Power generation and organics removal from wastewater using activated carbon nanofiber (ACNF) microbial fuel cells (MFCs)

Carbon-based materials are the most commonly used electrode material for anodes in microbial fuel cell (MFC), but are often limited by their surface areas available for biofilm growth and subsequent electron transfer process. This study investigated the use of activated carbon nanofibers (ACNF) as the anode material to enhance bacterial biofilm growth, and improve MFC performance. Qualitative and quantitative biofilm adhesion analysis indicated that ACNF exhibited better performance over the other commonly used carbon anodes (granular activated carbon (GAC), carbon cloth (CC)). Batch-scale MFC tests showed that MFCs with ACNF and GAC as anodes achieved power densities of 3.50 ± 0.46 W/m³ and 3.09 ± 0.33 W/m³ respectively, while MFCs with CC had a lower power density of 1.10 ± 0.21 W/m³ In addition, the MFCs with ACNF achieved higher contaminant removal efficiency (85 ± 4%) than those of GAC (75 ± 5%) and CC (70 ± 2%). This study demonstrated the distinct advantages of ACNF in terms of biofilm growth and electron transport. ACNF has a potential for higher power generation of MFCs to treat wastewaters.     

Nitrogen-doped carbon nanotubes with high activity for oxygen reduction in alkaline media

Nitrogen-doped carbon nanotubes (NCNTs) were prepared using a floating catalyst chemical vapour deposition method. The multiwalled NCNT contains 8.4 at% nitrogen and has a dimension of 100 nm in the diameter and 10-20 nm in the wall thickness. The catalytic activity and durability of the NCNTs towards oxygen reduction reaction (ORR) were evaluated by cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) techniques in KOH solution. In addition, the effects of KOH concentration on several ORR performance indicators of the NCNT catalyst, such as the number of electrons transferred, the diffusion-limiting current density, the onset and half-wave potentials, were also examined in electrolytes of various KOH concentrations, ranging from 0.1 to 12 M. Experimental results show that NCNTs exhibited comparable activity for ORR in alkaline electrolyte as compared with commercially available Pt/C catalyst, and much higher activity than commercial Ag/C catalysts. In addition, the NCNTs showed good stability from the potential cycling test, and the concentration of KOH had significant impact on the ORR performance indicators of the NCNT catalysts.     

FeNx nanoparticles embedded in three-dimensional N-doped carbon nanofibers as efficient oxygen reduction reaction electrocatalyst for microbial fuel cells in alkaline and neutral media

Herein, an approach is reported for the fabrication of 3D carbon nanofibers (CNFs) wrapped by carbon nanotubes (CNT) with graphitic carbon-encased FeNx nanoparticles originated from metal–organic frameworks (MOFs). It is found that Fe-FeNx@N-CNT/CNFs exhibits outstanding catalytic activity towards ORR, whose half-wave potential are 0.89 V and 0.87 V in alkaline and neutral environments, respectively, much higher than MOF-based catalysts reported so far and commercial Pt/C. When the obtained cathode catalysts are loaded in MFCs for power generation test, the experimental consequences show that the Fe-FeNx@N-CNT/CNFs cathode exhibits a supernal power density of 742.26 mW·m^?2 and output current density of 3241 mA·m^?2 which are comparable to Pt/C. The splendid ORR catalytic performance is mainly attributable to the three-dimensional structure of carbon nanofibers and the active sites of Fe-Nx. These result in a higher graphitization degree beneficial for electronic mobility, high specific surface area, benign mesoporous nanostructure and excellent mass transfer capability. The strategy provides a new scheme to devise and research Fe-Nx electrocatalysts with MOF-based for the conversion of clean and environment-friendly energy.     

The synthesis of Fe/N–C@CNFs and its electrochemical performance toward oxygen reduction reaction

