Guanine/Ionic Liquid Derived Ordered Mesoporous Carbon Decorated with AuNPs as Efficient NADH Biosensor and Suitable Platform for Enzymes Immobilization and Biofuel Cell Design

Guanine‐ionic liquid derived ordered mesoporous carbon (GIOMC) decorated with gold nanoparticles was used as electrocatalyste for NADH oxidation and electrochemical platform for immobilization of glucose dehydrogenase (GDH) enzyme. The resulting GIOMC/AuNPs on the glassy carbon electrode can be used as novel redox‐mediator free for NADH sensing and this integrated system (GIOMC/AuNPs/GDH) shows excellent electrocatalytic activity toward glucose oxidation. Furthermore, the ionic liquid derived ordered mesoporous carbon derivate with Ph‐SO₃H (IOMC‐PhSO₃H) decorated with AuNPs has been developed to bilirubin oxidase enzyme (BOD) immobilization and the GC/IOMC‐PhSO₃H/BOD integrated system shows excellent bioelectrocatalytic activity toward oxygen reduction reaction. The proposed mesostructured platforms decorated by AuNPs have been developed to enhance mass transfer and charge transfer from biocatalyst to electrode, leading these bioanode and biocathode used for biofuel cell assembly. Integration designed bioanode and biocathode yielding a membrane‐less glucose/O₂ biofuel cell with power density of 33 (mW.cm⁻²) at 257 mV. The open circuit voltage of this biofuel cell and maximum produced current density were 508 mV and 0.252 (mA.cm⁻²) respectively.     

Design of an Os Complex‐Modified Hydrogel with Optimized Redox Potential for Biosensors and Biofuel Cells

Multistep synthesis and electrochemical characterization of an Os complex‐modified redox hydrogel exhibiting a redox potential ≈+30 mV (vs. Ag/AgCl 3 m KCl) is demonstrated. The careful selection of bipyridine‐based ligands bearing N,N‐dimethylamino moieties and an amino‐linker for the covalent attachment to the polymer backbone ensures the formation of a stable redox polymer with an envisaged redox potential close to 0 V. Most importantly, the formation of an octahedral N6‐coordination sphere around the Os central atoms provides improved stability concomitantly with the low formal potential, a low reorganization energy during the Os^3+/2+ redox conversion and a negligible impact on oxygen reduction. By wiring a variety of enzymes such as pyrroloquinoline quinone (PQQ)‐dependent glucose dehydrogenase, flavin adenine dinucleotide (FAD)‐dependent glucose dehydrogenase and the FAD‐dependent dehydrogenase domain of cellobiose dehydrogenase, low‐potential glucose biosensors could be obtained with negligible co‐oxidation of common interfering compounds such as uric acid or ascorbic acid. In combination with a bilirubin oxidase‐based biocathode, enzymatic biofuel cells with open‐circuit voltages of up to 0.54 V were obtained.     

Redox‐Polymer‐Based High‐Current‐Density Gas‐Diffusion H2‐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. We report the fabrication of a dual‐gas diffusion electrode H₂/O₂ biofuel cell equipped with a [FeFe] hydrogenase/redox polymer‐based high‐current‐density H₂‐oxidation bioanode. The bioanodes show benchmark current densities of around 14 mA cm^?2 and the corresponding fuel cell tests exhibit a benchmark for a hydrogenase/redox polymer‐based biofuel cell with outstanding power densities of 5.4 mW cm^?2 at 0.7 V cell voltage. Furthermore, the highly sensitive [FeFe] hydrogenase is protected against oxygen damage by the redox polymer and can function under 5 % O₂.     

Electrochemical Properties of an Osmium(II) Copolymer Film and Its Electrocatalytic Ability Towards the Oxidation of Ascorbic Acid in Acidic and Neutral pH

Copolymerization of an osmium(II) functionalized pyrrole moiety, osmium‐bis‐N,N'‐(2,2′‐bipyridyl)‐N‐(pyridine‐4‐ylmethyl‐(8‐pyrrole‐1yl–octyl)‐amine)chloride ( I ) with 3‐methylthiophene was carried out. The resulting conducting polymer film exhibited a clear redox couple associated with the Os^3+/2+ response and the familiar conducting polymer backbone signature. The effect of film thickness upon the redox properties of the copolymer was investigated in organic electrolyte solutions. Scanning electron micrographs (SEM) along with energy dispersive X‐ray (EDX) spectra of the copolymerized films were undertaken, both after formation and redox cycling in neutral buffer solution. These clearly show that electrolyte is incorporated into the polymer film upon redox cycling through the Os^3+/2+ redox system. The Os^3+/2+ response associated with the copolymer was seen to be significantly altered in the presence of ascorbic acid both in acidic and neutral pH buffer solutions. This pointed to an electrocatalytic reaction between the ascorbic acid and the Os³⁺ form of the copolymer. Under acidic conditions the copolymer film exhibited a sensitivity of 1.76 (±0.05) μA/mM with a limit of detection (LOD) of 1.45 μM for ascorbic acid. Under neutral pH conditions the copolymer exhibited a sensitivity of 19.26 (±1.05) μA/mM with a limit of detection (LOD) of 1.28 μM for ascorbic acid.     

