Assessment of Glucose Oxidase Based Enzymatic Fuel Cells Integrated With Newly Developed Chitosan Membranes by Electrochemical Impedance Spectroscopy

Considerably stable enzymatic fuel‐cells (single cell and 5‐cells stack) were prepared by using chitosan based membranes along with glucose oxidase attached bioanode. Continuous operation of fuel‐cells were monitored under short circuit conditions reaching half‐life over a week. Detailed analysis for the effects of pH, temperature, buffer types and concentration on different type of in‐house produced chitosan membranes were performed by electrochemical impedance spectroscopy (EIS). EIS was utilized to observe, total electrolyte resistance, charge transfer properties, mass transfer and double layer effects on integrated fuel cells (single cell and 5‐cells stack). Performance of the fuel cells was also analyzed by the polarization experiments. Current density of the fuel cell increased at higher operation temperatures not only due to better enzyme kinetics, but also due to increase in electrolyte (membrane+buffer solution) conductivity. Buffer concentration in the fuel (glucose) solution was found as an important parameter. Under optimum fuel cell operation conditions (i. e. 30–40 °C, pH 5 0.3 M buffer solution), maximum current densities of 3.0–3.2 mA cm^?2 were reached. Low‐power devices (i. e. a calculator, step motor) were powered with 5‐cell stack producing 3 mW at 1.3 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.     

Pyrene‐Anderson‐Modified CNTs as Anode Materials for Lithium‐Ion Batteries

An organo‐functionalized polyoxometalate (POM)–pyrene hybrid (Py‐Anderson) has been used for noncovalent functionalization of carbon nanotubes (CNTs) to give a Py‐Anderson‐CNT nanocomposite through π–π interactions. The as‐synthesized nanocomposite was used as the anode material for lithium‐ion batteries, and shows higher discharge capacities and better rate capacity and cycling stability than the individual components. When the current density was 0.5 mA cm^?2, the nanocomposite exhibited an initial discharge capacity of 1898.5 mA h g^?1 and a high discharge capacity of 665.3 mA h g^?1 for up to 100 cycles. AC impedance spectroscopy provides insight into the electrochemical properties and the charge‐transfer mechanism of the Py‐Anderson‐CNTs electrode.     

Development of Reasonably Stable Chitosan Based Proton Exchange Membranes for a Glucose Oxidase Based Enzymatic Biofuel Cell

Chitosan based reasonably stable membranes were prepared as polymeric electrolyte and separator for enzymatic fuel cell applications. Glucose oxidase (GOx) bioanode centered biofuel cell with the developed chitosan membranes performed much better in stability with high current densities than that of the biofuel cell utilizing a 125 μ‐thick perfluorosulfonic acid‐type membrane (i. e. Nafion® 115). Proposed chitosan membrane structural stability was enhanced by employing cellulosic support materials and chemical crosslinking. The effects of pH, buffer type, buffer concentration, temperature on the manufactured chitosan membranes along with the biofuel cell system were investigated. The biofuel cell operation parameters were optimized for the current density and stability aspects and more than 3 mA cm^?2 current density was acquired from the cell at optimum conditions. Operational half‐life of the chitosan membrane was found as higher than the half‐life of the GOx immobilized bioanode. Therefore, this result indicates that chitosan membrane structural stability was not a limiting issue for the biofuel cell lifespan.     

A completely spray-coated membrane electrode assembly

We present a proton exchange membrane fuel cell (PEMFC) manufacturing route, in which a thin layer of polymer electrolyte solution is spray-coated on top of gas diffusion electrodes (GDEs) to work as a proton exchange membrane. Without the need for a pre-made membrane foil, this allows inexpensive, fast, large-scale fabrication of membrane-electrode assemblies (MEAs), with a spray-coater comprising the sole manufacturing device. In this work, a catalyst layer and a membrane layer are consecutively sprayed onto a fibrous gas diffusion layer with applied microporous layer as substrate. A fuel cell is then assembled by stacking anode and cathode half-cells with the membrane layers facing each other. The resultant fuel cell with a low catalyst loading of 0.1 mg Pt/cm² on each anode and cathode side is tested with pure H₂ and O₂ supply at 80 °C cell temperature and 92% relative humidity at atmospheric pressure. The obtained peak power density is 1.29 W/cm² at a current density of 3.25 A/cm². By comparison, a lower peak power density of 0.93 W/cm² at 2.2 A/cm² is found for a Nafion NR211 catalyst coated membrane (CCM) reference, although equally thick membrane layers (approx. 25 μm), and identical catalyst layers and gas diffusion media were used. The superior performance of the fuel cell with spray-coated membrane can be explained by a decreased low frequency (mass transport) resistance, especially at high current densities, as determined by electrochemical impedance spectroscopy.     

