Switchable Electrode Assemblies Employing Nano-Bio Hybrid Structures in Cascaded Enzymatic Fuel Cells

Enzymatic biofuel cells may become more accessible for applications powering portable or implantable electronic devices by extending the range and conversion efficiency of the fuels and oxidizers used. One of the major challenges of enzyme-modified electrodes is their susceptibility to time-dependent degradation of the active biocatalysts, which typically leads to limited operational lifetimes. Within this thesis, we introduce concepts and methodologies that promote enzymatic biofuel cells as alternative power sources. These concepts are exemplified and validated through a series of saccharide/oxygen-based enzymatic biofuel cells. To broaden the spectrum of usable biofuels and operational conditions, we describe integrated assemblies consisting of multi-substrate electrodes composed of enzymatic cascades immobilized to mesoporous carbon nanoparticle supports. In this design, entrapped electron relay molecules facilitate the electrical communication between the linked redox enzymes and the conductive carbon supports, thus efficiently mediating the oxidation of multiple fuels and reduction of oxidizers for the generation of electrical power. By using a cascade consisting of the enzymes invertase, mutarotase, glucose oxidase and fructose dehydrogenase, and by employing tetrathiafulvalen mediator units, we are able to effectively oxidize, separately and simultaneously, the fuels glucose, fructose and sucrose. A cathode consisting of the enzymes catalase and bilirubin oxidase, employing the mediator 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), is successfully shown to operate in environments of varied oxygen availability. Whereas bilirubin oxidase reduces oxygen to water under aerobic conditions, catalase catalyzes the disproportionation reaction of hydrogen peroxide to water and oxygen, allowing hydrogen peroxide to act as an internal source of oxygen under anaerobic operation conditions. A combined assembly of these cascaded electrode architectures yields a non-compartmentalized biofuel cell based on mediated electron transfer bioelectrocatalysis, operating with multiple fuels and oxidizer re-sources. This cell can be repeatedly switched between aerobic and anaerobic operating conditions without any significant decrease in discharge performance. To overcome limitations imposed by the time-dependent degradation of the biological components in enzymatic biofuel cells, we propose a magnetically assisted methodology to reenergize the cells. In this case, carbon coated magnetic nanoparticles are modified with fructose dehydrogenase or bilirubin oxidase. These can be channeled towards and away from designated current collectors by externally applied magnetic field gradients. The magneto-assisted loading of the current collectors results in direct electron transfer currents. Similarly, by applying appropriate magnetic field gradients, bioelectrocatalysis can be switched ON and OFF to generate power on demand, and the active components of the cell can be exchanged entirely to regenerate power. By repeatedly refreshing the particles at a deep stage of the discharge, the biofuel cell operation is considerably extended beyond a single full discharge. Taken individually and even more so when combined together, these concepts open new possibilities to exploit a broad range of fuels and oxidizers, and to harvest electrical energy from alternative biomass resources

Status Update on Bioelectrochemical Systems: Prospects for Carbon Electrode Design and Scale-Up

Bioelectrochemical systems (BES) employ enzymes, subcellular structures or whole electroactive microorganisms as biocatalysts for energy conversion purposes, such as the electrosynthesis of value-added chemicals and power generation in biofuel cells. From a bioelectrode engineering viewpoint, customizable nanostructured carbonaceous matrices have recently received considerable scientific attention as promising electrode supports due to their unique properties attractive to bioelectronics devices. This review demonstrates the latest advances in the application of nano- and micro-structured carbon electrode assemblies in BES. Specifically, in view of the gradual increase in the commercial applicability of these systems, we aim to address the stability and scalability of different BES designs and to highlight their potential roles in a circular bioeconomy

Magnetically induced enzymatic cascades – advancing towards multi-fuel direct/mediated bioelectrocatalysis

A generic method to magnetically assemble enzymatic cascades onelectrode surfaces is introduced. The versatile method enables the simultaneous activation of both direct and mediated electron transfer bioelectrocatalysis to harness different substrates, which can serve as multiple fuels and oxidizers in biofuel cells generating clean energy.ISSN:2516-023

Sustainably Sourced Mesoporous Carbon Molecular Sieves as Immobilization Matrices for Enzymatic Biofuel Cell Applications

Ordered mesoporous carbon CMK-3 sieves with a hexagonal structure and uniform pore size have recently emerged as promising materials for applications as adsorbents and electrodes. In this study, using sucrose as the sustainable carbon source and SBA-15 as a template, CMK-3 sieves are synthesized to form bioelectrocatalytic immobilization matrices for enzymatic biofuel cell (EFC) electrodes. Their electrochemical performance, capacitive features, and the stability of enzyme immobilization are analyzed and compared to commercially available multi-walled carbon nanotubes (MWCNT) using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The anodic reaction in the presence of glucose oxidase (GOx) and ferrocene methanol (FcMeOH) on the sustainably sourced CMK-3-based electrodes produces bioelectrocatalytic current responses at 0.5 V vs. saturated calomel electrode (SCE) that are twice as high as on the MWCNT-based electrodes under saturated glucose conditions. For the cathodic reaction, the MWCNT-based cathode performs marginally better than the CMK-3-based electrodes in the presence of bilirubin oxidase (BOD) and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS2−). The CMK-3-based EFCs assembled from the GOx anode and BOD cathode results in a power output of 93 μW cm−2. In contrast, the output power of MWCNT-based EFCs is approximately 53 μW cm−2. The efficiency of CMK-3 as a support material for biofuel cell applications is effectively demonstrated

Enzyme-Capped Relay-Functionalized Mesoporous Carbon Nanoparticles: Effective Bioelectrocatalytic Matrices for Sensing and Biofuel Cell Applications

The porous high surface area and conducting properties of mesoporous carbon nanoparticles, CNPs (<500 nm diameter of NPs, pore dimensions ∼6.3 nm), are implemented to design electrically contacted enzyme electrodes for biosensing and biofuel cell applications. The relay units ferrocene methanol, Fc-MeOH, methylene blue, MB⁺, and 2,2′-azino­bis(3-ethyl­benzo­thiazoline-6-sulfonic acid), ABTS^2–, are loaded in the pores of the mesoporous CNPs, and the pores are capped with glucose oxidase, GOx, horseradish peroxidase, HRP, or bilirubin oxidase, BOD, respectively. The resulting relay/enzyme-functionalized CNPs are immobilized on glassy carbon electrodes, and the relays encapsulated in the pores are sufficiently free to electrically contact the different enzymes with the bulk electrode supports. The Fc-MeOH/GOx CNP-functionalized electrode is implemented for the bio­electro­catalyzed sensing of glucose, and the MB⁺/HRP-modified CNPs are applied for the electrochemical sensing of H₂O₂. The ABTS^2–/BOD-modified CNPs provide an effective electrically contacted material for the bio­electro­catalyzed reduction of O₂ (<i>k</i>_cat = 94 electrons·s^–1). Integration of the Fc-MeOH/GOx CNP electrode and of the electrically wired ABTS^2–/BOD CNP electrode as anode and cathode, respectively, yields a biofuel cell revealing a power output of ∼95 μW·cm^–2