Development of an Osmium Redox Polymer Mediated Bioanode and Examination of its Performance in Gluconobacter oxydans Based Microbial Fuel Cell

Gluconobacter oxydans (G. oxydans ) cells together with an osmium redox polymer (ORP) [Osmium (2,2’‐bipyridine)2(poly‐vinylimidazole)10Cl]Cl were combined with a glassy carbon paste electrode (GCPE) to form a bioanode for a microbial fuel cell (MFC) based on G. oxydans . Although there are G.oxydans / ORP combined bioanode in the literature, as far as it is known, this system is the first one where G.oxydans /ORP bioanode is combined with a cathode and a MFC is formed. After the optimization of experimental parameters, analytical characteristics of ORP/G. oxydans /GCPE bioanode were investigated. ORP/G. oxydans /GCPE showed two linear ranges for ethanol substrate as 1.0–30 mM (R²=0.902) and 30–500 mM (R²=0.997) and analytical range as 1.0–1000 mM. Limit of detection (3.0 s/m) and limit of quantification (10 s/m) values were calculated as 1.29 mM and 4.30 mM respectively where the RSD value was 1.16 % for n=5. Combining the developed bioanode in the presence of 5.0 mM K₃Fe(CN)₆ mediator with a Pt wire cathode a double compartment MFC was obtained via a salt bridge. G. oxydans /GCPE bioanode based MFC had maximum power density of 0.133 μW cm⁻² (at 33.5 mV), maximum current density as 8.73 μA cm⁻² and OCP value of 156 mV. On the other hand, ORP/G. oxydans /GCPE based MFC showed maximum power density as 0.26 μW cm⁻² (at 46.8 mV), maximum current density as 15.079 μA cm^‐2 and OCP value of 176 mV.     

Rational design of quinones for high power density biofuel cells

Enzymatic fuel cells (EFCs) are devices that can produce electrical energy by enzymatic oxidation of energy-dense fuels (such as glucose). When considering bioanode construction for EFCs, it is desirable to use a system with a low onset potential and high catalytic current density. While these two properties are typically mutually exclusive, merging these two properties will significantly enhance EFC performance. We present the rational design and preparation of an alternative naphthoquinone-based redox polymer hydrogel that is able to facilitate enzymatic glucose oxidation at low oxidation potentials while simultaneously producing high catalytic current densities. When coupled with an enzymatic biocathode, the resulting glucose/O₂ EFC possessed an open-circuit potential of 0.864 ± 0.006 V, with an associated maximum current density of 5.4 ± 0.5 mA cm^–2. Moreover, the EFC delivered its maximum power density (2.3 ± 0.2 mW cm^–2) at a high operational potential of 0.55 V.     

A Membraneless Glucose/O2 Biofuel Cell Based on Pd Aerogels

In this study, we introduce the first membraneless glucose/O₂ biofuel cell using Pd‐based aerogels as electrode materials. The bioanode was fabricated with a coimmobilized mediator and glucose oxidase for the oxidation of glucose, in which ferrocenecarboxylic acid was integrated into a three‐dimensional porous beta‐cyclodextrin‐modified Pd aerogel to mediate the bioelectrocatalytic reaction. Bilirubin oxidase and Pd–Pt alloy aerogel were confined to an electrode surface, which realized the direct bioelectrocatalytic function for the reduction of O₂ to H₂O with a synergetic effect at the biocathode. By employing these two bioelectrodes, the assembled glucose/O₂ biofuel cell showed a maximum power output of 20 μW cm^?2 at 0.25 V.     

