Template Precursor Research Articles

Solvent-free mechanochemical synthesis of Mg-gallic acid complex for the fabrication of high-performance supercapacitor porous carbon

At molecular level, it is challenging to construct a porous carbon from magnesium based template and low cost precursor by a facile route for supercapacitive energy storage, e.g. solvent-free approach because the coordination of magnesium ion with organic ligands usually needs participation of solvent. Herein, a balling milling mediated coordination of magnesium acetate and gallic acid was developed in the absence of solvent to prepare porous carbon. The key of the present strategy lies in the generation of volatile HAc, orienting the reaction in a favorable direction for the formation of complexes. The resultant porous carbon (denoted BGMC) owns a high microporostiy ratio (24.2 % vs template-free derived ones of 11.1 %), open accessed microstructure and hydrophobic character. As electrode for supercapacitor, in aqueous electrolyte, the BGMC based supercapacitor achieves a high energy density of 19.2 Wh kg−1@900 W kg−1, while, in organic electrolyte of 1.0 M TEABF4/AN, the symmetric device based on BGMC delivers energy in a wide voltage window of 0–3.5 V with large energy of 34.4 Wh kg−1@1750 W kg−1, which is superior to those of recently reported carbon based devices. And more, at high current density of 10 A g−1, the BGMC device can resist continual charge/discharge for 30 000 cycles, showing an excellent cycling stability. Our strategy involving solvent-freely coordination of template and precursor molecule to prepare porous carbon open up a route with facile, scalable and easy-operable attributes towards the preparation of functional porous carbon.

Construction of hollow NiCo-LDH nanocages for electrochemical sensing of hydrazine based on template etching strategy

The improper use of hydrazine (N2H4) will cause serious pollution to the environment and harm to human health. It is essential to establish a rapid and sensitive detection method for N2H4 in the environment. In this study, NiCo-LDH self-assembled hollow nanocages (HNCs) are prepared by in-situ etching using Cu2O nanocube as precursor template. The unique hollow nanocage structure can significantly increase the active site of the catalyst, which is beneficial for ion transfer and charge transport, thereby improving the electrocatalytic performance of the N2H4 sensor. The detection linear range is 3 × 10−3 mM −2 mM and 3 μM to 6 mM, and the detection limit (LOD) is 0.135 μM (S/N = 3). Additionally, it shows good selectivity, reproducibility and stability. The constructed novel N2H4 electrochemical sensor has potential application prospects in environmental water samples.

A facile strategy for synthesis of flower-like FeNiS2 nanocomposite via integration of binary metal-organic framework and metal sulfide for enhanced electrocatalytic oxygen evolution reaction

Researchers are looking into boosted functional materials to address the rising demand for enhanced energy storage and efficient catalysts in producing and storing sustainable energy. Here, we report the development of an integrated binary metallic FeNi metal-organic framework (MOF) through a unique method termed reductive electrosynthesis. This MOF provides customized catalytic sites inside a highly porous material by connecting metal cations via 2-amino terephthalic acid connectors. However, the poor electrical conductivity and stability of pristine MOFs have made their practical implementation difficult. A thin FeNiS2/nickel foam (NF) nanocomposite based on the precursor and self-sacrificed FeNi-MOF template was developed to get beyond these restrictions. In addition to improving electrical conductivity, this unique structure supports FeNi-MOF porous structure. As a result, the outstanding functional electrocatalytic performance of FeNiS2/NF on oxygen evolution reaction in alkaline media was observed at low overpotential of ηj10 = 280 mV and a tafel slope of 35 mV/dec. This study provides a feasible way to produce highly stable and active nonprecious electrocatalysts for commercial water electrolysis applications.

