Hybrid Enzyme-Electrocatalyst Cascade Modified Gas-Diffusion Electrodes for Methanol Formation from Carbon Dioxide.

We propose a hybrid electrocatalytic-bioelectrocatalytic reaction cascade integrated on a gas diffusion electrode for CO reduction under selective formation of methanol. Ag-BiO selectively reduces gaseous CO to formate at neutral pH conditions. A subsequent enzymatic cascade comprising formaldehyde dehydrogenase and alcohol dehydrogenase, which are both nicotinamide adenine dinucleotide (NAD)-dependent, further reduce formate sequentially to formaldehyde and methanol.

Enzyme-Modified Microelectrode for Simultaneous Local Measurements of O and pH.

The use of miniaturized probes opens a new dimension in the analysis of (bio)chemical processes, enabling the possibility to perform measurements with local resolution. In addition, multiparametric measurements are highly valuable for a holistic understanding of the investigated process. Therefore, different strategies have been suggested for simultaneous local measurements of various parameters.

Flexible active-site loops fine-tune substrate specificity of hyperthermophilic metallo-oxidases.

Hyperthermophilic ('superheat-loving') archaea found in high-temperature environments such as Pyrobaculum aerophilum contain multicopper oxidases (MCOs) with remarkable efficiency for oxidizing cuprous and ferrous ions. In this work, directed evolution was used to expand the substrate specificity of P. aerophilum McoP for organic substrates.

A biomimetic assembly of folded photosystem I monolayers for an improved light utilization in biophotovoltaic devices.

In the fabrication of photosystem I (PSI)-based biodevices, the use of multilayered architectures aims to maximize the absorption of incident light that can be converted into high-energy electrons. The challenge in this strategy is to overcome the large driving force imposed by the photoinduced potential difference between the two terminal redox centers that are located at opposite sides of PSI, which translates into charge recombination resulting in sub-optimal performance of commonly implemented systems. The integration of PSI monolayers with electrodes using the Langmuir-Blodgett technique enables a preferential anisotropic orientation of PSI in a tightly packed structure, which minimizes short-circuiting processes and aids to improve the performance of PSI-based biodevices.

Bioelectrocatalytic CO Reduction by Redox Polymer-Wired Carbon Monoxide Dehydrogenase Gas Diffusion Electrodes.

The development of electrodes for efficient CO 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 (CODH II) using a cobaltocene-based low-potential redox polymer for the selective reduction of CO to CO over gas diffusion electrodes.

On the Mediated Electron Transfer of Immobilized Galactose Oxidase for Biotechnological Applications.

Invited for the cover of this issue are Felipe Conzuelo, Wolfgang Schuhmann, and co-workers at the Ruhr University Bochum. The image depicts the electrochemical conversion of glycerol and 5-(hydroxymethyl)furfural with an electrode made up of galactose oxidase electrically wired with a redox polymer. Read the full text of the article at 10.

A biophotoelectrode based on boronic acid-modified Chlorella vulgaris cells integrated within a redox polymer.

Green microalgae are gaining attention in the renewable energy field due to their ability to convert light into energy in biophotovoltaic (BPV) cells. The poor exogenous electron transfer kinetics of such microorganisms requires the use of redox mediators to improve the performance of related biodevices. Redox polymers are advantageous in the development of subcellular-based BPV devices by providing an improved electron transfer while simultaneously serving as immobilization matrix.

On the Mediated Electron Transfer of Immobilized Galactose Oxidase for Biotechnological Applications.

The use of enzymes as catalysts in chemical synthesis offers advantages in terms of clean and highly selective transformations. Galactose oxidase (GalOx) is a remarkable enzyme with several applications in industrial conversions as it catalyzes the oxidation of primary alcohols. We have investigated the wiring of GalOx with a redox polymer; this enables mediated electron transfer with the electrode surface for its potential application in biotechnological conversions.

Pyrroloquinoline quinone-dependent glucose dehydrogenase bioelectrodes based on one-step electrochemical entrapment over single-wall carbon nanotubes.

Development of effective direct electron transfer is considered an interesting platform to obtain high performance bioelectrodes. Therefore, designing of scalable and cost-effective immobilization routes that promotes correct direct electrical contacting between the electrode material and the redox enzyme is still required. As we present here, electrochemical entrapment of pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) on single-wall carbon nanotube (SWCNT)-modified electrodes was carried out in a single step during electrooxidation of para-aminophenyl phosphonic acid (4-APPA) to obtain active bioelectrodes.

Closing the Gap for Electronic Short-Circuiting: Photosystem I Mixed Monolayers Enable Improved Anisotropic Electron Flow in Biophotovoltaic Devices.

Well-defined assemblies of photosynthetic protein complexes are required for an optimal performance of semi-artificial energy conversion devices, capable of providing unidirectional electron flow when light-harvesting proteins are interfaced with electrode surfaces. We present mixed photosystem I (PSI) monolayers constituted of native cyanobacterial PSI trimers in combination with isolated PSI monomers from the same organism. The resulting compact arrangement ensures a high density of photoactive protein complexes per unit area, providing the basis to effectively minimize short-circuiting processes that typically limit the performance of PSI-based bioelectrodes.

