This report describes the development and the optimization of new synthesis routes yielding electrocatalysts for the oxygen reduction reaction (ORR) aimed at application in proton exchange membrane ...fuel cells (PEMFCs). The preparation protocols consist in the synthesis of two groups of hybrid inorganic–organic precursors, characterized by a different concentration of nitrogen, which subsequently undergo a high-temperature pyrolysis in inert atmosphere, washing and activation. The resulting materials show a well-controlled stoichiometry. The nitrogen incorporated in the support transforms the matrix into a supramolecular ligand, and stabilizes the electrocatalyst by coordinating the active metal clusters. The latter are composed of an “active metal” such as Pt or Pd, combined with one or more “co-catalyst” elements such as Au, Fe, Co and Ni. An extensive characterization of the carbon nitride electrocatalysts under the chemical, structural, morphological and electrochemical points of view is described, together with their use in membrane electrode assemblies (MEAs) tested in single fuel cells under operative conditions. Results indicated that the best electrocatalysts are those characterized by a “core–shell” morphology. These systems consist of metal carbon nitride materials with a low concentration of nitrogen (shell) supported on electronically conductive graphite nanoparticles (core). Promising results were obtained both in terms of ORR overpotential (
η) and of mass activity (
A
m). Indeed,
η resulted up to ∼30
mV lower with respect to reference Pt-based systems, and an
A
m equal to 0.3–0.4
g of Pd or Pt to achieve 1
kW was reached.
As highlighted by the recent roadmaps from the European Union and the United States, water electrolysis is the most valuable high‐intensity technology for producing green hydrogen. Currently, two ...commercial low‐temperature water electrolyzer technologies exist: alkaline water electrolyzer (A‐WE) and proton‐exchange membrane water electrolyzer (PEM‐WE). However, both have major drawbacks. A‐WE shows low productivity and efficiency, while PEM‐WE uses a significant amount of critical raw materials. Lately, the use of anion‐exchange membrane water electrolyzers (AEM‐WE) has been proposed to overcome the limitations of the current commercial systems. AEM‐WE could become the cornerstone to achieve an intense, safe, and resilient green hydrogen production to fulfill the hydrogen targets to achieve the 2050 decarbonization goals. Here, the status of AEM‐WE development is discussed, with a focus on the most critical aspects for research and highlighting the potential routes for overcoming the remaining issues. The Review closes with the future perspective on the AEM‐WE research indicating the targets to be achieved.
Water electrolysis: In this Review, the advantages and challenges of anion‐exchange membrane water electrolyzers are discussed. The status of their development with a focus on the most critical aspects for research is presented, highlighting the potential routes for overcoming the remaining issues, and future targets to be achieved are also presented.
The quest for the development of high performing secondary batteries is prompting the research activities in this field towards the exploitation of new cell concepts. In this concern, next-generation ...secondary batteries based on multivalent metals such as magnesium and tin are an important promise. In this report, a new family of multivalent metal-based ionic liquid (IL) electrolytes is developed. The proposed ILs are obtained by reacting 1-butyl-1-methylpyrrolidinium chloride (Pyr14Cl), dimethyl-tin dichloride and the highly electroactive δ-MgCl2 material. Thermal and vibrational spectroscopy studies reveal that the proposed electrolytes consist of domains of complex catenated 3D magnesium-organochlorostannate coordination networks neutralized by aggregates of Pyr14+ stacks. The anionic domains are composed by a network of catenated Me2xSnxCl2x+yy− repeat units bonded by MgClx bridges. Cyclic voltammetry studies reveal that the metal deposition and stripping processes occur with a low overpotential in the order of few tens of mV. Finally, broadband electrical spectroscopy studies show that these new IL electrolytes: (i) are characterized by a room temperature ionic conductivity in the order of 10−3 S cm−1; and (ii) exhibit host matrix relaxations which are very effective in facilitating the long-range charge migration processes responsible for the overall conductivity of materials.
