High-performance Microbial Fuel Cells Research Articles

Enhanced power generation by carbonized microsphere embedded with bimetallic carbides nanoparticles as efficient electrocatalyst in bioenergy harvesting systems

The performance and preparation method of anode are the key factors for power generation and magnified application of microbial fuel cell (MFC). This is because the anode plays an essential role in whole process for extracellular electron transfer (EET) as the carrier of exoelectrogens. In this work, dual-phased Mo2C-W2C microsphere are prepared on carbon-based matrices as binder-free anode by in-situ pyrolysis of Mo/W precursors. As expected, the Mo2C-W2C/CC anode exhibits brilliant electrocatalytic activity, electron harvesting capacity and improved EET rate, thus the maximum power density of corresponding MFC achieves 4.89 W/m2. The above enhancement can be attributed to the microspherical three-dimensional structure consisting of numerous carbon nanosheets embedded with Mo2C-W2C heterogeneous nanoparticles, which will provide more catalytic active sites for microbial metabolic reactions. The microbial community analysis indicates that the formation of electroactive biofilms has been promoted by the selective screening of Mo2C-W2C for exoelectrogens and other bacteria related to sulfur metabolism. Finally, the bioenergy harvesting system assembled with Mo2C-W2C electrocatalyst successfully charges the 12 V battery. This study provides a facile, low-cost modification method for the development of high-performance MFC anodic materials conducive to large-scale preparation and has a promising effect in practical application.

Sulphonated graphene oxide as functionalized filler for polymer electrolyte membrane with enhanced anti-biofouling in microbial fuel cells

This research focuses on the development of a polymer electrolyte membrane (PEM) which is intended to increase power generation while addressing the persistent issue of biofouling in microbial fuel cells (MFC). The central hypothesis of this research work is that a novel PEM made from sulphonated polyether ether ketone (SPEEK) grafted with styrene sulphonic acid (SSA) integrated with sulphonated graphene oxide (SGO) will improve the membrane properties as well as enhance the anti-biofouling effect. The optimal percentage of SSA grafting has been determined based on physicochemical properties of the membrane. Various weight percentages of SGO (2.5, 5, 7.5, & 10 wt%) were introduced to the SPEEK/SSA base polymer to augment the physicochemical properties and also to defend against biofouling. Among the tested membranes, the SPEEK/SSA+5 % SGO composite membrane demonstrates the highest water uptake (106.2±1.9 %) and ion exchange capacity (1.55±0.2 meq g−1). Due to these superior properties, it achieves the maximum power density of 203 mW m−2 and an open circuit voltage (OCV) surpassing 700 mV. The crystal violet assay performed post-MFC operation affirms that the nanocomposite membrane effectively inhibits bacterial fouling. This study positions itself as a solution for long-term, high-performance MFC operations, all while significantly increasing power output and reducing biofouling concerns.

High-Performance Macroporous Free-Standing Microbial Fuel Cell Anode Derived from Grape for Efficient Power Generation and Brewery Wastewater Treatment.

Microbial fuel cells (MFCs) have the potential to directly convert the chemical energy in organic matter into electrical energy, making them a promising technology for achieving sustainable energy production alongside wastewater treatment. However, the low extracellular electron transfer (EET) rates and limited bacteria loading capacity of MFCs anode materials present challenges in achieving high power output. In this study, three-dimensionally heteroatom-doped carbonized grape (CG) monoliths with a macroporous structure were successfully fabricated using a facile and low-cost route and employed as independent anodes in MFCs for treating brewery wastewater. The CG obtained at 900 °C (CG-900) exhibited excellent biocompatibility. When integrated into MFCs, these units initiated electricity generation a mere 1.8 days after inoculation and swiftly reached a peak output voltage of 658 mV, demonstrating an exceptional areal power density of 3.71 W m-2. The porous structure of the CG-900 anode facilitated efficient ion transport and microbial community succession, ensuring sustained operational excellence. Remarkably, even when nutrition was interrupted for 30 days, the voltage swiftly returned to its original level. Moreover, the CG-900 anode exhibited a superior capacity for accommodating electricigens, boasting a notably higher abundance of Geobacter spp. (87.1%) compared to carbon cloth (CC, 63.0%). Most notably, when treating brewery wastewater, the CG-900 anode achieved a maximum power density of 3.52 W m-2, accompanied by remarkable treatment efficiency, with a COD removal rate of 85.5%. This study provides a facile and low-cost synthesis technique for fabricating high-performance MFC anodes for use in microbial energy harvesting.

