(Invited) Bacterial Biofilms As Active Components of Electrocatalytic and Photoelectrochemical Systems for Reduction of Carbon Dioxide

Abstract

Most of the bacterial species form biofilms, in which microorganisms are attached to a surface and they are held together by extracellular polymeric substances that they produce. They tend to grow almost everywhere both on living or non-living surfaces. Biofilms are able to propagate charge within their structures and to transfer effectively electrons at interfaces, as well as they could exhibit electrocatalytic properties (e.g. in Microbial Fuels Cells). The application of microbes provides better flexibility: experiments with fuel cells can be operated at normal conditions (temperatures and pressures). Wide variety of microbial metabolic pathways gives the possibility to use aggregates of bacteria in diverse processes. Proposed electrochemical studies using bacterial biofilms (in the form of thin coatings on the glassy carbon electrodes) can be considered as an attempt to find efficient methods of using the energy produced by microorganisms and converting it to electricity.The ultimate goal of the present research has been to determine whether it is possible under laboratory conditions to perform electrocatalytic processes using the hybrid (composite) layers composed of aggregates of bacteria in pristine or modified forms. A biofilm formed by a strain of Yersinia enterocolitica (Y. enterocolitica) is characterized by a high physicochemical stability over a wide pH range (4-10) and temperatures (0-40°C).The subject of interest is a fairly complex reaction, electroreduction of carbon dioxide. There has been growing interest in the search of electrocatalytic anf photoelectrochemical systems capable of efficient conversion of carbon dioxide into fuels and utility chemicals. Our previously performed studies have clearly shown that the Y. enterocolitica biofilm itself has no activity with respect to reduction of CO2, however it acts as a good matrix for the catalytic (e.g. noble metal or metaloorganic) centers [1,2], because it affects the reaction mechanism and appears to decrease overpotential of the electroreduction processes. The conducted research shows that the composite materials containing bacterial biofilms can be successfully used to construct systems that have an electrocatalytic reactivity in the reduction of carbon dioxide. In particular, the influence of the biological matrix on the catalytic activity of different transition metal nanoparticles (Pd, Pt, Ru, PtRu) in the carbon dioxide conversion process will be compared. Here, the successful system based on platinum nanoparticles deposited on the biological carrier, Y. enterocolitica biofilm, supported onto conductive polymer (polyaniline) and utilizing multi-walled carbon nanotubes should be mentioned. We will also address the possibility of dispersing the organometallic ruthenium (II) complex in the biological layer (biofilm). Indeed, the ruthenium (II) complex has been immobilized in the biofilm matrix by successive modification of the liquid medium (Luria-Bertani medium) for culturing bacteria with a solution of the complex compound. In addition, the biological matrix was used (along with the ruthenium (II) complex molecules dispersed in its layer) as a protective coating, stabilizing the unstable p-type semiconductor - copper (I) oxide. The proposed hybrid co-catalytic system showed activity during the photoelectrochemical reduction of carbon dioxide and stability under semi-neutral experimental conditions. Finally, we are going to address the design of the above-mentioned catalytically active systems emphasizing the need to control the structure of the studied hybrid materials (in addition to their stability). Among important issues is the viability of bacteria in the biological membrane as well as elucidation of the role of the bacterial biofilm during the carbon dioxide reduction.[1] Seta E., Lotowska W., Rutkowska I.A., Wadas A., Raczkowska A., Nieckarz. M., Brzostek K., Kulesza P.J., Australian Journal of Chemistry 69 (2016) 411-418.[2] Lotowska W., Rutkowska I.A., Seta E., Szaniawska E., Wadas A., Raczkowska A., Brzostek K., Kulesza P.J., Electrochimica Acta 213 (2016) 314-323.