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•Ionic liquid electrolytes for secondary battery applications are proposed.•Metal is depositing with low overpotential and good current density.•Broadband electrical spectroscopy clarifies the conductivity mechanism.•Complex catenated Mg-based anionic 3D networks are formed.
The electrical relaxation and polarization phenomena of electrospun PVDF (P)/Nafion (N) blended fiber mats (P/N0.9M and β–PM) and membranes (P/N0.9MM) are compared with those of the solvent-cast ...membrane of identical composition (NC and P/N0.9C). The nature of the interactions between the two blended polymer components, that plays a pivotal role in the electrical nature of the resulting materials, is found to be governed by the fabrication method, with those materials obtained via electrospinning undergoing a “reciprocal templating” phenomenon that renders their electrical behavior (especially when in the dry state) significantly different from that of the blended membrane obtained via solvent casting. Broadband Electrical Spectroscopy (BES) demonstrates that the electric response of the blended materials is modulated by polarization phenomena and by α, β, and γ dielectric relaxation events of Nafion domains supported on β-PVDF. The coupling between the relaxations of β-PVDF with those of Nafion matrix is directly correlated to the “reciprocal templating” effect, which modulates the interactions between Nafion and PVDF in electrospun membranes. Two types of conductivity mechanisms characterize the H+ migration within the polymer blends: (1) interdomain H+ migration events by “charge-exchange” phenomena along percolation pathways and (2) H+ exchange between delocalization bodies (DBs) at binding sites at the interface between domains with different ε, size, and morphology. The electrical response of the electrospun membranes also suggests that they do not comprise water clusters with a large size such as those typically observed in pristine Nafion. Rather, the adsorbed H2O molecules, under wet conditions, form thin solvation shells wrapping the polar side chains of the Nafion component. At T = 80 °C, the conductivity of the studied materials decreases in the order NC (0.043 S·cm–1) ≈ P/N0.9C (0.042 S·cm–1) > P/N0.9M (0.031 S·cm–1) > P/N0.9MM (0.011 S·cm–1).
An extensive morphological and structural study of two bimetallic “core–shell” carbon nitride nano‐electrocatalysts with active sites based on Pt and Ni or on Pt and Fe is reported. The core–shell ...electrocatalysts are obtained by the pyrolysis of a precursor obtained by decorating a support composed of conducting particles with a hybrid inorganic–organic material. The electrocatalysts were investigated by high‐resolution TEM, powder X‐ray diffraction, and μ‐Raman spectroscopy. The morphological and structural information presented here provides 1) insight into the microscopic features, affecting the electrochemical performance of the electrocatalyst materials determined in both ex situ measurements and single‐cell configurations; and 2) an opportunity to study the effect of the different precursor chemistries on the structure and morphology of the bimetallic core–shell carbon nitride nano‐electrocatalysts.
Power of two: Bimetallic “core–shell” carbon nitride oxygen reduction reaction nano‐electrocatalysts are investigated (see picture). A model is proposed to rationalize the morphology and structure of the electrocatalysts, and to interpret the electrochemical behavior and performance of the materials.
A chemically stable copolymer poly(2,6 dimethyl 1,4 phenylene oxide)-b-poly(vinyl benzyl trimethyl ammonium) with two ion exchange capacities, 3.2 and 2.9 meq g−1, was prepared as anion exchange ...membranes (AEM-3.2 and AEM-2.9). These materials showed high OH− conductivities of 138 mS.cm−1 and 106 mS.cm−1, for AEM-3.2 and AEM-2.9 respectively, at 60°C, and 95% RH. The OH− conductivity = 45 mS.cm−1 for AEM-3.2 at 60% RH and 60°C in the absence of CO2. Amongst the ions studied, only OH− is fully dissociated at high RH. The lower Ea = 10-13 kJ.mol−1 for OH− compared to F− ∼ 20 kJ.mol−1 in conductivity measurements, and of H2O from self-diffusion coefficients suggests the presence of a Grotthuss hopping transport mechanism in OH− transport. PGSE-NMR of H2O and F− show that the membranes have low tortuosity, 1.8 and 1.2, and high water self-diffusion coefficients, 0.66 and 0.26 × 10−5 cm2.s−1, for AEM-3.2 and AEM-2.9 respectively. SAXS and TEM show that the membrane has several different sized water environments, ca. 62 nm, 20 nm, and 3.5 nm. The low water uptake, λ = 9-12, reduced swelling, and high OH− conductivity, with no chemical degradation over two weeks, suggests that the membrane is a strong candidate for electrochemical applications.