Fabrication of a Molybdenum Dioxide/Multi-Walled Carbon Nanotubes Nanocomposite as an Anodic Modification Material for High-Performance Microbial Fuel Cells.

A nanocomposite of multi-walled carbon nanotubes (MWCNTs) decorated with molybdenum dioxide (MoO2) nanoparticles is fabricated through the reduction of phosphomolybdic acid hydrate on functionalized MWCNTs in a hydrogen-argon (10%) atmosphere in a tube furnace. The MoO2/MWCNTs composite is proposed as an anodic modification material for microbial fuel cells (MFCs). MWCNTs have outstanding physical and chemical peculiarities, with functionalized MWCNTs having substantially large electroactive areas. In addition, combined with the exceptional properties of MoO2 nanoparticles, the synergistic advantages of functionalized MWCNTs and MoO2 nanoparticles give a MoO2/MWCNTs anode a large electroactive area, excellent electronic conductivity, enhanced extracellular electron transfer capacity, and improved nutrient transfer capability. Finally, the power harvesting of an MFC with the MoO2/MWCNTs anode is improved, with the MFC showing long-term repeatability of voltage and current density outputs. This exploratory research advances the fundamental application of anodic modification to MFCs, simultaneously providing valuable guidance for the use of carbon-based transition metal oxide nanomaterials in high-performance MFCs.

Asymmetric reactors as an innovative approach for optimum microbial fuel cells performance

Microbial fuel cells (MFCs) exhibit asymmetric overpotentials and redox potentials/rates at the cathode and anode. However, the impact of this asymmetric on power density and anode microbial community remains poorly understood. In this study, asymmetric reactors were designed for H-type MFCs to investigate this configuration. Contrary to the initial expectation of increased MFC power output with larger cathode volumes, it was unexpectedly found that the small-cathode reactor outperformed the large-cathode reactor, achieving a 61 % increase in maximum power density. Electrochemical characterization revealed a slightly lower charge transfer resistance (29.34 Ω) in the small-cathode reactor with carbon-felt anode biofilm in PBS. Moreover, 16S rRNA sequence analysis showed that the small-cathode reactor harbored a higher proportion of anaerobic bacteria (83 %), lower species diversity, and a higher abundance of exoelectrogens. Additionally, higher abundances of key gene modules (top eight), such as quinone oxidoreductase and citrate cycle, were observed in the small-cathode reactor. The anode biofilms in both reactors also synthesized some vitamins, such as menaquinone and thiamine. Furthermore, compared to the large-cathode reactor, each set of the small-cathode reactor saved ¥ 20, 23 g of borosilicate, and 55 mL of cathode electrolytes. This study sheds light on the interplay between reactor conformation and performance, contributing to the development of low-cost, high-performance MFCs for real field conditions.

Hierarchical modulation of extracellular electron transfer processes in microbial fuel cell anodes for enhanced power output through improved Geobacter adhesion

Although microbial fuel cell (MFC) technology is nearing practical realization, the challenge of attaining higher power output continues to impede its widespread implementation. In this study, we successfully developed free-standing three-dimensional high-performance anode materials for MFCs using a straightforward "one-step" process based on garlic. The resulting anode not only promotes the accumulation of biomass and the enrichment of exoelectrogen Geobacter but also facilitates interfacial extracellular electron transfer. This led to rapid start-up within just three days, a robust power density of 12.37 W/m3, and an impressive 24.04 % coulombic efficiency in mixed-culture MFC reactors. Our investigation into the underlying mechanisms of exocellular electron transfer revealed improvements in both direct electron transfer and mediated electron transfer processes. Notably, the fabrication of carbonized garlic MFC anodes proves to be technically competitive and economically relevant. It not only paves the way for the development of high-performance MFCs but also provides valuable insights for the rational design of materials related to microbial electrochemical technologies.

