Miglena Slavova
a) Institute of Electrochemistry and Energy Systems “Academician Evgeni Budevski”, Acad. Georgi Bonchev 10 Str., 1113 Sofia, Bulgaria. b) “Todor Kableshkov” University of Transport, 158 Geo Milev Str., 1574 Sofia,
Bulgaria

Elena Mihaylova-Dimitrova
Institute of Electrochemistry and Energy Systems “Academician Evgeni Budevski”, Acad. Georgi Bonchev 10 Str., 1113 Sofia,
Bulgaria

Emiliya Mladenova
Institute of Electrochemistry and Energy Systems “Academician Evgeni Budevski”, Acad. Georgi Bonchev 10 Str., 1113 Sofia,
Bulgaria

Borislav Abrashev
Institute of Electrochemistry and Energy Systems “Academician Evgeni Budevski”, Acad. Georgi Bonchev 10 Str., 1113 Sofia,
Bulgaria

Blagoy Burdin
Institute of Electrochemistry and Energy Systems “Academician Evgeni Budevski”, Acad. Georgi Bonchev 10 Str., 1113 Sofia,
Bulgaria

Daria Vladikova
Institute of Electrochemistry and Energy Systems “Academician Evgeni Budevski”, Acad. Georgi Bonchev 10 Str., 1113 Sofia,
Bulgaria