The one-dimensional filamentous carbon nanofibers hold great promise to substitute noble catalysts ascribing to the excellent physicochemical properties, environmentally friendly, easy to prepare, etc. Synthesizing non-noble catalysts with outstanding electro-catalytic activity for oxygen reduction reaction and excellent durability and application in the field of commercialization still exist lots of challenges. Herein, we report a facile synthesis of carbon nanofibers coated with iron doping nitrogen-carbon (Fe/N–C@CNFs) derived from carbon nanofibers coated with polyaniline (PANI@CNFs) via chemical vapor deposition and heat-treatment, which exhibit an outstanding catalytic activity toward oxygen reduction reaction. In detail, the Fe/N–C@CNFs exhibit onset potential of 0.99 V (vs RHE) and half-wave potential of 0.80 V (vs RHE) in 0.1 M KOH solution, indicating superior electrochemical activity for oxygen reduction reaction (ORR). Meantime, the transferred electron number of oxygen reduction reaction was 3.77, suggesting a nearly 4e⁻ transferring process with little intermediate product (H₂O₂). Moreover, the relative current value of carbon nanofibers coated with nitrogen-carbon film (N–C@CNFs) and Fe/N–C@CNFs maintain 89.6% and 88.2% respectively after 40,000 s, exhibiting good stability and durability. This facile and easy method could provide inspiration for synthesizing carbon nanofibers-based (CNFs-based) oxygen reduction reaction catalysts with excellent catalytic activity and good stability.     

Electrospun iron and nitrogen co-containing porous carbon nanofibers as high-efficiency electrocatalysts for oxygen reduction reaction

One-dimensional carbon nanofibers hold great promise to be potential candidates as high-efficiency electrocatalysts for oxygen reduction reaction (ORR). However, the catalysts in powder form always aggregate when preparing catalyst layer, which significantly hinders the extensive application. Herein, we report the facile synthesis of iron and nitrogen co-containing porous carbon nanofibers derived from PAN nanofibers existing as a flexible film via the electrospinning method, which could avoid aggregation when fabricating catalyst layer of fuel cells. The Fe–N/N–C NFs exhibit onset potential of 0.95 V and the half-wave potential of 0.78 V in 0.1 M KOH solution, suggesting superior electro-catalytic activity for ORR. Meantime, for Fe–N/N–C NFs catalyst, it shows a nearly four electron transferring process and the current density only decreases by 14.2% after 40,000 s. This easy and facile method provides a new idea for synthesis of oxygen reduction reaction with high-activity and good-stability.     

Trace amount of ceria incorporation by atomic layer deposition in Co/CoOx-embedded N-doped carbon for efficient bifunctional oxygen electrocatalysis: Demonstration and quasi-operando observations

As a promising class of alternatives to noble metal-based oxygen electrocatalysts, hybrids of metal/metal oxide (M/MO) and N-doped carbon have been widely explored. To address the often-insufficient catalytic activity of single M/MO-embedded N–C systems, researchers have introduced a second M/MO, usually via wet processes. In this work, we leverage the unique capability of atomic layer deposition (ALD) to enable the introduction of a trace amount of ceria throughout a Co/CoO_x-embedded N-doped carbon nanostructure in a highly uniform and dispersed manner to maximize heterogeneous interfacial areas and thus catalytically active sites. An optimally prepared catalyst achieves an ORR onset potential of 0.95 V (0.1 M KOH) and an OER potential of 1.53 V at 10 mA cm⁻² (1 M KOH) and exhibits excellent cyclic durability. Quasi-operando observations reveal the multifaceted roles of the tiny amount of introduced ceria in facilitating electrocatalytic activity and enhancing durability. The ceria activates reactant adsorbates and transfers the activated intermediates to neighboring CoO_x and electronically couples with Co and N species for enhanced catalytic activity. A high concentration of trivalent Ce state is readily and continuously restored during ORR/OER for an uninterrupted activation of reactants, also contributing to a highly stable reaction.     

Bio-cathode materials evaluation in microbial fuel cells: A comparison of graphite felt,carbon paper and stainless steel mesh materials

The choice of the cathode material is crucial for every bio-cathode microbial fuel cell (MFC) setup. The commonly used biocathode materials, Graphite felt (GF), carbon paper (CP) and stainless steel mesh (SSM) were compared and evaluated in terms of current density, power density, and polarization. The maximum current density and power density of the MFC with GF-biocathode achieved 350 mA m⁻² and 109.5 mW m⁻², which were higher than that of the MFC with CP-biocathode (210 mA m⁻² and 32.7 mW m⁻²) and the MFC with SSM-biocathode (18 mA m⁻² and 3.1 mW m⁻²). The polarization indicated that the biocathode was the limiting factor for the three MFC reactors. Moreover, cyclic voltammetry (CV) showed that the microorganisms on the biocathode played a major role in oxygen reduction reaction (ORR) for GF- and CP-biocathode but SSM-biocathode. Electrochemical impedance spectroscopy suggested that GF biocathode performed better catalytic activity toward ORR than that of CP- and SSM-biocathode, also supported by CV test. Additionally, the MFC with GF-biocathode had the highest Coulombic Efficiency. The results of this study demonstrated GF was the most suitable biocathode for MFCs application among the three types of materials when using anaerobic sludge as inoculums.     