Effect of hydrofluoric acid-modified Co3O4/Y-type molecular sieves on MFC performance

Microbial fuel cell (MFC) is a green technology that facilitates resource utilization of wastewater by generating electricity while degrading organic and ammonia nitrogen pollutants. The anode plays a crucial role in the MFC performance, demanding excellent electrochemical performance and high stability. In this paper, a new high-performance anode of Co3O4 composite Y molecular sieve (Co3O4/Y) was prepared, and the effect of the Co3O4 ratio and hydrofluoric acid (HF) modification on the Co3O4/Y performance was also investigated. The results showed that the Co3O4/Y, synthesized through the hydrothermal method with 30 wt% loading of Co3O4 followed by 10 % HF treatment, demonstrated superior electrochemical performance, which had the highest redox peak current density, the largest current response area, and the maximum exchange current density of 0.038 mA/cm2. Four anode catalysts of MFC, namely, blank carbon cloth (CC), Co3O4-CC, Co3O4/Y-CC, and H-Co3O4/Y-CC were prepared, and four groups of MFCs were constructed for the treatment of mixed wastewater consisting of the aged landfill leachate and shale gas fracturing wastewater. Notably, the H-Co3O4/Y-CC group showed the best performance in power generation, achieving a maximum stabilized output voltage (448 mV), a maximum power density (1179 mW/m2), and a minimum apparent internal resistance (466 Ω). Additionally, the removal rate of ammonia nitrogen exceeded 40 % in the mixed wastewater of the 4 groups of MFCs. This study provided a viable strategy for fabricating high-performance MFC anode materials and offered insights into the simultaneous disposal of domestic and industrial wastewater in MFCs.

Carbonaceous Anodes and Compatible Exoelectrogens in High-Performance Microbial Fuel Cells: A Review

Carbonaceous Anodes and Compatible Exoelectrogens in High-Performance Microbial Fuel Cells: A Review

Improving EET kinetics and energy conversion efficiency of 3D hydrophilic composite hydrogel through 2D direction biofilm growth

The limited power output of microbial fuel cells (MFCs) has impeded their widespread adoption application. Thoughtful selection of a suitable anode material not only enhances extracellular electron transfer (EET) efficiency but also stimulates microbial adhesion and proliferation. Herein, a three-dimensional conductive polymer hydrogel MXene/(polypyrrole)-(polyacrylamide) (MPP) is proposed, which can enhance the power generation performance of the bioanode by promoting the enrichment of microorganisms in the two-dimensional direction. The integration of hydrogel molecular chains within the layers of MXene effectively inhibits the self-aggregation of MXene layers, thereby facilitating the formation of ion transport channels for expedited charge storage. As a result, the maximum power density increases from 3.12 W/m3 (CF) to 6.71 W/m3 (MPP-25), the protein content of MPP-25 bioanode (59.66 ± 2.39 mg/cm2) is 3.34 times higher than that of CF (17.85 ± 1.53 mg/cm2), and the exchange current density value increases from 0.06 mA/cm2 (CF) to 0.26 mA/cm2. Conductive hydrogels prepared by MXene as a modifier are a promising bioelectrocatalyst for high-performance MFCs.

2D covalent organic framework/reduced graphene oxide hybrid hydrogel for simultaneous power generation and organic contamination degradation in microbial fuel cell

Microbial fuel cells (MFCs) are promising devices that convert chemical energy into electrical energy via extracellular electron transfer between bacteria and electrodes. However, inefficient extracellular electron transfers and bacteria/electrode interactions often limit their performance. Herein, we demonstrate a hybrid hydrogel assembled by a 2D covalent organic framework (COF) and reduced graphene oxide (rGO) nanosheets as anode materials for MFCs. The 2D COF nanosheets effectively prevent the stacking of rGO nanosheets, resulting in the hybrid hydrogel with a high specific surface area (313.2 m2/g), abundant mesopores and macropores, and high electrical conductivity (492 S/m). The COF material also brings many quinone groups as redox mediators to facilitate electron transfer between bacteria and electrodes. The COF/rGO hybrid hydrogel enhances the growth of Shewanella decolorationis S12 cells, even under the influence of different organic dyes. Dense biofilms are formed on the hybrid hydrogel's surface and inside its macropores, further improving extracellular electron transfers. Assembled MFCs using COF/rGO anodes deliver a maximum power density of 905.1 mW/m2 and can operate for 600 h. They also enable simultaneous power generation and fast organic contamination degradation in electrolytes. This work shows the potential of using 2D nanoarchitectures to promote high-performance MFCs.

