Abstrakt
Cobalt-nitrogen-carbon (Co-N-C) systems are promising Pt-free catalysts for oxygen reduction reaction (ORR). Among other, ionic liquids (ILs) are currently being actively used as a source of nitrogen and carbon for obtaining Co-N-C electrocatalysts via pyrolysis.
At the same time, known ILs-derived Co-N-C catalysts are characterized by either not high enough ORR activity or methods of their production are complex and multi-stage. Here, for the first time the possibility of increasing the efficiency of Co-N-C ORR electrocatalysts due to the use in precursor composition of deep eutectic solvents (DES) based on 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) or tetrafluoroborate ([Bmim]BF4) and hydrated Co(NO3)(2) or CoCl2 instead of mixture of IL and salt of Co (II) was shown.
The advantages of using DES as precursors are the high content of cobalt and nitrogen in them, as well as the ability to provide uniform distribution of Co and N atoms in the electrocatalyst given the structure of DES. It was found that DES nature afects composition catalysts and the type of domanant active sites, which leads to diferences in their catalytic performance towards ORR.
It was shown, that obtained Co-N-C electrocatalysts in their ORR-activity in the alkaline electrolyte (onset potential of 0.96-0.99 V vs. RHE, half-wave potential of 0.85-0.89 V, and a Tafel slope of 37-50 mV/dec) are almost not inferior to Pt/C catalyst, and are also characterized by high long-term electrochemical stability.
The reduction of oxygen on the DES-derived Co-N-C catalysts is mainly occurs under 4-electron mechanism.