Biosensor/Biofuel Cell System for Lactate Detection in Sweat, Targeted Towards Human Performance

Effects of atmospheric air plasma treatment of graphite and carbon felt electrodes on the anodic current from Shewanella attached cells

Carbon felt electrode coated with WS ₂ enables a high‐performance polysulfide/ferricyanide flow battery

Activity gradient carbon felt electrodes for vanadium redox flow batteries

Facile preparation of an oxygen-functionalized carbon felt electrode to improve VO2+/VO2+ redox chemistry in vanadium redox flow batteries

Electro-conductive carbon felt (CF) material is composed by bonding together different lengths of carbon filaments resulting in a porous structure with a significant internal surface that facilitates enhanced electrochemical reactions. Owing to its excellent electrical properties, CF is found in numerous electrochemical applications, such as electrodes in redox flow batteries, fuel cells, and electrochemical desalination apparatus. CF electro-conductivity mostly arises from the close contact between the surface of two electrodes and the long carbon fibers located between them. Electrical conductivity can be improved by a moderate pressing of the CF between conducting electrodes. There exist large amounts of experimental data regarding CF electro-conductivity. However, there is a lack of analytical theoretical models explaining the CF electrical characteristics and the effects of compression. Moreover, CF electrodes in electrochemical cells are immersed in different electrolytes that affect the interconnections of fibers and their contacts with electrodes, which in turn influence conductivity. In this paper, we investigated both the role of CF compression, as well as the impact of electrolyte characteristics on electro-conductivity. The article presents results of measurements, mathematical analysis of CF electrical properties, and a theoretical analytical explanation of the CF electrical conductivity which was done by a stochastic description of carbon filaments disposition inside a CF frame.

Polypyrrole-coated hierarchical porous composites nanoarchitectures for advanced solid-state flexible hybrid devices

One of the main issues of enzymatic biofuel cells is the need to develop stable bioelectrodes. However, there is no standard method to study bioelectrode stability. In this study, laccase and anthracene modified multiwall carbon nanotubes (anth-MWCNTs) were used in conjunction with different immobilization polymers in order to increase the stability of the biocathodes. A series of stability assays were used to understand the operational stability of the biocathode in a biofuel cell environment. The immobilization matrices used in this study were tetrabutyl ammonium bromide modified Nafion (TBAB modified Nafion), octyl modified linear polyethylenimine (C8-LPEI), and vapor deposited tetramethyl orthosilicate (TMOS) gels. The decrease in activity of the galvanostatic and potentiostatic measurements over a 24 hour period of the TBAB modified Nafion were 4.0 ± 0.6% and 4.1 ± 0.4%; C8-LPEI were 0.7 ± 0.1% and 9.6 ± 0.5%; and TMOS were 4.1 ± 0.1% and 10 ± 2.0%, respectively. This data show that potentiostatic measurements provide a harsher environment for the enzyme and result in lower stability, as well as showing that the TBAB modified Nafion offers a more stabilizing immobilization strategy compared to the C8-LPEI or TMOS matrices.

Electrochemical detection and simultaneous removal of endocrine disruptor, bisphenol A using a carbon felt electrode

The electrodes (anode and cathode) have an important role in the efficiency of a microbial fuel cell (MFC), as they can determine the rate of charge transfer in an electrochemical process. In this study, nanoporous gold electrode, prepared from commercially available gold-made compact disk, is utilized as the anode in a two-chamber MFC. The performance of nanoporous gold electrode in the MFC is compared with that of gold film, carbon felt and acid-heat-treated carbon felt electrodes which are usually employed as the anode in the MFCs. Electrochemical surface area of nanoporous gold electrode exhibits a 7.96-fold increase rather than gold film electrode. Scanning electron microscopy analysis also indicates the homogeneous biofilm is formed on the surface of nanoporous gold electrode, while the biofilm formed at the surface of acid-heat-treated carbon felt electrode shows rough structure. Electrochemical studies show although modifications applied on carbon felt electrodes improve its performance, nanoporous gold electrode, due to its structure and better electrochemical properties, acts more efficiently as the MFC’s anode. The maximum power density produced by nanoporous gold anode is 4.71 mW m−2 at current density of 16.00 mA m−2, while this value for acid-heat-treated carbon felt anode is 3.551 mW m−2 at current density of 9.58 mA m−2.

