The design of new catalysts for polymer electrolyte membrane fuel cells must be guided by two equally important fundamental principles: optimization of their catalytic behaviour as well as the long-term stability of the metal catalysts and supports in hostile electrochemical. The methods used to improve catalytic activity are diverse, ranging from the alloying and dealloying of platinum to the synthesis of platinum core–shell catalysts. However, methods to improve the stability of the carbon supports and catalyst nanoparticles are limited, especially during shutdown (when hydrogen is purged from the anode by air) and startup (when air is purged from the anode by hydrogen) conditions when the cathode potential can be pushed up to 1.5 V. Under the latter conditions, stability of the cathode materials is strongly affected (carbon oxidation reaction) by the undesired oxygen reduction reaction (ORR) on the anode side. This emphasizes the importance of designing selective anode catalysts that can efficiently suppress the ORR while fully preserving the Pt-like activity for the hydrogen oxidation reaction. Here, we demonstrate that chemically modified platinum with a self-assembled monolayer of calix[4]arene molecules meets this challenging requirement.
COBISS.SI-ID: 34569477
In addition to quinolones, which are O,O ligands, we have also decided to prepare ruthenium complexes of various ß-diketonates. Such ligands coordinate similarly as quinolones and it is known that their metal complexes exert interesting physico-chemical and biological properties. Five different fluorinated β-diketone ligands in the presence of sodium methoxide easily react with the organoruthenium precursor generating neutral complexes 1–5 with typical ‘‘piano-stool’’ geometry. All synthesized compounds were characterized by multinuclear NMR, X-ray diffraction and other standard physico-chemical methods. It was found that these compounds are ready-touse catalysts, which are efficient for direct arylation of 2-phenylpyridine. Literature data revealed that frequently, compounds with catalytic properties exert also biological activity and we plan to test biological activity of isolated compounds in the future.
COBISS.SI-ID: 36426757
This study investigates several CNT-supported Pd-based catalysts and compares their morphological as well as electrochemical characteristics for formic acid electro-oxidation. Pd/C catalysts were prepared via various impregnation methods, using different reaction media (EtOH, MeOH, THF, H2O) or reducing agents (hydroquinone or SDS). The average mean particle sizes of the precipitated Pd varied from 2.6 nm to 18.0 nm. It was further shown that the particle size of Pd/C dispersions can be easily controlled by changing the solvent and experimental conditions during the preparation procedure. Measurements of catalytic activity by using cyclic voltammetry revealed strong particle size dependence of the anodic peak current density. The electro-oxidation of formic acid may be kinetically-controlled or diffusion-controlled regarding the Pd morphological characteristics.
COBISS.SI-ID: 36573189
The preparation of polymer-functionalized graphene nanoribbons (PF-GNRs) in a one-pot synthesis is described. Multiwalled carbon nanotubes (MWCNTs) were intercalated by potassium under vapor- or liquid-phase conditions, followed by the addition of vinyl or epoxide monomers, resulting in PF-GNRs. Scanning electron microscopy, thermogravimetric mass spectrometry, and X-ray photoelectron spectroscopy were used to characterize the PF-GNRs. Also explored here is the correlation between the splitting of MWCNTs, the intrinsic properties of the intercalants and the degree of defects and graphitization of the starting MWCNTs. The PF-GNRs could have applications in conductive composites, transparent electrodes, heat circuits, and supercapacitors.
COBISS.SI-ID: 36526597
The alkali diaqua complexes of hydrogen chloranilic acid of [KHCA(H2O)2], [RbHCA(H2O)2] and [CsHCA(H2O)2], and the salt of NH4HCA·2H2O were prepared and their crystal structures determined. The homologues of lithium and sodium are not stable, but their analogues [LiHCAEtOH] and [Na5HCA (CA)2(H2O)10] were obtained. All crystal structures studied, with exception of [LiHCAEtOH], reveal 3D-hydrogen bond networks with pronounced ππ interactions between anions supported by attractive polar interactions; the shortest separation distance between the centroids [3.229(2) Å] of the hydrogen chloranilate rings in a face-to-face stack is observed in the structure of [KHCA(H2O)2]. The analysis presented is focused on noncovalent interactions that direct self-assembly of molecules, which is importan also for bilogical systems.
COBISS.SI-ID: 516331545