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A new redox polymer/bilirubin oxidase (BOD)-based gas diffusion electrode was designed to be implemented as the non-current and non-stability limiting biocathode in a glucose/O2 biofuel cell that acts as a self-powered glucose biosensor. For the proof-of-concept, a bioanode comprising the Os-complex modified redox polymer P(VI-co-AA)-[Os(bpy)2Cl]Cl and FAD-dependent glucose dehydrogenase to oxidize the analyte was used. In order to develop an optimal O2-reducing biocathode for the biofuel cell Mv-BOD as well as Bp-BOD and Mo-BOD have been tested in gas diffusion electrodes in direct electron transfer as well as in mediated electron transfer immobilized in the Os-complex modified redox polymer P(VI-co-AA)-[Os(diCl-bpy)2]Cl2. The resulting biofuel cell exhibits a glucose-dependent current and power output in the concentration region between 1 and 10mM. To create a more realistic test environment, the performance and long-term stability of the biofuel cell-based self-powered glucose biosensor has been investigated in a flow-through cell design.

The development of electrodes for efficient CO2 reduction while forming valuable compounds is critical. The use of enzymes as catalysts provides the advantage of high catalytic activity in combination with highly selective transformations. We describe the electrical wiring of a carbon monoxide dehydrogenase II from Carboxydothermus hydrogenoformans (ChCODH II) using a cobaltocene-based low-potential redox polymer for the selective reduction of CO2 to CO over gas diffusion electrodes. High catalytic current densities of up to −5.5 mA cm−2 are achieved, exceeding the performance of previously reported bioelectrodes for CO2 reduction based on either carbon monoxide dehydrogenases or formate dehydrogenases. The proposed bioelectrode reveals considerable stability with a half-life of more than 20 h of continuous operation. Product quantification using gas chromatography confirmed the selective transformation of CO2 into CO without any parasitic co-reactions at the applied potentials.

Using viologen-based redox polymers to wire a variety of different hydrogenases to electrodes and gas diffusion electrodes is the basis to mitigate high potential deactivation of the enzyme, deactivation by molecular O2, as well as for high-current density H2 oxidation bioanodes. To overcome electron transfer limitations by electron hopping within the viologen-modified polymer film, a new redox polymer was designed with the highest possible viologen content together with monomers bearing crosslinking units. In combination with an immobilization sequence consisting of oxidative grafting of amino functions, covalent attachment of polymer units to these functionalities, and crosslinking of the polymer layers, an unprecedently fast electron transfer became possible. This enabled a very high current density normalized by the amount of the [NiFe] hydrogenase embedded within a viologen polymer on gas diffusion electrodes.

Power hardware-in-the-loop (PHiL) simulations provide a powerful environment in the critical process of testing new components and controllers. In this work, we aim to explain the impact of time delays in a PHiL setup and recommend how to consider them in different investigations. The general concept of PHiL, with its necessary components, is explained and the benefits compared to pure simulation and implemented field tests are presented. An example for a flexible PHiL environment is shown in form of the Power Hardware-in-the-Loop Simulation Laboratory (PHiLsLab) at TU Hamburg. In the PHiLsLab, different hardware components are used as the simulator to provide a grid interface via an amplifier system, a real-time simulator by OPAL-RT, a programmable logic controller by Bachmann, and an M-DUINO microcontroller. Benefits and limitations of the different simulators are shown using case examples of conducted investigations. Essentially, all platforms prove to be appropriate and sufficiently powerful simulators, if the time constants and complexity of the investigated case fit the simulator performance. The communication interfaces used between simulator and amplifier system differ in communication speed and delay; therefore, they have to be considered to determine the level of dynamic interactions between the simulated rest of system and the hardware under test.

Additional file 1.