An anion exchange membrane (AEM) was made with a modified polyketone (PK). AEMs of polyamines were prepared in a three-step procedure: (I) PK synthesis using ethylene and carbon monoxide, supported ...by a Pd catalyst, followed by the introduction of 1,2-diaminopropane to yield the polymeric amines; (II) solvent casting of the modified PK with a low degree of amination; (III) iodomethylation to form the AEM (PK-PDAPm(I)), followed by ion exchange with KOH (PK-PDAPm(OH)).
The structure of the modified polyketone was characterized using FT-IR, and UV–vis spectroscopy, demonstrating the successful introduction of amine in the PK. The conductivity of the AEM was studied using broadband electric spectroscopy (BES) in the temperature range from −100 to 120°C: the highest value of 9×10−4 S·cm−1 was reached at 120°C for the ionic conductivity of PK-PDAPm(I), followed by PK-PDAPm(OH) with values of the same order of magnitude (10−4 S·cm−1). Thermogravimetry showed that the material is thermally stable up to 200°C.
Solid polymer electrolytes consisting of CO2-derived poly(ethylene carbonate) (PEC), LiPF6, and plasticizers (glycerol or 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide, EMImTFSI) ...were prepared by a simple casting method, and their dielectric relaxation behavior was evaluated using broadband electric spectroscopy (BES), which clarified the correlation between the polymer motion and ionic conduction. From the DSC and BES results, it was revealed that the addition of plasticizer decreased the glass transition temperature and increased the dc conductivity (σdc) of the PEC electrolyte. The BES results also revealed that the plasticizer increased the segmental motion of PEC and improved σdc, and the plasticizing effect of EMImTFSI on the PEC electrolyte was larger than that of glycerol. From the results of the Walden plot and fragility analysis, it was expected that the degree of decoupling ε and fragility m would increase with the addition of plasticizer because these plasticizers weaken the interactions between the PEC chains and Li ions in the electrolyte.Plasticized poly(ethylene carbonate) (PEC)/LiPF6 electrolytes were prepared and evaluated their ion-conductive and dielectric relaxation behavior using broadband electric spectroscopy (BES). The BES results indicated that the plasticizer accelerates segmental motion of PEC and improve the dc conductivity, and the plasticizing effect of ionic liquid (EMImTFSI) on the PEC electrolyte is larger than that of glycerol. From the results of the Walden plot and fragility analysis, it was revealed that the degree of decoupling and the value of fragility increase by the addition of plasticizer, and these plasticizers weaken interactions between PEC chains and Li ions in the electrolyte.
Molecular engineering of manganese(II) diamine diketonate precursors is a key issue for their use in the vapor deposition of manganese oxide materials. Herein, two closely related β-diketonate ...diamine Mn
adducts with different fluorine contents in the diketonate ligands are examined. The target compounds were synthesized by a simple procedure and, for the first time, thoroughly characterized by a joint experimental-theoretical approach, to understand the influence of the ligand on their structures, electronic properties, thermal behavior, and reactivity. The target compounds are monomeric and exhibit a pseudo-octahedral coordination of the Mn
centers, with differences in their structure and fragmentation processes related to the ligand nature. Both complexes can be readily vaporized without premature side decompositions, a favorable feature for their use as precursors for chemical vapor deposition (CVD) or atomic layer deposition applications. Preliminary CVD experiments at moderate growth temperatures enabled the fabrication of high-purity, single-phase Mn
O
nanosystems with tailored morphology, which hold great promise for various technological applications.
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