Electrode/Electrolyte Interplay in Electrochemical Capacitor

Professor, Member of Polish Academia of Science and Academia Europaea,

Poznan University of Technology, Poland

In electrochemical capacitors (ECs), the electrostatic attraction of ions is responsible for charge storage at the electrode/electrolyte interface. Thus, ECs are perfectly adapted for high-power applications, yet they suffer from a low energy density. In relation to the electrode material (most often activated carbon), micropores are indispensable for storing of ions, yet small mesopores are also required for a high charge propagation. As a rule of thumb, the closed pores do not take part in charge accumulation, and the pores smaller than the ion’s size will not participate in the electric double layer (EDL) formation. However, a partial de-solvation of ions should not be excluded. Hence, matching the pore size of carbons with the dimensions of ions plays a key role, and the soft templating method is well adapted approach. Moreover, the capacitance dependence on the structural ordering of the electrode material supplies crucial information on the charge storage mechanism. Materials with numerous edge defects favor the electrolyte decomposition, thereby reducing its stability window. Regarding the electrolyte, ECs in organic medium operate at high voltage (ca. 3V), but it is flammable, toxic and requires a neutral atmosphere for EC assembly. Lately, high research interest is dedicated to novel electrolytes as water in salt and deep eutectic solvents, where specific interactions at the electrode/electrolyte interface play a crucial role. A redox activity of the electrode material originating from the presence of heteroatoms and redox couples introduced into electrolyte or electrode can also be an enormous source of charge. Hence, electrode-electrolyte interactions contribute very significantly to boosting the performance of ECs.

Elzbieta Frackowiak is a full professor at Poznan University of Technology (Institute of Chemistry and Technical Electrochemistry) in Poland. Her research field is energy storage/conversion with special emphasis on electrochemical capacitors, lithium-ion batteries, fuel cells, redox flow batteries and hydrogen electrosorption in carbon materials. In 2011, she was awarded the Prize of the Foundation for Polish Science and Officer’s Cross of Polonia Restituta Order. She is also member of the Polish Academy of Sciences (Vice-President 2015-2018), Fellow of Royal Society of Chemistry, Fellow of International Society of Electrochemistry, and Member of Academia Europaea. Frackowiak is author of ca. 200 peer-reviewed papers, 24 book chapters and 50 patents. Her papers have resulted in over 36,000 citations and her h-index is 74 (Google Scholar).