Nitrogen and phosphorus co-doped carbon modified activated carbon as an efficient oxygen reduction catalyst for microbial fuel cells

Article abstract of DOI:10.1039/c7ra12907f

Activated carbon (AC) is an environmentally sustainable oxygen reduction reaction (ORR) catalyst and widely used in MFCs due to its intrinsic high specific surface area and mesoporous characteristics, but it shows relatively high ORR over-potential thus low electrocatalytic activity. In this study, a method of doped carbon modification was employed to decrease the over-potential and improve the ORR electrocatalytic activity of the AC catalyst. Nitrogen and phosphorus co-doped carbon modified AC (NPC@AC) was prepared by coating phytic acid doped polyaniline onto AC through in situ oxidative polymerization and subsequent high-temperature pyrolysis. The as-prepared NPC@AC possessed a large surface area of ～649.3 m² g^-1 inherited from AC and a low ORR over-potential with a highly positive onset potential of +0.22 V vs. Ag/AgCl from NPC, thus showing an enhanced ORR electrocatalytic activity in neutral solution compared to the pristine AC, and even better than the pure NPC. The air-cathode MFC using the NPC@AC catalyst generated a much higher open circuit voltage of 0.753 V and two times higher power density of 1223 mW m^-2 than that using the pristine AC catalyst of about 0.432 V and 595 mW m^-2, respectively.

Full text of DOI:10.1039/c7ra12907f

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PAPER
Nitrogen and phosphorus co-doped carbon
modified activated carbon as an efficient oxygen
reduction catalyst for microbial fuel cells†
Cite this: RSC Adv., 2018, 8, 848
*
Kang Lv, Hua Zhang and Shuiliang Chen
Activated carbon (AC) is an environmentally sustainable oxygen reduction reaction (ORR) catalyst and widely
used in MFCs due to its intrinsic high specific surface area and mesoporous characteristics, but it shows
relatively high ORR over-potential thus low electrocatalytic activity. In this study, a method of doped
carbon modification was employed to decrease the over-potential and improve the ORR electrocatalytic
activity of the AC catalyst. Nitrogen and phosphorus co-doped carbon modified AC (NPC@AC) was
prepared by coating phytic acid doped polyaniline onto AC through in situ oxidative polymerization and
subsequent high-temperature pyrolysis. The as-prepared NPC@AC possessed a large surface area of
ꢀ649.3 m2 gꢁ1 inherited from AC and a low ORR over-potential with a highly positive onset potential of
+0.22 V vs. Ag/AgCl from NPC, thus showing an enhanced ORR electrocatalytic activity in neutral solution
compared to the pristine AC, and even better than the pure NPC. The air-cathode MFC using the NPC@AC
catalyst generated a much higher open circuit voltage of 0.753 V and two times higher power density of
1223 mW mꢁ2 than that using the pristine AC catalyst of about 0.432 V and 595 mW mꢁ2, respectively.
Received 30th November 2017
Accepted 18th December 2017
DOI: 10.1039/c7ra12907f
rsc.li/rsc-advances
noble metal oxides,12–15 nitrogen-doped carbon nanotubes16
and graphene,17 and so on. Although these alternatives have
1. Introduction
been proved to be high efficient ORR catalysts for MFCs, the
disadvantages, such as high manufacturing cost and complex
fabrication procedure, hinder their practical application.
Activated carbon (AC) is a low-cost carbon material with large
surface area (>500 m2 gꢁ1) and has been widely used for
adsorption, purication, catalyst and catalyst carrier.18,19 AC is
also a cost-effective ORR catalyst for the air-cathode of
MFCs.20–24 It has been reported that air-cathode using AC as
ORR catalyst generated relatively higher power densities and
showed better long-term durability than that using Pt/C catalyst.
However, the electrocatalytic activity of the pristine AC toward
ORR is unsatisfactory due to its high ORR over-potential. Direct
doping of nitrogen is an effective strategy to improve the elec-
trocatalytic activity of the AC for ORR.25–28 However, the
improvement on the electrocatalytic activity of the AC is limited
because a relatively low content of nitrogen (typically below 2%)
can be incorporated to the AC. To further increase the content
of N doping in the AC, Fe–N co-doped carbon had been incor-
porated to the AC and led to great increase of electrocatalytic
performance of AC for ORR.29,30
Thanks to the dual-function of electricity generation and waste
removal, microbial fuel cells (MFCs) have been targeted as
a promising technology for the applications of renewable bio-
energy, wastewater treatment, bio-sensing and bioremedia-
tion.1–3 The cathode is a crucial component of an MFC that
determines its cost and performance. Notwithstanding, the
oxygen reduction reaction (ORR) is the most important cathodic
reaction in fuel cell technology (including MFCs) for power
generation due to its high biochemical standard potential
(+0.82 V vs. SHE) and its abundant availability from air. The
most feasible cathode conguration for large-scale application
of MFCs is the air-cathode because its use solves the issue of
limited oxygen solubility in water and makes purging obsolete.
