Organelle-based biofuel cells: Immobilized mitochondria on carbon paper electrodes

This paper details the development of a mitochondria-based biofuel cell. We show that mitochondria can be immobilized at a carbon electrode surface and remain intact and viable. The electrode-bound mitochondria drive complete oxidation of pyruvate as shown by Carbon-13 NMR and serve as the anode of the biofuel cell where they convert the chemical energy in a biofuel (such as pyruvate) into electrical energy. These are the first organelle-based fuel cells. Researchers have previously used isolated enzymes and complete microbes for fuel cells, but this is the first evidence that organelles can support fuel cell-based energy conversion. These biofuel cells provide power densities of 0.203 ± 0.014 mW/cm², which is in between the latest immobilized enzyme-based biofuel cells and microbial biofuel cells, while providing the efficiency of microbial biofuel cells.     

Bis-Aniline-Crosslinked Enzyme–Metal Nanoparticle Composites on Electrodes for Bioelectronic Applications

The electrical contacting of redox enzymes with electrodes is the most fundamental requirement for the development of amperometric biosensors and biofuel cell elements. We describe a novel method to prepare electrically contacted metallic nanoparticles (NPs) or carbon nanotubes (CNTs)/enzyme hybrid composites on electrodes that act as amperometric biosensors or as the constituents of biofuel cells. Au NPs or Pt NPs were modified with thioaniline electropolymerizable groups, and so were the enzymes glucose oxidase (GOx) or bilirubin oxidase (BOD). Electrochemical polymerization of the thioaniline-functionalized Pt NPs and GOx on a thioaniline monolayer-modified Au surface led to the formation of a bis-aniline-bridged Pt NPs/GOx composite electrode that enabled the analysis of glucose through the electrocatalyzed reduction of H₂O₂. Similarly, a Pt NPs/BOD composite-functionalized electrode showed electrocatalytic activity toward the reduction of O₂ to H₂O. Also, a Au NPs/GOx composite-functionalized electrode revealed direct electrical contacting between the enzyme and the electrode through the electrocatalytic reduction of the bis-aniline bridges, and this enabled the bioelectrocatalytic oxidation and the amperometric sensing of glucose. Finally, a biofuel cell consisting of an anode modified with Nile blue/NAD⁺/alcohol dehydrogenase on carbon nanotubes, and a cathode composed of the bis-aniline-crosslinked Pt NPs/BOD composite was constructed. The biofuel cell operates with a power output corresponding to 200 μW cm^-2.     

Utilization of enzyme cascades for complete oxidation of lactate in an enzymatic biofuel cell

Lactate/lactic acid has been considered as a biofuel for enzymatic biofuel cells, but only with single enzyme bioanodes containing lactate dehydrogenase. A single enzyme-based bioanode results in the oxidation of lactate to pyruvate, which only allows for 2 of the total of 12 electrons to be harnessed from the lactate leaving the majority of the energy density of the fuel in the oxidized product (pyruvate); thereby, resulting in low energy density biofuel cells. This paper details an enzyme cascade for complete oxidation of lactate immobilized on a bioanode and employed in a lactate/air biofuel cell. This paper shows that complete oxidation of lactate increases the current density and power density of the biofuel cell, in a similar trend as was observed for complete oxidation of pyruvate in an enzymatic biofuel cell.     

Nanosized Si/cellulose fiber/carbon composites as high capacity anodes for lithium-ion batteries: A galvanostatic and dilatometric study

Recently, we reported a simple method for obtaining nanosized silicon with promising electrochemical properties as an anode material for lithium-ion batteries; the method involves the formation of a composite electrode with cellulose fibers. It is demonstrated that the performance of these electrodes can be enhanced by the addition of conductive carbon black (CCB). This beneficial effect is not only a result of the improvement of electrical conductivity and inter-particle contacts, but also due to a reduction of the expansion and shrinkage undergone by the electrode when Li is inserted into Si or extracted from Li_xSi, as revealed by in situ electrochemical dilatometry measurements. The best results were obtained with a CCB of high surface area and porosity. The Si/cellulose fiber/carbon electrodes obtained delivered charge capacities as high as 1800 mAh g⁻¹ and exhibited good capacity retention on cycling. These electrodes also exhibited lower expansion/shrinkage compared to carbon-free electrodes on discharging and charging the cell, respectively.     

