Elo Kibena-Põldsepp

Electrocatalysis of oxygen reduction on heteroatom-doped nanocarbons and transition metal–nitrogen–carbon catalysts for alkaline membrane fuel cells

Over the last decade, great progress has been made in the development of non-precious metal catalysts for the electrochemical oxygen reduction reaction (ORR). Among these, heteroatom-doped carbon nanomaterials and transition metal–nitrogen–carbon (M–N–C) catalysts are especially advantageous in an alkaline environment, showing high electrocatalytic activity for the ORR and good durability. Over the past few years, substantial achievements have also been made in improving the performance of anion exchange membrane fuel cells (AEMFCs) and the commercialisation of these devices has emerged as a viable option. This review article provides an outline to the most relevant studies of the ORR on heteroatom-doped nanocarbons and M–N–C type catalysts in alkaline media. In addition, an overview of the studies employing these materials as cathodes in AEMFCs is presented. A separate section is devoted to the results obtained with alkaline direct methanol and ethanol fuel cells. Further perspectives in the field of AEMFC research and development are also highlighted.

Electrochemical properties of gold and glassy carbon electrodes electrografted with an anthraquinone diazonium compound using the rotating disc electrode method

In this paper, gold and glassy carbon (GC) electrodes were electrochemically grafted with anthraquinone (AQ) groups derived from Fast Red AL salt via electrochemical reduction of AQ diazonium cations. For the first time, the electrografting was performed by combining the cyclic voltammetry (CV) or potential step method with the rotating disc electrode (RDE) technique in order to prepare thick films of AQ on Au and GC electrodes. For comparison purposes, a CV or potential step method without the RDE was also used. The attachment of thick AQ films to the Au electrode surface was confirmed by X-ray photoelectron spectroscopy and atomic force microscopy. The highest surface concentration value (ΓAQ) of AQ on the Au and GC electrodes (ca. 2.1 × 10−8 and 1.8 × 10−8 mol cm−2, respectively) was obtained by employing the combination of CV and RDE methods during the electrografting procedure. The oxygen reduction reaction results revealed that the electrochemical behaviour of AQ-modified Au electrodes does not depend on the ΓAQ value similar to the GC electrodes modified with thick AQ films. However, some differences were observed when the blocking effect of thick AQ films on Au and GC electrodes towards the ferri/ferrocyanide redox probe was studied.

Oxygen Reduction on Catalysts Prepared by Pyrolysis of Electrospun Styrene–Acrylonitrile Copolymer and Multi-walled Carbon Nanotube Composite Fibres

For the first time, the oxygen reduction reaction (ORR) is studied on pyrolysed electrospun multi-walled carbon nanotube (MWCNT) and styrene–acrylonitrile (SAN) composite fibre catalysts in alkaline medium. Scanning electron microscopy images revealed that the prepared catalysts mainly consist of MWCNTs, while nitrogen doping of the catalysts is confirmed by X-ray photoelectron spectroscopy. This indicates that SAN can be used as a nitrogen precursor. The ORR studies carried out by rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) methods showed that the prepared catalysts were considerably more active towards the ORR than the pristine MWCNTs.Graphical Abstract