Optimization of process parameters using response surface methodology (RSM) for power generation via electrooxidation of glycerol in T-Shaped air breathing microfluidic fuel cell (MFC)

The present work focuses on the optimization of operating parameters using Box Behnken design (BBD) in RSM to obtain maximum power density from a glycerol based air-breathing T-shaped MFC. The major parameters influencing the experiment for enhancing the cell performance in MFC are glycerol/fuel concentration, anode electrolyte/KOH concentration, anode electrocatalyst loading and cathode electrolyte/KOH concentration. The ambient oxygen is used as the oxidant. The acetylene black carbon (C_AB) supported laboratory synthesized electrocatalyst Pd–Pt (16:4)/C_AB is used as anode electrocatalyst and commercial Pt (40 wt%)/C_HSA as the cathode electrocatalyst. The quadratic model predicts the appropriate operating conditions to achieve highest power density from the laboratory designed T-shaped MFC. The p-value of less than 0.0001 and F-value of greater than 1 i.e., 26.32 indicate that the model is significant. The optimum conditions predicted by the RSM model were glycerol concentration of 1.07 M, anode electrolyte concentration of 1.62 M anode electrocatalyst loading of 1.12 mg/cm² and cathode electrolyte concentration of 0.69 M. The negligible deviation of only 1.07% between actual/experimental power density (2.76 mW/cm²) and predicted power density (2.79 mW/cm²) was recorded. This model reasonably predicts the optimum conditions using Pd–Pt (16:4)/C_AB electrocatalyst to obtain maximum power density from glycerol based MFC.     

Using rhodium as a cathode catalyst for enhancing performance of microbial fuel cell

Rhodium with activated carbon as carbon base layer (Rh/AC) was exploited as an oxygen reduction reaction (ORR) catalyst to explore its applicability in microbial fuel cell (MFC). Four MFCs were fabricated using the Rh/AC catalyst, adopting varying Rh loadings of 0.5, 1.0 and 2.0 mg cm⁻² and without Rh on carbon felt cathode in order to understand the optimum loading of this catalyst to enhance the performance of MFC. The participation of Rh/AC in ORR was confirmed by cyclic voltammetry and electron impedance spectroscopy analysis, which supported the enhanced charge transfer capacity of the cathode modified with the prepared catalysts. Volumetric power density of MFC was found to be improved by 2.6 times when Rh/AC was used as cathode catalyst (9.36 W m⁻³) at a loading of 2.0 mg cm⁻² in comparison to the control MFC (3.65 W m⁻³) without Rh on the cathode. It was thus inferred that the increase in the Rh loading up to 2 mg cm⁻² can improve the performance of MFC significantly.     

Biomass pectin-derived N,S-enriched carbon with hierarchical porous structure as a metal-free catalyst for enhancing bio-electricity generation

Heteroatoms-doped carbon-based materials (with non-precious metals or no metals) with porous structure have already shown high catalytic activities for oxygen reduction reaction (ORR), especially in microbial fuel cells (MFCs). Here, we use pectin extracted from pomelo peels as carbon source to prepare metal-free and sulphur/nitrogen co-doped partially-graphitized carbon (HP-SN-PGCs) by using silica nanospheres as sacrificial templates. Single-chamber MFC (SC-MFC) with HP-SN-PGC-0.5 (0.5 g of silica) cathode has the shortest start-up time (45 h) and lowest charge transfer resistance (19.3 Ω). The maximum power density of HP-SN-PGC-0.5 (1161.34 mW m⁻²) cathode is higher than that of Pt/C (1116.90 mW m⁻²) at the initial cycle. After 75 d operation, power density of HP-SN-PGC-0.5 cathode only declines 4.6%, which is more stable than that of Pt/C (37.69%). HP-SN-PGC-0.5 has a highly porous structure (869.25 m² g⁻¹) by removal of templates and Fe species (as the graphitization catalyst) to facilitate exposure of active sites and diffusion of ORR-related intermediates (OH⁻ and HO₂⁻, etc) to accessible active sites. N and S species provide highly active sites to enhance OH⁻ generation to conduct the 4e⁻ ORR process. Thus, this study presents a viable ORR catalyst with high activity and long-term stability for bio-electricity generation from organic wastewater in SC-MFCs.     

