Unmodified Anode Research Articles

Mesoporous nitrogen-doped carbon@graphene nanosheets as ultra-stable anode for lithium-ion batteries – Melamine as surface modifier than nitrogen source

Nitrogen-doped carbon materials are highly appealing next-generation anode for Li-ion battery owing to high energy density, conducting and porous structure, and a large number of ion-binding sites. However, the formation of micropores limits the ion/electrolyte diffusion at high discharge rate leading to underutilization of active material, capacity fading, and low cycle stability, hindering their practical application. Herein, we report mesoporous-rich carbon hybrid comprising of zeolitic imidazolate framework (ZIF)-derived nitrogen-doped carbon-anchored graphene using melamine as the surface modifier and pore expander. A high specific capacity of 775 (after 1100 cycles) and 675 mAh g−1 (after 1000 cycles) were obtained at current densities of 1000 and 2000 mA g−1 (4C) which is two-fold higher than the initial capacity. The melamine-modified anode exhibited excellent cycle retention of 163% at 1000 mA g−1 after 800 cycles, compared to 91% for the unmodified anode, indicating the activation process through the mesoporous channels. Superior cycle retention and long cycle life were attributed to the melamine-induced features viz mesoporous structure and defective sites formed on carbon/graphene facilitating efficient electrolyte percolation/ion transport and Li-ion storage, respectively. This strategy provides a promising approach for the design of ZIFs-derived carbon materials for high-performance Li-ion batteries.

Enhanced Performance of a Single Chamber Microbial Fuel Cell Using NiWO4/Reduced Graphene Oxide Coated Carbon Cloth Anode

AbstractMicrobial fuel cell (MFC) technology has potential to generate bioelectricity. However, the low power density problem is considerably associated with anode materials and its performance. In this study, modified anodes for single chamber MFC (SMFC) have been developed using NiWO4 impregnated on reduced graphene oxide (rGO) (NWG) composite. The analytical and morphological properties of rGO, NiWO4 particles and NWG composites have been characterized by FTIR, XRD, SEM and TEM. The electrochemical activity and capacitance of modified anode(s) are determined by cyclic voltammetry and galvanostatics charge‐discharge, respectively. Modified NWG composite (2 mmol)‐carbon cloth (CC) anode has highest capacitance value of 47.27 ± 0.18 F cm−2. The maximum power density obtained by modified NWG composite (2 mmol)‐CC anode was observed to be 1128 ± 42 mW m−2 which was 6.57 times higher than the unmodified anode (171 ± 8 mW m−2). Electrochemical impedance spectra results indicate a substantial improvement in electron transfer between the microbes and the modified NWG composites‐CC anodes. The decrease in the internal resistance of SMFC system is observed due to the improved electrochemical capacitance and synergistic effect between NiWO4 and rGO. In conclusion, modified NWG composites‐CC anodes enhance the performance considerably and show excellent potential in electrode surface electrocatalyst modifier in MFCs.

Improving Electrochemical Performance of Carbon Felt Anode by Modifying With Akaganeite in Marine Benthic Microbial Fuel Cells

AbstractEnhancing the electrochemical performance of anode is a critical step for improving the power output of marine benthic microbial fuel cells (BMFCs). An active anode involving the akaganeite (β‐FeOOH)‐coated carbon felt was proposed in present study. Results showed that electrochemical performance of modified anode was significantly improved. The peak current density of oxidation reaction increased from 0.664 to 6.107 A m−2. The exchange current density was improved from 11.75 × 10−3 to 151.36 × 10−3 mA cm−2. Electron transfer resistance decreased from 13.4 to 1.407 Ω, while the surface capacitance dramatically increased. The maximum power density of the BMFCs equipped with modified anode approached to 504.2 mW m−2, 2.3 times higher than that with unmodified anode. Moreover, relative abundance of dissimilatory iron reducing bacteria (DIRB) on the modified anode increased. Finally, a molecule synergetic mechanism containing electrostatic interaction and bacteria recognition between DIRB and β‐FeOOH was proposed to interpret the improvement of modified anode.

Dendrite-Free Li Metal Anode for Rechargeable Li-SO2 Batteries Employing Surface Modification with a NaAlCl4-2SO2 Electrolyte.