Evaluation of the electron transport chain inhibition and uncoupling of mitochondrial bioelectrocatalysis with antibiotics and nitro-based compounds

Mitochondrial bioelectrocatalysis can be useful for sensing applications due to the unique metabolic pathways than can be selectively inhibited and uncoupled in mitochondria. This paper details the comparison of different inhibitors and nitro-containing explosive uncouplers in a mitochondria-catalyzed biofuel cell for self-powered explosive sensing. Previous research has reported inhibition of pyruvate oxidation at a mitochondria-modified electrode followed by nitroaromatic uncoupling of current and power. We have previously used oligomycin as the antibiotic and nitrobenzene as the uncoupler of the membrane in the mitochondria-catalyzed biofuel cell, but no comprehensive comparison of various mitochondria inhibitors or explosives has been performed. Results are discussed here for inhibitors targeting complex I, complex III, ATP synthases, adenine nucleotide transport and monocarboxylic acid transport. Reactivation with nitrobenzene was possible in the presence of these inhibitors: oligomycin, 3,3′-diindolylmethane, atractyloside, rotenone, α-cyano-4-hydroxy cinnamic acid and antimycin A. All eleven explosives studied, including: 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), caused uncoupling of the mitochondria function and could be detected by the biosensor.     

Functionalized carbon support with sulfonated polymer for direct methanol fuel cells

Recently electrodes for direct methanol fuel cell (DMFC) have been developed for getting high fuel cell performances by controlling composition of catalysts and sulfonated polymers, developing catalyst particles, modifying carbon supports, etc. The electrodes in DMFCs are porous layers, which are composed of catalyst, which is black or carbon supported, and sulfonated polymers in a blended form. In the present study, carbon support for catalysts was functionalized to play dual roles of a mass transport and a catalyst support. The functionalized carbon support was characterized and compared with pristine one by thermal and spectroscopic analysis, and loading of platinum (Pt) catalysts on modified support was performed by gas reduction. The electrodes with Pt on functionalized carbon support were fabricated, though the conventional electrodes were prepared with sulfonated polymer and Pt catalysts. Membrane electrode assembly with Pt catalyst on functionalized support showed a higher DMFC performance of 30 mW cm⁻² at 50 °C without using additional sulfonated polymer. Integration of electrode components in one body has another advantage of easier and simpler process in preparing electrodes for DMFCs. Improved DMFC performance of the electrode containing functionalized carbon was be attributed to a better mass transport which maximize the catalytic activities.     

Facile direct electron transfer in glucose oxidase modified electrodes

Glucose oxidase (GOx) is widely used in the glucose biosensor industry. However, mediatorless direct electron transfer (DET) from GOx to electrode surfaces is very slow. Recently, mediatorless DET has been reported via the incorporation of nanomaterials such as carbon nanotubes and nanoparticles in the modification of electrodes. Here we report GOx electrodes showing DET without the need for any nanomaterials. The enzyme after immobilization with poly-l-lysine (PLL) and Nafion^® retains the biocatalytic activities and oxidizes glucose efficiently. The amperometric response of Nafion-PLL-GOx modified electrode is linearly proportional to the concentration of glucose up to 10 mM with a sensitivity of 0.75 μA/mM at a low detection potential (−0.460 V vs. Ag/AgCl). The methodology developed in this study will have impact on glucose biosensors and biofuel cells and may potentially simplify enzyme immobilization in other biosensing systems.     

石墨烯/聚苯胺修饰阳极对微生物燃料电池性能的影响

纳米材料修饰阳极可显著提高微生物燃料电池（MFC）性能,本研究主要探索了石墨烯、聚苯胺和石墨烯/聚苯胺复合修饰电极对MFC产电性能的影响。使用电化学方法电镀石墨烯于碳布表面,进一步通过原位聚合法制备聚苯胺来修饰碳布电极。将修饰电极装载入双室型MFC中,测量其产电性能,并对电极进行表征,测量电化学性能。通过扫描电镜观察到, 碳布能够被修饰上石墨烯和聚苯胺,并且聚苯胺附着于碳纤维或石墨烯薄层表面,形成棒状的纳米结构。产电性能方面,装载石墨烯/聚苯胺修饰电极的MFC最大输出电压最高,达到了（291±22）mV,比装载空白碳布电极的对照组MFC提高了175%以上。石墨烯/聚苯胺电极组MFC的最大输出功率密度同样最高,达到了（653 ± 25）mW·m^-2,为空白碳布对照组的10.5倍。实验结果表明：石墨烯/聚苯胺复合修饰电极可有效利用石墨烯导电性好和聚苯胺生物相容性高的优点,显著提高MFC的产电性能。     

Carbon electrodes in the ferrous/thionine photogalvanic cell: a quantitative study of electrode selectivity

The role of electrode selectivity in the performance of the ferrous/thionine photogalvanic cell has been studied using various carbon materials as light electrode. The open-circuit voltage of the cell is found to depend strongly on the type of carbon electrode used. This dependency can be quantitatively accounted for in terms of electrode kinetics. The leuco-thionine oxidation is about equally fast at all types of carbon electrode studied. Those electrodes that give rise to a high open-circuit voltage are selective owing to the suppression of the ferric reduction. This slow ferric/ferrous electron transfer has been related to the hydrophobicity of the electrode surface.     