The non-limiting availability of oxygen at air cathodes, ulti-
mately, makes it possible to achieve higher current densities.4–6
Unfortunately, the sluggish ORR kinetics demands the use of
efficient electrocatalysts. Pt-based catalysts are rstly used as
the ORR catalyst in lab-scale MFC reactors.7 However, their high
cost and poor stability hampering their use in practical appli-
cations of MFCs.8,9 Various alternative ORR catalysts to Pt have
been proposed, including transition metal complexes,10,11 non-
It had been reported that introduction of a second hetero-
atom, such as B, S or P, to the N-doped carbon nanomaterials,
was able to modulate the electronic and surface polarities, thus
further increase the ORR catalyst activity of the carbon nano-
material.31–34 At this point, those prior ndings inspire us to
explore a proper method on incorporated co-doped carbon to
the AC to improve its ORR electrocatalytic activity. In this
Department of Chemistry and Chemical Engineering, Jiangxi Normal University,
Nanchang, 330022, China. E-mail: slchenjxnu@jxnu.edu.cn; Fax: +86 791 8120740;
Tel: +86 791 8120536
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c7ra12907f
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study, N and P co-doped carbon was incorporated to the AC reference and counter electrode, respectively. For cyclic vol-
(denoted as NPC@AC) by coating phytic acid doped polyaniline tammetry (CV) test, the catalysts were loaded onto a common
through in situ oxidative polymerization and subsequent high- glass carbon (F ¼ 3 mm) and used as the working electrode.
temperature pyrolysis. The NPC@AC combined the good char- 1 mg catalyst was dispersed in a mixture solution containing
acteristics of high specic surface area of the AC and low ORR 250 mL deionized water and 25 mL of 5 wt% Naon® dispersion
over-potential of the NPC, thus enhanced ORR electrocatalytic under sonication and formed a catalyst ink; then, 5 mL catalyst
activity in neutral solutions comparing to the pure AC and NPC. ink was pipetted onto a mirror-polished glassy carbon electrode
MFC using the NPC@AC catalyst generated two times higher and naturally dried up. For linear scanning voltammetry (LSV)
power density than that using the pristine AC catalyst.
tests, rotating disk electrode (RDE, F ¼ 5 mm) and rotating
ring-disk electrode (RRDE, F ¼ 5 mm) were used. 15 mL catalyst
ink was used for both RDE and RRDE. The LSV tests were
conducted on the bi-potentiostat (Bio-logic, VMP3) equipped
with a speed controller (AFMSRCE, Pine Instrument Co., USA).
The electron transfer numbers (n) of catalysts were calculated
according to the following equation:
2. Experimental
2.1 Preparation of NPC@AC
NPC@AC was prepared by a two-step process including phytic acid
(PA) doped polyaniline coating and subsequent high-temperature
pyrolysis. The coating of PA doped polyaniline onto AC was real-
ized by in situ oxidative polymerization polyaniline in the presence
of PA. In a typical procedure, 0.0625 mol ammonium persulfate
was dissolved in 50 mL deionized water under stirring to prepare
solution A. Solution B was prepared by mixing 50 mmol PA,
250 mmol aniline monomers in 100 mL of deionized water.
Various amount of AC was dispersed in solution B. Aer both
Id
n ¼ 4 ꢃ
Id þ Ir=N
where Id and Ir represent the disk and ring current, respectively. N
refers to the collection efficiency of Pt ring and is taken as 40% in
this study, which determined by the reduction of K3Fe[CN]6.
solutions being cooled down to 4 ꢂC, solution A was poured into B 2.3 MFCs construction and operation
and mixed swily by mechanical stirring, and kept under 4 ꢂC for
Single-chamber cubic air-cathode MFC set-up was used to
8 hours without stirring. Aer washing with deionized water for
three times to remove the excess acid and salts, the resultant PA
doped carbon coated AC composite was dried and subsequently
put into a tube furnace for pyrolysis. The pyrolysis process was
conducted by heating to 950 ꢂC with a temperature ramp of
5 C min in argon and annealing for 2 h at the nal tempera-
ture. Aer naturally cooling to below 200 ꢂC, the NPC@AC
samples with NPC/AC ratio of 0.25, 0.4, 0.7 and 1.7 were obtained.