Dendritic growth of a Li metal anode during cycling is one of major issues to be addressed for practical application of Li metal rechargeable batteries. Herein, we demonstrate that surface modification of Li metal with a Na-containing SO2 electrolyte can be an effective way to prevent dendritic Li growth during cell operation. The surface-modified Li metal anode exhibited no dendritic deposits even under a high areal capacity (5 mA h cm-2) and a high current density (3 mA cm-2), whereas the unmodified anode showed typical filamentary Li deposition. The surface-modified Li metal anode also demonstrated significantly enhanced electrochemical performance, which could be attributed to the newly formed Na-containing inorganic surface layer that exhibits uniform and dense properties. Consequently, surface modification with a Na-containing SO2 inorganic electrolyte is suggested as one of the most effective ways to realize a highly stable Li metal anode with dendrite-free Li deposition for Li metal-based rechargeable batteries.

Rational Design of Superior, Coking-Resistant, Nickel-Based Anodes through Tailoring Interfacial Reactions for Solid Oxide Fuel Cells Operated on Methane Fuel.

The reaction between a Ni-Y2 O3 -stabilized ZrO2 (Ni-YSZ) cermet anode and La5.4 WO12-δ (LW) during cell fabrication is utilized to reduce carbon deposition in solid oxide fuel cells operated on methane fuel. The effect of the phase reactions on the microstructure, electrical conductivity, chemical interactions, and coking resistance of the anodes are systematically investigated. Nix Wy and La-doped YSZ are formed by phase reactions and the synergistic effect between them increases the coking resistance dramatically. 2 wt % is demonstrated to be the optimal amount of LW to modify Ni-YSZ to achieve best coking resistance. The cell with Ni-YSZ-2 wt % LW anode demonstrates a superior peak power density of 943 mW cm-2 at 800 °C with humidified methane as fuel, which is 10 % higher than that of Ni-YSZ (859 mW cm-2 ). Furthermore, the cell is stable for 200 h in methane fuel with no clear performance degradation while the cell with unmodified anode fails after 0.5 h's operation. In summary, we provide a new way to rationally design Ni-based cermet anode with high electrocatalytic activity and excellent coking resistance.

Effect of Amino Acid Addition in Marine Sediment on Electrochemical Performance in Microbial Fuel Cells

AbstractAs exogenous substances, L‐methionine, L‐threonine and L‐lysine were added into the marine sediment to construct marine sediments microbial fuel cells (MSMFCs) and the effects on the anodic electrochemical activity were following investigated. The results show that the addition of the amino acid increases anodic electrochemical activity, and the anode in L‐methionine modified sediment presents better performance than others. The specific capacitance of anode in L‐methionine modified sediment (192.00 F cm−2) is 4.0 times bigger than that of anode in unmodified sediment, generating a maximum current density of 2.560 × 10−4 A cm−2. In their Tafel curves, the anodic exchange current density in the L‐methionine modified sediment (2.14 × 10−6 A cm−2) is 93.04 times higher than that of unmodified anode, which suggests that the electrochemical activity of redox, anti‐polarization ability and electron transfer kinetic activity are improved significantly. The MSMFC with L‐methionine modified sediment generates the higher power densities than the blank (143.2 mW m−2 versus 59.2 mW m−2), and its current also increases by 2.8 times. This demonstrates that L‐methionine provides a practical advantage on the anodic electrochemical and battery performance. Therefore, amino acids are good tools to evaluate its power generation of the MSMFCs.

Catalyst enhancing aluminum titanate for increasing strength of nickel-zirconia cermets

Aluminum titanate (ALT), a catalyst-enhancing phase in nickel-zirconia SOFC anodes, has been observed to have the secondary benefit of increasing flexure strength. Ni-YSZ cermet discs doped with 5wt% ALT exhibit 150% of stress at failure of non-doped samples in equibiaxial flexure tests. Also observed is a ∼25% increase in toughness, which may be related to the localized introduction of tetragonal zirconia, or alternatively, that the sintering enhancement effect of ALT yields modified flaw geometry at cermet interfaces. Comparison of non-doped and doped Ni-YSZ σ50% values indicates that the thickness of ALT enhanced anodes could be reduced by ∼20% while maintaining the flexural strength of an unmodified anode.

Enhanced Bioelectrocatalysis of Shewanella oneidensis MR-1 by a Naphthoquinone Redox Polymer

Shewanella oneidensis MR-1 is the model organism used in microbial fuel cells (MFCs). A great deal of research has focused on this bacterium to improve extracellular electron transfer (EET) and subsequently the power output in MFCs. Here, we report on the enhanced bioelectrocatalysis of S. oneidensis MR-1 by using a naphthoquinone redox polymer (NQ-LPEI) on a modified carbon felt electrode. A maximum anodic current of 3.70 ± 0.40 A m–2 is obtained in a three-electrode setup, a value 15 times higher than that obtained for an anode that did not contain the NQ-LPEI redox polymer (0.24 ± 0.05 A m–2). Additionally, a maximum power output of 0.53 ± 0.02 W m–2 was obtained in single-chamber MFCs where the NQ-LPEI modified anode was utilized. The power output was significantly higher than that obtained for MFCs with unmodified anodes (0.19 ± 0.05 W m–2). These findings suggest that NQ-LPEI could be used with known electrogenic microorganisms to further improve the performances of MFCs.