Nitrogen‐doped Carbon–CoOx Nanohybrids: A Precious Metal Free Cathode that Exceeds 1.0 W cm−2 Peak Power and 100 h Life in Anion‐Exchange Membrane Fuel Cells

Efficient and durable nonprecious metal electrocatalysts for the oxygen reduction (ORR) are highly desirable for several electrochemical devices, including anion exchange membrane fuel cells (AEMFCs). Here, a 2D planar electrocatalyst with CoO_x embedded in nitrogen‐doped graphitic carbon (N‐C‐CoO_x) was created through the direct pyrolysis of a metal–organic complex with a NaCl template. The N‐C‐CoO_x catalyst showed high ORR activity, indicated by excellent half‐wave (0.84 V vs. RHE) and onset (1.01 V vs. RHE) potentials. This high intrinsic activity was also observed in operating AEMFCs where the kinetic current was 100 mA cm^?2 at 0.85 V. When paired with a radiation‐grafted ETFE powder ionomer, the N‐C‐CoO_x AEMFC cathode was able to achieve extremely high peak power density (1.05 W cm^?2) and mass transport limited current (3 A cm^?2) for a precious metal free electrode. The N‐C‐CoO_x cathode also showed good stability over 100 hours of operation with a voltage decay of only 15 % at 600 mA cm^?2 under H₂/air (CO₂‐free) reacting gas feeds. The N‐C‐CoO_x cathode catalyst was also paired with a very low loading PtRu/C anode catalyst, to create AEMFCs with a total PGM loading of only 0.10 mg_Pt‐Ru cm^?2 capable of achieving 7.4 W mg^?1_PGM as well as supporting a current of 0.7 A cm^?2 at 0.6 V with H₂/air (CO₂ free)—creating a cell that was able to meet the 2019 U.S. Department of Energy initial performance target of 0.6 V at 0.6 A cm^?2 under H₂/air with a PGM loading <0.125 mg cm^?2 with AEMFCs for the first time.     

Multiblock poly(Phenylene ether nitrile)s with pendant sulfoalkoxyl side chain for H2/air fuel cells at low humidity condition

A series of multiblock poly(phenylene ether nitrile)s with pendant sulfoalkoxyl side chains have been developed as proton exchange membranes for fuel cells. The membranes were obtained by a solution casting method and exhibited good thermal stability, flexibility, and mechanical strength. The membranes displayed well‐developed microphase separation, which largely contributed to their excellent ion conduction ability. One of the new membranes with a low ion exchange capacity of 1.57 mequiv g^?1 showed higher proton conductivity than Nafion 212 over the entire RH range (30–95%). The maximum power output generated in a single cell test reached up to 0.754, 0.640, and 0.414 W cm^?2 at 70 °C under 80%, 50%, and 30% RH conditions, respectively. The current density of the membrane obtained at 0.6 V (I _0.6) was as high as 640 mA cm^?2, which was much higher than that of Nafion 212 (375 mA cm^?2 at 30% RH), suggesting its superiority for a more rapid system start‐up. Furthermore, the in situ durability test at 50% RH was performed at a constant current loading, and the membrane did not show any significant voltage reduction over the 400 h testing period. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1940–1948     

High‐Performance Chemically Regenerative Redox Fuel Cells Using a NO3−/NO Regeneration Reaction

In this study, we proposed high‐performance chemically regenerative redox fuel cells (CRRFCs) using NO₃⁻/NO with a nitrogen‐doped carbon‐felt electrode and a chemical regeneration reaction of NO to NO₃⁻ via O₂. The electrochemical cell using the nitrate reduction to NO at the cathode on the carbon felt and oxidation of H₂ as a fuel at the anode showed a maximal power density of 730 mW cm⁻² at 80 °C and twofold higher power density of 512 mW cm⁻² at 0.8 V, than the target power density of 250 mW cm⁻² at 0.8 V in the H₂/O₂ proton exchange membrane fuel cells (PEMFCs). During the operation of the CRRFCs with the chemical regeneration reactor for 30 days, the CRRFCs maintained 60 % of the initial performance with a regeneration efficiency of about 92.9 % and immediately returned to the initial value when supplied with fresh HNO₃.     

