In the development of biofuel cells great effort is dedicated to achieving outstanding figures of merit, such as high stability, maximum power output, and a large open circuit voltage. Biofuel cells ...with immobilized redox mediators, such as redox polymers with integrated enzymes, show experimentally a substantially higher open circuit voltage than the thermodynamically expected value. Although this phenomenon is widely reported in the literature, there is no comprehensive understanding of the potential shift, the high open circuit voltages have not been discussed in detail, and hence they are only accepted as an inherent property of the investigated systems. We demonstrate that this effect is the result of a Nernstian shift of the electrode potential when catalytic conversion takes place in the absence or at very low current flow. Experimental evidence confirms that the immobilization of redox centers on the electrode surface results in the assembled biofuel cell delivering a higher power output because of charge storage upon catalytic conversion. Our findings have direct implications for the design and evaluation of (bio)fuel cells with pseudocapacitive elements.
Realizing the potential: The integration of pseudocapacitive materials in electrodes for (bio)fuel cells gives rise to a Nernstian shift in the electrode potential. This leads in practice to an increased open circuit voltage and consequently increased power at large cell voltages.
Oxygenic photosynthetic organisms perform solar energy conversion of water and CO
to O
and sugar at a broad range of wavelengths and light intensities. These cells also metabolize sugars using a ...respiratory system that functionally overlaps the photosynthetic apparatus. In this study, we describe the harvesting of photocurrent used for hydrogen production from live cyanobacteria. A non-harmful gentle physical treatment of the cyanobacterial cells enables light-driven electron transfer by an endogenous mediator to a graphite electrode in a bio-photoelectrochemical cell, without the addition of sacrificial electron donors or acceptors. We show that the photocurrent is derived from photosystem I and that the electrons originate from carbohydrates digested by the respiratory system. Finally, the current is utilized for hydrogen evolution on the cathode at a bias of 0.65 V. Taken together, we present a bio-photoelectrochemical system where live cyanobacteria produce stable photocurrent that can generate hydrogen.
We propose the very first “Nernstian biosupercapacitor”, a biodevice based on only one redox polymer: poly(vinyl imidazole‐co‐allylamine)Os(bpy)2Cl, and two biocatalysts. At the bioanode ...PQQ‐dependent glucose dehydrogenase reduces the Os3+ moieties at the polymer to Os2+ shifting the Nernst potential of the Os3+/Os2+ redox couple to negative values. Concomitantly, at the biocathode the reduction of O2 by means of bilirubin oxidase embedded in the same redox polymer leads to the oxidation of Os2+ to Os3+ shifting the Nernst potential to higher values. Despite the use of just one redox polymer an open circuit voltage of more than 0.45 V was obtained during charging and the charge is stored in the redox polymer at both the bioanode and the biocathode. By connecting both electrodes via a predefined resistor a high power density is obtained for a short time exceeding the steady state power of a corresponding biofuel cell by a factor of 8.
Conversion and storage: A Nernstian biodevice utilizing a concentration gradient of immobilized redox species, which are identical on both positive and negative electrodes, generated with the help of redox enzymes, converts chemical energy directly into electrical energy, which is capacitively stored within the same volume used for conversion.
A light-controlled multiplexing platform has been developed on the basis of a quantum dot-sensitized inverse opal TiO
electrode with integrated biocatalytic reactions. Spatially resolved illumination ...enables multiplexed sensing and imaging of enzymatic oxidation reactions at relatively negative applied potentials.
Differential pulse voltammetry has often been considered one of the most suitable techniques for electroanalytical applications. However, the voltammetric parameters used are often chosen without a ...proper examination of their effect on the resulting response. In this lab experiment, the students are guided to a more informed choice of the electrochemical parameters to apply depending on the application sought. In the first part of the experiment, we highlight how each voltammetric parameter affects the signal-to-noise ratio and the resolution of the voltammetric response of hydroquinone, taken as an example of the application of this electrochemical technique. A Design of Experiment is then applied to optimize the intensity and the sharpness of the oxidation peak response. Finally, an analogous approach is followed to optimize the peak resolution of an equimolar hydroquinone and catechol mixture to achieve the best separation among the peak current response for the two electrochemical processes. Thanks to these two experiments, the student will identify the correct choice of parameters to optimize as key factors for achieving the best analytical performance in specific applications.
