Operando analysis of the interfaces in electrochemical capacitors
Poznan University of Technology, Institute of Chemistry and Technical Electrochemistry
Abstract: The reversibility of the charge/discharge processes during long-term cycling is crucial for electrochemical capacitor application. Extending of capacitor voltage in water medium from 1.23 V to 2V is indispensable to be competitive to organic based capacitors present in the market. In this case, the energy of both systems is comparable.
Introducing redox active species in the electrolyte and/or at the electrode/electrolyte interface is a good strategy to involve faradaic reactions as additional source of pseudocapacitance. The electrosorption of hydrogen into microporous carbon plays a dual role: an increase of capacitance values and a shift of operating potential to more negative values. Such redox species as halides (iodides I-1/I2, bromides Br-1/Br2) will be considered and they are extremely beneficial for the positive electrode. The effect of carbon porosity on charge accumulation, reversible energy storage and power delivery is crucial; the pore size should match with the ion dimensions especially if they are bulky. Carbons with a suitable micro/meso ratio allow the redox active species to be efficiently used at the electrode/electrolyte interface.
Operando techniques such as in-situ Raman spectroscopy have been used in various electrolytes (sulfates, nitrates, iodides, bromides…) to evaluate the stability of the carbon electrode against oxidation in the presence of neutral and redox species. The evolution of gases was also monitored during polarization by mass spectrometry. Interestingly the limit of optimal potential and reversibility of redox reactions were precisely evaluated.
The detailed electrical examination of such capacitors (by galvanostatic charge/discharge, cyclic voltammetry, electrochemical impedance spectroscopy, floating etc.) confirmed a good cycling, perfect charge dynamics as well as beneficial energy and power values.
Major field of research: storage of energy in capacitors, accumulators (e.g. Li-ion batteries), fuel cells.
Investigated materials: nanotextured carbons (functionalized, doped by nitrogen, oxygen, iodine), carbon nanotubes, activated carbons, composites, conducting polymers.
Elzbieta Frackowiak has considerable academic achievements proved with over 160 papers in international journals, 24 book chapters and 20 patents with citation number over 14800, Hirsch-index 51 and copious number of invited keynotes and plenary lectures during international conferences (more than 50). She is also a co-editor of 2 books. She is an Advisory Board Member in Energy & Environmental Science and served in Electrochimica Acta journals. Presently she is an Associate Editor of Carbon (Elsevier).
As recognition of her accomplishments, she was chosen in international voting as Chair-Elect (2009-2010), Chair (2011-2012) and Past-Chair (2013-2014) of the Division 3 „Electrochemical Energy Conversion and Storage” in the International Society of Electrochemistry. In 2011, she was awarded the Prize of the Foundation for Polish Science for “Investigation of novel carbon materials and their composites for electrochemical energy conversion and storage”. She is also member as well as vice-president of the Polish Academy of Sciences.