Bimetallic ZIF-derived heteroatomic-doped bioanode catalysts for enhanced power production in microbial fuel cells

Binary composite nanoparticles (NPs) are considered anode materials with development potential. Herein, we synthesized two composite NPs, namely Mn-Co3O4/NPs and Mn-Co9S8/NPs, by codoping O, S and C based on bimetallic zeolitic imidazolate framework (Co-Mn-ZIF) precursors. The modified carbon felt (CF) Mn-Co3O4/NPs@CF and Mn-Co9S8/NPs@CF integrated into the microbial fuel cells (MFCs) exhibited the highest volume power densities of 4.58 ± 0.11 and 5.12 ± 0.15 W m−3, respectively, which were higher than that of the precursor anode Co-Mn-ZIF (2.70 ± 0.07 W m−3). In addition, microbial community structure analysis showed that the Mn-Co3O4/NPs@CF and Mn-Co9S8/NPs@CF bioanodes were substantially enriched with electricity-producing bacteria such as Geoalkalibacter, Thermovirga, and Desulfuromonas. The synergistic effect of the binary metal composites along with their oxides and sulfides, facilitated the extracellular electron transfer and biofilm formation. These results demonstrate the advantageous properties of heteroatom-doped binary metal NPs, including high electrical conductivity and good biocompatibility. These NPs serve as excellent anode materials for fabricating high-performance MFCs.

Fe/N Codoped Paper Carbon Fiber Foam Promoted Extracellular Electron Transfer for a High-Performance Microbial Fuel Cell

Fe/N Codoped Paper Carbon Fiber Foam Promoted Extracellular Electron Transfer for a High-Performance Microbial Fuel Cell

High-performance anode electrocatalyst of MnCo2S4-Co4S3/ bamboo charcoal for stimulating power generation in microbial fuel cell

ABSTRACT Microbial fuel cell (MFC) is a promising technology for recovering energy in wastewater through bacterial metabolism. However, it always suffers from low power density and electron transfer efficiency, restricting the application. This study fabricated the MnCo2S4-Co4S3/bamboo charcoal (MCS-CS/BC) through an easy one-step hydrothermal method, and the material was applied to carbon felt (CF) to form high-performance MFC anode. MCS-CS/BC-CF anode exhibited lower Rct (10.1 Ω) than BC-CF (17.24 Ω) and CF anode (116.1 Ω), exhibiting higher electrochemical activity. MCS-CS/BC-CF anode promoted the electron transfer rate and resulted in enhanced power density, which was 9.27 times higher (980 mW m-2) than the bare CF (105.7 mW m-2). MCS-CS/BC-CF anode showed the best biocompatibility which attracted distinctly larger biomass (146.27 mg/μL) than CF (20 mg/μL) and BC-CF anode (20.1 mg/μL). The typical exoelectrogens (Geobacter and etc.) took dramatically higher proportion on MCS-CS/BC-CF anode (59.78 %) than CF (2.99 %) and BC-CF anode (26.67 %). In addition, MCS-CS/BC stimulated the synergistic effect between exoelectrogens and fermentative bacteria, greatly favoring the extracellular electron transfer rate between bacteria and the anode and the power output. This study presented an efficient way of high-performance anode electrocatalyst fabrication for stimulating MFC power generation, giving suggestions for high-efficient energy recovery from wastewater.

Boosting bioelectricity generation using three-dimensional nitrogen-doped macroporous carbons as freestanding anode

Microbial fuel cells (MFCs) have been shown as a promising technology for sustainable energy production and wastewater treatment. However, the still relatively insignificant power generation and high costs of MFCs limit its large-scale application. Herein, we report a facile and low-cost route to construct nitrogen-doped 3D macroporous carbon (NPVP-RFC) via pyrolysis of self-assembled structure of cross-linked resorcinol–formaldehyde resin (RF), polyvinyl pyrrolidone (PVP) and dicyandiamide (DCDA). The as-prepared NPVP-RFC material provides a large specific surface area for high-density loading of bacteria. Moreover, the incorporation of active N species into carbon frameworks offers a hydrophilic surface with good electrolyte wettability and increased conductivity for promoting biofilm adhesion and enhancing extracellular electron transfer (EET) process, thus enabling a high-power output. Thus, the NPVP-RFC MFCs achieve fast start-up time of 2.9 days and maximum volumetric power density of 9.23 W/m3 at 21.48 A/m3. Notably, the NPVP-RFC MFCs show good and stable performance for beer brewery wastewater treatment, achieving a maximum volumetric power density of 6.38 W/m3, chemical oxygen demand (COD) removal efficiency of 84.83%, and a columbic efficiency of 35.57%. This work provides a facile and low-cost synthesis technique for fabricating high-performance MFC anodes for use in microbial energy harvesting.