Long-term activity of covalent grafted biocatalysts during intermittent use of a glucose/O2 biofuel cell

The operational stability of enzymes in a concentric glucose/O₂ biofuel cell has been significantly improved with the synthesis of grafted enzyme electrodes compared to entrapped enzyme electrodes. The concentric device combined glucose electro-oxidation by glucose oxidase at the anode and oxygen electro-reduction by bilirubin oxidase at the cathode. The entrapped enzyme electrodes were prepared from physical immobilization of the enzymes by a polypyrrole polymer onto the electrode surface. The grafted enzyme electrodes were synthesized by grafting the enzymes via alkyl spacer arms to a poly(aminopropylpyrrole) film onto the electrode surface. From spectrophotometric and electrochemical analyses, it was demonstrated that the spacer arms increased the operational stability and enzyme mobility that favoured electron transfer from their active sites to the electrode.The maximum power output of the assembled biofuel cell was 20 μW cm⁻², at 0.20 V with 10 mM glucose in phosphate buffer pH 7.4. The grafted enzyme electrodes presented an unprecedented operational stability as the maximum of power density of the BFC remains constant after intermittent use over a 45-day period. This was a remarkable improvement compared to electrodes with entrapped enzymes, which lost 74% of their initial power density after intermittent use over a 17-day period.     

葡萄糖氧化酶在修饰碳纳米管上的电化学

将葡萄糖氧化酶（GOx）分别固定在多壁碳纳米管（MWNT）、氨基化碳纳米管（AMWNTs）和羧基化碳纳米管（MWNTs-COOH）修饰的电极表面,电化学测量表明固定在羧基和氨基碳纳米管上的GOx式量电位基本没变,而峰电流得到了很大提高。尤其是氨基化碳纳米管上的GOx的峰电流是未功能化碳管上GOx的4倍多。进一步研究Nafion/GOx-AMWNTs/GC电极的电化学行为,发现固定在AMWNTs上的GOx可进行直接准可逆的氧化还原反应,而且固定在AMWNTs上的GOx有良好的稳定性。氨基改性碳纳米管电极载体材料有望显著提高GOx生物燃料电池性能。     

Evaluation of carbon electrodes and electrosynthesis of coumestan and catecholamine derivatives in the FM01-LC electrolyser

This work extends the range of electrodes and conditions under which the FM01-LC reactor has been used in a laboratory environment and evaluates the performance of carbon electrodes. Reticulated vitreous carbon (RVC) has been used to provide a stable, inert, three-dimensional electrode surface for organic electrosynthesis; its performance is compared to that of nickel mesh for the oxidation of catechol to o-quinone. This product was then reacted in situ with (i) 4-hydroxycoumarin and (ii) 1,3-dimethylbarbituric acid to produce, respectively, coumestan and catecholamine, products of synthetic interest. In mass transport experiments using hydroquinone oxidation as a model reaction, performance was similar to nickel electrodes, but Sherwood numbers were reduced by about 5–10% when carbon electrodes were used. The best-performing RVC electrode, however, showed poorer behaviour than its nickel counterpart. Yields for the production of coumestan and catecholamine were approximately 45% and 25%, respectively, although this was mostly due to extraction problems, since current efficiencies were both in the region of 65–70%. The electrode material, rather than the fluid flow behaviour, leads to a reduction in overall cell efficiency; this is confirmed by studies which show a film forming on the surface of the electrode.     