Design of a bioelectrocatalytic electrode interface for oxygen reduction in biofuel cells based on a specifically adapted Os-complex containing redox polymer with entrapped Trametes hirsuta laccase

The design of the coordination shell of an Os-complex and its integration within an electrodeposition polymer enables fast electron transfer between an electrode and a polymer entrapped high-potential laccase from the basidiomycete Trametes hirsuta. The redox potential of the Os^3+/2+-centre tethered to the polymer backbone (+ 720 mV vs. NHE) is perfectly matching the potential of the enzyme (+ 780 mV vs. NHE at pH 6.5). The laccase and the Os-complex modified anodic electrodeposition polymer were simultaneously precipitated on the surface of a glassy carbon electrode by means of a pH-shift to 2.5. The modified electrode was investigated with respect to biocatalytic O₂ reduction to H₂O. The proposed modified electrode has potential applications as biofuel cell cathode.     

An Air‐breathing Carbon Cloth‐based Screen‐printed Electrode for Applications in Enzymatic Biofuel Cells

We report a prototype air‐breathing carbon cloth‐based electrode that was fabricated starting from a commercially available screen‐printed electrode equipped with a transparent ITO working electrode (DropSens, ref. ITO10). The fabrication of the air‐breathing electrodes is straightforward, shows satisfactory reproducibility and a good electrochemical response as evaluated by means of [Fe(CN)₆]^3?/4? voltammetry. The gas‐diffusion electrodes were successfully modified with the O₂ reducing enzyme bilirubin oxidase from Myrothecium verrucaria in a direct electron transfer regime. The enzyme modified electrodes showed a remarkable high current density for O₂ reduction in passive air‐breathing mode of up to 5 mA cm^?2. Moreover, the enzyme modified electrodes were applied as O₂ reducing biocathodes in a glucose/air enzymatic biofuel cell in combination with a high current density glucose oxidase/redox polymer bioanode. The biofuel cell provides a high maximum power density of (0.34±0.02) mW cm^?2 at 0.25 V. The straightforward design, low cost and the high reproducibility of these electrodes are considered as basis for standardized measurements under gas‐breathing conditions and for high throughput screening of gas converting (bio‐)catalysts.     

Electroenzymatic Nitrogen Fixation Using a MoFe Protein System Immobilized in an Organic Redox Polymer

We report an organic redox‐polymer‐based electroenzymatic nitrogen fixation system using a metal‐free redox polymer, namely neutral‐red‐modified poly(glycidyl methacrylate‐co‐methylmethacrylate‐co‐poly(ethyleneglycol)methacrylate) with a low redox potential of ?0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N₃^?, NO₂^? and N₂ to NH₃ catalyzed by the MoFe protein via the polymer‐bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments produced 209±30 nmol NH₃ nmol MoFe^?1 h^?1 from N₂ reduction. ¹⁵N₂ labeling experiments and NMR analysis were performed to confirm biosynthetic N₂ reduction to NH₃.     

A High‐Voltage Molecular‐Engineered Organic Sensitizer–Iron Redox Shuttle Pair: 1.4 V DSSC and 3.3 V SSM‐DSSC Devices

The development of high voltage solar cells is an attractive way to use sunlight for solar‐to‐fuel devices, multijunction solar‐to‐electric systems, and to power limited‐area consumer electronics. By designing a low‐oxidation‐potential organic dye ( RR9 )/redox shuttle (Fe(bpy)₃^3+/2+) pair for dye‐sensitized solar‐cell (DSSC) devices, the highest single device photovoltage (1.42 V) has been realized for a DSSC not relying on doped TiO₂. Additionally, Fe(bpy)₃^3+/2+ offers a robust, readily tunable ligand platform for redox potential tuning. RR9 can be regenerated with a low driving force (190 mV), and by utilizing the RR9 /Fe(bpy)₃^3+/2+ redox shuttle pair in a subcell for a sequential series multijunction (SSM)‐DSSC system, one of the highest known three subcell photovoltage was attained for any solar‐cell technology (3.34 V, >1.0 V per subcell).     

Base-Modified DNA Labeled by [Ru(bpy)3]2+ and [Os(bpy)3]2+ Complexes: Construction by Polymerase Incorporation of Modified Nucleoside Triphosphates,Electrochemical and Luminescent Properties,and Applications

Modified 2′-deoxynucleoside triphosphates (dNTPs) bearing [Ru(bpy)₃]²⁺ and [Os(bpy)₃]²⁺ complexes attached via an acetylene linker to the 5-position of pyrimidines (C and U) or to the 7-position of 7-deazapurines (7-deaza-A and 7-deaza-G) have been prepared in one step by aqueous cross-couplings of halogenated dNTPs with the corresponding terminal acetylenes. Polymerase incorporation by primer extension using Vent (exo-) or Pwo polymerases gave DNA labeled in specific positions with Ru²⁺ or Os²⁺ complexes. Square-wave voltammetry could be efficiently used to detect these labeled nucleic acids by reversible oxidations of Ru^2+/3+ or Os^2+/3+. The redox potentials of the Ru²⁺ complexes (1.1–1.25 V) are very close to that of G oxidation (1.1 V), while the potentials of Os²⁺ complexes (0.75 V) are sufficiently different to enable their independent detection. On the other hand, Ru²⁺-labeled DNA can be independently analyzed by luminescence. In combination with previously reported dNTPs bearing ferrocene, aminophenyl, and nitrophenyl tags, the Os-labeled dATP has been successfully used for “multicolor” redox labeling of DNA and for DNA minisequencing.     

