Study on Glucose Biofuel Cells Using an Electrochemical Noise Device

An electrochemical noise (ECN) device was utilized for the first time to study and characterize a glucose/O₂ membraneless biofuel cell (BFC) and a monopolar glucose BFC. In the glucose/O₂ membraneless BFC, ferrocene (Fc) and glucose oxidase (GOD) were immobilized on a multiwalled carbon nanotubes (MWCNTs)/Au electrode with a gelatin film at the anode; and laccase (Lac) and an electron mediator, 2,2′‐azinobis (3‐ethylbenzothiazoline‐6‐sulfonate) diammonium salt (ABTS), were immobilized on a MWCNTs/Au electrode with polypyrrole at the cathode. This BFC was performed in a stirred acetate buffer solution (pH 5.0) containing 40 mmol/L glucose in air, with a maximum power density of 8 μW/cm², an open‐circuit cell voltage of 0.29 V, and a short‐circuit current density of 85 μA/cm², respectively. The cell current at the load of 100 kΩ retained 78.9% of the initial value after continuous discharging for 15 h in a stirred acetate buffer solution (pH 5.0) containing 40 mmol/L glucose in air. The performance decrease of the BFC resulted mainly from the leakage of the ABTS mediator immobilized at the cathode, as revealed by the two‐channel quartz crystal microbalance technique. In addition, a monopolar glucose BFC was performed with the same anode as that in the glucose/O₂ membraneless BFC in a stirred phosphate buffer solution (pH 7.0) containing 40 mmol/L glucose, and a carbon cathode in Nafion‐membrane‐isolated acidic KMnO₄, with a maximum power density of 115 μW/cm², an open‐circuit cell voltage of 1.24 V, and a short‐circuit current density of 202 μA/cm², respectively, which are superior to those of the glucose/O₂ membraneless BFC. A modification of the anode with MWCNTs for the monopolar glucose BFC increased the maximum power density by a factor of 1.8. The ECN device is highly recommended as a convenient, real‐time and sensitive technique for BFC studies.     

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.     

Preparation of an Electrode Modified with an Electropolymerized Film as a Mediator of NADH Oxidation and Its Application in an Ethanol/O2 Biofuel Cell

This paper reports a novel mediator for the oxidation of β‐nicotinamide adenine dinucleotide (NAD⁺/NADH), an electropolymeric film (pAPRu) of [Ru(NH₂‐phen)₃]²⁺. A pAPRu‐modified electrode was prepared via electropolymerization and exhibited catalytic activity toward the electrochemical oxidation of NADH due to the imine moieties of pAPRu. The electrochemical oxidation of ethanol was observed using an alcohol dehydrogenase (ADH)‐immobilized electrode. A compartmentless ethanol/O₂ biofuel cell composed of an ADH anode and a bilirubin oxidase cathode was constructed. The maximum current density and the maximum power density of the biofuel cell were 190 µA cm^?2 and 31 µW cm^?2 (at 0.29 V), respectively.     

Preparation of Close‐Packed Silver Nanoparticles on Graphene to Improve the Enzyme Immobilization and Electron Transfer at Electrode in Glucose/O2 Biofuel Cell

In this study, chemical reduced graphene‐silver nanoparticles hybrid (AgNPs @CR‐GO ) with close‐packed AgNPs structure was used as a conductive matrix to adsorb enzyme and facilitate the electron transfer between immobilized enzyme and electrode. A facile route to prepare AgNPs @CR‐GO was designed involving in β ‐cyclodextrin (β ‐CD ) as reducing and stabilizing agent. The morphologies of AgNPs were regulated and controlled by various experimental factors. To fabricate the bioelectrode, AgNPs @CR‐GO was modified on glassy carbon electrode followed by immobilization of glucose oxidase (GOx ) or laccase. It was demonstrated by electrochemical testing that the electrode with close‐packed AgNPs provided high GOx loading (Γ =4.80 × 10⁻¹⁰ mol•cm⁻²) and fast electron transfer rate (k _s=5.76 s⁻¹). By employing GOx based‐electrode as anode and laccase based‐electrode as cathode, the assembled enzymatic biofuel cell exhibited a maximum power density of 77.437 μW •cm⁻² and an open‐circuit voltage of 0.705 V.     