Low-cost and sustainable fabrication of waste rubber derived porous carbon for o-nitrophenol removal with high practical application potential: A waste salt-free and recyclable template strategy

The large-scale utilization of nitrophenols and the rapid replacement of rubber products have led to an explosive increase in emissions and waste. Herein, we report a low-cost, sustainable, recyclable nano ZnO-templating synthesis strategy to fabricate porous carbon materials derived from waste rubber. Zinc acetate, employed as the template precursor, can be readily removed and recycled through acetic acid leaching, thereby mitigating production expenses and circumventing the generation of saline wastewater throughout the synthetic procedure. The porous carbons fabricated possess tunable textural characteristics, as well as in-situ doping of oxygen-containing species. The sample of WRPC-1.25 owning high specific surface area of 1088.68 m2/g and volume of 2.58 cm3/g exhibits remarkable adsorption capacity of 393.42 mg/g for ONP in batch and of 300.2 mg/g in fixed bed continuous flow adsorption test. Additionally, the WRPC-1.25 demonstrates excellent practical application potential for ONP removal both in the continuous dynamic adsorption-regeneration cycles and environmental test. Based on material characterization, adsorption evaluation tests and theoretical calculations, the synergistic adsorption mechanism of ONP on carbon surfaces, governed by pore filling, dispersion effects, and strong electrostatic attraction originating from oxygen functional groups, was elucidated.

Synthesis of Metallic and Metal Oxide Nanoparticles Using Homopolymers as Solid Templates: Luminescent Properties of the Eu+3 Nanoparticle Products

Starting from poly(4-vinylpyridine) ((P4VP)n), poly(2-vinylpyridine) ((P2VP)n), and [N=P(O2CH2CF3)]m-b-P2VP20 block copolymers, a series of metal-containing homopolymers, (P4VP)n⊕MXm, (P2VP)n⊕MXm, and [N=P(O2CH2CF3)]m-b-P2VP20]⊕MXm MXm = PtCl2, ZnCl2, and Eu(NO3)3, have been successfully prepared by using a direct and simple solution methodology. Solid-state pyrolysis of the prepared metal-containing polymeric precursors led to the formation of a variety of different metallic and metal oxide nanoparticles (Pt, ZnO, Eu2O3, and EuPO4) depending on the composition and nature of the polymeric template precursor. Thus, whereas Eu2O3 nanostructures were obtained from europium-containing homopolymers ((P4VP)n⊕MXm and (P2VP)n⊕MXm), EuPO4 nanostructures were achieved using phosphorus-containing block copolymer precursors, [N=P(O2CH2CF3)]m-b-P2VP20]⊕MXm with MXm = Eu(NO3)3. Importantly, and although both Eu2O3 and EuPO4 nanostructures exhibited a strong luminescence emission, these were strongly influenced by the nature and composition of the macromolecular metal-containing polymer template. Thus, for P2VP europium-containing homopolymers ((P4VP)n⊕MXm and (P2VP)n⊕MXm), the highest emission intensity corresponded to the lowest-molecular-weight homopolymer template, [P4VP(Eu(NO3)3]6000, whereas the opposite behavior was observed when block copolymer precursors, [N=P(O2CH2CF3)]m-b-P2VP20]⊕MXm MXm= Eu(NO3)3, were used (highest emission intensity corresponded to [N=P(O2CH2CF3)]100-b-[P2VP(Eu(NO3)3)x]20). The intensity ratio of the emission transitions: 5D0 → 7F2/5D0 → 7F1, suggested a different symmetry around the Eu3+ ions depending on the nature of the polymeric precursor, which also influenced the sizes of the prepared Pt°, ZnO, Eu2O3, and EuPO4 nanostructures.

Lanthanum‐Nickel‐Based Mixed‐Oxide‐Coated Nickel Electrodes for the OER Electrocatalysis