Biofuel Cell Based on Anode and Cathode Modified by Glucose Oxidase

A single compartment biofuel cell (BFC) based on an anode and a cathode powered by the same fuel glucose is reported. Glucose oxidase (GOx) from Aspergillus niger was applied as a glucose consuming biocatalyst for both anode and cathode of the BFC. The 5‐amino‐1,10‐phenanthroline modified graphite rod electrode (GRE) with cross‐linked GOx was used as the bioanode, and the GRE with co‐immobilised horseradish peroxidase and GOx was exploited as the biocathode of the BFC. The open‐circuit voltage of the designed BFC exceeded 450 mV and a maximal power density of 3.5 µW/cm² was registered at a cell voltage of 300 mV.     

全酶型乙醇/氧气生物燃料电池的构筑及性能研究

本文以乙醇脱氢酶（ADH）和胆红素氧化酶（BOD）为生物催化剂,以碳纳米管为电极材料,构筑了全酶型乙醇/氧气生物燃料电池. 将乙醇脱氢酶负载于单壁碳纳米管（SWCNT）上,采用亚甲基绿（MG）为NADH的电化学催化剂,实现乙醇的生物电化学催化氧化,制备了生物燃料电池ADH/MG/SWCNT/GC的电极（阳极）. 同时,将胆红素氧化酶固定于单壁碳纳米管上,通过其直接电子转移,实现了氧气的生物电化学催化还原,制得生物燃料电池的BOD/SWCNT/GC阴极. 据此构筑了全酶型的无膜生物燃料电池,在空气饱和40 mmol·L^-1乙醇磷酸缓冲溶液中该电池开路电压为0.53 V,最大输出功率密度为11 μW·cm^-2. 以商品化伏特酒作为燃料,该生物燃料电池最大输出功率为3.7 μW·cm^-2.     

A Z‐Scheme‐Inspired Photobioelectrochemical H2O/O2 Cell with a 1 V Open‐Circuit Voltage Combining Photosystem II and PbS Quantum Dots

A biohybrid photobioanode mimicking the Z‐scheme has been developed by functional integration of photosystem II (PSII) and PbS quantum dots (QDs) within an inverse opal TiO₂ architecture giving rise to a rather negative water oxidation potential of about ?0.55 V vs. Ag/AgCl, 1 m KCl at neutral pH. The electrical linkage between both light‐sensitive entities has been established through an Os‐complex‐modified redox polymer (P_Os), which allows the formation of a multi‐step electron‐transfer chain under illumination starting with the photo‐activated water oxidation at PSII followed by an electron transfer from PSII through P_Os to the photo‐excited QDs and finally to the TiO₂ electrode. The photobioanode was coupled to a novel, transparent, inverse‐opal ATO cathode modified with an O₂‐reducing bilirubin oxidase for the construction of a H₂O/O₂ photobioelectrochemical cell reaching a high open‐circuit voltage of about 1 V under illumination.     

Fuel‐Free Bio‐photoelectrochemical Cells Based on a Water/Oxygen Circulation System with a Ni:FeOOH/BiVO4 Photoanode

A bio‐photoelectrochemical cell (BPEC) based on a fuel‐free self‐circulation water–oxygen–water system was fabricated. It consists of Ni:FeOOH modified n‐type bismuth vanadate (BiVO₄) photoanode and laccase catalyzed biocathode. In this BPEC, irradiation of the photoanode generates photocurrent for photo‐oxidation of water to oxygen, which is reduced to water again at the laccase biocathode. Of note, the by‐products of two electrode reactions could continue to be reacted, which means the H₂O and O₂ molecules are retained in an infinite loop of water–oxygen–water without any sacrificial chemical components. As a result, the assembled fuel‐free BPEC exhibits good performance with an open‐circuit potential of 0.97 V and a maximum power density of 205 μW cm^?2 at 0.44 V. This BPEC based on a self‐circulation system offers a fuel‐free model to enhance multiple energy conversion and application in reality.     

