Following a 15-year-long investigation on graphene, two-dimensional (2D) carbon-rich conjugated frameworks (CCFs) have attracted growing research interest as a new generation of multifunctional materials. Typical 2D CCFs include 2D π-conjugated polymers (also classified as 2D π-conjugated covalent organic frameworks) and 2D π-conjugated metal–organic frameworks, which are characterized by layer-stacked periodic frameworks with high in-plane π-conjugation. These unique structures endow 2D CCFs with regular porosities, large specific surface areas, and superior chemical stability. In addition, 2D CCFs exhibit certain notable properties (e.g., excellent electronic conductivity, designable topologies, and defined catalytic/redox-active sites), which have motivated increasing efforts to explore 2D CCFs for electrochemical energy applications. In this Perspective, the structural features and synthetic principles of 2D CCFs are briefly introduced. Moreover, we discuss recent achievements in 2D CCFs designed for various electrochemical energy conversion (electrocatalysis) and storage (supercapacitors and batteries) applications. Particular emphasis is placed on analyzing the precise structural regulation of 2D CCFs. Finally, we provide an outlook about the future development of synthetic 2D CCFs for electrochemical applications, which concerns novel monomer design, chemical methodology/strategy establishment, and a roadmap toward practical applications.

In dieser Dissertation wurden das Auftreten und die ökologische Bedeutung Vivianits in Süßwassersedimenten erforscht. Vivianit ist das am weitensten verbreitete reduzierte Eisenphosphatmineral, das sich in Gewässersedimenten bildet. Über die Mechanismen der Vivianitbildung in Sedimenten und die quantitative Rolle des Minerals für die Speicherung von Phosphor ist bisher wenig bekannt. Die neuen Erkenntnisse dieser Arbeit basieren auf der Entwicklung einer neuartigen Methode, die eine direkte Identifikation Vivianits mittels Röntgendiffraktometrie in Sedimenten erlaubte. Es gelang erstmalig, Vivianit in Oberflächensedimenten zu quantifizieren. Die vorliegende Arbeit zeigt, dass Vivianit signifikant, mit 10-40 %, zur Phosphorretention in Süßwassersedimenten beitragen kann. Die Untersuchung der Bildungsbedingungen Vivianits in unterschiedlichen Gewässersedimenten Norddeutschlands zeigte, dass das molare Schwefel zu Eisen Verhältnis des Sediments als ein wichtiger Indikator für die Bedingungen identifiziert, welche die Triebkräfte für die An- und Abwesenheit Vivianits darstellen. Eine Eutrophierung von Gewässern und der damit verbundene Anstieg der Sulfidproduktion kann dabei die Bildung Vivianits beeinträchtigen, und eine Abnahme des Phosphorbindungsvermögens des Sediments zur Folge haben. Die vorliegende Arbeit macht deutlich, dass eine artifizielle Erhöhung des Eisengehaltes des Sediments im Rahmen einer Seenrestaurierung eine Vivianitbildung induzieren kann und so langfristig zu einem erhöhten Phosphorrückhalt führt. Sättigungsberechnungen ergaben, dass ein hinsichtlich Vivianits übersättigtes Porenwasser kein sicheres Indiz für die Anwesenheit des Minerals ist. Die Berechnungen sind nicht in der Lage die kleinskaligen chemischen Bedingungen im Porenraum des Sediments abzubilden. Die Untersuchungen zeigen, dass die Bildung von Vivianit einen wichtigen Prozess der Phosphorbindung in Gewässersedimenten darstellt, der bislang jedoch weitestgehend vernachlässigt wurde. / In this thesis, the occurrence and environmental relevance of vivianite in freshwater sediments were explored. Vivianite is the most common reduced iron phosphate mineral which forms in sedimentary environments. Not much is known about the mechanisms which lead to vivianite formation in surface sediments, and about the quantitative role of vivianite in phosphorus sequestration. The development of a novel sediment preparation technique allowed the direct identification of vivianite by powder X-ray diffraction. Notably, for the first time, vivianite was quantified in surface freshwater sediments. The study examplifies that vivianite can significantly contribute to the phosphorus retention in surface freshwater sediments, accounting for 10-40 % of total sedimentary phosphorus. The exploration of vivianite in different surface freshwater sediments located in northern Germany revealed that the sedimentary sulphur to iron ratio is a valuable indicator for the conditions that are important drivers behind the formation or absence of vivianite. It has been demonstrated that eutrophication and the accompanied increase in sulphide production hampers vivianite formation, leading to a decreased phosphorus binding capacity of sediments through increased sediment sulphidization. The present study also revealed, that an iron addition as a measure of lake restoration can trigger vivianite formation, and significantly increases the long-term phosphorus retention of sediments. Pore water equilibrium calculations demonstrated that supersaturated pore water is not sufficient to predict the occurrence of the mineral in situ. Those calculations often fail to predict the occurrence of vivianite because they do not adequately represent chemical conditions within sediment microenvironments. In summary, the formation of vivianite in aquatic sediments constitutes an important process in phosphorus sequestration which has so far largely been ignored.