ABSTRACTThe anodic oxygen evolution reaction (OER) remains a bottleneck for electrocatalytic water splitting due to its sluggish kinetics and, thus, high overpotentials. This limits water electrolysis as a key technology for the generation of hydrogen as a sustainable alternative to fossil fuels. For alkaline water splitting, perovskite phases (ABO3) with earth‐abundant first‐row transition‐metals have emerged as a promising material class for OER electrocatalysts. Among these, LaNiO3 has been found to exhibit high intrinsic OER activity. To increase catalyst utilization, a high surface area of the catalyst is desirable and can be achieved by impregnation of porous templates. In this work, La–Ni‐based oxides were prepared via impregnation of activated carbon and subsequent heating, combining precursor calcination and template removal into one step. The phase structure of the samples is analyzed via powder X‐ray diffractometry, and the morphology is determined by scanning electron microscopy. The synergistic effect of B‐site mixing iron as well as A‐site mixing strontium into LaNiO3 is studied and found to increase its OER activity, confirming the activity‐enhancing effect of Fe in Ni‐based OER electrocatalysts. To allow for facile technical application of the catalysts, the electrodes are prepared by coating a perovskite ink onto Ni‐metal as industrially relevant substrates, followed by calcination.

Fe-Doped CoNi layered hydrogencarbonate hierarchical Nano-Array assisted growth of ZIF-67 as an efficient OER/UOR bifunctional catalyst reaction for Overall Urea-Water electrolysis

The design of efficient electrocatalysts for OER and UOR is essential for achieving sustainable hydrogen production and enabling simultaneous wastewater treatment. Here, a versatile fabrication method for the in-situ growth of ZIF-67 from hydrocarbonate as a template for three-dimensional hierarchical nano-arrays. This strategy provides an opportunity for controllably tuning the interfacial assembly of MOFs materials on precursor template nanomaterials. The obtained MIM@Fe0.1-CoNi CH/NF exhibited enhanced electrocatalytic performance as an electrocatalytic anode for the OER and UOR. The MIM@Fe0.1-CoNi CH/NF required only 194 mV and 285 mV overpotentials to achieve the current densities of 10 and 100 mA·cm−2 in the electrolyte of 1.0 M KOH, and the overpotentials in the 1.0 M KOH + 0.5 M Urea electrolyte requires only 1.31 V (vs.RHE) to achieve a current density of 10 mA·cm−2. Notably, (+)MIM@Fe0.1-CoNi CH/NF || Pt/C/NF(−) achieves 10 mA·cm−2 in urea-assisted electrolysis at only 1.36 V (vs.RHE). The excellent catalytic performance was attributed to the modification of the CoNi CH/NF template by Fe3+ and 2-MIM, which modulated the Ni2+ and Co2+ electronic structures and optimised the adsorption behaviour of the OER/UOR intermediates. Overall, this work provides a strategy for preparing desirable catalysts for clean energy and wastewater treatment.

Double core–shell hollow nanocage CuO@Co3O4 for the selective hydrogenolysis of C–O bonds of lignin without external hydrogen

The design of a highly active Cu-Co catalyst for catalytic transfer hydrogenolysis of lignin without the use of external hydrogen remains highly challenging. In this work, Cu2O was initially encapsulated in ZIF-67, and subsequently Cu2O@ZIF-67 was utilized as a precursor and sacrificial template to prepare the unique double core–shell hollow nanocage CuO@Co3O4. Co and Cu, serving as Lewis acid sites and dehydrogenation sites for the hydrogen-donor solvent isopropanol, respectively, exhibited synergistic enhancement, further increasing the catalytic activity. Under the optimal conditions of 220 °C, 1 MPa N2, and 4 h, the catalyst achieved 100 % conversion of 2-phenoxy-1-phenylethanol and 100 % yield towards cyclohexanol and ethylbenzene. Furthermore, the catalyst remained stable and reusable after 5 cycles, providing a practicable guidance for the value-added conversion of lignin.

Synthesis of porous carbon-encapsulated MoxC/Co based on NaCl template and ZIF-67 towards enhancing electromagnetic wave absorption

Although molybdenum carbide (MoxC) has emerged as an effective absorber of electromagnetic (EM) waves, its practical application is hindered by impedance mismatch and single loss mechanism. Herein, we developed a one-step method for creating NaCl template precursors assembled with ZIF-67 to produce porous multiple components of MoxC composites. The MoxC-Co/C composites exhibit a minimum reflection loss (RLmin) of −59.69 dB with a bandwidth of 3.12 GHz at a thickness of 1.50 mm. The RLmin reaches −71.39 dB with a bandwidth of 4.08 GHz at a thickness of 2.09 mm. The flower-like MoxC-Co/C composites are capable of improving impedance matching and offering multiple loss mechanisms such as interfacial polarization, dipolar polarization, conductive loss and magnetic loss, resulting in enhanced EM wave absorption. Thus, our work featured a simple strategy to provide a unique insight into fabricating high-performance EM wave absorbers on molybdenum carbon basis.

