TY - JOUR A1 - Perovic, Milena A1 - Qin, Qing A1 - Oschatz, Martin T1 - From molecular precursors to nanoparticles BT - tailoring the adsorption properties of porous carbon materials by controlled chemical functionalization JF - Advanced functional materials N2 - Nanoporous carbon materials (NCMs) provide the "function" of high specific surface area and thus have large interface area for interactions with surrounding species, which is of particular importance in applications related to adsorption processes. The strength and mechanism of adsorption depend on the pore architecture of the NCMs. In addition, chemical functionalization can be used to induce changes of electron density and/or electron density distribution in the pore walls, thus further modifying the interactions between carbons and guest species. Typical approaches for functionalization of nanoporous materials with regular atomic construction like porous silica, metal-organic frameworks, or zeolites, cannot be applied to NCMs due to their less defined local atomic construction and abundant defects. Therefore, synthetic strategies that offer a higher degree of control over the process of functionalization are needed. Synthetic approaches for covalent functionalization of NCMs, that is, for the incorporation of heteroatoms into the carbon backbone, are critically reviewed with a special focus on strategies following the concept "from molecules to materials." Approaches for coordinative functionalization with metallic species, and the functionalization by nanocomposite formation between pristine carbon materials and heteroatom-containing carbons, are introduced as well. Particular focus is given to the influences of these functionalizations in adsorption-related applications. KW - composites KW - heteroatoms KW - metal species KW - porous carbon materials KW - surface KW - functionalization Y1 - 2020 U6 - https://doi.org/10.1002/adfm.201908371 SN - 1616-301X SN - 1616-3028 VL - 30 IS - 41 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Qin, Qing A1 - Oschatz, Martin T1 - Overcoming chemical inertness under ambient conditions BT - a critical view on recent developments in Ammonia synthesis via electrochemical N-2 reduction by asking five questions JF - ChemElectroChem N2 - Ammonia (NH3) synthesis by the electrochemical N-2 reduction reaction (NRR) is increasingly studied and proposed as an alternative process to overcome the disadvantages of Haber-Bosch synthesis by a more energy-efficient, carbon-free, delocalized, and sustainable process. An ever-increasing number of scientists are working on the improvement of the faradaic efficiency (FE) and NH3 production rate by developing novel catalysts, electrolyte concepts, and/or by contributing theoretical studies. The present Minireview provides a critical view on the interplay of different crucial aspects in NRR from the electrolyte, over the mechanism of catalytic activation of N-2, to the full electrochemical cell. Five critical questions are asked, discussed, and answered, each coupled with a summary of recent developments in the respective field. This article is not supposed to be a complete summary of recent research about NRR but provides a rather critical personal view on the field. It is the major aim to give an overview over crucial influences on different length scales to shine light on the sweet spots into which room for revolutionary instead of incremental improvements may exist. KW - N-2 reduction KW - ammonia synthesis KW - catalysis KW - catalysts KW - electrolytes Y1 - 2022 U6 - https://doi.org/10.1002/celc.201901970 SN - 2196-0216 VL - 7 IS - 4 SP - 878 EP - 889 PB - Wiley-VCH CY - Weinheim ER - TY - GEN A1 - Perovic, Milena A1 - Qin, Qing A1 - Oschatz, Martin T1 - From molecular precursors to nanoparticles BT - tailoring the adsorption properties of porous carbon materials by controlled chemical functionalization T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Nanoporous carbon materials (NCMs) provide the "function" of high specific surface area and thus have large interface area for interactions with surrounding species, which is of particular importance in applications related to adsorption processes. The strength and mechanism of adsorption depend on the pore architecture of the NCMs. In addition, chemical functionalization can be used to induce changes of electron density and/or electron density distribution in the pore walls, thus further modifying the interactions between