Regulating flow field design on carbon felt electrode towards high power density operation of vanadium flow batteries

Implantable bioelectronics devices need internal power sources that are capable of delivering adequate electrical power. Here we report a hybrid glucose/O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> biofuel cell wherein the glucose bioanode of pyroquinoline quinone glucose dehydrogenase (PQQ-GDH) modified chitosan buckypaper (BP) is coupled with an oxygen reducing cathode constructed from bacterial nanocellulose (BNC) pellicle crosslinked with multi-walled carbon nanotubes (MWCNTs) coated with gold and colloidal platinum (co-Pt). The flexible and electrically conductive enzyme functionalized BP-PQQ-GDH bioanode and enzyme-free BNC-Au-co-Pt biocathode harnessed the biochemical energy of glucose via the oxidation of glucose and reduction of molecular oxygen to generate electrical power. The hybrid biofuel cell system exhibited an open circuit voltage and power density of 476 mV and 66.56 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, with a current density of 654 μA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the presence of 20 mM glucose. At physiological glucose concentration, the biofuel cell exhibited an open circuit voltage and power density of 453 m V and 45.54 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, with a current density of 594 μA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This facile strategy to prepare flexible conductive electrodes for the development of hybrid glucose/O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> biofuel cell system can be readily extended to diverse applications in hybrid glucose biofuel cell and biosensor technology.

With dwindling fossil resources and growing environmental concerns, clean and efficient energy conversion and storage technologies are getting more and more attention from the public. Lithium ion batteries, redox flow batteries as well as fuel cells hold the promise and burden to sustain our energy-demanding society. In recent years, several efforts have been addressed to vanadium redox flow batteries (VRFB) which show great promise for the economical storage of electrical energy intermittently available from wind and solar. The excess energy is stored in liquid electrolytes using the four oxidation states of Vanadium, V2+/3+ at the negative, V4+/5+at the positive side. The liquid electrolytes flow through porous carbon felt electrodes, which provide a heterogeneous reaction surface. The main reasons to use carbon felts are their corrosion resistance in acidic electrolyte, high overpotential towards the unwanted hydrogen evolution reaction (HER) and low material costs. In addition, their activity towards the positive and negative reaction, respectively, can be modified using thermal oxidation in air atmosphere, acid treatment, heteroatom doping, and others. With respect to stationary applications with projected system runtimes of 10˙000 hours and more, not only activity, but also durability of the electrode materials moves into the focus of current research. It has been reported [1] that the carbon felts undergo significant degradation when cycled for a certain number of times. However, already the electro-less contact with the highly acidic electrolytes seems to affect the felts properties. In this study, static electro-less ageing and dynamic degradation of heat-treated carbon felt electrodes were investigated by combining different electrochemical and analytical methods. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to monitor the performance loss of the carbon-based electrodes, whereas scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were applied to study cause and effects of material’s degradation. In this respect, oxygen functional groups, electron conductivity, wettability, accessible surface area and other characteristics play an important role. In general, the HER is a parasitic reaction, which should be hindered in favor of the V3+ reduction. It has been reported that bismuth additions to the electrolyte enhance the activity of the felt for the negative reaction without enhancing the HER [2]. However, the competition between HER and V3+reduction can also be used as an indicator of the felt’s state of health when probed at different temperatures and in different electrolyte concentrations. We will discuss this for differently degraded felts. Furthermore, we use our battery tester with implemented reference electrodes to compare the individual half-cell potentials with full cell potentials and to study the effect of different cut-off voltages on the projected electrode degradation. Higher cut-off potentials might prove effective for the system’s operation strategy, if they do not lead to the expected increased degradation phenomena. [1] I. Derr, M. Bruns, J. Langner, A. Fetyan, J. Melke, C. Roth „Degradation of all-vanadium redox flow batteries (VRFB) investigated by electrochemical impedance and X-ray photoelectron spectroscopy: Part 2 electrochemical degradation, Journal of Power Sources 325 (2016) 351-359. [2] B. Li, M. Gu, Z. Nie, Y. Shao, Q. Luo, X. Wei, X. Li, J. Xiao, C. Wang, V. Sprenkle, W. Wang Nano Letters. 13 (2013) 1330-1335.

The activity of urease varies by its redox reaction. Active urease has an SH group that is essential to exhibit its activity, however, oxidation agents such as quinone compounds can oxidize the SH group in urease and a S–S bond is produced, resulting in the loss of enzyme activity. The reduction potential of cystine was almost the same as that of the recovery of urease activity. In this work, it has been found that the SH group of urease can be oxidized by not only chemical reaction but also by the direct electrode oxidation of urease and the produced S–S bond can be reduced to SH group by chemical and electrode reactions, and the original enzyme activity is recovered. This research shows that the regulation of urease activity is easily possible by changing the electrode potential of the porous carbon felt immobilized urease. The variation of urease activity was monitored by ammonia or carbon dioxide electrode equipped with the urease immobilized carbon felt, and the ammonia or carbon oxide generated from urea can transfer through the carbon felt to reach the each gas permeable membrane. The combination of gas electrode with porous conducting material such as carbon can supply the novel device for the electrochemical investigation of enzyme activity.

Covalent co-immobilization of glucose oxidase and ferrocenedicarboxylic acid for an enzymatic biofuel cell

Oxidation of NADH produced by a lactate dehydrogenase immobilised on poly(aniline)–poly(anion) composite films