Boosting Hydrogen Oxidation Activity of Ni in Alkaline Media through Oxygen‐Vacancy‐Rich CeO2/Ni Heterostructures

The search for highly efficient platinum group metal (PGM)‐free electrocatalysts for the hydrogen oxidation reaction (HOR) in alkaline electrolytes remains a great challenge in the development of alkaline exchange membrane fuel cells (AEMFCs). Here we report the synthesis of an oxygen‐vacancy‐rich CeO₂/Ni heterostructure and its remarkable HOR performance in alkaline media. Experimental results and density functional theory (DFT) calculations indicate the electron transfer between CeO₂ and Ni could lead to thermoneutral adsorption free energies of H* (ΔG_H*). This, together with the promoted OH* adsorption strength derived from the abundance of oxygen vacancies in the CeO₂ species, contributes to the excellent HOR performance with the exchange current density and mass activity of 0.038 mA cm_Ni^?2 and 12.28 mA mg_Ni^?1, respectively. This presents a new benchmark for PGM‐free alkaline HOR and opens a new avenue toward the rational design of high‐performance PGM‐free electrocatalysts for alkaline HOR.     

The Solid‐Phase Synthesis of an Fe‐N‐C Electrocatalyst for High‐Power Proton‐Exchange Membrane Fuel Cells

The environmentally friendly synthesis of highly active Fe‐N‐C electrocatalysts for proton‐exchange membrane fuel cells (PEMFCs) is desirable but remains challenging. A simple and scalable method is presented to fabricate Fe^II‐doped ZIF‐8, which can be further pyrolyzed into Fe‐N‐C with 3 wt % of Fe exclusively in Fe‐N₄ active moieties. Significantly, this Fe‐N‐C derived acidic PEMFC exhibits an unprecedented current density of 1.65 A cm^?2 at 0.6 V and the highest power density of 1.14 W cm^?2 compared with previously reported NPMCs. The excellent PEMFC performance can be attributed to the densely and atomically dispersed Fe‐N₄ active moieties on the small and uniform catalyst nanoparticles.     

A Pd/C‐CeO2 Anode Catalyst for High‐Performance Platinum‐Free Anion Exchange Membrane Fuel Cells

One of the biggest obstacles to the dissemination of fuel cells is their cost, a large part of which is due to platinum (Pt) electrocatalysts. Complete removal of Pt is a difficult if not impossible task for proton exchange membrane fuel cells (PEM‐FCs). The anion exchange membrane fuel cell (AEM‐FC) has long been proposed as a solution as non‐Pt metals may be employed. Despite this, few examples of Pt‐free AEM‐FCs have been demonstrated with modest power output. The main obstacle preventing the realization of a high power density Pt‐free AEM‐FC is sluggish hydrogen oxidation (HOR) kinetics of the anode catalyst. Here we describe a Pt‐free AEM‐FC that employs a mixed carbon‐CeO₂ supported palladium (Pd) anode catalyst that exhibits enhanced kinetics for the HOR. AEM‐FC tests run on dry H₂ and pure air show peak power densities of more than 500 mW cm^?2.     

Development of nano-catalyzed membrane for PEM fuel cell applications

Nano-catalyzed membrane with different platinum (Pt) catalyst loadings (0.25 to 1 mg cm^?2) was investigated for proton exchange membrane fuel cell applications, and the Pt loading on the Nafion membrane was prepared by non-equilibrium impregnation reduction method. The prepared catalyzed membranes were subjected to various characterisations, namely, X-ray diffraction, high-resolution scanning electron microscopy (HRSEM) with energy-dispersive X-ray, cyclic voltammetry, polarisation and electrochemical impedance spectroscopy. The polycrystalline fcc cubic structure and the particle size of Pt catalyst were estimated by X-ray diffraction analysis. The membrane with 0.4 mg cm^?2 of Pt loading exhibits a favourable surface morphology which is confirmed by HRSEM image. Electrochemical investigations were clearly evident that the uniform distributions of Pt particles with fine pores on Nafion membrane facilitated the three-phase boundary which leads to a better cell performance. Electrochemical impedance spectroscopy demonstrated that the cell constructed using 0.4 mg cm^?2 of platinum-loaded membrane has lower resistance than the other Pt loading.     

Fabrication of a micro-direct methanol fuel cell using microfluidics

A direct-methanol fuel cell containing three parts: microchannels, electrodes, and a proton exchange membrane (PEM), was investigated. Nafion resin (NR) and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (PS) were used as PEMs. Preparation of PEMs, including compositing with other polymers and their solubility, was performed and their proton conductivity was measured by a four point probe. The results showed that the 5 % Nafion resin has lower conductivity than the 5 % PS solution. The micro-fuel cell contained two acrylic channels, PEM, and two platinum catalyst electrodes on a silicon wafer. The assembled micro-fuel cells used 2 M methanol at the flow rate of 1.5 mL min^?1 in the anode channel and 5 × 10^?3 M KMnO₄ at the flow rate of 1.5 mL min^?1 in the cathode channel. The micro-fuel cell with the electrode distance of 300 ??m provided the power density of 59.16 ??W cm^?2 and the current density of 125.60 ??A cm^?2 at 0.47 V.     