Sensitive electrochemical biosensor for Ustilaginoidea Virens short-stranded DNA segment via higher-ordered G-quadruplex multimerization induced by LAMP/H+-responsive i-motif folding

By using variable loop-mediated isothermal amplification byproduct H+ ions (vLAMP/H+) as signal transducer, exploring the electrochemical assay of short-stranded DNA segment related to U. virens (uDNA, 21-nt) is intriguing. Herein, we report the first design of a sensitive electrochemical biosensor for uDNA as targeting input promoter of vLAMP, for which a discernible template hairpin and a precursor hairpin are well-designed. The specific recognition and complementary hybridization among them form a double-dumbbell DNA structure tethering two stem-loop motifs that is served as template precursor to operate vLAMP for DNA+1 polymerization via nucleotide incorporation, generating vLAMP/H+ to modulate pH-responsive i-motif folding of a C-rich strand. A ferrocene-tagged G-rich strand is dehybridized and incubated in modified electrode surface including an amino-labeled G-rich strand that adopts compact G-quadruplex (G4) conformation. This G4, as an initiator, guides the ‘head-to-tail’ π-π stacking of electroactive tags for developing higher-ordered wire-like G4 multimers (G4W), which are stably held together via interquadruplex multimerization. No involving additional nucleic acid amplifiers, numerous electroactive mediators are repetitively cascaded, thereby significantly amplifying the current readout signal and achieving sensitive electrochemical detection of U. virens. Benefited from simple and rapid vLAMP/H+-G4W route, our assay strategy would provide a new paradigm to create applicable electrochemical biosensors for diverse short-stranded DNA biomarkers by altering LAMP operation modes readily.

Tricomponent direct co-assembly to nitrogen-doped, ordered mesoporous carbon@silica frameworks with enhanced nitrogen stability and multi-functionalities

Ordered mesoporous carbon@silica hybrid frameworks with high nitrogen content and good stabilities show great significance to improve their functionalities. Herein, we report novel nitrogen-doped (3.51 ∼ 4.62 wt%) and ordered mesoporous carbon@silica frameworks (N-OMC@SiO2) with reinforced nitrogen stability. The N-OMC@SiO2 were designed from tricomponent direct co-assembly between block copolymer template and mixed precursors containing urea and tetramethoxysilane without using additional solvent. The N-OMC@SiO2 have large BET surface areas (444.3 ∼ 674.9 m2/g), uniform mesoporous channels (5.8 ∼ 10.9 nm) with well-defined hexagonal symmetry, and stable carbon@silica “reinforced concrete” framework that can be transformed into carbon@silicon by controllable reduction. The nitrogen sites were firmly embedded into their frameworks via the formation of Si-N bonding. Thus, the resulted N-OMC@SiO2 exhibit multi-functionalities and enhanced recyclability in acid waste gas capture and gaseous sulfides catalytic utilization, better than many reported porous adsorbents and catalysts. This study may help develop stable and efficient N-OMCs nanocomposites for acidic gas selective removal.

Porous layered ZnV2O4@C synthesized based on a bimetallic MOF as a stable cathode material for aqueous zinc ion batteries.

