Standardized procedures important for improving single-component ceramic fuel cell technology

Standardized procedures important for improving single-component ceramic fuel cell technolog

Effect of Li₄Ti₅O₁₂ Particle Size on the Performance of Lithium Ion Battery Electrodes at High C‑Rates and Low Temperatures

Two different Li₄Ti₅O₁₂ materials were investigated: smaller primary particle size forming large secondary particle aggregates (LTO-SP, surface area 22 m²/g) and larger primary particle size with less secondary particle aggregates (LTO-LP, surface area 7 m²/g). Both samples were synthesized using the same high temperature solid state synthesis but different end processing, resulting in the same crystalline structure but different particle morphology. At 0.1C measured discharge capacities were close to the theoretical capacity of Li₄Ti₅O₁₂ (175 mAh/g), and similar capacities were obtained at low C-rates and room temperature for both LTO-SP and LTO-LP. However, higher capacities were obtained with LTO-SP at high C-rates and −20 °C indicating beneficial effect of small particle size and large surface area. Shapes of the charge/discharge curves were different for LTO-SP and LTO-LP, and this is attributed to the large surface area of LTO-SP which affects the electrochemical performance because of different reaction potentials at surface sites versus bulk

Bismuth and CO Coadsorption on Platinum Nanoparticles

CO adsorption onto Pt- and Pt-based catalysts is a very relevant topic in electrocatalysis, and in particular, in fuel cells research. CO is known to be the main responsible of the poisoning of the catalysts and consequent decrease on performance of the fuel cells devices. In this paper, density functional theory (DFT) calculations and experiments were combined to access the effect of modifying Pt nanoparticles with Bi on CO adsorption. CO adsorption energies were calculated for Pt sites nearby Bi atoms in different type of structures: Pt clusters with Bi as surface adatom and Pt clusters with Bi as surface and subsurface dopant (alloys). The results show that, when compared with pure Pt, the adsorption energies for CO are lower on PtBi clusters in both adatom and surface alloy configurations. Subsurface PtBi alloys reveal higher adsorption energies for CO but these structures are energetically very unfavorable. On the basis of the calculations, a high degree of mobility of Bi on the surface was found in the presence of CO. These results suggest that the experimental differences between cyclic voltammogram before and after CO stripping can be due to a reorganization of the Bi layer on the catalyst when CO is coadsorbed. It was also experimentally observed, that CO oxidation peaks on the modified electrodes shift to higher potentials with increasing Bi coverage. These results suggest a higher effect of the decrease of CO coverages on the oxidation process than the decrease of the biding energies for Pt–CO in the presence of Bi

Functionalized Carbon Nanotubes with Ni(II) Bipyridine Complexes as Efficient Catalysts for the Alkaline Oxygen Evolution Reaction

Among current technologies for hydrogen production as an environmentally friendly fuel, water splitting has attracted increasing attention. However, the efficiency of water electrolysis is severely limited by the large anodic overpotential and sluggish reaction rate of the oxygen evolution reaction (OER). To overcome this issue, the development of efficient electrocatalyst materials for the OER has drawn much attention. Here, we show that organometallic Ni­(II) complexes immobilized on the sidewalls of multiwalled carbon nanotubes (MWNTs) serve as highly active and stable OER electrocatalysts. This class of electrocatalyst materials is synthesized by covalent functionalization of the MWNTs with organometallic Ni bipyridine (bipy) complexes. The Ni-bipy-MWNT catalyst generates a current density of 10 mA cm^–2 at overpotentials of 310 and 290 mV in 0.1 and 1 M NaOH, respectively, with a low Tafel slope of ∼35 mV dec^–1, placing the material among the most active OER electrocatalysts reported so far. Different simple analysis techniques have been developed in this study to characterize such a class of electrocatalyst materials. Furthermore, density functional theory calculations have been performed to predict the stable coordination complexes of Ni before and after OER measurements

Hydrogen evolution in alkaline medium on intratube and surface decorated PtRu catalyst

For anion exchange membrane (AEM) electrolysis, challenges include finding an optimal catalyst for hydrogen  evolution reaction (HER), as the noble metals are scarce while non-noble metals are inferior. Here, the noble  metal amount is reduced in a straightforward solution synthesis which produces Pt-Ru surface nanoparticles and  unique intratube nanowires decorated on single walled carbon nanotubes (SWNT). In half-cell tests, 5 wtPtRu-%  Pt-Ru SWNT demonstrates stable 10 mA cm− 2 HER current at 46 mV overpotential and outperforms commercial  electrocatalysts. When integrated in an AEM electrolyser, a high current density of 500 mA cm− 2 at a low voltage  of 1.72 V is achieved with 34 µg cm− 2 metal loading. First-principles calculations reveal that both the Pt-Ru alloy  nanoparticle and intratube nanowires promote near optimal H* binding energy, thereby releasing the H2 faster.  Thus, our approach yields an active low metal loading alkaline HER catalyst without sacrificing the performance  in an AEM electrolyser. </p

Biomimetic Oxygen Reduction by Cofacial Porphyrins at a Liquid–Liquid Interface

Oxygen reduction catalyzed by cofacial metalloporphyrins at the 1,2-dichlorobenzene–water interface was studied with two lipophilic electron donors of similar driving force, 1,1′-dimethylferrocene (DMFc) and tetrathiafulvalene (TTF). The reaction produces mainly water and some hydrogen peroxide, but the mediator has a significant effect on the selectivity, as DMFc and the porphyrins themselves catalyze the decomposition and the further reduction of hydrogen peroxide. Density functional theory calculations indicate that the biscobaltporphyrin, 4,5-bis­[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene, Co₂(DPX), actually catalyzes oxygen reduction to hydrogen peroxide when oxygen is bound on the “exo” side (“dock-on”) of the catalyst, while four-electron reduction takes place with oxygen bound on the “endo” side (“dock-in”) of the molecule. These results can be explained by a “dock-on/dock-in” mechanism. The next step for improving bioinspired oxygen reduction catalysts would be blocking the “dock-on” path to achieve selective four-electron reduction of molecular oxygen

Enhanced Electrochemical Hydrogenation of Benzaldehyde to Benzyl Alcohol on Pd@Ni-MOF by Modifying the Adsorption Configuration

Electrocatalytic hydrogenation (ECH) approaches under ambient temperature and pressure offer significant potential advantages over thermal hydrogenation processes but require highly active and efficient hydrogenation electrocatalysts. The performance of such hydrogenation electrocatalysts strongly depends not only on the active phase but also on the architecture and surface chemistry of the support material. Herein, Pd nanoparticles supported on a nickel metal–organic framework (MOF), Ni-MOF-74, are prepared, and their activity toward the ECH of benzaldehyde (BZH) in a 3 M acetate (pH 5.2) aqueous electrolyte is explored. An outstanding ECH rate up to 283 μmol cm–2 h–1 with a Faradaic efficiency (FE) of 76% is reached. Besides, higher FEs of up to 96% are achieved using a step-function voltage. Materials Studio and density functional theory calculations show these outstanding performances to be associated with the Ni-MOF support that promotes H-bond formation, facilitates water desorption, and induces favorable tilted BZH adsorption on the surface of the Pd nanoparticles. In this configuration, BZH is bonded to the Pd surface by the carbonyl group rather than through the aromatic ring, thus reducing the energy barriers of the elemental reaction steps and increasing the overall reaction efficiency