Philipp Weide

Co@Co3O4 Encapsulated in Carbon Nanotube‐Grafted Nitrogen‐Doped Carbon Polyhedra as an Advanced Bifunctional Oxygen Electrode

Efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are vitally important for various energy conversion devices, such as regenerative fuel cells and metal-air batteries. However, realization of such electrodes is impeded by insufficient activity and instability of electrocatalysts for both water splitting and oxygen reduction. We report highly active bifunctional electrocatalysts for oxygen electrodes comprising core-shell Co@Co3O4 nanoparticles embedded in CNT-grafted N-doped carbon-polyhedra obtained by the pyrolysis of cobalt metal-organic framework (ZIF-67) in a reductive H2 atmosphere and subsequent controlled oxidative calcination. The catalysts afford 0.85 V reversible overvoltage in 0.1 m KOH, surpassing Pt/C, IrO2 , and RuO2 and thus ranking them among one of the best non-precious-metal electrocatalysts for reversible oxygen electrodes.

MnxOy/NC and CoxOy/NC Nanoparticles Embedded in a Nitrogen-Doped Carbon Matrix for High-Performance Bifunctional Oxygen Electrodes†

Reversible interconversion of water into H2 and O2, and the recombination of H2 and O2 to H2O thereby harnessing the energy of the reaction provides a completely green cycle for sustainable energy conversion and storage. The realization of this goal is however hampered by the lack of efficient catalysts for water splitting and oxygen reduction. We report exceptionally active bifunctional catalysts for oxygen electrodes comprising Mn3O4 and Co3O4 nanoparticles embedded in nitrogen-doped carbon, obtained by selective pyrolysis and subsequent mild calcination of manganese and cobalt N4 macrocyclic complexes. Intimate interaction was observed between the metals and nitrogen suggesting residual M-N(x) coordination in the catalysts. The catalysts afford remarkably lower reversible overpotentials in KOH (0.1 M) than those for RuO2, IrO2, Pt, NiO, Mn3O4, and Co3O4, thus placing them among the best non-precious-metal catalysts for reversible oxygen electrodes reported to date.

Co3O4–MnO2–CNT Hybrids Synthesized by HNO3 Vapor Oxidation of Catalytically Grown CNTs as OER Electrocatalysts

An efficient two‐step gas‐phase method was developed for the synthesis of Co3O4–MnO2–CNT hybrids used as electrocatalysts in the oxygen evolution reaction (OER). Spinel Co–Mn oxide was used for the catalytic growth of multiwalled carbon nanotubes (CNTs) and the amount of metal species remaining in the CNTs was adjusted by varying the growth time. Gas‐phase treatment in HNO3 vapor at 200 °C was performed to 1) open the CNTs, 2) oxidize encapsulated Co nanoparticles to Co3O4 as well as MnO nanoparticles to MnO2, and 3) to create oxygen functional groups on carbon. The hybrid demonstrated excellent OER activity and stability up to 37.5 h under alkaline conditions, with longer exposure to HNO3 vapor up to 72 h beneficial for improved electrocatalytic properties. The excellent OER performance can be assigned to the high oxidation states of the oxide nanoparticles, the strong electrical coupling between these oxides and the CNTs as well as favorable surface properties rendering the hybrids a promising alternative to noble metal based OER catalysts.

The effect of Cu and Fe cations on NH3-supported proton transport in DeNOx-SCR zeolite catalysts

Proton transport studies revealed the different influence of Fe and Cu cations on the NH3–zeolite interaction and the NO–zeolite interaction in the presence of adsorbed NH3. At low temperatures, after NH3 saturation, Cu-ZSM-5 is more reactive than Fe-ZSM-5 for NO activation forming highly mobile NH4+ intermediates.

Immobilization of Proteins in their Physiological Active State at Functionalized Thiol Monolayers on ATR-Germanium Crystals

Protein immobilization on solid surfaces has become a powerful tool for the investigation of protein function. Physiologically relevant molecular reaction mechanisms and interactions of proteins can be revealed with excellent signal‐to‐noise ratio by vibrational spectroscopy (ATR‐FTIR) on germanium crystals. Protein immobilization by thiol chemistry is well‐established on gold surfaces, for example, for surface plasmon resonance. Here, we combine features of both approaches: a germanium surface functionalized with different thiols to allow specific immobilization of various histidine‐tagged proteins with over 99 % specific binding. In addition to FTIR, the surfaces were characterized by XPS and fluorescence microscopy. Secondary‐structure analysis and stimulus‐induced difference spectroscopy confirmed protein activity at the atomic level, for example, physiological cation channel formation of Channelrhodopsin 2.