These samples were denoted as NPC@AC-x, x represents the NPC/
AC ratio. For comparison, the N mono-doped carbon and P mono-
doped carbon modied AC were also prepared, and denoted as
NC@AC and PC@AC, respectively. The NC@AC and PC@AC were
prepared using the same procedures and same amount of reac-
tants as that of the NPC@AC-0.7 sample, but using hydrochloric
acid to replace the phytic acid when preparing NC@AC, and do
not using aniline when preparing PC@AC.
measure the catalytic performance of the AC-based ORR catalysts
in the MFC. The air-cathodes were fabricated by rolling method
according to previous reports,28,35 using polyuortetraethylene
(PTFE) as binder and stainless steel mesh as current collector.
The mass ratio of catalyst/PTFE was controlled to be about 4/1 and
ꢁ1
ꢂ
the loading of catalyst was controlled to be about 20 mg cmꢁ2
.
Graphite ber brushes (Jilin Chemical Fiber Group Co., Ltd.,
China) heat-treated at 450 ꢂC for 30 min were used as anodes. A
resistor with resistance of 1000 U was loaded between the brush
anode and air-cathode. All MFCs were inoculated with effluent
from another MFC, which was initially inoculated with waste-
water from local wastewater treatment plant and operated for
over 6 months. To keep the metabolism of bacteria, each reactor
was fed with a medium containing acetate (1 g Lꢁ1), vitamin
solution (12.5 mL Lꢁ1), trace element solution (12.5 mL Lꢁ1) in
50 mM phosphate buffer solution (PBS: pH 7.0, 10.9233 g Lꢁ1
Na2HPO4$12H2O, 3.042 g Lꢁ1 NaH2PO4$2H2O, 0.31 g Lꢁ1
NH4Cl, 0.13 g Lꢁ1 KCl). The medium was refreshed as soon as
the voltage dropped below 100 mV. The cell voltage was moni-
tored every minute by a date collection system (HIOKI LR8431-
30). Polarization and power density curves were obtained by
varying external circuit resistance with each resistor used for
a full batch cycle. The power density and current density were
normalized to the projected area of the air-cathode (7 cm2).
Each measurement was repeated for at least three times.
2.2 Characterization and electrochemical test
The morphological characterization of the AC catalysts was
conducted by using scanning electron microscope (SEM, Vega3,
TESCAN) and transmission electron microscope (TEM, JEM-
2100, JEOL). X-ray photoelectron spectroscopy (XPS, PHI Quan-
tera SXM™) was introduced to exam the elemental composition
and chemical state of samples. The crystalline structure was
analyzed with powder X-ray diffraction (XRD, X'Pert-PRO) with
a Cu K(alpha) target radiation source (l ¼ 0.154056 nm). The
Raman spectra were recorded on a LabRAM Aramis (Horiba Jobin
Yvon S.A.S) with a 633 nm wavelength laser.
3. Results and discussion
3.1 Electrocatalytic activity of NPC@AC with different NPC/
All electrochemical measurements were conducted at
a three-electrode system with 50 mM phosphate buffer solution
(PBS, pH ¼ 7.0) as electrolyte. Ag/AgCl (25 ꢂC, saturated KCl The NPC@AC samples were fabricated by a two-step process
internal solution) and Pt foil electrode were used as the including in situ oxidative polymerization and high-temperature
AC ratio
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Fig. 1 Cyclic voltammograms of NPC@AC electrocatalysts with different ratio of NPC/AC. (A) Pristine AC, (B) NPC@AC-0.25, (C) NPC@AC-0.4,
(D) NPC@AC-0.7, (E) NPC@AC-1.4, (F) NPC, conducted in N2 (red color) and O2 (black color) saturated neutral 50 mM PBS. The scan rate is
100 mV sꢁ1. The double-head arrows point out the ORR current densities at ꢁ0.5 V and the single-head arrows show the onset potentials.