Oxygen transport through laccase biocathodes for a membrane-less glucose/O2 biofuel cell

The present study reports the development of operational membrane-less glucose/O₂ biofuel cell based on oxygen contactor. Glucose oxidation was performed by glucose oxidase (GOx) co-immobilized with the mediator 8-hydroxyquinoline-5-sulfonic acid hydrate (HQS) at the anode, whereas oxygen was reduced by laccase co-immobilized with 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS²⁻) at the cathode. Both enzymes and mediators were immobilized within electropolymerized polypyrrole polymers.Nevertheless, this system is limited by the secondary reaction of O₂ electro-reduction at the anode that reduces the electron flow through the anode and thus the output voltage. In order to avoid the loss of current at the anode in glucose/O₂ biofuel cell, we developed a strategy to supply dissolved oxygen separate from the electrolyte. Porous carbon tubes were used as electrodes and modified on the external surface by the couple enzyme/mediator. The inside of the cathode tube was continuously supplied with saturated dioxygen solution diffusing from the inner to the external surface of the porous tube. The assembled biofuel cell was studied under nitrogen at 37 °C in phosphate buffer at pH 5.0 and 7.0. The maximum power density reached 27 μW cm⁻² at a cell voltage of 0.25 V at pH 5.0 with 10 mM glucose. The power density was twice as high as compared to the same system with oxygen bubbling directly in the cell.     

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.     

A Membrane‐Free Neutral pH Formate Fuel Cell Enabled by a Selective Nickel Sulfide Oxygen Reduction Catalyst

Polymer electrolyte membranes employed in contemporary fuel cells severely limit device design and restrict catalyst choice, but are essential for preventing short‐circuiting reactions at unselective anode and cathode catalysts. Herein, we report that nickel sulfide Ni₃S₂ is a highly selective catalyst for the oxygen reduction reaction in the presence of 1.0 m formate. We combine this selective cathode with a carbon‐supported palladium (Pd/C) anode to establish a membrane‐free, room‐temperature formate fuel cell that operates under benign neutral pH conditions. Proof‐of‐concept cells display open circuit voltages of approximately 0.7 V and peak power values greater than 1 mW cm⁻², significantly outperforming the identical device employing an unselective platinum (Pt) cathode. The work establishes the power of selective catalysis to enable versatile membrane‐free fuel cells.     

A Biofuel Cell Based on Biocatalytic Reactions of Lactate on Both Anode and Cathode Electrodes – Extracting Electrical Power from Human Sweat

Electrodes composed of carbon fibers were modified with graphene nano‐sheets in order to increase their surface area and facilitate electrochemical reactions. Electrocatalytic species, such as Meldola's blue (MB) and hemin were immobilized on the graphene surface due to their π‐π stacking and then used for electrocatalytic oxidation of NADH and reduction of H₂O₂, respectively. Further modification of these electrodes with enzymes producing NADH and H₂O₂ in situ (lactate dehydrogenase, LDH, and lactate oxidase, LOx, respectively), allowed assembling of a biofuel cell operating in the presence of lactate, oxygen and NAD⁺. The cathode of the biofuel cell required lactate and O₂ for its operation, while the anode operated in the presence of lactate and NAD⁺. Notably, both bioelectrocatalytic electrodes operated in the presence of lactate, one producing H₂O₂ in the reaction catalyzed by LOx in the presence of O₂, second producing NADH in the reaction catalyzed by LDH in the presence of NAD⁺. Both reactions were performed in the biofuel cell without separation of the cathodic and anodic solutions and with no need of a membrane. The biofuel cell was tested in solutions mimicking human sweat and then in real human sweat samples, demonstrating substantial power release being able to activate electronic devices.     