Vanadium-based oxides are considered potential cathode materials for aqueous zinc ion batteries (AZIBs) due to their distinctive layered (or tunnel) structure suitable for zinc ion storage. However, the structural instability and sluggish kinetics of vanadium-based oxides have limited their capacity and cycling stability for large-scale applications. To overcome these shortcomings, here a porous vanadium-based oxide doped with zinc ions and carbon with the molecular formula ZnV2O4@C (ZVO@C) as the cathode material is synthesized by the pyrolysis of a bimetallic MOF precursor containing Zn/V. This electrode demonstrates a remarkable specific capacity of 425 mA h g-1 at 0.5 A g-1 and excellent cycling stability with about 97% capacity retention after 1000 cycles at 10 A g-1. The excellent electrochemical performance of ZVO@C can be attributed to more reaction active sites and the faster reaction kinetics for zinc ion diffusion and storage brought about by the porous layered spinel-type tunnel structure with high surface area and massive mesoporosity, as well as the enhanced electron transport efficiency and more stable channel structure achieved from the doped conductive carbon. The reaction mechanism and structural evolution of the ZVO@C electrode are analyzed using X-ray diffraction and X-ray photoelectron spectroscopy, revealing the formation of a new phase of ZnxV2O5·nH2O during the first charge, which participates in reversible cycling together with ZVO@C during the charging and discharging processes. Moreover, the energy storage mechanism is revealed, in which zinc ions and hydrogen ions jointly participate in intercalation and extraction. The present study demonstrates that constructing composite vanadium-based oxides based on bimetallic organic frameworks as precursor templates is an effective strategy for the development of high-performance cathode materials for AZIBs.

Atomically dispersed Pt on MOF-derived In2O3 for chemiresistive formaldehyde gas sensing

Single-atom catalysts (SACs) supported on inorganic materials have been confirmed as effective active sites in catalytic reaction. In order to develop gas sensing material with high performance, we reported an atomically dispersed Pt on MOF-derived In2O3 via N doped graphene (NG) sacrificial templating route for the first time. This synthesis strategy, which combines metal-organic frameworks (MOF) precursor and NG template, not only greatly regulates the physicochemical properties of In2O3, but also makes the single-atom Pt be anchored on In2O3. Herein, the effect of Pt and NG was discussed based on various characterization methods. Gas sensing tests revealed that the highly dispersed Pt helps to improve the HCHO sensing performance. The Pt SACs inclusion increases the specific surface area, the contents of oxygen vacancies and adsorbed oxygen species of In2O3, thus increasing the active sites on the surface. These enhancements result in high response (750.4 to 100 ppm), good selectivity, rapid response (2 s to 100 ppm) and low theoretical limit of detection (8.4 ppb) of Pt1-In2O3 based sensor to HCHO. In a word, atomically dispersed Pt loaded MOF-derived In2O3 is an efficient sensing material for selective detection of HCHO.

Effects of Synthesis Conditions of Na0.44MnO2 Precursor on the Electrochemical Performance of Reduced Li2MnO3 Cathode Materials for Lithium-Ion Batteries.

Li2MnO3 nanobelts have been synthesized via the molten salt method that used the Na0.44MnO2 nanobelts as both the manganese source and precursor template in LiNO3-LiCl eutectic molten salt. The electrochemical properties of Li2MnO3 reduced via a low-temperature reduction process as cathode materials for lithium-ion batteries have been measured and compared. Particularly investigated in this work are the effects of the synthesis conditions, such as reaction temperature, molten salt contents, and reaction time on the morphology and particle size of the synthesized Na0.44MnO2 precursor. Through repeated synthesis characterizations of the Na0.44MnO2 precursor, and comparing the electrochemical properties of the reduced Li2MnO3 nanobelts, the optimum conditions for the best electrochemical performance of the reduced Li2MnO3 are determined to be a molten salt reaction temperature of 850 °C and a molten salt amount of 25 g. When charge-discharged at 0.1 C (1 C = 200 mAh g-1) with a voltage window between 2.0 and 4.8 V, the reduced Li2MnO3 synthesized with reaction temperature of Na0.44MnO2 precursor at 850 °C and molten salt amounts of 25 g exhibits the best rate performance and cycling performance. This work develops a new strategy to prepare manganese-based cathode materials with special morphology.

Tuning the Cerium-Based Metal-Organic Framework Formation by Template Effect and Precursor Selection.