Scalable Fabrication of Biophotoelectrodes by Means of Automated Airbrush Spray-Coating.

The fabrication and electrochemical evaluation of transparent photoelectrodes consisting of Photosystem I (PSI) or Photosystem II (PSII) is described, which are embedded and electrically wired by a redox polymer. The fabrication process is performed by an automated airbrush-type spray coating system, which ensures controlled and scalable electrode preparation. As proof of concept, electrodes with a surface area of up to 25 cm were prepared.

Redox-Polymer-Based High-Current-Density Gas-Diffusion H -Oxidation Bioanode Using [FeFe] Hydrogenase from Desulfovibrio desulfuricans in a Membrane-free Biofuel Cell.

The incorporation of highly active but also highly sensitive catalysts (e.g. the [FeFe] hydrogenase from Desulfovibrio desulfuricans) in biofuel cells is still one of the major challenges in sustainable energy conversion.

Light-controlled imaging of biocatalytic reactions via scanning photoelectrochemical microscopy for multiplexed sensing.

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.

Tuning Light-Driven Water Oxidation Efficiency of Molybdenum-Doped BiVO by Means of Multicomposite Catalysts Containing Nickel, Iron, and Chromium Oxides.

Mo-doped BiVO has emerged as a promising material for photoelectrodes for photoelectrochemical water splitting, however, still shows a limited efficiency for light-driven water oxidation. We present the influence of an oxygen-evolution catalyst composed of Ni, Fe, and Cr oxides on the activity of Mo:BiVO photoanodes. The photoanodes are prepared by spray-coating, enabling compositional and thickness gradients of the incorporated catalyst.

Enhanced sensitivity of scanning bipolar electrochemical microscopy for O detection.

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.

Microscopic Determination of Carrier Density and Mobility in Working Organic Electrochemical Transistors.

A comprehensive understanding of electrochemical and physical phenomena originating the response of electrolyte-gated transistors is crucial for improved handling and design of these devices. However, the lack of suitable tools for direct investigation of microscale effects has hindered the possibility to bridge the gap between experiments and theoretical models. In this contribution, a scanning probe setup is used to explore the operation mechanisms of organic electrochemical transistors by probing the local electrochemical potential of the organic film composing the device channel.

Extended Operational Lifetime of a Photosystem-Based Bioelectrode.

The development of bioelectrochemical assemblies for sustainable energy transformation constitutes an increasingly important field of research. Significant progress has been made in the development of semiartificial devices for conversion of light into electrical energy by integration of photosynthetic biomolecules on electrodes. However, sufficient long-term stability of such biophotoelectrodes has been compromised by reactive species generated under aerobic operation.

Biological imaging with scanning electrochemical microscopy.

Scanning electrochemical microscopy (SECM) is a powerful and versatile technique for visualizing the local electrochemical activity of a surface as an ultramicroelectrode tip is moved towards or over a sample of interest using precise positioning systems. In comparison with other scanning probe techniques, SECM not only enables topographical surface mapping but also gathers chemical information with high spatial resolution. Considerable progress has been made in the analysis of biological samples, including living cells and immobilized biomacromolecules such as enzymes, antibodies and DNA fragments.

A gas breathing hydrogen/air biofuel cell comprising a redox polymer/hydrogenase-based bioanode.

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.

A fully protected hydrogenase/polymer-based bioanode for high-performance hydrogen/glucose biofuel cells.

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 Open Circuit Voltage in Biofuel Cells: Nernstian Shift in Pseudocapacitive Electrodes.

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.

Live cyanobacteria produce photocurrent and hydrogen using both the respiratory and photosynthetic systems.

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.

Light-induced formation of partially reduced oxygen species limits the lifetime of photosystem 1-based biocathodes.

Interfacing photosynthetic proteins specifically photosystem 1 (PS1) with electrodes enables light-induced charge separation processes for powering semiartificial photobiodevices with, however, limited long-term stability. Here, we present the in-depth evaluation of a PS1/Os-complex-modified redox polymer-based biocathode by means of scanning photoelectrochemical microscopy. Focalized local illumination of the bioelectrode and concomitant collection of HO at the closely positioned microelectrode provide evidence for the formation of partially reduced oxygen species under light conditions.

In Operando Investigation of Electrical Coupling of Photosystem 1 and Photosystem 2 by Means of Bipolar Electrochemistry.

Electrochemical communication between two photobioelectrochemical half-cells based on photosystem 1 and photosystem 2 is investigated in operando. The driving force for the electron-transfer reactions is applied in a wireless mode using bipolar electrochemistry with the actual electrode potentials being self-regulated by the redox processes. Four parameters are assessed to understand the overall performance and elucidate the limiting reactions of the photobioelectrochemical cell.