Activation of polymer blend carbon nanofibres by alkaline hydroxides and their hydrogen storage performances

In the present work we study the hydroxide activation (NaOH and KOH) of phenol-formaldehyde resin derived CNFs prepared by a polymer blend technique to prepare highly porous activated carbon nanofibres (ACNFs). Morphology and textural characteristics of these ACNFs were studied and their hydrogen storage capacities at 77 K (at 0.1 MPa and at high pressures up to 4 MPa) were assessed, and compared, with reported capacities of other porous carbon materials.Phenol-formaldehyde resin derived carbon fibres were successfully activated with these two alkaline hydroxides rendering highly microporous ACNFs with reasonable good activation process yields up to 47 wt.% compared to 7 wt.% yields from steam activation for similar surface areas of 1500 m²/g or higher. These nano-sized activated carbons present interesting H₂ storage capacities at 77 K which are comparable, or even higher, to other high quality microporous carbon materials. This observation is due, in part, to their nano-sized diameters allowing to enhance their packing densities to 0.71 g/cm³ and hence their resulting hydrogen storage capacities.     

One-step carbonization of ZIF-8 in Mn-containing ambience to prepare Mn,N co-doped porous carbon as efficient oxygen reduction reaction electrocatalyst

Economical and efficient non-noble metal catalysts should be developed practically, instead of commercial Pt/C for fuel cells. In this paper, manganese, nitrogen co-doped porous carbon (Mn–N–C) was synthesized to catalyze oxygen reduction reaction (ORR) through the one-step carbonization of ZIF-8 in the Mn-containing (MnCl₂) atmosphere. During the carbonization process, MnCl₂ gas was captured with ZIF-8 and then transformed into uniform Mn–N active sites distributed in the porous carbon materials. The Mn–N–C catalyst exhibited plentiful porous structures, large specific surface areas, high graphitization and conductivity, which contributed to the transfer and transport of charge and exposed more active sites. The Mn–N–C catalyst exhibited superior catalytic ability in alkaline and acidic solutions. Half-wave potential of the Mn–N–C could reach 0.88 and 0.73 V in 0.1 M KOH and 0.5 M H₂SO₄, respectively. In addition, the Mn–N–C catalyst showed a prominent stability after the stability test of 18,000 s. Excellent electrochemical performance and endurance make the Mn–N–C expect to be an effective ORR catalyst to build high-performance fuel cells.     

Iron chelates as low-cost and effective electrocatalyst for oxygen reduction reaction in microbial fuel cells

Iron-chelated electrocatalysts for the oxygen reduction reaction (ORR) in a microbial fuel cell (MFC) were prepared from sodium ferric ethylenediamine-N,N′-bis(2-hydroxyphenylacetic acid) (FeE), sodium ferric diethylene triamine pentaacetic acid (FeD) supported on carbon Vulcan XC-72R carbon black and multi-walled carbon nanotubes (CNTs). Catalyst morphology was investigated by TEM; and the total surfaces areas as well as the pore volumes of catalysts were examined by nitrogen physisorption characterization. The catalytic activity of the iron based catalysts towards ORR was studied by cyclic voltammetry, showing the higher electrochemical activity of FeE in comparison with FeD and the superior performance of catalysts supported on CNT rather than on Vulcan XC-72R carbon black. FeE/CNT was used as cathodic catalyst in a microbial fuel cell (MFC) using domestic wastewater as fuel. The maximum current density and power density recorded are 110 (mA m⁻²) and 127 ± 0.9 (mW m⁻²), respectively. These values are comparable with those obtained using platinum on carbon Vulcan (0.13 mA m⁻² and 226 ± 0.2 mW m⁻²), demonstrating that these catalysts can be used as substitutes for commercial Pt/C.     