The novel metal-organic framework [(CH3)2NH2]2[Ce2(bdc)4(DMF)2]·2H2O (Ce-MOF, H2bdc-terephthalic acid, DMF-N,N-dimethylformamide) was synthesized by a simple solvothermal method. Ce-MOF has 3D connectivity of bcu type with a dinuclear fragment connected with eight neighbors, while three types of guest species are residing in its pores: water, DMF, and dimethylammonium cations. Dimethylamine was demonstrated to have a decisive templating effect on the formation of Ce-MOF, as its deliberate addition to the solvothermal reaction allows the reproducible synthesis of the new framework. Otherwise, the previously reported MOF Ce5(bdc)7.5(DMF)4 (Ce5) or its composite with nano-CeO2 (CeO2@Ce5) was obtained. Various Ce carboxylate precursors and synthetic conditions were explored to evidence the major stability of Ce-MOF and Ce5 within the Ce carboxylate-H2bdc-DMF system. The choice of precursor impacts the surface area of Ce-MOF and thus its reactivity in an oxidative atmosphere. The in situ PXRD and TG-DTA-MS study of Ce-MOF in a nonoxidative atmosphere demonstrates that it eliminates H2O and DMF along with (CH3)2NH guest species in two distinct stages at 70 and 250 °C, respectively, yielding [Ce2(bdc)3(H2bdc)]. The H2bdc molecule is removed at 350 °C with the formation of novel modification of Ce2(bdc)3, which is stable at least up to 450 °C. According to the total X-ray scattering study with pair distribution function analysis, the most pronounced local structure transformation occurs upon departure of DMF and (CH3)2NH guest species, which is in line with the in situ PXRD experiment. In an oxidative atmosphere, Ce-MOF undergoes combustion to CeO2 at a temperature as low as 390 °C. MOF-derived CeO2 from Ce-MOF, Ce5, and CeO2@Ce5 exhibits catalytic activity in the CO oxidation reaction.

General Formation of Interfacial Assembled Hierarchical Micro‐Nano Arrays for Biomass Upgrading‐Coupled Hydrogen Production

AbstractConstruction of efficient catalysts to couple biomass upgrading with hydrogen production is significant for improving energy efficiency, which remains a challenge. Herein, a general method for manufacturing 3D hierarchical micro‐nano arrays consisting of template framework and nanoparticle‐decorated nanosheets is reported. This strategy provides an opportunity to controllably tailor the interfacial assembly of nanosheets on precursor template materials. The obtained Co@NiMoO‐Ni/NF exhibits enhanced electrocatalytic performance for biomass oxidation and hydrogen production. It only needs 1.21 V to achieve 10 mA cm−2 for 5‐hydroxymethylfurfural electrooxidation reaction (HMFOR) assisted H2 evolution reaction (HER). The good catalytic performance is ascribed to the intense interaction between template (Co) and nanoparticle‐decorated nanosheets (NiMoO‐Ni), which tunes the electron structure of the catalyst to optimize the adsorption behavior of HMFOR/HER intermediates and promote the bonds breakage of key intermediates in the HMFOR/HER process. This work thus provides a strategy for designing ideal catalysts for biomass upgrading‐coupled H2 production.

Facile synthesis of ultrafine iron-cobalt (FeCo) nanocrystallite-embedded boron/nitrogen-codoped porous carbon nanosheets: Accelerated water splitting catalysts