Zeolitic Imidazolate Frameworks Derived Co9S8/Nitrogen-Doped Hollow Porous Carbon Spheres as Efficient Bifunctional Electrocatalysts for Rechargeable Zinc–Air Batteries

The development of nonprecious metal-based electrocatalysts with remarkable catalytic activity and long-cycling lifespan toward oxygen reduction reaction (ORR) and evolution reaction (OER) is especially important for rechargeable zinc–air batteries (ZABs). Herein, monodispersed Co₉S₈ nanoparticles embedded in nitrogen-doped hierarchically porous hollow carbon spheres (Co₉S₈ NPs/NHCS) are synthesized through a template-assisted strategy followed by a co-assembly, thermal annealing, and sulfurization process. Benefiting from larger specific surface area, hierarchically porous hollow structure, and carbon nanotubes self-growth, the obtained Co₉S₈ NPs/NHCS-0.5 electrocatalyst exhibits decent performance for ORR (E_1/2=0.85 V) and OER (E₁₀=1.55 V). A rechargeable ZAB assembled using the Co₉S₈ NPs/NHCS-0.5 as air cathode delivers a maximum power density of 116 mW cm⁻², high open circuit voltage of 1.47 V, and good durability (no obvious voltage decay after 1200 cycles (200 hours)). Such a hierarchically porous hollow structure of Co₉S₈ NPs/NHCS-0.5 provides a confined space shell and an interconnected hollow core to achieve outstanding bifunctional catalytic activity and cycling stability, which surpass the benchmark Pt/C-RuO₂.     

Concentric glucose/O2 biofuel cell

A concentric glucose/O₂ biofuel cell has been developed. The device is constituted of two carbon tubular electrodes, one in the other, and combines glucose electrooxidation at the anode and oxygen electroreduction at the cathode. The anodic catalyst is glucose oxidase co-immobilized with the mediator 8-hydroxyquinoline-5-sulfonic acid hydrate, and the cathodic catalyst is bilirubin oxidase co-immobilized with the mediator 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt. Both enzymes and mediators are entrapped at the surface of the tubular electrodes by an electrogenerated polypyrrole polymer. The originality of the concentric configuration is to compartmentalize the anode and cathode electrodes and to supply dissolved oxygen separate from the electrolyte in order to avoid secondary reactions. The dissolved oxygen circulates through the inside of the cathode tube and diffuses from the inner to the external surface of the tube to react directly with the immobilized bilirubin oxidase. The assembled biofuel cell is studied at 37 °C in phosphate buffer pH 7.4. We show the influence of the thickness of the polypyrrole polymer on the electrochemical activity of the biocathodes. We also demonstrate the effect of the chemical reticulation of the enzymes by glutaraldehyde within the polymer on the performances of the bioelectrodes. The maximum power density delivered by the assembled glucose/O₂ biofuel cell reaches 42 μW cm⁻², evaluated from the geometric area of the electrodes, at a cell voltage of 0.30 V with 10 mM glucose. The results demonstrate that the concentric design of the BFC based on compartmented electrodes is a promising architecture for further development of micro electronic devices.     

Lead dioxide as an alternative catalyst to platinum in microbial fuel cells

Lead dioxide (PbO₂) was compared to platinum (Pt) as a cathode catalyst in a double-cell microbial fuel cell (MFC) utilizing glucose as a substrate in the anode chamber. Four types of cathodes were tested in this study including two PbO₂ cathodes fabricated using a titanium base with butanol or Nafion^® binders and PbO₂ paste, one Pt/carbon cathode fabricated using a titanium base with a carbon–Pt paste, and a commercially available Pt/carbon cathode made from carbon paper with Pt on one side. The power density and polarization curves were compared for each cathode and cost estimates were calculated. Results indicate the PbO₂ cathodes produced between 2 and 4× more power than the Pt cathodes. Furthermore, the PbO₂ cathodes produced between 2 and 17× more power per initial fabrication or purchase cost than the Pt cathodes. This study suggests that cathode designs that incorporate PbO₂ instead of Pt could possibly improve the feasibility of scaling up MFC designs for real world applications by improving power generation and lowering production cost.     

Direct Electrochemistry of Multi‐Copper Oxidases at Carbon Nanotubes Noncovalently Functionalized with Cellulose Derivatives