One-step complexation and self-template strategy to synthesis bimetal Fe/Mn–N doped interconnected hierarchical porous carbon for enhancing catalytic oxygen reduction reaction

Currently, it is still a challenge in the research of fuel cells and zinc-air battery to use a facile method to prepare efficient and low-cost cathode oxygen reduction reaction (ORR) catalysts to replace the precious metal Pt-based catalyst. Herein, we reported a one-step complexation of ethylenediaminetetraacetic acid disodium (EDTA-2Na) with transition metals (M) and self-template strategy to synthesis an bimetal Fe/Mn–N doped interconnected hierarchical porous carbon material for efficient catalytic ORR. In addition to being a carbon source, EDTA-2Na can very well fix M atoms in the carbon precursory by complexation, which is beneficial for M atoms to be anchored in the carbon structure by N atoms, thus forming the M-N_x catalytic active site. During pyrolysis, meanwhile, Na ions in EDTA-2Na not only acted as self-template to form the interconnected porous structure but also separated M atoms from each other, which also suppressed the aggregation and growth of the M atoms. More importantly, the prepared bimetal Fe/Mn–N doped interconnected hierarchical porous carbon (Fe/Mn–NIHPC) showed better catalytic ORR performance (half-wave potentials of 0.86 V vs. RHE) than those prepared by single metal elements (Fe or Mn). And Fe/Mn–NIHPC also exhibited better catalytic ORR activity and durability, compared with the Pt/C (20 wt%) catalyst.     

A dual photoelectrode-based double-chambered microbial fuel cell applied for simultaneous COD and Cr (VI) reduction in wastewater

Cerium oxide (CeO₂) and cuprous oxide (Cu₂O) were used for the first time as photoanode and photocathode, respectively, in a microbial fuel cell (MFC) for simultaneous reduction of chemical oxygen demand (COD) and Cr(VI) in wastewater. The photoelectrodes, viz. Photoanode and photocathode were separately prepared by impregnating activated carbon fiber (ACF) with the respective metal oxide nanoparticles, followed by growing carbon nanofibers (CNFs) on the ACF substrate using catalytic chemical vapor deposition. The MFC, operated under visible light irradiation, showed reduction in COD and Cr(VI) by approximately 94 and 97%, respectively. The MFC also generated high bioelectricity with a current density of ~6918 mA/m² and a power density of ~1107 mW/m². The enhanced performance of the MFC developed in this study was attributed to the combined effects of the metal oxide photocatalysts, the graphitic CNFs, and the microporous ACF substrate. The MFC based on the inexpensive transition metal oxides-based photoelectrodes developed in this study has a potential to be used at a large scale for treating the industrial aqueous effluents co-contaminated with organics and toxic Cr(VI).     

Enhanced electrochemical performance in microbial fuel cell with carbon nanotube/NiCoAl-layered double hydroxide nanosheets as air-cathode

The ternary component NiCoAl-layered double hydroxide (NiCoAl-LDH) and carbon nanotube (CNT) nano-composite (CNT/NiCoAl-LDH) were successfully prepared by a simple hydrothermal method. The NiCoAl-LDH nanosheets were effectively and uniformly grown on CNTs, forming a cross-linked conductive network structure, and stainless steel (SS) mesh was used as the base to load CNT/NiCoAl-LDH for microbial fuel cell (MFC) cathode. X-ray diffraction (XRD) results presented that the CNT/NiCoAl-LDH hybrid exhibited the (003), (006), (012), (015), (018), (110) and (113) crystal planes of hydrotalcite reflection. The surface functional groups C-O, C=O, C-H, C-N and M-O of the hybrid were confirmed. The cross-linked network structure of the hybrid was observed and the content and proportion of each element of the hybrid were found. CNT/NiCoAl-LDH showed excellent catalytic oxygen reduction reaction (ORR) ability by cyclic voltammetry (CV) and linear voltammetry (LSV) due to its abundant electrochemical active sites and excellent conductivity. The maximum output voltage of CNT/NiCoAl-LDH catalyst as MFC cathode was 450 mV, the maximum power density was 433.5 ± 14.8 mW/m², and the maximum voltage stabilization time was 7–8 d. The results indicated that the CNT/NiCoAl-LDH hybrid was full potential as a high-performance, low-cost MFC cathode catalyst in future.     