Regulating the Electronic Structure of Cu-Nx Active Sites for Efficient and Durable Oxygen Reduction Catalysis to Improve Microbial Fuel Cell Performance.

The efficient and durable oxygen reduction reaction (ORR) catalyst is of great significance to boost power generation and pollutant degradation in microbial fuel cells (MFCs). Although transition metal-nitrogen-codoped carbon materials are an important class of ORR catalysts, copper-nitrogen-codoped carbon is not considered a suitable MFC cathode catalyst due to the insufficient performance and especially instability. Herein, we report a three-dimensional (3D) hierarchical porous copper, nitrogen, and boron codoped carbon (3DHP Cu-N/B-C) catalyst synthesized by the dual template method. The introduced B atom as an electron donor increases the electron density around the Cu-Nx active site, which significantly promotes the efficiency of the ORR process and stabilizes the active site by preventing demetallization. Thus, the 3DHP Cu-N/B-C catalyst exhibited excellent ORR performance with the half-wave potential of 0.83 V (vs reversible hydrogen electrode (RHE)) in a 0.1 M KOH electrolyte and 0.68 V (vs RHE) in a 50 mM PBS electrolyte. Meanwhile, 3DHP Cu-N/B-C had satisfactory stability with 94.16% current retention after 24 h of chronoamperometry test, which is better than that of 20% Pt/C. The MFCs using 3DHP Cu-N/B-C not only showed a maximum power density of up to 760.14 ± 19.03 mW m-2 but also operating durability of more than 50 days. Moreover, the 16S rDNA sequencing results presented that the 3DHP Cu-N/B-C catalyst had a positive effect on the microbial community of the MFC with more anaerobic electroactive bacteria in the anode biofilm and fewer aerobic bacteria in the cathode biofilm. This study provides a new approach for the development of Cu-based ORR electrocatalysts as well as guidance for the rational design of high-performance MFCs.

Polyaniline@N-doped macroporous carbon foam as self-supporting anodes for microbial fuel cells

The inefficient extracellular electron transfer (EET) is detrimental to power generation and waste degradation in microbial fuel cells (MFCs). Herein, we report a self-supporting anode for MFCs prepared by graphitization of steamed bread slices followed by in-situ polymerization to fabricate polyaniline@N-doped macroporous carbon foam (PANI@NMCF). The natural nitrogen-containing wheat flour was fermented and carbonized to form NMCF with a high specific surface area of 818.1 m2 g−1. After the NMCF surface modified by PANI, the enhanced hydrophilicity and conductivity of the PANI@NMCF anode would facilitate microbial adhesion, biofilm formation, and electron transfer. The surface improvements enhance the EET process for high-performance MFCs, including a short startup time of 21.7 h, high maximum output power density of 1160 ± 17 mW m−2, and decolourisation efficiency of 88.6 ± 1.2% for 36 h. The chemical oxygen demand removal efficiency was about 84.6 ± 1.1% at end of the operating cycles. This work provides a good foundation for our future development of carbon-based electrode materials for energy conversion and storage devices.

Biomass-Derived Carbon Anode for High-Performance Microbial Fuel Cells

Although microbial fuel cells (MFCs) have been developed over the past decade, they still have a low power production bottleneck for practical engineering due to the ineffective interfacial bioelectrochemical reaction between exoelectrogens and anode surfaces using traditional carbonaceous materials. Constructing anodes from biomass is an effective strategy to tackle the current challenges and improve the efficiency of MFCs. The advantage features of these materials come from the well-decorated aspect with an enriched functional group, the turbostratic nature, and porous structure, which is important to promote the electrocatalytic behavior of anodes in MFCs. In this review article, the three designs of biomass-derived carbon anodes based on their final products (i.e., biomass-derived nanocomposite carbons for anode surface modification, biomass-derived free-standing three-dimensional carbon anodes, and biomass-derived carbons for hybrid structured anodes) are highlighted. Next, the most frequently obtained carbon anode morphologies, characterizations, and the carbonization processes of biomass-derived MFC anodes were systematically reviewed. To conclude, the drawbacks and prospects for biomass-derived carbon anodes are suggested.