Use of Pt/M(UPD) (M = Pb, Tl, Bi) modified electrodes to the catalytic electroreduction of heterocyclic nitro compounds—I. 3-nitro-1H-1,2,4-triazole

Platinum UPD modified electrodes (Pt/M(UPD), where M = Pb, Tl, Bi) have been used to study electroreduction of 3-nitro-1H-1,2,4-triazole (NTr) in aqueous acid, alkaline and intermediate pH buffer solutions. At these modified electrodes, NTr undergoes a four-electron reduction which occurs via electron-transfer mechanism and not by hydrogenation mechanism as occurs at Pt itself. In strongly acid solutions the electrode process follows the ECCE sequence with the second chemical reaction being responsible for kinetically-controlled limiting currents. The slow chemical step in the ECCE sequence is a dehydration reaction of the N,N-dihydroxyamine intermediate. The kinetics of this homogeneous chemical reaction has been studied as a function of temperature and solution pH by using rotating disc data. Moreover, polarographic data for NTr are also given in this paper. In strongly basic media, the Pt/M(UPD) surfaces exhibit an unexpected enhanced catalytic activity for the nitro-group electroreduction compared to that of mercury.     

Novel bipolar electrodes for battery applications

A novel bipolar graphite felt electrode for use in redox flow batteries and other electrochemical systems is described. The new electrode features a unique approach in the design of bipolar electrodes, employing carbon black free, nonconductive polymer materials as substrates. This innovation allows a dramatic reduction of processing time and cost compared to conventional carbon polymer composite electrodes used in bipolar battery systems. The conductivity of the new electrode assembly is similar to that of conventional bipolar electrodes, however, it shows significant improvements in mechanical properties. The functionality of these novel electrodes has been evaluated in the vanadium redox battery application and the results show comparable performance with conventional composite materials. An important operational advantage, however, is that side reactions leading to the deterioration of conductive filler in the electrode substrate material (i.e., electrode delamination due to CO₂-evolution) during cell overcharging are eliminated, making these electrodes more durable than the conventional designs. To date, these bipolar electrodes have been applied in vanadium redox cells but their design and properties promise further applications in a range of other redox flow batteries and bipolar electrochemical cell systems.     

Direct electron transfer and electrocatalysis of glucose oxidase immobilized on glassy carbon electrode modified with Nafion and mesoporous carbon FDU-15

In this paper, it was found that glucose oxidase (GOD) has been stably immobilized on glassy carbon electrode modified with mesoporous carbon FDU-15 (MC-FDU-15) and Nafion by simple technique. The sorption behavior of GOD immobilized on MC-FDU-15 matrix was characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-vis), FTIR, respectively, which demonstrated that MC-FDU-15 could facilitate the electron exchange between the active center of GOD and electrode. The direct electrochemistry and electrocatalysis behavior of GOD on the modified electrode were characterized by cyclic voltammogram (CV) which indicated that GOD immobilized on Nafion and MC-FDU-15 matrices display direct, reversible and surface-controlled redox reaction with an enhanced electron transfer rate constant of 4.095 s⁻¹ in 0.1 M phosphate buffer solution (PBS) (pH 7.12). Furthermore, it was also discovered that, in the presence of O₂, GOD immobilized on Nafion and MC-FDU-15 matrices could produce a linear response to glucose. Thus, Nafion/GOD-MC-FDU-15/GC electrode is hopeful to be used in glucose biosensor. In addition, GOD immobilized on MC-FDU-15 and Nafion matrices possesses an excellent bioelectrocatalytic activity for the reduction of O₂. So, the Nafion/GOD-MC-FDU-15/GC electrode can be utilized as the cathode in biofuel cell.     

A glassy carbon electrode modified by a copolymer of Co-tetrakis (para-aminophenyl)porphyrin and ortho-phenylenediamine. Characterization and electrocatalytic sulfite oxidation behavior of a basic extract from red wine

In this work, we present a comparison among three glassy carbon electrodes modified by Co-porphyrin, ortho-phenylenediamine, or both simultaneously. This comparison shows the differences among the electrochemical behavior, morphological characteristics and electrocatalytic behavior toward the sulfite oxidation of these electrodes. The electrode modified by Co-porphyrin, ortho-phenylenediamine and copolymer has been investigated in detail for the comparision of electrocatalytic activity towards the sulfite oxidation. In the case of the glassy carbon-modified electrodes, the presence of the copolymer enhances the electrocatalytic performance of the modified electrodes in spite of the non-catalytic response (compared to the bare glassy carbon) of both homopolymer-modified electrodes toward the oxidation of sulfite. Additionally, the oxidation of sulfite extracted from red wine is shown. The copolymer-modified electrode is capable of oxidizing the extracted free sulfite in a 0.02 M NaOH solution. Through the addition of standards method, a concentration of free sulfite in a Chilean red wine sample was determined to be 44 ppm.     