carbons and guest species. Typical approaches for functionalization of nanoporous materials with regular atomic construction like porous silica, metal-organic frameworks, or zeolites, cannot be applied to NCMs due to their less defined local atomic construction and abundant defects. Therefore, synthetic strategies that offer a higher degree of control over the process of functionalization are needed. Synthetic approaches for covalent functionalization of NCMs, that is, for the incorporation of heteroatoms into the carbon backbone, are critically reviewed with a special focus on strategies following the concept "from molecules to materials." Approaches for coordinative functionalization with metallic species, and the functionalization by nanocomposite formation between pristine carbon materials and heteroatom-containing carbons, are introduced as well. Particular focus is given to the influences of these functionalizations in adsorption-related applications. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1191 KW - composites KW - heteroatoms KW - metal species KW - porous carbon materials KW - surface functionalization Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-516140 SN - 1866-8372 ER - TY - JOUR A1 - Qin, Qing A1 - Zhao, Yun A1 - Schmallegger, Max A1 - Heil, Tobias A1 - Schmidt, Johannes A1 - Walczak, Ralf A1 - Gescheidt-Demner, Georg A1 - Jiao, Haijun A1 - Oschatz, Martin T1 - Enhanced Electrocatalytic N-2 Reduction via Partial Anion Substitution in Titanium Oxide-Carbon Composites JF - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition N2 - The electrochemical conversion of N-2 at ambient conditions using renewably generated electricity is an attractive approach for sustainable ammonia (NH3) production. Considering the chemical inertness of N-2, rational design of efficient and stable catalysts is required. Therefore, in this work, it is demonstrated that a C-doped TiO2/C (C-TixOy/C) material derived from the metal-organic framework (MOF) MIL-125(Ti) can achieve a high Faradaic efficiency (FE) of 17.8 %, which even surpasses most of the established noble metal-based catalysts. On the basis of the experimental results and theoretical calculations, the remarkable properties of the catalysts can be attributed to the doping of carbon atoms into oxygen vacancies (OVs) and the formation of Ti-C bonds in C-TixOy. This binding motive is found to be energetically more favorable for N-2 activation compared to the non-substituted OVs in TiO2. This work elucidates that electrochemical N-2 reduction reaction (NRR) performance can be largely improved by creating catalytically active centers through rational substitution of anions into metal oxides. KW - ammonia synthesis KW - anion substitution KW - MOF-derived catalysts KW - N-2 fixation KW - non-noble metal catalysts Y1 - 2019 U6 - https://doi.org/10.1002/anie.201906056 SN - 1433-7851 SN - 1521-3773 VL - 58 IS - 37 SP - 13101 EP - 13106 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Qin, Qing A1 - Heil, T. A1 - Schmidt, J. A1 - Schmallegger, Max A1 - Gescheidt, Georg A1 - Antonietti, Markus A1 - Oschatz, Martin T1 - Electrochemical Fixation of Nitrogen and Its Coupling with Biomass Valorization with a Strongly Adsorbing and Defect Optimized Boron-Carbon-Nitrogen Catalyst JF - ACS Applied Energy Materials N2 - The electrochemical conversion of low-cost precursors into high-value chemicals using renewably generated electricity is a promising approach to build up an environmentally friendly energy cycle, including a storage element. The large-scale implementation of such process can, however, only be realized by the design of cost-effective electrocatalysts with high efficiency and highest stability. Here, we report the synthesis of N and B codoped porous carbons. The constructed B-N motives combine abundant unpaired electrons and frustrated Lewis pairs (FLPs). They result in desirable performance for electrochemical N-2 reduction reaction (NRR) and electrooxidation of 5-hydroxymethylfurfural (HMF) in the absence of any metal cocatalyst. A maximum Faradaic efficiency of 15.2% with a stable NH3 production rate of 21.3 mu g h(-1) mg(-1) is obtained in NRR. Besides, 2,5-furandicarboxylic acid (FDCA) is first obtained by using non-metalbased electrocatalysts at a conversion of 71% and with yield of 57%. Gas adsorption experiments elucidate the relationship between the structure and the ability of the catalysts to activate the substrate molecules. This