The INM program division Energy Materials develops and investigates functional materials for electrochemical applications. Fields of application include, but are not limited to, energy storage & recovery (supercapacitors, batteries), energy harvesting, and electrochemical water treatment (capacitive deionization). Nanoporous carbons and carbon hybrid materials are derived from organic and inorganic precursors. Modification of the synthesis parameters allows us to precisely tune the chemical composition, crystal structure, and resulting physical & electrochemical properties. On a length scale, our materials range from sub-nanometer pores (e.g., carbide-derived carbons), to nanoparticles (e.g., carbon onions, novolac-derived carbons) and electrospun nanofibers up to mm- and cm-range monoliths. A key focus of our research activities relates to electrochemical methods and novel in situ techniques.
Electrochemical energy storage (EES) can achieve high efficiency and rapid charge/discharge cycles. This is particularly true for supercapacitors, a device technology that excels in power density and longevity. Supercapacitors may rely just on ion electrosorption (double-layer capacitors) or enhance their energy density by employing also Faradaic charge transfer (pseudocapacitors). The former is, by the virtue of the charge storage mechanism, distinct from batteries or fuel cells. We also investigate redox reactions and investigate hybrid and battery materials (e.g., lithium sulfur battery). The development of a reliable measurement technique and benchmarking cycling performance stability are complemented by in situ methods to gain more detailed insights into energy storage mechanisms. We also investigate cost effective and environmentally friendly synthesis methods and materials.
Ion electrosorption is not only a powerful method to store energy, but can also be employed to effectively remove ions, for example, from salt water. Capacitive deionization (CDI) is based on the physical process of double-layer formation and ion immobilization for ionic species dissolved in a flowing stream passing by (or passing through) electrically charged electrodes. The high energy efficiency relates to the removal of ions rather than removal of water: for one electric charge at each electrode (cathode and anode), on anion and one cation can be (ideally) removed. This charge can largely be recovered during discharging. CDI can also be operated in a fully continuous matter by employing flow electrodes. The use of hybrid materials is a powerful way to further enhance the salt sorption capacity of carbon electrodes.
Abb. 3 Kapazitive Entionisierung
Novel carbon and hybrid materials are an important aspect of our work. In particular, we focus on porous materials with a well-developed pore size distribution and high surface area. Precursor-derived carbons are an important group of materials which can be obtained from bio mass, polymers, or carbides. Polymers enable us to freely design complex shapes, such as thin films, beads, or fibers. Carbide-derived carbons (CDC) and novolac-derived carbons are particularly interesting because of the very high level of control over the pore size distribution. Such model carbons are ideal to investigate the electrochemical performance with in situ techniques, such as methods based on spectroscopy, diffraction, or dilatometry. Hybrid materials enable us to capitalize the electrical conductivity of carbon and the redox activity of metal oxides, metal nitrides, or electroactive polymers. We also synthesize carbons with defined redox active functional surface groups. Redox active carbon hybrids enable us to significantly improve the energy density of electrochemical energy storage devices.
A) Kohlenstoff-Komposit-Ekektride, B) Kohlenstoffnanozwiebel mit Chinonen, C) Manganoxid auf Kohlenstoffnanofaser, D) Metallkarbid/Nanokohlenstoff Hybrid-Faser