Open Access

Show Abstract ▼

Abstract: Decoherence in superconducting quantum circuits, caused by loss mechanisms like material imperfections and two-level system (TLS) defects, remains a major obstacle to improving the performance of quantum devices. In this work, we present atomic-level characterization of cross-sections of a Josephson junction and a spiral resonator to assess the quality of critical interfaces. Employing scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDS) and electron-energy loss spectroscopy (EELS), we identify structural imperfections associated with oxide layer formation and carbon-based contamination, and correlate these imperfections to the pattering and etching steps in the fabrication process and environmental exposure. These results help to understand that TLS imperfections at critical interfaces play a key role in limiting device performance, emphasizing the need for an improved fabrication process.

Show Abstract ▼

Abstract: Catalytic hydrogenation reactions represent one of the most important transformations in the chemical industry. In the light of the required defossilization of the chemical value chain, the development of new, highly selective hydrogenation catalysts is of utmost importance to deal with renewable resources, such as biomass, recycled feedstock, or CO2. In that regard, this thesis deals with the preparation, characterization and application of metal nanoparticles (NPs) on molecularly modified surfaces for thermo- and electrocatalytic hydrogenation reactions. In the thermocatalytic systems, Mn-based NPs are investigated (monometallic and bimetallic MnRu NPs), as this earth-abundant metal possesses a low environmental impact and generally low toxicity. In addition, the electrocatalytic hydrogenation of alkenes, aldehydes and ketones using a Pickering emulsion-based system is described. Here, Pd NPs on molecularly modified carbon nanotubes are evaluated as catalyst. Firstly, small (1-10 nm) Mn NPs are immobilized on different carbon-based supports, as well as on a supported ionic liquid phase (SILP). Different synthetic methods are developed in order to optimize the properties of the NPs on each respective support, which are investigated using various characterization methods. The materials are evaluated for different catalytic transformations, with the catalytic transfer hydrogenation of aldehydes and ketones using Mn@SILP being found to be best performing. This material is demonstrated to be more active than previously reported Mn NP-based systems. X-ray absorption studies showed that the catalytic activity is highly dependent on the oxidation state of Mn. Followingly, bimetallic MnRu@SILP materials are prepared and characterized. Tuning the metal ratio of Mn:Ru enables the selective targeting of different products for substrates containing multiple reducible moieties. Furthermore, the alloying state of these NPs is investigated in order to assess its importance for the performance of the catalysts. The last part of this thesis deals with electrocatalytic hydrogenation (ECH) reactions, which offer an attractive way for the use of renewable electricity for chemical transformations. As water is used as solvent and hydrogen donor, the application of this reaction type for the conversion of apolar, organic systems is rather limited. In order to overcome this challenge, a Pickering emulsion-based system is developed. Herein, the apolar substrates are located within oil droplets, which are surrounded by an aqueous phase, providing the protons and high conductivity. This emulsion is stabilized by Pd NPs on molecularly modified CNTs. These CNTs additionally conduct electricity to the interface where the reaction is catalyzed by the Pd NPs. The mechanism of the ECH of alkenes is investigated and the reaction rate and Faradaic efficiency surpassed state-of-the-art Pd membrane reactors. The ECH system is further extended to the ECH of aldehydes and ketones to the respective alcohols. Here, the subsequent deoxygenation products can be also be yielded, which was not demonstrated yet in the electrocatalytic application of Pd NPs. Overall, this work contributes towards the development of novel catalytic systems for selective hydrogenation reactions. It can be demonstrated that metal NPs on molecularly modified surfaces represent a class of highly tunable catalysts. Their NP composition, choice of support and molecular modifier are varied to design highly efficient and selective catalysts for thermo- and electrocatalytic hydrogenation reactions.