This study describes the direct electron transfer of multi‐copper oxidases, i.e., laccase (from Trametes versicolor) and bilirubin oxidase (BOD, from Myrothecium verrucaria) at multiwalled carbon nanotubes (MWNTs) noncovalently functionalized with biopolymers of cellulose derivatives, i.e., hydroxyethyl cellulose (HEC), methyl cellulose (MC), and carboxymethyl cellulose (CMC). The functionalization of the MWNTs with the cellulose derivatives is found to substantially solubilize the MWNTs into aqueous media and to avoid their aggregation on electrode surface. Under anaerobic conditions, the redox properties of laccase and BOD are difficult to be defined with cyclic voltammetry at either laccase/MWNT‐modified or BOD/MWNT‐modified electrodes. The direct electron transfer properties of laccase and BOD are thus studied in terms of the bioelectrocatalytic activities of the laccase/MWNT‐modified and BOD/MWNT‐modified electrodes toward the reduction of oxygen and found to be facilitated at the functionalized MWNTs. The possible application of the laccase‐catalyzed O₂ reduction at the laccase/MWNT‐modified electrode is illustrated by constructing a CNT‐based ascorbate/O₂ biofuel cell with the MWNT‐modified electrode as the anode for the oxidation of ascorbate biofuel.     

Biofuel Cell Operating in Vivo in Rat

Biocatalytic electrodes made of buckypaper were modified with PQQ‐dependent glucose dehydrogenase on the anode and with laccase on the cathode. The enzyme modified electrodes were assembled in a biofuel cell which was first characterized in human serum solution and then the electrodes were placed onto exposed rat cremaster tissue. Glucose and oxygen dissolved in blood were used as the fuel and oxidizer, respectively, for the implanted biofuel cell operation. The steady‐state open circuitry voltage of 140±30 mV and short circuitry current of 10±3 µA (current density ca. 5 µA cm^?2 based on the geometrical electrode area of 2 cm²) were achieved in the in vivo operating biofuel cell. Future applications of implanted biofuel cells for powering of biomedical and sensor devices are discussed.     

Powerful connection of laccase and carbon nanotubes: Material for mediator-free electron transport on the enzymatic cathode of the biobattery

We describe the preparation of laccase/single-walled carbon nanotube bioconjugates, their application for the modification of electrodes and application of the electrodes as cathodes for the catalytic reduction of oxygen in a hybrid biofuel cell with Zn anode. Carbon nanotubes functionalized with aminoethyl residues, activated and reacted with laccase show high bioelectrocatalytic activity and are promising for the biofuel cell applications. The power density of the cell was 1 mW cm^− 2 at working voltage of 0.8 V. The open circuit voltage of this hybrid cell was as high as 1.5 V.     

Carbon‐Nanotube‐Supported Bio‐Inspired Nickel Catalyst and Its Integration in Hybrid Hydrogen/Air Fuel Cells

A biomimetic nickel bis‐diphosphine complex incorporating the amino acid arginine in the outer coordination sphere was immobilized on modified carbon nanotubes (CNTs) through electrostatic interactions. The functionalized redox nanomaterial exhibits reversible electrocatalytic activity for the H₂/2 H⁺ interconversion from pH 0 to 9, with catalytic preference for H₂ oxidation at all pH values. The high activity of the complex over a wide pH range allows us to integrate this bio‐inspired nanomaterial either in an enzymatic fuel cell together with a multicopper oxidase at the cathode, or in a proton exchange membrane fuel cell (PEMFC) using Pt/C at the cathode. The Ni‐based PEMFC reaches 14 mW cm⁻², only six‐times‐less as compared to full‐Pt conventional PEMFC. The Pt‐free enzyme‐based fuel cell delivers ≈2 mW cm⁻², a new efficiency record for a hydrogen biofuel cell with base metal catalysts.     

A Biofuel Cell Based on Biocatalytic Reactions of Glucose on Both Anode and Cathode Electrodes

Biofuel cells based on electrocatalytic oxidation of NADH and reduction of H₂O₂ have been prepared using carbon fiber electrodes functionalized with graphene nano‐flakes. The electrochemical oxidation of NADH was catalyzed by Meldola's blue (MB), while the reduction of H₂O₂ was catalyzed by hemin, both catalysts were adsorbed on the graphene flakes due to their π‐π staking. In the next set of experiments, the MB‐ and hemin‐electrodes were additionally modified with glucose dehydrogenase (GDH) and glucose oxidase (GOx), respectively. The enzyme catalyzed reactions in the presence of glucose, NAD⁺ and O₂ resulted in the production of NADH and H₂O₂ in situ. The produced NADH and H₂O₂ were oxidized and reduced, respectively, at the bioelectrocatalytic electrodes, thus producing voltage and current generated by the biofuel cell. The enzyme‐based biofuel cells operated in a human serum solution modelling an implantable device powered from the natural biofluid. Finally, two enzyme‐based biofuel cell connected in series and operating in the serum solution produced electrical power sufficient for activation of an electronic watch used as an example device.     

