Utilisation of pyrochlore-typeoxideas catalyst in bioanode of coffee mac microbial fuel cell: Boost of electric voltage and reduction of wastes

ABSTRACT

This study is a contribution to development of material based on transition metal oxides with application in electrochemical devices. A pyrochlore-like solid solution with general chemical formula Bi_1.2Ce_0.3Sb_1.5CuO₇ was synthesised. The pyrochlore structure was determined by X-ray powder diffraction. The pressed pyrochlore powder sample was analysed by scanning electron microscopy to show effect of substitution fraction of cerium and to determine its grain size and morphology. Energy dispersive of X-rays was performed to confirm effective substitution of bismuth for cerium. The EDX analysis was supported by X-ray photoelectron spectroscopy which also gave information on respective oxidation states of cations. Several modes of vibration due to metal-oxygen bonds of pyrochlore-like material were studied by Fourier-transform infrared spectroscopy. The results suggested that this compound contained major component of pyrochlore and minor component of CeO₂. The dielectric measurements carried out at frequency 1 MHz in temperature range –40°C–90°C proved that pyrochlore compound possessed dielectric constants ranging between 12 and 28. Furthermore, owing to its high electrical conductivity, synthesised material has been utilised as bioanode in a microbial fuel cell. This bio-electrochemical device converted organic wastes into electricity using microorganisms as biocatalysts. It displayed greater electron transfer from electroactive biofilm towards the bioanode by improving its electrical energy output. The presence of pyrochlore in electrode allowed a power density of 25 mW/m². It was almost the same as that obtained with a graphite carbon modified by the conducting polymer polypyrrole. The MFC with pyrochlore solid oxide was advantageously more stable having longer lifetime and indicating its suitability to substitute the polypyrrole at the bioanode. Besides, the colour of the coffee mac leachate in the anolyte (anode compartment) became less dark, which means that the maximum chemical oxygen demand (COD) was removed and converted into electric energy.

KEYWORDS:

• Pyrochlore
• synthesis
• characterisation
• catalyst
• microbial fuel cell
• electricity generation
• waste treatment

Acknowledgments

We thank Dr. Kathrin Müller for XPS measurement, Sabine Prill-Diemer for SEM/EDX analysis, and Christine Stefani for XRPD characterisation (Max-Planck-InstitutefürFestkörperforschung – Stuttgart, Germany). We are also grateful to the German Academic Exchange Service for financial support during short-term internship.

Disclosure statement

No potential conflict of interest was reported by the author(s).