Endeavor toward competitive electrochlorination by comparing the performance of easily affordable carbon electrodes with platinum

Kinetics of chloride ion oxidation was studied on graphite, glassy carbon (GC), and platinum electrodes. The performance of the electrodes was monitored using the cumulative productivity and current efficiency of the cell as indicators. It was seen that the performance of the working electrode improved with repeated uses, the current efficiency increased from 22% in the third use to about 46% in the tenth use. The study also revealed that the role of diffusion to the total anodic current was insignificant and chloride ions were transported at the electrode surface only by conduction. The hypochlorite production in case of platinum was about 3.66 times than that of graphite and GC with the current efficiency of 75% in contrast to 46% found in graphite and GC. But platinum undergoes passivation to a significant extent unlike the graphite and GC electrodes. Chronopotentiometry experiments confirmed the passivation process in platinum electrodes, showed a steep rise in potential from 1.2 to 2?V while the electrode potential was uniformly maintained at 1.7?V in carbon electrodes. The highest i_o, exchange current density value was observed at 0.45?mA/cm² in 0.5?M electrolyte, which is an indication of improved electrocatalytic activity with increased molar concentration. After continuous uses the corrosion rate studies revealed that platinum and GC electrodes were corrosion resistant whereas graphite underwent corrosion at the rate of 0.006?mm/h. The study dictated that carbon electrodes has great potential to be used as an alternatives to platinum electrodes, however, further investigations are required to assess its practical applicability in the public water supply system.     

Electrocatalytic Oxidation of Formic Acid at Pt Modified Electrodes: Substrate Effect of Unsintered Au Nano‐Structure

A Pt‐modified Au catalyst featured with novel layered structures and ultra‐low Pt loading has been designed and electrochemically fabricated on a glassy carbon (GC) electrode. SEM characterization suggests that as‐formed Pt/Au/GC electrode grows in a Stranski–Krastanov mode, resulting in a nearly ideal layered structure with Au at the inner layer and Pt at the outer layer. The electrocatalytic activity of the synthesized Pt/Au/GC electrode towards formic acid electrooxidation was studied, and comparative experiments with other modified electrodes (i.e., Pt/GC, Pt/Au, and Pt/Pt) were also conducted. As a result, the electrocatalytic activity of the outer‐layered Pt depends significantly on the intrinsic properties of the substrates. The prepared Pt/Au/GC electrode with Au nanoparticles modified GC as the substrate shows remarkable catalytic activity for the formic acid oxidation, much higher than that of its counterparts, Pt/GC, Pt/Au, and Pt/Pt electrodes. Additionally, the measured electrochemical impedance spectra indicate that the charge‐transfer resistance for formic acid electrooxidation on Pt/Au/GC electrode is smaller than that on other Pt modified electrodes.     

Preliminary comparative studies of zinc and zinc oxide electrodes on corrosion reaction and reversible reaction for zinc/air fuel cells

Even though Zn/air energy system is considered to be a promising power energy source, it has been limited to be applied for an electrically rechargeable system basically due to the problem of the irreversible reaction and the corrosion reaction. In this paper a novel attempt has been made to compare the behavior of zinc electrode with a zinc oxide electrode and a modified zinc oxide electrode containing zinc oxide and lead oxide. The hydrogen overpotential is favorable in the zinc electrode, and the modified zinc oxide electrode shows the improved properties showing the more negative potential than the case of the zinc oxide electrode. Investigations of cyclic voltammogram reveal that the pure zinc electrode is irreversible, while both the zinc oxide and the modified zinc oxide electrodes are reversible. However, as far as dendrite formation is concerned there is no marked improvement in case of the zinc oxide and the modified zinc oxide electrodes.     

A study of the electrochemical behaviour of electrodes in operating solid-state supercapacitors

The electrochemical behaviour of electrodes and of complete solid-state supercapacitors has been studied by cyclic voltammetry (CV) and galvanostatic charge/discharge (CD) measurements using two independent electrochemical equipments. The first one controlled the execution of the test and recorded the voltage and current values of the complete supercapacitor while the other one recorded the potential changes of the single electrodes. In this work, two different types of capacitors were studied: (a) a symmetric supercapacitor using carbon electrodes, and (b) a hybrid (asymmetric) supercapacitor with ruthenium oxide/carbon in the positive electrode and carbon in the negative electrode. The studies evidenced that in the symmetric capacitors the positive electrode controlled the capacitive performance and an optimal mass ratio from 1.2:1 to 1.3:1 between the positive and the negative electrodes was found in the investigated conditions. For the hybrid supercapacitor it was observed that the ruthenium-based positive electrode influenced the capacitive performance of carbon-based negative electrode and that an accurate balance of carbon loading in the negative electrode was necessary.