Enhancing proton conductivity of proton exchange membrane with SPES nanofibers containing porous organic cage

Effective proton conducting sites and establishing proton channels are two critical factors in developing high‐performance proton exchange membranes. This study first establishes a strategy in designing effective proton conducting channels for Nafion by using solution blowing of sulfonated polyethersulfone (SPES) nanofibers containing CC3, which is an emerging porous organic cage that possesses the advantages of dissolvable organic solvents and high proton conduction from its interconnected three‐dimensional pore structure. Our strategy results in SPES nanofiber networks with CC3 uniformly involved in and composite membranes with Nafion‐filled interfiber voids. Benefiting from such structural features, the composite membrane exhibits high proton conductivity (0.315 S cm^?1 at 80°C and 100% RH), low methanol permeability (0.69 × 10^?7 cm² S^?1), excellent water absorption, thermal and dimensional stability, and single‐cell performance. This study provides not only a valuable reference for the application of CC3 but also a new idea for establishment of proton transfer channels.     

Structural modification of chitosan biopolymer as a novel polyelectrolyte membrane for green power generation

In the present study, a series of bioresource polyelectrolytes based on chitosan were synthesized and assessed for applicability in direct methanol fuel cells (DMFCs). A binary cross‐linking agent (sulfosuccinic acid/glutaraldehyde) was used for the structural modification of chitosan and membranes comprising various amounts of sulfosuccinic acid (0, 8, 12, and 16 wt% SSA/wt chitosan) were prepared. It was found that by increasing the sulfonate groups' content up to 16 wt%, proton conductivity and methanol permeability properties reach the values of 0.0452 S cm^?1 and 9.6 × 10^?7 cm² sec^?1, respectively. Based on the membrane selectivity evaluation and activation energy measurements of proton conduction, the optimum composition of cross‐linking agent was determined. The optimum composition resulted in a relatively high proton conductivity of 0.0452 S cm^?1 and a low methanol permeability of 9.6 × 10^?7 cm² sec^?1. Moreover, the optimum proton exchange membrane exhibited selectivity value of 47,100 in comparison with the corresponding value of 40,500 for Nafion® 117. The fabricated membranes showed acceptable oxidative and hydrolytic stability. Furthermore, single cell DMFC performance test revealed a power density of 17 mW cm^?2 at 30°C and 41 mW cm^?2 at 60°C in a 2 M methanol feed. Hence, prepared proton‐conducting bioresource ionomers could have promising potential in the field of green power generation as a low cost and biodegradable polyelectrolyte. Copyright © 2009 John Wiley & Sons, Ltd.     

Degradation Investigation of Electrocatalyst in Proton Exchange Membrane Fuel Cell at a High Energy Efficiency

The development of high efficient stacks is critical for the wide spread application of proton exchange membrane fuel cells (PEMFCs) in transportation and stationary power plant. Currently, the favorable operation conditions of PEMFCs are with single cell voltage between 0.65 and 0.7 V, corresponding to energy efficiency lower than 57%. For the long term, PEMFCs need to be operated at higher voltage to increase the energy efficiency and thus promote the fuel economy for transportation and stationary applications. Herein, PEMFC single cell was investigated to demonstrate its capability to working with voltage and energy efficiency higher than 0.8 V and 65%, respectively. It was demonstrated that the PEMFC encountered a significant performance degradation after the 64 h operation. The cell voltage declined by more than 13% at the current density of 1000 mA cm⁻², due to the electrode de-activation. The high operation potential of the cathode leads to the corrosion of carbon support and then causes the detachment of Pt nanoparticles, resulting in significant Pt agglomeration. The catalytic surface area of cathode Pt is thus reduced for oxygen reduction and the cell performance decreased. Therefore, electrochemically stable Pt catalyst is highly desirable for efficient PEMFCs operated under cell voltage higher than 0.8 V.     