work opens up deep insights for the rational design of non-metal-based catalysts for potential electrocatalytic applications and the possible enhancement of their activity by the introduction of FLPs and point defects at grain boundaries. KW - non-metal catalysis KW - porous carbon KW - heteroatoms KW - N-2 reduction KW - HMF oxidation Y1 - 2019 U6 - https://doi.org/10.1021/acsaem.9b01852 SN - 2574-0962 VL - 2 IS - 11 SP - 8359 EP - 8365 PB - American Chemical Society CY - Washington ER - TY - THES A1 - Qin, Qing T1 - Chemical functionalization of porous carbon-based materials to enable novel modes for efficient electrochemical N2 fixation T1 - Chemische Funktionalisierung von porösen Materialien auf Kohlenstoffbasis zur Ermöglichung neuartiger Verfahren für eine effiziente elektrochemische N2-Fixierung N2 - The central motivation of the thesis was to provide possible solutions and concepts to improve the performance (e.g. activity and selectivity) of electrochemical N2 reduction reaction (NRR). Given that porous carbon-based materials usually exhibit a broad range of structural properties, they could be promising NRR catalysts. Therefore, the advanced design of novel porous carbon-based materials and the investigation of their application in electrocatalytic NRR including the particular reaction mechanisms are the most crucial points to be addressed. In this regard, three main topics were investigated. All of them are related to the functionalization of porous carbon for electrochemical NRR or other electrocatalytic reactions. In chapter 3, a novel C-TixOy/C nanocomposite has been described that has been obtained via simple pyrolysis of MIL-125(Ti). A novel mode for N2 activation is achieved by doping carbon atoms from nearby porous carbon into the anion lattice of TixOy. By comparing the NRR performance of M-Ts and by carrying out DFT calculations, it is found that the existence of (O-)Ti-C bonds in C-doped TixOy can largely improve the ability to activate and reduce N2 as compared to unoccupied OVs in TiO2. The strategy of rationally doping heteroatoms into the anion lattice of transition metal oxides to create active centers may open many new opportunities beyond the use of noble metal-based catalysts also for other reactions that require the activation of small molecules as well. In chapter 4, a novel catalyst construction composed of Au single atoms decorated on the surface of NDPCs was reported. The introduction of Au single atoms leads to active reaction sites, which are stabilized by the N species present in NDPCs. Thus, the interaction within as-prepared AuSAs-NDPCs catalysts enabled promising performance for electrochemical NRR. For the reaction mechanism, Au single sites and N or C species can act as Frustrated Lewis pairs (FLPs) to enhance the electron donation and back-donation process to activate N2 molecules. This work provides new opportunities for catalyst design in order to achieve efficient N2 fixation at ambient conditions by utilizing recycled electric energy. The last topic described in chapter 5 mainly focused on the synthesis of dual heteroatom-doped porous carbon from simple precursors. The introduction of N and B heteroatoms leads to the construction of N-B motives and Frustrated Lewis pairs in a microporous architecture which is also rich in point defects. This can improve the strength of adsorption of different reactants (N2 and HMF) and thus their activation. As a result, BNC-2 exhibits a desirable electrochemical NRR and HMF oxidation performance. Gas adsorption experiments have been used as a simple tool to elucidate the relationship between the structure and catalytic activity. This work provides novel and deep insights into the rational design and the origin of activity in metal-free electrocatalysts and enables a physically viable discussion of the active motives, as well as the search for their further applications. Throughout this thesis, the ubiquitous problems of low selectivity and activity of electrochemical NRR are tackled by designing porous carbon-based catalysts with high efficiency and exploring their catalytic mechanisms. The structure-performance relationships and mechanisms of activation of the relatively inert N2 molecules are revealed by either experimental results or DFT calculations. These fundamental understandings pave way for a future optimal design and targeted promotion of NRR catalysts with porous carbon-based structure, as well as study of new N2 activation