Electrospinning iron-doped carbon fiber to simultaneously boost both mediating and direct biocatalysis for high-performance microbial fuel cell

The sluggish extracellular electron transfer between the microorganisms and the electrode impedes the broad industrialization of microbial fuel cells (MFCs). Previous works have reported anodes made from iron compounds can improve the output power of MFCs but the underlying mechanism is still unclear. Here, we innovatively prepare a uniform iron ion-mixed carbon precursor to directly electrospinning iron-doped carbon nanofibers (Fe–CNF). The optimized Fe–CNF anode exhibits greatly improved bio-electrocatalytic performance in MFCs, which delivers 8.67 times higher than that of the undoped CNF one. More importantly, results reveal that Fe-doping forms Fe3C in anode, which greatly promotes the adsorption of the mediator flavins for faster mediation electron transfer between substrate and cells, while directly contacting the proteins of cell membrane leads strong direct electron transfer, thereby simultaneously boost both mediation and direct electrochemistry processes. A facile approach to synthesis of high-performance MFCs anode materials for simultaneously boost both mediation and direct electron transfer rate while providing scientific insights in designs of efficient bioelectrochemical systems is furnished by this work.

Thermally Expanded Graphite Incorporated with PEDOT:PSS Based Anode for Microbial Fuel Cells with High Bioelectricity Production

Modification of anodes with highly biocompatible materials could enhance bacterial adhesion, growth, and improve the rate of electron-transfer ability in microbial fuel cells (MFCs). As such, there has been increasing interest in the development of innovative anode materials to prepare high-performance MFCs. We report the synthesis of poly(3,4-ethylene dioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) doped with thermally expanded graphite (TEG) composite coated carbon felt (CF) as anode for MFCs. For this purpose, as-synthesized PEDOT:PSS/TEG composite was characterized using high-resolution scanning electron microscopy (HR-SEM), Raman and Fourier transform infrared (FT-IR) spectroscopies which indicated successful incorporation of TEG within PEDOT:PSS film. Furthermore, the electrochemical activity of the PEDOT:PSS/TEG coated CF was employed as the anode in the MFCs with sewage water as an anolyte. PEDOT:PSS/TEG@CF anode exhibited higher ion-transfer ability, superior bio-electrochemical conductivity, and excellent capacitance. Using the PEDOT:PSS/TEG@CF anode, we have constructed MFCs which exhibited good power (68.7 mW m−2) and current (969.3 mA m−2) densities compared to the unmodified CF based anode. The reliability of the MFCs performance was also investigated by testing three independently prepared MFCs with PEDOT:PSS/TEG@CF anodes which all showed a constant voltage (∼540 mV) due to the higher stability and biocompatibility of PEDOT:PSS/TEG@CF.

High-performance anode material based on S and N co-doped graphene/iron carbide nanocomposite for microbial fuel cells

The power generation performance of microbial fuel cells (MFCs) is greatly influenced by the anode material. Here, iron carbide nanoparticles doped with nitrogen and sulfur are prepared by a simple one-step pyrolysis method and used as the anode of a medialess MFCs. The charge transfer resistance (R ct ) after biofilm formation is 12.36 Ω, while the R ct of the CC anode is 1526 Ω. Most importantly, this anode not only facilitates bacterial adhesion but also effectively promotes the transfer of extracellular electrons. Therefore, this anode has a fast start-up time of 2.9 days, a high voltage value of 636.9 mV, and an impressive power density (PD) of 3.86 W m −2 . The excellent performance of the S,N-GR/Fe 3 C/CC anode can be attributed to its outstanding biocompatibility and electrical conductivity and reveals great potential to be used in practical applications of high-performance MFCs. • Iron carbide doped with S and N can improve the performance of MFCs. • The MFCs with S,N-GR/Fe 3 C/CC anode own the peak power density of 3.86 W m −2 . • The charge transfer resistance is reduced by 123.5 times. • S,N-GR/Fe 3 C/CC anode has excellent biocompatibility.