A novel electrolytic titrator design - Coating platinum cathodes with an electron sink using Nafion® and hexaammineruthenium (III)

Water electrolysis produces a constant flux of H+ and OH− ions at the anode and cathode respectively. If the distance between the electrodes is reduced significantly, the pH gradients produced at the electrode surfaces become steep, and recombination of species is near instantaneous. In this experimental work, we show how microfabricated platinum cathodes coated with Nafion®, and further loaded with hexaammineruthenium (III) (Ru(NH3)63+) ions, can inhibit the production of OH− ions. Electrons from the cathode reduce Ru(NH3)63+ to Ru(NH3)62+ instead of water. Simultaneously, a constant flux of H+ ions from the un-modified anode, titrates the sample. The Nafion® film's coating, redox couple film loading, stability and pH related changes at the electrode surfaces, have all been studied. Crucial to the development of the electrolytic titrator, this research work shows the importance of crystalline ion-exchange membranes and an optimised method of loading them with redox couples.

MnO-Co composite modified Ni-SDC anode for intermediate temperature solid oxide fuel cells

MnO-Co composite was employed to modify a Ni-Sm0.2Ce0.8O2−x anode. The electrochemical performance of the MnO-Co modified anode was evaluated on an anode-supported solid oxide fuel cell in dry hydrogen and dry methane, separately. The modified anode exhibited much higher peak power density in H2 compared with the original anode at the same condition. For example, the peak power density by the modified anode was 1756mWcm−2 at 700°C, compared with 1322mWcm−2 by the original anode at the same temperature. The higher peak power density of modified anode was attributed to its much lower polarization resistance and relatively higher porosity. However, it showed a worse stability than the unmodified anode in dry methane at 650°C due to severer carbon deposition.

Hybridization of photoanode and bioanode to enhance the current production of bioelectrochemical systems

Bacterial extracellular electron transfer is one of the main bottlenecks in determining the efficiency of bioelectrochemical systems. Here, we report a photobioanode that combines carbon material with a photocatalyst (α-Fe2O3), utilizing visible light to accelerate biofilm formation and extracellular electron transfer in bioelectrochemical systems. Cyclic voltammetric studies of this photobioanode revealed active electron transfer at the anode/biofilm interface. The charge-transfer resistance of the anode/biofilm was ca. 46.6 Ω, which is half that of the unmodified anode. In addition, the results of confocal laser scanning microscopy and bacterial community analysis indicate that the photobioanode and light can accelerate biofilm formation and enrich exoelectrogens. When equipped in photo-bioelectrochemical systems, the start-up time was shortened from about 2.5 days to 1.1 days. The maximum current density of photo-bioelectrochemical systems was almost twice that of a control bioelectrochemical system. In addition, the current density of the photo-bio-electrochemical cell (PBEC) showed almost no decrease after being subjected to 40 d of illumination. This photobioanode is therefore a cost-effective, energy-clean, environment-friendly anode with high electrocatalytic activity and long-term stability, which has broad prospects in various processes, including wastewater treatment, bioelectricity generation, bioelectricity synthesis, and hydrogen production.

Enhanced performance of microbial fuel cells by using MnO2/Halloysite nanotubes to modify carbon cloth anodes

The modification of anode materials is important to enhance the power generation of MFCs (microbial fuel cells). A novel and cost-effective modified anode that is fabricated by dispersing manganese dioxide (MnO2) and HNTs (Halloysite nanotubes) on carbon cloth to improve the MFCs' power production was reported. The results show that the MnO2/HNT anodes acquire more bacteria and provide greater kinetic activity and power density compared to the unmodified anode. Among all modified anodes, 75 wt% MnO2/HNT exhibits the highest electrochemical performance. The maximum power density is 767.3 mWm−2, which 21.6 higher than the unmodified anode (631 mW/m2). Besides, CE (Coulombic efficiency) was improved 20.7, indicating that more chemical energy transformed to electricity. XRD (X-Ray powder diffraction) and FTIR (Fourier transform infrared spectroscopy) are used to characterize the structure and functional groups of the anode. CV (cyclic voltammetry) scans and SEM (scanning electron microscope) images demonstrate that the measured power density is associated with the attachment of bacteria, the microorganism morphology differed between the modified and the original anode. These findings demonstrate that MnO2/HNT nanocomposites can alter the characteristics of carbon cloth anodes to effectively modify the anode for practical MFC applications.