modes. N2 - Die zentrale Motivation der Arbeit war es, mögliche Lösungen und Konzepte zur Verbesserung der Leistung (z.B. Aktivität und Selektivität) der elektrochemischen N2-Reduktionsreaktion (NRR) anzubieten. Da poröse Materialien auf Kohlenstoffbasis in der Regel ein breites Spektrum an strukturellen Eigenschaften aufweisen, könnten sie vielversprechende NRR-Katalysatoren sein. Daher sind das fortgeschrittene Design neuartiger poröser Materialien auf Kohlenstoffbasis und die Untersuchung ihrer Anwendung in der elektrokatalytischen NRR einschließlich der besonderen Reaktionsmechanismen die wichtigsten Punkte, die angegangen werden müssen. In diesem Zusammenhang wurden drei Hauptthemen untersucht. Alle von ihnen stehen im Zusammenhang mit der Funktionalisierung von porösem Kohlenstoff für elektrochemische NRR oder andere elektrokatalytische Reaktionen. In Kapitel 3 wurde ein neuartiger C-TixOy/C-Nanokomposit beschrieben, der durch einfache Pyrolyse von MIL-125(Ti) gewonnen wurde. Ein neuartiger Modus für die N2-Aktivierung wird durch Dotierung von Kohlenstoffatomen aus nahegelegenem porösem Kohlenstoff in das Aniongitter von TixOy erreicht. Durch den Vergleich der NRR-Leistung von M-Ts und die Durchführung von DFT-Berechnungen wird festgestellt, dass die Existenz von (O-)Ti-C-Bindungen in C-dotiertem TixOy die Fähigkeit zur Aktivierung und Reduktion von N2 im Vergleich zu unbesetzten OVs in TiO2 erheblich verbessern kann. Die Strategie, Heteroatome rational in das Aniongitter von Übergangsmetalloxiden zu dotieren, um aktive Zentren zu schaffen, kann viele neue Möglichkeiten eröffnen, die über den Einsatz von edelmetallbasierten Katalysatoren hinausgehen, auch für andere Reaktionen, die ebenfalls die Aktivierung von kleinen Molekülen erfordern. In Kapitel 4 wurde über eine neuartige Katalysatorkonstruktion aus Au-Einzelatomen berichtet, die auf der Oberfläche von NDPCs dekoriert sind. Die Einführung von Au-Einzelatomen führt zu aktiven Reaktionsstellen, die durch die in NDPCs vorhandenen N-Spezies stabilisiert werden. So ermöglichte die Interaktion innerhalb von hergestellten AuSAs-NDPCs-Katalysatoren eine vielversprechende Leistung für die elektrochemische NRR. Für den Reaktionsmechanismus können Au-Einzelstandorte und N- oder C-Spezies als frustrierte Lewis-Paare (FLPs) fungieren, um den Elektronenabgabe- und Rückgabeprozess zur Aktivierung von N2-Molekülen zu verbessern. Diese Arbeit bietet neue Möglichkeiten für das Design von Katalysatoren, um eine effiziente N2-Fixierung unter Umgebungsbedingungen durch die Nutzung recycelter elektrischer Energie zu erreichen. Das letzte in Kapitel 5 beschriebene Thema konzentrierte sich hauptsächlich auf die Synthese von dualem heteroatomdotiertem porösem Kohlenstoff aus einfachen Vorläufern. Die Einführung von N- und B-Heteroatomen führt zur Konstruktion von N-B-Motiven und frustrierten Lewis-Paaren in einer mikroporösen Architektur, die ebenfalls reich an Punktdefekten ist. Dies kann die Adsorptionskraft verschiedener Reaktanden (N2 und HMF) und damit deren Aktivierung verbessern. Infolgedessen weist BNC-2 eine wünschenswerte elektrochemische NRR- und HMF-Oxidationsleistung auf. Gasadsorptionsexperimente wurden als einfaches Werkzeug zur Aufklärung des Zusammenhangs zwischen Struktur und katalytischer Aktivität eingesetzt. Diese Arbeit liefert neue und tiefe Einblicke in das rationale Design und den Ursprung der Aktivität bei metallfreien Elektrokatalysatoren und ermöglicht eine physikalisch tragfähige Diskussion der aktiven Motive, sowie die Suche nach deren weiteren Anwendungen. Während dieser Arbeit, die allgegenwärtigen Probleme der niedrigen Selektivität und Aktivität der elektrochemischen NRR werden durch die Gestaltung poröser Katalysatoren auf Kohlenstoffbasis mit hoher Effizienz und die Erforschung ihrer katalytischen Mechanismen. Die Struktur-Leistungsbeziehungen und Aktivierungsmechanismen der relativ inerten N2-Moleküle werden entweder durch experimentelle Ergebnisse oder DFT-Berechnungen aufgezeigt. Diese grundlegenden Erkenntnisse ebnen den Weg für ein zukünftiges optimales Design und eine gezielte Förderung von NRR-Katalysatoren mit poröser Kohlenstoffstruktur, sowie für die Untersuchung neuer N2-Aktivierungsmodi. KW - N2 fixation KW - porous carbon-based materials KW - ammonia KW - selectivity KW - N2-Fixierung KW - porösen Materialien auf Kohlenstoffbasis KW - Ammoniak KW - Selektivität Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-443397 ER -