Combined Intrinsic and Extrinsic Proton Conduction in Robust Covalent Organic Frameworks for Hydrogen Fuel Cell Applications

Developing new materials for the fabrication of proton exchange membranes (PEMs) for fuel cells is of great significance. Herein, a series of highly crystalline, porous, and stable new covalent organic frameworks (COFs) have been developed by a stepwise synthesis strategy. The synthesized COFs exhibit high hydrophilicity and excellent stability in strong acid or base (e.g., 12 m NaOH or HCl) and boiling water. These features make them ideal platforms for proton conduction applications. Upon loading with H₃PO₄, the COFs (H₃PO₄@COFs) realize an ultrahigh proton conductivity of 1.13×10^?1 S cm^?1, the highest among all COF materials, and maintain high proton conductivity across a wide relative humidity (40–100 %) and temperature range (20–80 °C). Furthermore, membrane electrode assemblies were fabricated using H₃PO₄@COFs as the solid electrolyte membrane for proton exchange resulting in a maximum power density of 81 mW cm^?2 and a maximum current density of 456 mA cm^?2, which exceeds all previously reported COF materials.     

Carbon Nanotubes Decorated with CoP Nanocrystals: A Highly Active Non‐Noble‐Metal Nanohybrid Electrocatalyst for Hydrogen Evolution

The development of effective and inexpensive hydrogen evolution reaction (HER) electrocatalysts for future renewable energy systems is highly desired. The strongly acidic conditions in proton exchange membranes create a need for acid‐stable HER catalysts. A nanohybrid that consists of carbon nanotubes decorated with CoP nanocrystals (CoP/CNT) was prepared by the low‐temperature phosphidation of a Co₃O₄/CNT precursor. As a novel non‐noble‐metal HER catalyst operating in acidic electrolytes, the nanohybrid exhibits an onset overpotential of as low as 40 mV, a Tafel slope of 54 mV dec^?1, an exchange current density of 0.13 mA cm^?2, and a Faradaic efficiency of nearly 100 %. This catalyst maintains its catalytic activity for at least 18 hours and only requires overpotentials of 70 and 122 mV to attain current densities of 2 and 10 mA cm^?2, respectively.     

Synthesis and Properties of Novel Side‐Chain Sulfonated Poly(Arylene Ether Sulfone)s for Proton Exchange Membranes

A series of novel side‐chain sulfonated poly(arylene ether sulfone) (SPAES) multiblock and random copolymers were synthesized by condensation polymerization from a new disulfonated aryl sulfone monomer, 4,4′‐difluoro‐2,2′‐bis(3‐sulfobenzoyl)diphenyl sulfone disodium salt (DFBSPS). The chemical structures of DFBSPS and the SPAESs were characterized by proton nuclear magnetic resonance (¹H NMR) and Fourier transform infrared (FTIR) spectra. The SPAES membranes prepared by solution cast method exhibited high tensile strength (50–71 MPa) and high radical oxidative stability. They could keep their morphology and maintain proton conductivities after hydrolysis test in 95 °C water for 1000 h. They also showed smaller swelling ratio in in‐plane direction than in through‐plane direction and such an anisotropic effect was more significant for the multiblock copolymers than for the random ones. The multiblock copolymer membranes exhibited higher proton conductivity than the random ones with similar ion exchange capacities (IECs). Preliminary hydrogen‐oxygen fuel cell tests were performed at 60 °C and 80% relative humidity (RH). The results showed that the single cell equipped with the multibiock copolymer membrane SB3 exhibited 0.12 W cm^?2 higher maximum output power density than the one equipped with the random copolymer membrane SR3 (with the same IEC), indicating much better performance of the former. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2304–2313     

A Versatile Iron–Tannin‐Framework Ink Coating Strategy to Fabricate Biomass‐Derived Iron Carbide/Fe‐N‐Carbon Catalysts for Efficient Oxygen Reduction

The conversion of biomass into valuable carbon composites as efficient non‐precious metal oxygen‐reduction electrocatalysts is attractive for the development of commercially viable polymer electrolyte membrane fuel‐cell technology. Herein, a versatile iron–tannin‐framework ink coating strategy is developed to fabricate cellulose‐derived Fe₃C/Fe‐N‐C catalysts using commercial filter paper, tissue, or cotton as a carbon source, an iron–tannin framework as an iron source, and dicyandiamide as a nitrogen source. The oxygen reduction performance of the resultant Fe₃C/Fe‐N‐C catalysts shows a high onset potential (i.e. 0.98 V vs the reversible hydrogen electrode (RHE)), and large kinetic current density normalized to both geometric electrode area and mass of catalysts (6.4 mA cm^?2 and 32 mA mg^?1 at 0.80 V vs RHE) in alkaline condition. This method can even be used to prepare efficient catalysts using waste carbon sources, such as used polyurethane foam.