(Invited) Hybrid Electrocatalysts for Bioelectrooxidation of Small Alcohols: Ethanol and Ethylene Glycol

Abstract

Over the last decades researchers have focused to enhance the electrocatalytic activity of the biosystems, increasing the energy generation and electronic conductivity into the biofilms. The use of enzymes immobilized onto the surface of electrodes as the main catalyst in biological fuel cells has been extensively reported. A biofuel cell provides a means to obtain clean, renewable energy and have great potential to be used as alternative energy source for low power devices. There still a lot of important issues in the development of these device, one of them, is to obtain the maximum energy from the fuel. In order to enhance the power density of enzymatic biofuel cell (EBFC) it is necessary to increase the degree of oxidation of the fuel, so that all the electrons from the fuel can be harvested. One approach is the immobilization of a group of enzymes to perform a cascade in order to maximize the fuel oxidation. Recently, we have concentrated our goal to the develop hybrid biofilms employing MWCNT in order to immobilize efficiently the enzymes. In this context we added organic catalyst (TEMPO (2,2,6,6- tetramethylpiperidin-1-yl) oxyl) or metallic nanoparticles (MWCNT/Pt, MWCNT/PtSn and MWCNT/Au) to the biofilms to create a hybrid catalytic system able to catalyze the complete electrooxidation of ethanol (ET) and ethylene glycol (EG) into CO2. In the case of ethanol extraction of 12 electrons per molecule at a single hybrid anode has been obtained with success. This simple methodology can replace the use of enzymatic cascade (7-8 enzymes) and may improve the application in biofuel cells. The electrochemical response of the enzyme system (MWCNT-COOH/LPEI/OxOx) at increasing concentrations of ethanol confirms the excellent activity of these hybrid bioanodes. Product analysis by HPLC techniques allowed us to correlate the increase in current with the formation of CO2or other more oxidable compounds as main product. In the case of EG the metallic catalyst was shifting the onset oxidation potential to lower potentials (200 mV) compared with TEMPO. The maximum power densities reached values around 351 µW cm-2 in the case of MWCNT/PtSn-OxOx for EG and 315 µW cm-2 for MWCNT-COOH/Pyrene-TEMPO/OxDc bioanode. Fig 1 show the products formed for EG. The modification of nanomaterials to obtain a large energy output form an enzymatic system will be highlighted. Therefore, the system open a new alternative of high performance hybrid-EBFC-based enabling the development of efficient EBFC based on alcohols.Acknowledge: FAPESP (grants # 2017/20431-7 and 2014/50945-4 ), CNPq (grant (465571/2014-0) and CAPES 001. Army Research Office MURI (W911NF-14-1-0263). Figure 1