A biofuel cell based on pyrroloquinoline quinone and microperoxidase-11 monolayer-functionalized electrodes

A pyrroloquinoline quinone (PQQ) monolayer-functionalized-Au-electrode and a microperoxidase-11 (MP-11)-modified Au-electrode are used as catalytic anode and cathode in a biofuel cell element, respectively. The cathodic oxidizer is H₂O₂ whereas the anodic fuel-substrate is 1,4-dihydronicotinamide adenine dinucleotide, NADH. The PQQ-monolayer electrode catalyzes the oxidation of NADH in the presence of Ca²⁺ ions. The MP-11-functionalized electrode catalyzes the reduction of H₂O₂. The biofuel cell generates an open-circuit voltage, V_oc, of ca. 320 mV and a short-circuit current density, I_sc, of ca. 30 μA·cm⁻². The maximum electrical power, W_max, extracted from the cell is 8 μW at an external load of 3 kΩ. The fill factor of the biofuel cell, f=W_max·I_sc⁻¹·V_oc⁻¹, is ca. 25%.     

Microchip-based ethanol/oxygen biofuel cell

One of the limitations of lab-on-a-chip technology has been the lack of integrated power supplies for powering various devices on the chip. This research focused on design of a stackable, microchip-based biofuel cell. The biofuel cell is powered by the addition of ethanol through a flow channel to a bioanode. The bioanode contains a micromolded carbon ink anode that has been modified with two layers. The first layer is poly(methylene green), which is an electrocatalyst for NADH oxidation; the second layer is a membrane that contains an immobilized enzyme, alcohol dehydrogenase. Each layer was characterized electrochemically. It was found that the poly(methylene green) layer is kinetically-limited, but when the complete bioanode is formed, the bioanode is diffusion-limited due to slow mass transport of NADH within the modified Nafion membrane. When used relative to an external platinum cathode, the biofuel cell showed maximum open circuit potentials of 0.34 V and maximum current densities of 53.0 +/- 9.1 microA cm(-2). This research demonstrates the feasibility of a microfabricated biofuel cell device.     

A High‐Energy‐Density Potassium Battery with a Polymer‐Gel Electrolyte and a Polyaniline Cathode

A safe, rechargeable potassium battery of high energy density and excellent cycling stability has been developed. The anion component of the electrolyte salt is inserted into a polyaniline cathode upon charging and extracted from it during discharging while the K⁺ ion of the KPF₆ salt is plated/stripped on the potassium‐metal anode. The use of a p‐type polymer cathode increases the cell voltage. By replacing the organic‐liquid electrolyte in a glass‐fiber separator with a polymer‐gel electrolyte of cross‐linked poly(methyl methacrylate), a dendrite‐free potassium anode can be plated/stripped, and the electrode/electrolyte interface is stabilized. The potassium anode wets the polymer, and the cross‐linked architecture provides small pores of adjustable sizes to stabilize a solid‐electrolyte interphase formed at the anode/electrolyte interface. This alternative electrolyte/cathode strategy offers a promising new approach to low‐cost potassium batteries for the stationary storage of electric power.     

Size‐Dependence of the Activity of Gold Nanoparticle‐Loaded Titanium(IV) Oxide Plasmonic Photocatalyst for Water Oxidation

Mesoporous TiO₂ nanocrystalline film was formed on fluorine‐doped tin oxide electrode (TiO₂/FTO) and gold nanoparticles (NPs) of different sizes were loaded onto the surface with the loading amount kept constant (Au/TiO₂/FTO). Visible‐light irradiation (λ>430 nm) of the Au/TiO₂/FTO photoanode in a photoelectrochemical cell with the structure of photoanode|0.1 m NaClO4 aqueous solution|Ag/AgCl (reference electrode)|glassy carbon (cathode) leads to the oxidation of water to oxygen (O₂). We show that the visible‐light activity of the Au/TiO₂/FTO anode increases with a decrease in Au particle size (d) at 2.9≤d≤11.9 nm due to the enhancement of the charge separation and increasing photoelectrocatalytic activity.