Designing two-dimensional (2D) porous carbon nanosheets is expected to boost the water splitting efficiency of low-cost iron (Fe) and cobalt (Co)-based catalysts. Nevertheless, the aggregations, tedious preparation procedures, and expensive precursors for synthesizing 2D porous carbon nanosheets have hindered their widespread application. Herein, for the first time, we developed a low-cost method for large-scale and rapid synthesis of the three-dimensional (3D) hierarchically porous architectures self-assembled by the ultrafine FeCo nanoparticles embedded and boron/nitrogen-codoped 2D porous carbon nanosheets (denoted as FeCo@BNPCNS). The optimal FeCo@BNPCNS-900 exhibited abundant porous channels, a large surface area, and vast carbon edges/defects. Therefore, 8.10 at% electrochemically active boron (B)/nitrogen (N) centers were doped into the porous carbon nanosheets. In an alkaline solution, the optimal FeCo@BNPCNS-900 nanosheets revealed excellent hydrogen evolution reaction (HER) electrocatalytic activity, surpassing commercial 20 wt% Pt/C. For instance, the HER potential at 10 mA cm−2 [-50.6 mV vs. reversible hydrogen electrode (RHE)] of FeCo@BNPCNS-900 was even 19.3 mV more positive than that of commercial 20 wt% Pt/C (-69.9 mV vs. RHE). Meanwhile, its oxygen evolution reaction (OER) catalytic activity was just a little worse than ruthenium oxide (RuO2). The water electrolysis cell of FeCo@BNPCNS-900 nanosheets just required a small voltage of 1.589 V for full water splitting to achieve 10 mA cm−2, even 70.3 mV more negative than that of the state-of-the-art 20 wt% Pt/C||RuO2 benchmark (1.660 V) with outstanding stability. The perfect 3D hierarchically porous and honeycomb-like architecture, abundant porous channels/mesopores, and uniformly dispersed electrocatalytically active sites on FeCo@BNPCNS-900 nanosheets were responsible for the outstanding water splitting performance. Finally, this study provides an efficient strategy for the large-scale, rapid, and low-cost synthesis of 2D porous carbon nanosheets without using any template, surfactant, or expensive precursors.

Heterogeneous Interface Engineering of Bi‐Metal MOFs‐derived ZnFe2O4–ZnO‐Fe@C Microspheres via Confined Growth Strategy Toward Superior Electromagnetic Wave Absorption

AbstractHeterogeneous interface regulation plays an important role in tailoring the intrinsic electromagnetic (EM) properties for obtaining excellent EM wave absorption, which still faces huge challenge. In this work, bi‐metal MOFs‐derived ZnFe2O4–ZnO‐Fe@C (ZZFC) microspheres with custom‐built heterogeneous interfaces are successfully fabricated via a confined growth strategy. Bi‐metal Fe–Zn–ZIF with tailored coordination structure and chemical bonding are first selected as the precursor template. After undergoing the annealing process, the metal Fe2+ host is converted into magnetic Fe nanoparticles (NPs). The Zn2+ host is transformed into semiconductor zinc oxide (ZnO) with increasing (101) crystal‐oriented growth. At the same time, metal hosts Fe2+ and Zn2+ are further reacted to synthesize the zinc ferrite (ZnFe2O4). Formed Fe nanoparticles catalyze organic ligands to constitute graphitized carbon layers, which confine the further growth of ZnFe2O4, ZnO, and Fe NPs. Combined with the well impendence and synergy absorption mechanism (magnetic loss, interface polarization, and conduction loss), optimized magnetic–dielectric ZnFe2O4–ZnO‐Fe@C microspheres exhibit outstanding EM wave absorption with the minimum reflection loss −66.5 dB at only 2.0 mm thickness. Bi‐metal MOF‐derived magnetic–dielectric absorption materials with tailored heterogeneous interfaces provide a new sight to design an efficient EM wave absorption system.

Mesoporous Nanocarbon-Based PGM-Free Electrocatalysts Prepared with MgO-Template for Anion-Exchange Membrane Fuel Cell