The integration of sensitive catalysts in redox matrices opens up the possibility for their protection from deactivating molecules such as O2. FeFe‐hydrogenases are enzymes catalyzing H2 ...oxidation/production which are irreversibly deactivated by O2. Therefore, their use under aerobic conditions has never been achieved. Integration of such hydrogenases in viologen‐modified hydrogel films allows the enzyme to maintain catalytic current for H2 oxidation in the presence of O2, demonstrating a protection mechanism independent of reactivation processes. Within the hydrogel, electrons from the hydrogenase‐catalyzed H2 oxidation are shuttled to the hydrogel–solution interface for O2 reduction. Hence, the harmful O2 molecules do not reach the hydrogenase. We illustrate the potential applications of this protection concept with a biofuel cell under H2/O2 mixed feed.
Reactivation is optional: FeFe‐hydrogenase in a redox hydrogel can be exposed to O2 under turnover conditions for H2 oxidation. A stable catalytic current is maintained, which indicates that the protection mechanism is based only on O2 reduction at the hydrogel surface.
Hydrogen is one of the most promising alternatives for fossil fuels. However, the power output of hydrogen/oxygen fuel cells is often restricted by mass transport limitations of the substrate. Here, ...we present a dual-gas breathing H
/air biofuel cell that overcomes these limitations. The cell is equipped with a hydrogen-oxidizing redox polymer/hydrogenase gas-breathing bioanode and an oxygen-reducing bilirubin oxidase gas-breathing biocathode (operated in a direct electron transfer regime). The bioanode consists of a two layer system with a redox polymer-based adhesion layer and an active, redox polymer/hydrogenase top layer. The redox polymers protect the biocatalyst from high potentials and oxygen damage. The bioanodes show remarkable current densities of up to 8 mA cm
. A maximum power density of 3.6 mW cm
at 0.7 V and an open circuit voltage of up to 1.13 V were achieved in biofuel cell tests, representing outstanding values for a device that is based on a redox polymer-based hydrogenase bioanode.
An enzymatic biofuel cell is integrated on a screen‐printed electrode as a basis for a self‐powered biosensor. A glucose/O2 biofuel cell consisting of a pyrroloquinoline quinone‐dependent glucose ...dehydrogenase embedded within an Os‐complex modified redox polymer bioanode to oxidize glucose and a non‐limiting bilirubin oxidase‐based gas diffusion biocathode in the direct‐electron transfer regime for the reduction of O2 showed a glucose‐dependent current and power output. For full integration on a single screen‐printed electrode, a miniaturized agar salt bridge was introduced between the two bioelectrodes to ensure operation of the assembly in a two‐compartment configuration with each electrode operating at optimal conditions.
The Scanning Bipolar Electrochemical Microscope (SBECM) allows precise positioning of an electrochemical micro-probe serving as bipolar electrode that can be wirelessly interrogated by coupling the ...electrochemical detection reaction with an electrochemiluminescent reporting process. As a result, the spatially heterogeneous concentrations of an analyte of interest can be converted in real time into a map of sample reactivity. However, this can only be achieved upon optimization of the analytical performance ensuring adequate sensitivity. Here, we present the evaluation and optimized operation of the SBECM for the detection of small changes in local O2 concentrations. Parameters for achieving an improved sensitivity as well as possibilities for improving the signal-to-noise ratio in the optical signal readout are evaluated. The capability of the SBECM for O2 detection is shown at controlled conditions by recording the topography of a patterned sample and monitoring O2 evolution from a photoelectrocatalyst material.
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•Experimental conditions are optimized for highly sensitive O2 detection using SBECM.•O2 availability at the sensing pole is directly related to ECL signal at the reporter pole.•A single electrode or an array of electrodes can be used for analyte detection.•AC modulation of the signal enables to improve the signal-to-noise ratio.•Effective detection of O2 evolution at an n-type semiconductor model sample is demonstrated.
Hydrogenases with Ni- and/or Fe-based active sites are highly active hydrogen oxidation catalysts with activities similar to those of noble metal catalysts. However, the activity is connected to a ...sensitivity towards high-potential deactivation and oxygen damage. Here we report a fully protected polymer multilayer/hydrogenase-based bioanode in which the sensitive hydrogen oxidation catalyst is protected from high-potential deactivation and from oxygen damage by using a polymer multilayer architecture. The active catalyst is embedded in a low-potential polymer (protection from high-potential deactivation) and covered with a polymer-supported bienzymatic oxygen removal system. In contrast to previously reported polymer-based protection systems, the proposed strategy fully decouples the hydrogenase reaction form the protection process. Incorporation of the bioanode into a hydrogen/glucose biofuel cell provides a benchmark open circuit voltage of 1.15 V and power densities of up to 530 µW cm
at 0.85 V.
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