Preparation and Characterization of Mixed‐Valent Osmium Hexacyanoferrate/Silicomolybdate Hybrid Films and Their Electrocatalytic Properties

A polynuclear mixed‐valent osmium hexacyanoferrate/silicomolybdate film electrode has been prepared using repetitive cyclic voltammetry. The cyclic voltammograms have been recorded for the deposition of a mixed‐valent osmium hexacyanoferrate/silicomolybdate hybrid film directly from the mixture of Os³⁺, Fe(CN₆)^3?, and SiMo₁₂O₄₀^4? ions from the acidic aqueous solutions. The polynuclear mixed‐valent osmium hexacyanoferrate/silicomolybdate film exhibited four redox couples. The electrocatalytic properties of the osmium hexacyanoferrate/silicomolybdate film electrode have been studied. The modified electrode has shown good electrocatalytic properties towards the oxidation of dopamine, ascorbic acid, epinephrine, norepinephrine, and reduction of IO₃^?, Fe³⁺.     

Direct electrochemistry and spectroelectrochemistry of osmium substituted horseradish peroxidase

In this contribution the substitution of the central protoporphyrin IX iron complex of horseradish peroxidase by the respective osmium porphyrin complex is described. The direct electrochemical reduction of the Os containing horseradish peroxidase (OsHRP) was achieved at ITO and modified glassy carbon electrodes and in combination with spectroscopy revealed the three redox couples Os^IIIHRP/Os^IVHRP, Os^IVHRP/Os^VHRP and Os^VHRP/Os^VIHRP. The midpoint potentials differ dependent on the electrode material used with E_1/2 (Os^III/IV) of − 0.4 V (ITO) and − 0.25 V (GC), E_1/2 (Os^IV/^V) of − 0.16 V (ITO) and + 0.10 V (GC), and E_1/2 (Os^V/VI)of + 0.18 V (ITO), respectively. Moreover, with immobilised OsHRP the direct electrocatalytic reduction of hydrogen peroxide and tert-butyl hydroperoxide was observed. In comparison to electrodes modified with native HRP the sensitivity of the OsHRP-electrode for tert-butyl hydroperoxide is higher.     

Electrochemical Preparation,Characterization, and Electrocatalytic Properties of OsPtCl6 Film Electrodes Towards Reduction of NAD+, Chloroacetic Acids,and Nitrous Oxide

Stable electroactive mixed films of osmium oxide/hexachloroplatinate, osmium oxide and platinum have been deposited on different electrode materials by cycling the electrode potential repetitively in solution containing Os³⁺ and PtCl . The film growth of was monitored by using cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The cyclic voltammetric features of modified electrode in Os³⁺ solution resembles that of surface wave, and involves ions‐exchange with Os³⁺ ions present in the solution. Based on the SEM results the modifier was considered as one‐dimensional, mixed‐valent polymeric film, and stabilized by Os^3+/2+ counter ions. Finally, the electrocatalytic activity of the modified electrode was examined toward reduction of NAD⁺, chloroacetic acids and nitrous oxide.     

Plasmonic osmium hydrosols: Preparation,characterization, and properties

A simple route for the synthesis of mesoporous and plasmonic chitosan supported osmium hydrosols (Os⁰) has been reported using osmium (III)-sodium borohydride redox reaction at room temperature. The composition and morphology of nanoparticles were determined with XRD, XPS, TEM, EDX, SEM, FTIR and N₂-adsorption desorption techniques. No SPR band of Os⁰ at 485 nm was observed for the same redox reaction with cetyltrimethylammonium bromide (CTAB) for ca. 120 min at room temperature. The surface oxidation of Os⁰ into OsO₂ was detected by XRD and XPS. XRD shows the presence of chitosan onto the surface of nanoparticles. The average pore size, and pore volume were found to be 7.23 nm, and 0.239 cc/g, respectively, for Os⁰. The persulfate activation catalytic activity was tested in situ chemical oxidation of basic red 2 (safranin) under activated and un-activated persulfate. Safranin was adsorbed onto the Os⁰ and complex was formed. The oxidation of dye follows pseudo-first order kinetics (k_app = 14.8 × 10^-3 min⁻¹ at [S₂O₈^2-] = 3.3 mM). The activated system showed a much higher dye oxidation rate compared to either S₂O₈^2- or Os⁰ alone. The activation energy (E_a = 105 kJ/mol) was calculated for the system by using Arrhenius equation. The reaction mechanism of Os⁰ activation of persulfate was elucidated and discussed.