Metal-based anode for high performance bioelectrochemical systems through photo-electrochemical interaction

This paper introduces a novel composite anode that uses light to enhance current generation and accelerate biofilm formation in bioelectrochemical systems. The composite anode is composed of 316L stainless steel substrate and a nanostructured α-Fe2O3 photocatalyst (PSS). The electrode properties, current generation, and biofilm properties of the anode are investigated. In terms of photocurrent, the optimal deposition and heat-treatment times are found to be 30 min and 2 min, respectively, which result in a maximum photocurrent of 0.6 A m−2. The start-up time of the PSS is 1.2 days and the maximum current density is 2.8 A m−2, twice and 25 times that of unmodified anode, respectively. The current density of the PSS remains stable during 20 days of illumination. Confocal laser scanning microscope images show that the PSS could benefit biofilm formation, while electrochemical impedance spectroscopy indicates that the PSS reduce the charge-transfer resistance of the anode. Our findings show that photo-electrochemical interaction is a promising way to enhance the biocompatibility of metal anodes for bioelectrochemical systems.

Anode decoration with biogenic Pd nanoparticles improved power generation in microbial fuel cells

ABSTRACT An anode electrode has been modified using biogenic palladium (Bio-Pd) nanoparticles aimed to establish a bifunctional anode and enhance its performance in microbial fuel cells (MFCs). Bio-Pd nanoparticles are fabricated via Pd (II) reduction by Shewanella oneidensis and coated to carbon cloth as anode catalyst. The electrocatalytic activity of the Pd catalyst at electrode towards fermentation products of formate, lactate, acetate are assessed using cyclic voltammetry (CV). The performance of MFCs with the Bio-Pd anode is investigated through measuring polarization curve, power density and electrochemical impedance spectroscopy (EIS). Results show the Bio-Pd electrode exhibits an enhanced electrocatalytic activity towards the fermentation products. With a Bio-Pd anode (2 mg/cm 2 Pd), the maximum power density and coulombic efficiency of MFCs are enhanced by 14% and 31% respectively, compared to that with an unmodified anode. Modification with Bio-Pd nanoparticles significantly reduces the charge transfer resistance of MFCs. The Bio-Pd modified anode possesses both electro-oxidative and microbial metabolic functions, which may contribute to the improved performance of MFCs.

Performance Enhancement with a Hydrophilic Self-Immobilized Redox Mediator Modified Anode in Chlorella vulgaris-based Microbial Solar Cell

In this study, a new approach to improving the performance of a Chlorella vulgaris-based microbial solar cell (MSC) by using a riboflavinyl-salicylaldehyde-4-aminosalicylic-1-tetracarboxylate ester (RSA) modified carbon rod anode was reported. It has strong hydrophilicity but can be easily soluble in organic solvents rather than water and can be attached to the surface of a plain carbon rod without using any carrier. The single-chamber MSC operated with this RSA modified anode and a cupric hexacyanoferrate modified cathode achieved a maximum power density of 0.847 W/m2, which was 7 times higher than that obtained from the MSC equipped with an unmodified anode. The scanning electron microscopy (SEM) results indicated that there was no biofilm formed on the anode surface. Charge transfer was facilitated only by RSA modification.

Synergetic effect of conductive polymer poly(3,4-ethylenedioxythiophene) with different structural configuration of anode for microbial fuel cell application

PEDOT was synthesized by chemical polymerisation and characterised for its electrochemical insights. Three different anode configuration, namely graphite plate (GP), carbon cloth (CC) and graphite felt (GF) were then loaded with a fixed amount of PEDOT (2.5mg/m2) denoted as GP-P, CC-P and GF-P respectively. The PEDOT coating improved the electrochemical characteristics and electron transfer capabilities of the anodes. They also contributed for enhanced MFC performances with maximum energy generation along with coulombic efficiency than the unmodified anodes. The morphological characteristics like higher surface area and open structure of felt material promoted both microbial formation and electrochemical active area. A maximum current density of 3.5A/m2 was achieved for GF-P with CE and COD of 51% and 86% respectively. Thus, the GF-P anode excelled among the studied anodes with synergetic effect of PEDOT coating and structural configuration, making it as a potential optimum anode for MFC application.

