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.
Enzymatic hydrolysis of lignocellulosic biomass for biofuel production relies on complex multi-enzyme ensembles. Continuous and accurate measurement of the released key products is crucial in ...optimizing the industrial degradation process and also investigating the activity and interaction between the involved enzymes and the insoluble substrate. Amperometric biosensors have been applied to perform continuous cellobiose measurements during the enzymatic hydrolysis of pure cellulose powders. The oxygen-sensitive mediators used in these biosensors restricted their function under physiological or industrial conditions. Also, the combined measurements of the hydrolysis products cellobiose and glucose require a high selectivity of the biorecognition elements. We employed an Os(2,2′-bipyridine)2ClCl-modified polymer and cellobiose dehydrogenase to fabricate a cellobiose biosensor, which can accurately and specifically detect cellobiose even in the presence of oxygen and the other main product glucose. Additionally, a glucose biosensor was fabricated to simultaneously measure glucose produced from cellobiose by β-glucosidases. The cellobiose and glucose biosensors work at applied potentials of +0.25 and +0.45 V versus Ag|AgCl (3 M KCl), respectively, and can selectively detect their substrate. Both biosensors were used in combination to monitor the hydrolysis of pure cellulose of low crystallinity or industrial corncob samples. The obtained results correlate with the high-performance liquid chromatography pulsed amperometric detection analysis and demonstrate that neither oxygen nor the presence of redox-active compounds from the lignin fraction of the corncob interferes with the measurements.
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.
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.
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► Silica nanoparticles of various diameters are prepared and characterized. ► The Stöber sol–gel process is optimized for desired particle properties. ► High water concentrations and ...calcination result in nonporous particles. ► Low polydispersity results under conditions where T has a weak effect on diameter. ► Surface area analysis confirms sphericity, nonporosity and low polydispersity.
The synthesis of Stöber silica particles as basis for redox modifications is optimized for desired properties, in particular diameter in a wide sub-micrometer range, spherical shape, monodispersity, the absence of porosity, and aggregation free isolability for characterization and later covalent modification. The materials are characterized by SEM, DLS, nitrogen sorption isotherms, helium as well as Gay-Lussac (water) pycnometry, and DRIFT spectroscopy. Particles with diameters between approximately 50 and 800nm are obtained by varying the concentrations of the reagents and reactants, the type of solvent as well as the temperature. The use of high water concentrations and post-synthetic calcination at 600°C results in silica particles that can be considered as nonporous with respect to the size of the active molecules to be immobilized. The effect of reaction temperature on size distribution is identified. Low polydispersity is achieved by performing the reaction in a temperature range in which a change in temperature has only a weak or no effect on the final particle diameter. Upon optimization of the sol–gel process, the shape of the particles is still spherical. The agreement between experimental and geometric data is within the expected precision of the characterization techniques.
Carbon electrodes in the sub-micrometer scale were modified with polymer/enzyme films for the fabrication of miniaturized amperometric glucose sensors. The electrodes were modified by means of ...electrochemically induced co-deposition of various polymers and glucose converting enzymes by (i) activation of protected crosslinkers and formation of a dense crosslinker-polymer network that is able to entrap the biocatalyst on the electrode surface and by (ii) using an electrodeposition paint that was deposited on chemically modified carbon electrodes upon a basic pH shift. The polymer matrixes were equipped with Os-complexes that act as redox shuttles for the electron transfer between the electrode surface and the entrapped redox enzyme. The polymer/enzyme modified electrodes were active toward the oxidation of glucose with a sensitivity in the pA mM−1 range. A linear current response was observed for a glucose concentration of up to 15 mM depending on the polymer/enzyme combination. Owing to their geometry in the sub-micron range, the developed sensors are expected to measure glucose with minimal invasiveness down to the single cell level.
This manuscript provides the first systematic characterization of the electrochemical properties of the high mobility n-type polymer poly{N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis ...(dicarboximide)-2,6-diyl-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)) and its corresponding monomer 2,6-bis(2-bromothien-5-yl)naphthalene-1,4,5,8-tetracarboxylic-N,N′-bis(2-octyldodecyl) diimide (Br-NDI2OD-T2-Br) by cyclic voltammetry and in situ spectroelectrochemistry. Both monomer and polymer reveal a 2-fold reduction to the dianion via a radical anion species. The comparison between monomeric and polymeric species allows the explanation of the electrochemical behavior of P(NDI2OD-T2) according to redox polymers with localization of charges on the naphthalene bisimide unit. Measurements with electrolyte gated transistors suggest electron hopping transport according to mixed valence conductivity. In the last section of this paper we discuss a significant first cycle effect upon electrochemical reduction which had not been reported for n-type polymers before. The effect is even more pronounced for samples with controlled morphology, that is, high amounts of aggregation in the films. In agreement with solution experiments we attribute the appearance of the signal at −1.04 V (E 1/2 = −1.00 V) to the radical anion form of the solvated species.
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.
•Redox polymers are used for the immobilization and electrical wiring of enzymes.•Rational design of redox polymers is important for the fabrication of efficient bioelectrodes.•Redox polymers are ...used for the fabrication of novel biosensors and biofuel cells.•Redox polymers can protect sensitive biocatalyst from O2.•Redox polymers are used as charge storage matrix in biosupercapacitors.
Redox polymers are widely applied in bioelectrochemical applications. Thus, the design of novel polymers and tuning of mediator properties, in particular the redox potential, plays a crucial role for the fabrication of highly efficient bioelectrodes. This review summarizes recent developments and advances in redox polymers that were used for the development of various bioelectrochemical devices, i.e. amperometric biosensors, bioelectrocatalysis and energy conversion/storage systems.
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