electrode is performed potentiostatically using a two electrode setup in an aqueous solution of CdSO4, EDTA, and Na2S2O3. The synthesis process is rapid and convenient. The as-fabricated foams were characterized through XRD, BET, SEM and EDX analysis. The obtained data revile fabrication of Cu2S, Ag2S and CdS foams with porous and ramified walls and high surface area. The applicability of as-fabricated Cu2S in the photodegradation of methylene blue is reported, as a proof of concept. The proposed approaches demonstrate a practical route toward preparation of porous metal sulfide foams via electrodeposition and galvanic replacement.

High temperature morphology and stability of nanoporous Ag foams

Nanoporous silver foams (75 % porosity) synthesized by dealloying Ag25Al75 using two different electrolytes were heat treated in either argon or vacuum in order to induce changes in the morphology and ligament size. Several techniques including scanning electron microscopy, Raman spectroscopy, and X-ray powder diffraction are utilized to study the elevated temperature morphology and oxide formation. The ligament sizes increase with heat treating temperature, except for the sample heat treated in vacuum at 600 °C. Results show no significant silver oxide formation for any of the foams.

Strength scale behavior of nanoporous Ag, Pd and Cu foams

A comprehensive study of the deformation mode for nanoporous Au, Pd, Cu and Ag foams is presented. Several nanoporous models that include surface, nodes and ligament size effects are investigated within the scope of elastic buckling or plastic collapse foam models. The predictions from the deformation models are then compared to experimental foams hardness values for a wide range of ligament sizes. Results show that plastic collapse appears to be the dominant failure mode for all the nanoporous foams. Small deviations from the plastic collapse models are attributed to irregular cell size and relative density estimations.