Anion-exchange membrane fuel cells (AEMFCs) are receiving more and more attention as a viable alternative to proton-exchange membrane fuel cells, because they permit the use of precious metal-free electrocatalysts for oxygen reduction reaction (ORR), such as transition metal and nitrogen-doped carbon nanomaterials, containing MNx ORR-active sites.1 However, in addition to active sites, the structure of the catalyst support material is also essential to ensure efficient mass transfer in the catalyst layer, especially in AEMFCs where mass transport issues are caused by the higher loading that PGM-free catalysts require.2 Easily removable inorganic particles like MgO offer a sustainable alternative to silica-based templates to achieve optimal porosity. The catalyst materials can be created via a template-directed synthesis, by pyrolyzing a carbon precursor with MgO or other thermally unstable magnesium compounds like acetate or citrate. The precursors break down by heat-treatment to create MgO nanoparticles, which are subsequently dissolved using dilute acids such as HCl.3 Unlike with silica-based templates, scaling up the method is significantly easier and more sustainable since no corrosive chemicals like hydrofluoric acid are used in the process.Using HoneyolTM (a mixture of alkylresorcinols) as the carbon source and magnesium acetate as the template precursor, we demonstrate a straightforward MgO template-assisted approach for obtaining mesoporous nitrogen and transition metal co-doped nanocarbon catalysts for AEMFCs.4 The effect of the mass ratio of Honeyol to magnesium acetate on the porosity and electrocatalytic activity of the catalysts was studied. The addition of Mg acetate increases the surface area of the materials, the prepared materials are mostly mesoporous with a broad pore size distribution. The catalyst with the highest electrocatalytic activity toward the ORR was synthesized using a 2:1 mass ratio of Honeyol to Mg acetate. The bimetallic FeCoNC-MgOAc catalyst displayed the highest electrocatalytic activity surpassing the benchmark Pt/C catalyst, showing a E 1/2 value of -0.14 V vs. SCE in the RDE test. The catalyst demonstrated excellent stability, only a minor decay was observed after 15,000 potential cycles (ΔE 1/2 = 10 mV). In AEMFC as the cathode catalyst, FeCoNC-MgOAc reached a peak power density of 0.92 W cm-2 (Figure 1), more than twice higher as the untemplated FeCoNC catalyst and slightly surpassing the benchmark Pt/C (20 wt.%). The catalyst also displayed promising durability in AEMFC with a minor voltage degradation rate of 0.0017 V h–1 after 24 h. References Osmieri, L.; Pezzolato, L.; Specchia, S. Recent Trends on the Application of PGM-Free Catalysts at the Cathode of Anion Exchange Membrane Fuel Cells. Current Opinion in Electrochemistry 2018, 9, 240–256.Dekel, D. R. Review of Cell Performance in Anion Exchange Membrane Fuel Cells. Journal of Power Sources 2018, 375, 158–169.Morishita, T.; Tsumura, T.; Toyoda, M.; Przepiórski, J.; Morawski, A. W.; Konno, H.; Inagaki, M. A Review of the Control of Pore Structure in MgO-Templated Nanoporous Carbons. Carbon 2010, 48 (10), 2690–2707.Kisand, K.; Sarapuu, A.; Douglin, J. C.; Kikas, A.; Treshchalov, A.; Käärik, M.; Piirsoo, H.-M.; Paiste, P.; Aruväli, J.; Leis, J.; Kisand, V.; Tamm, A.; Dekel, D. R.; Tammeveski, K. Templated Nitrogen-, Iron-, and Cobalt-Doped Mesoporous Nanocarbon Derived from an Alkylresorcinol Mixture for Anion-Exchange Membrane Fuel Cell Application. ACS Catalysis 2022, 12 (22), 14050–14061. Figure 1

Hard-templated macroporous alumina with thick mesoporous walls: The key factors of pore formation

This paper focuses on the key factors contributing to pore formation in hard-templated macroporous alumina. Special attention is paid to the formation of a connected pore structure. Two series of samples were prepared, each with different content of the polymeric template. The pore structure of alumina was designed using polystyrene and acrylic copolymers as hard templates. Alumina differed in crystallite morphology (round-like and rod-like) and pore structure (bottleneck-like and slit-like). The templates differed in particle size (100 and 250 nm) and physical state (powder and suspension). All the samples were characterized by N2 adsorption, Hg porosimetry, XRD, and SEM. The data obtained indicate that a hard template made of polymeric particles has the following functions: fixing the pore size and shape, sintering small pores of the material, and creating additional channels to connect macropores. Regardless of the type of polymeric template and Al2O3 precursor, a connected pore system can be formed by adding more than 20 wt% of the template.