Palladium Nanoparticles Supported on Nitrogen-Doped Carbon Nanotubes as a Release-and-Catch Catalytic System in Aerobic Liquid-Phase Ethanol Oxidation

Pd nanoparticles supported on carbon nanotubes were applied in the selective oxidation of ethanol in the liquid phase. The characterization of the surface and bulk properties combined with the catalytic tests indicated the dissolution and redeposition of Pd under the reaction conditions. A dynamic interplay within the Pd life cycle was identified to be responsible for the overall reactivity. Nitrogen‐doped carbon nanotubes were found to act as an excellent support for the Pd catalyst system by efficiently stabilizing and recapturing the Pd species, which resulted in high activity and selectivity to acetic acid.

Cobalt boride modified with N-doped carbon nanotubes as a high-performance bifunctional oxygen electrocatalyst

The development of reversible oxygen electrodes, able to drive both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), is still a great challenge. We describe a very efficient and stable bifunctional electrocatalytic system for reversible oxygen electrodes obtained by direct CVD growth of nitrogen-doped carbon nanotubes (NCNTs) on the surface of cobalt boride (CoB) nanoparticles. A detailed investigation of the crystalline structure and elemental distribution of CoB before and after NCNT growth reveals that the NCNTs grow on small CoB nanoparticles formed in the CVD process. The resultant CoB/NCNT system exhibited outstanding activity in catalyzing both the OER and the ORR in 0.1 M KOH with an overvoltage difference of only 0.73 V between the ORR at −1 mA cm−2 and the OER at +10 mA cm−2. The proposed CoB/NCNT catalyst showed stable performance during 50 h of OER stability assessment in 0.1 M KOH. Moreover, CoB/NCNT spray-coated on a gas diffusion layer as an air-breathing electrode proved its high durability during 170 galvanostatic charge–discharge (OER/ORR) test cycles (around 30 h) at ±10 mA cm−2 in 6 M KOH, making it an excellent bifunctional catalyst for potential Zn–air battery application.

New insight into calcium tantalate nanocomposite photocatalysts for overall water splitting and reforming of alcohols and biomass derivatives

The photocatalytic properties of different calcium tantalate nanocomposite photocatalysts with optimized phase composition were studied without the addition of any co-catalysts in the photoreforming of different alcohols including the biomass conversion by-product glycerol, as well as after modification with double-layered NiOx (Ni/NiO) co-catalyst in overall water splitting (OWS). Nanocomposite photocatalyst consisting of cubic α-CaTa2O6/orthorhombic β-CaTa2O6 coexisting phases always possesses the highest photocatalytic performance. For overall water splitting, a loading of 0.5 wt. % NiOx exhibits the best activities with stable stoichiometric H2 and O2 evolution rates.

Decoupling the Effects of High Crystallinity and Surface Area on the Photocatalytic Overall Water Splitting over β-Ga2O3 Nanoparticles by Chemical Vapor Synthesis

Chemical vapor synthesis (CVS) is a unique method to prepare well-defined photocatalyst materials with both large specific surface area and a high degree of crystallinity. The obtained β-Ga2 O3 nanoparticles were optimized for photocatalysis by reductive photodeposition of the Rh/CrOx co-catalyst system. The influence of the degree of crystallinity and the specific surface area on photocatalytic aqueous methanol reforming and overall water splitting (OWS) was investigated by synthesizing β-Ga2 O3 samples in the temperature range from 1000 °C to 1500 °C. With increasing temperature, the specific surface area and the microstrain were found to decrease, whereas the degree of crystallinity and the crystallite size increased. Whereas the photocatalyst with the highest specific surface area showed the highest aqueous methanol reforming activity, the highest OWS activity was that for the sample with an optimum ratio between high degree of crystallinity and specific surface area. Thus, it was possible to show that the facile aqueous methanol reforming and the demanding OWS have different requirements for high photocatalytic activity.

Oxidative photo-deposition of chromia: tuning the activity for overall water splitting of the Rh/CrOx co-catalyst system

Employing an oxidative photodeposition of CrOx the well-known Rh/CrOx co-catalyst system was prepared on different semiconductors. These photocatalysts showed up to 25% higher overall water splitting activities compared with conventionally prepared materials. The enhancement is attributed to a favorable selective deposition of CrOx caused by charge-directed deposition.