An efficient Co-N/C electrocatalyst for oxygen reduction facilely prepared by tuning cobalt species content

Transition metal and nitrogen co-doped carbon catalysts for the oxygen reduction reaction (ORR) have emerged as promising candidates to replace the expensive platinum catalysts but still remain a great challenge. Herein, a novel and efficient nitrogen-doped carbon material with metal cobalt co-dopant (Co–N/C) has been prepared by pyrolyzing porphyrin-based covalent organic polymer where Co is anchored. The optimized 10%-Co-N/C catalyst through facilely and efficiently tuning the cobalt content is carefully characterized by XRD, Raman, XPS, SEM and TEM for composition and microstructure analysis. This catalyst with only 0.56% Co exhibits an excellent ORR catalytic activity with a positive half-wave potential of 0.816 V (vs. RHE) in 0.1 M KOH solution, which is comparable to that of commercial Pt/C (20 wt%). Notably, the 10%-Co-N/C catalyst displays better electrochemical stability with only a loss of 5.1% of its initial current density in chronoamperometric measurement and also gives rise to stronger methanol tolerance than Pt/C. The good ORR catalytic behaviour for this catalyst may be attributed to the dispersion of the Co-N_X active sites via adjusting the contents of cobalt species in porous organic framework.     

Efficient oxygen reduction in a microbial fuel cell based on carbide-derived carbon electrode synthesized using thiourea as the single source of electroconductive heteroatoms and graphitic carbon

A novel one step method was developed to dope nitrogen (N), sulfur (S) and carbon (C) in the Fe nanoparticles-dispersed carbon nanofibers (CNFs) grown over carbide-derived carbon (CDC), using thiourea as the single source of N, S and C. The synthesized N/S-Fe-CNF/CDC electrode was successfully used in a microbial fuel cell (MFC). When tested as the oxygen reduction reaction (ORR) catalyst, the electrode achieved a high current density (2.261 ± 0.002 mA/cm²), high OCP (0.611 ± 0.005 V), high stability upto 400 cycles, response time of ∼11 s, electron transfer number in the range 3.73–4.03, and Tafel slopes of −0.0627 and −0.183 V/dec at low and high current densities, respectively. A first order kinetics and a 4e⁻ pathway were deduced from the ORR analysis. Notably, the fabricated MFC based on the prepared electrode produced a high current density of 1.3887 ± 0.002 mA/cm², high OCP of 0.626 ± 0.005 V and maximum power density of 0.238 ± 0.002 mW/cm², attributed to the synergistic effects of heteroatoms, Fe nanoparticles, and CNFs.     

Zr enhanced Fe,N, S co-doped carbon-based catalyst for high-efficiency oxygen reduction reaction

Fe-N_x catalysts have received widespread attention in recent years due to their excellent catalytic performance, hoping to replace platinum for oxygen reduction reactions (ORR). In recent years, more studies have shown that when the catalyst contains two or more metals doped, its catalytic performance will be improved. Herein, using the high temperature pyrolysis method, through the incorporation of the second phase metal (Zr), melamine as the nitrogen source, and thiourea as the sulfur source, a high-activity carbon-based catalyst doped with Fe and Zr bimetals was synthesized. Originating from the strong interaction between Fe species and ZrO₂ clusters and the promotion of O₂ adsorption by ZrO₂ nanoparticles supported on nitrogen-doped carbon, this catalyst has a better ORR electrocatalytic performance than 46% TKK commercial platinum carbon in 0.1 M KOH, exhibiting an onset potential of 1.047 V vs RHE, a half-wave potential of 0.909 V vs RHE. It provides a new idea for the preparation of high-performance bimetallic-doped carbon-based electrocatalysts.     

Which determines power generation of microbial fuel cell based on carbon anode,surface morphology or oxygen-containing group?

To clarify the role of carbon surface nature in the power generation of microbial fuel cell (MFC) based on carbon anode, three carbon felt samples, obtained by simple water cleaning (CCF), heating (HCF) and oxidation with ammonium persulfate (ACF), were characterized with SEM, BET, FTIR, cyclic voltammetry and acid titration, and their performances as anode of MFC were investigated with polarization curve measurement, chronoamperometry and chronopotentiometry. It is found that the power output of MFC depends on the morphology rather than the oxygen-containing group concentration of the carbon felt surface. CCF, HCF and ACF have their surface oxygen-containing groups of 1.52, 0.8 and 0.45 mM m⁻² and specific surface areas of 0.33, 0.65 and 1.19 m² g⁻¹, but yield their maximal power densities of 606, 858 and 990 mW m⁻², respectively. This study suggests that intensive attention should be paid to the design of surface morphology in order to improve power generation of MFC.