Oxide incorporation into Ni-based solid oxide fuel cell anodes for enhanced sulfur tolerance during operation on hydrogen or biogas fuels: A comprehensive thermodynamic study

The effect of the incorporation of oxides (CeO2, CaO, MgO, SrO, BaO) into SOFC anodes on sulfur poisoning of Ni catalysts is investigated by means of a comprehensive thermodynamic study. The results demonstrate that sulfur chemical potential controls the value of bulk nickel sulfide activity, which, in turn, is a function of sulfur coverage on Ni surface. It is found that oxide incorporation into anodes can reduce the sulfur chemisorption on Ni by lowering the sulfur chemical potential. BaO incorporation may be the best option for IT-SOFCs. The strong affinity of BaO towards sulfur significantly reduces the sulfur coverage on Ni surface, from values in the range of 0.91–0.96 to 0.54–0.58, for wet hydrogen atmosphere, in such a way that catalyst poisoning can be completely prevented. In situ regeneration of BaO could occur by means of a local reaction between BaS and OH species that are generated by dissociative chemisorption of H2O. The highest H2S concentration allowed in a BaO-modified anode depends on fuel composition: 100 ppm for wet hydrogen (3%H2O), and 30–45 ppm for biogas, varying according to CH4/CO2 molar ratio. In the case of biogas, enhanced sulfur tolerance can be achieved provided that the BaCO3 phase cannot be formed. For modified and unmodified anodes, the degree of sulfur poisoning was found to decrease with increasing CH4/CO2 molar ratio in biogas. Although ceria can effectively suppress carbon deposition due to oxygen storage capacity, it cannot alleviate sulfur poisoning of Ni under carbon-free conditions. At carbon deposition boundary, ceria increases the tolerance toward H2S in the biogas only modestly.

Poly (3,4-ethylenedioxythiophene) promotes direct electron transfer at the interface between Shewanella loihica and the anode in a microbial fuel cell

Anode modification is an effective method for enhancing extracellular electron transportation and improving the power density of microbial fuel cells (MFCs). In this study, a new conductive polymer called poly (3,4-ethylenedioxythiophene) (PEDOT) is electrochemically polymerized to modify the anode. The surface of the electrochemically polymerized PEDOT layer has a widespread porous structure. Both the anode electrochemical discharge experiment and MFC discharge test demonstrate the improved performance of the PEDOT-modified anode compared with a plain anode. Cyclic voltammetry and electrochemical impedance spectroscopy analyses show that the PEDOT modification increases the availability of redox active sites and reduces the interfacial electron transfer resistance of the anode. Compared with the unmodified anode, the PEDOT anodic modification improves the power density by 43%–140 mW m−2. Possible mechanisms are proposed to help understand the function of the PEDOT-modified anodic layer.

Effect of zeolite-coated anode on the performance of microbial fuel cells

BACKGROUND For a microbial fuel cell (MFC), the anode material plays a key part in power generation. Modification of conventional carbon-based anode materials is an effective strategy to improve MFC performance. RESULTS Two different zeolites, namely, mobil catalytic materials number 41 (MCM-41) and NaX, were used to modify graphite felt anodes and compared with unmodified anodes in dual-chamber MFCs. Fourier transform infrared analysis verified that MCM-41 and NaX zeolites were successfully coated onto the bare graphite felt surface. Results showed that NaX zeolite is a favorable, affordable material for anode modification of MFCs. This zeolite improved MFC performance considerably. Its maximum power density (215.3 ± 6.4 mW m−2) and CE value (50.0% ± 2.0%) were 152.1% and 36.2% higher than those of the unmodified anode, respectively. According to scanning electron microscopy, cyclic voltammetry, and the amount of anode biomass, the superhydrophilicity of the NaX zeolite-modified anode was a vital reason for thick anode biofilm formation and accelerated anodic bio-electrochemical reactions. The improved specific surface area of the anode and properties of the microporous NaX zeolite were responsible for the enhancement of MFC performance. CONCLUSIONS Graphite felt anode modified by NaX zeolite resulted in improved power generation by a MFC. © 2013 Society of Chemical Industry

Menadione-Modified Anodes for Power Enhancement in Single Chamber Microbial Fuel Cells

As anode fabrication with different materials has been proven to be a successful alternative for enhancing power generation in the microbial fuel cells, a new approach to improved performance of MFCs with the use of menadione/carbon powder composite-modified carbon cloth anode has been explored in this study. Menadione has formal potential to easily accept electrons from the outer membrane cytochromes of electroactive bacteria that can directly interact with the solid surface. Surface bound menadione was able to maintain an electrical wiring with the trans-membrane electron transfer pathways to facilitate extracellular electron transfer to the electrode. In a single chamber air cathode MFC inoculated with aerobic sludge, maximum power density of was achieved, which was 25% higher than that of an unmodified anode. The observed high power density and improved coulomb efficiency of 61% were ascribed to the efficient electron shuttling via the immobilized menadione.