Open Access

Show Abstract ▼

Abstract: Aqueous zinc-ion batteries (AZIBs) are increasingly seen as promising options for stationary energy storage, given their high volumetric capacity, intrinsic safety, and affordability. To enable their widespread adoption for large-scale applications, improvements in AZIB performance and stability, particularly in cathode materials like MnO2, are essential. Enhancing cathode properties—specifically achieving high-loading, high-capacity, and high-stability—is critical for AZIBs industrialization. High-loading cathodes accommodate more active material per unit area, increasing energy density and reducing the battery's footprint. High-capacity cathodes store more energy per unit mass or volume, crucial for applications requiring long-duration energy storage, such as grid-level energy balancing. Moreover, high-stability cathodes ensure long-term performance and reliability, crucial for industrial environments where downtime is costly. Nevertheless, with the escalation of unit mass loading, the dynamics of electron and ion transport within the electrode diminish, significantly impacting both capacity and cycle stability. This phenomenon is commonly referred to as the "Trilemma" in battery technology. This thesis proposes a decoupling enhancement strategy for surface and bulk materials to achieve these cathode properties simultaneously, advancing AZIBs industrialization. By focusing on electron and ion transport dynamics in Mn-based cathodes of AZIBs, the research develops a high-loading cathode based on designs of electrode structure (free-standing three-dimensional network), material property (double-ion pre-intercalation), fabrication process design (slurry treatment), facilitating high-loading cathode applications in Ah-level full cells. The study employs physicochemical and electrochemical characterizations, along with ex-situ material characterization and computational simulations, to elucidate cathode engineering details. Overall, this research aims to address critical factors in AZIBs development, laying the groundwork for their widespread industrial use in energy storage applications. The PhD project encompasses three primary works, outlined below: (1) MnO2-based cathodes in AZIBs offer stability and safety yet face challenges in slow kinetics due to low electrical conductivity, crucial for rapid charging devices. Addressing these hurdles, a sodium-intercalated manganese oxide (NMO) with 3D varying thinness carbon nanotubes (VTCNTs) network is proposed as a binder-free cathode (NMO/VTCNTs) without heat treatment. This novel network, utilizing low-thinness CNTs (LTCNTs) and high-thinness CNTs (HTCNTs), enhances specific capacity and mass loading. The interconnected CNTs withstand deformation, providing extra Zn2+ storage and efficient ion/electron migration routes. The NMO is evenly distributed within CNTs, improving structural stability and transport rates. The cathodes achieve loading of 5 mg cm−2, retaining high specific capacities of 329 mAh g−1 after 120 cycles at 0.2 A g−1, 225 mAh g−1 after 200 cycles at 1 A g−1, and 158 mAh g−1 after 1000 cycles at 2 A g−1. This construction strategy offers insights into achieving high mass loading and capacity, presenting significant potential for industrial application. (2) This study introduces a dual-ion co-intercalation strategy to enhance Mn-based cathodes in AZIBs. By incorporating both sodium and copper ions into δ-MnO2 (NCMO), stable cycling performance and high specific capacity are simultaneously achieved, even under high mass loading. Pre-intercalated Na+ boosts the Cu2+-driven activation of the Mn2+/Mn4+ redox process, while the smaller ionic radius of Cu2+ accelerates diffusion for improved charge/discharge kinetics. At lower mass loadings, the synergistic action of Na+ and Cu2+ sustains a prolonged capacity enhancement, whereas at higher loadings it enables a reversible Mn deposition/dissolution process.

Open Access

Show Abstract ▼

Abstract: The catalytic hydrogenation of amides with molecular hydrogen (H2) is an appealing route for the synthesis of valuable amines entering in the preparation of countless organic compounds. Running effective amide hydrogenation under mild H2 pressures is challenging although desirable to preclude the need for specialized high-pressure technologies in research and industry. Here we show that magnetocatalysis with standard supported catalysts enables unprecedented amide hydrogenation at mild conditions. Widely available and commercial platinum on alumina (Pt/Al2O3) was functionalized with iron carbide nanoparticles (ICNPs) to allow for localized and rapid magnetic induction heating resulting in the activation of neighboring Pt sites by thermal energy transfer. Exposure of the ICNPs@Pt/Al2O3 catalyst to an alternating current magnetic field enables highly active and selective hydrogenation of a range of amides at a reactor temperature of 150 °C under 3 bar or even ambient pressure of H2. ICNPs@Pt/Al2O3 reacts adaptively to fluctuations in electricity supply mimicking the use of intermittent renewable energy sources. This work may pave the way toward a greatly enhanced practicability of amide hydrogenation at the laboratory and production scales, and demonstrates more generally the broad potential of the emerging field of magnetocatalysis for synthetic chemistry.

Open Access

Show Abstract ▼

Abstract: Organic molecular crystals encompass a vast range of materials from pharmaceuticals to organic optoelectronics, proteins and waxes in biological and industrial settings. Crystal defects from grain boundaries to dislocations are known to play key roles in mechanisms of growth1,2 and in the functional properties of molecular crystals3,4,5. In contrast to the precise analysis of individual defects in metals, ceramics and inorganic semiconductors enabled by electron microscopy, substantially greater ambiguity remains in the experimental determination of individual dislocation character and slip systems in molecular materials3. In large part, nanoscale dislocation analysis in molecular crystals has been hindered by the low electron doses required to avoid irreversibly degrading these crystals6. Here we present a low-dose, single-exposure approach enabling nanometre-resolved analysis of individual dislocations in molecular crystals. We demonstrate the approach for a range of crystal types to reveal dislocation character and operative slip systems unambiguously.