pyrolysis. Here, aniline and PA were used as the nitrogen and outperforms that of the NC@AC and PC@AC modied by
phosphorus sources, respectively. In order to investigate the mono-doped carbon. Furthermore, the RDE voltammograms of
effect of NPC/AC ratio on the ORR electrocatalytic activity of the the NPC@AC-0.7 display a nearly one-step process of ORR at
NPC@AC, cyclic voltammograms were performed in neutral different rotating speeds (Fig. 2B), implying a four-electron ORR
media. As shown in Fig. 1, the NPC modication could bring pathway. Moreover, RRDE measurements were conducted to
great increase of ORR onset potential to the AC-based catalysts. study the generation of hydrogen peroxide for different catalysts
The ORR onset potential of NPC@AC positively shi from 0 V of (Fig. 2C). As expected, the NPC@AC-0.7 shows lower hydrogen
the pristine AC to +0.15 V of the NPC@AC-0.7, is kept at peroxide generation than that of other catalysts. The average
about +0.14 V with further increase the NPC content. Moreover, electron transfer numbers (n) of the NPC@AC-0.7 catalyst based
the NPC modication also leads to increase in the ORR on the RRDE measurements is about 3.6 (Fig. 2D). As can be
current density. The NPC@AC-0.7 delivers a current density of seen, the NPC@AC-0.7 possesses excellent electrocatalytic
1.07 mA cmꢁ2, which is 30% higher ORR current density than activity for ORR in terms of positive ORR onset potential and
that of the pristine AC and even the pure NPC. In view of the high disc current, highlighting the importance of the N, P co-
best ORR electrocatalytic performance in terms of the more doping and mesoporous structure for ORR.
positive ORR onset potential and current density, thus the
NPC@AC-0.7 were selected for further electrochemical perfor-
mance investigation and compared to the single N doped
3.2 Morphological and elemental characterization
SEM morphological analyses demonstrate that the NPC@AC-0.7
(NC@AC) and P doped (PC@AC) carbon modied AC.
exhibits a nanorod network surface (Fig. 3A and B) inherited
RDE voltammograms were performed in O2-saturated
from the PA doped PANi@AC. High-resolution transmission
microscope (HR-TEM) image in Fig. 3C reveals that the
NPC@AC-0.7 sample exhibits an edge-like graphitic carbon
50 mM PBS and the results are shown in Fig. 2A. Aer doped
carbon modication, the onset potential of the AC-based cata-
lysts show a great positive shi from 0 V (pristine AC) to +0.22 V
structure, which might be derived from of the NPC. To further
(NPC@AC-0.7), the ORR current densities also great increase,
detect the possible crystalline structure in the NPC@AC-0.7,
which is well in accordance to the CV results discussed in the
XRD and Raman analyses were performed and the corre-
preceding paragraph. Moreover, the ORR electrocatalytic
sponding results are presented in Fig. S1.† XRD patterns in
activity of the NPC@AC-0.7 modied by co-doped carbon
Fig. S1A† show that the pristine AC only has a board peak at
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Fig. 2 Electrocatalytic activity of the catalysts for ORR. (A) LSV curves of NPC@AC-0.7, NC@AC, PC@AC and pristine AC catalysts loaded on RDE
at speed of 1600 rpm in O2-saturated neutral 50 mM PBS. (B) LSV curves of NPC@AC-0.7 in O2-saturated neutral 50 mM PBS at various rotating
speeds. (C) Ring current response of different catalysts based on the RRDE measurements at a rotating speed of 1600 rpm in O2-saturated
neutral 50 mM PBS. Scan rate is 10 mV sꢁ1. (D) Electron transfer number (n) of different catalysts at different potentials.
Fig. 3 SEM images of the (A) PANi@AC and (B) NPC@AC. (C) High-resolution TEM image, (D) SEM and corresponding element mapping images
of the NPC@AC-0.7. The element mapping images for C, N and P demonstrate a uniform distribution of the elements.
around 23ꢂ corresponding to the (002) of the carbon. A new of graphitic carbon structure. Moreover, the intensity of the
broad peak at around 43ꢂ corresponding to the (100) appears (100) NPC@AC-0.7 is stronger than that in the mono-doped
aer incorporation of doped carbons, indicating the existence carbon, NC@AC and PC@AC, demonstrating a higher average
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Table 1 Characteristics and textural parameters of AC-based catalysts
Elemental analysis (at%)
Samples
SBET (m2 gꢁ1
)
Vpore (cm3 gꢁ1
)
ID/IG
C
N
O
P
NPC@AC-0.7
NC@AC
PC@AC
649.2
500.6
456.0
943.5
0.656
0.514
0.364
0.919
1.26
1.42
1.52
1.64
86.87
92.61
88.29
92.53
4.54
4.60
0.55
1.22
6.37
2.80
7.57
6.24
2.21
—
3.59
—
Pristine AC
Fig. 4 XPS spectra of catalyst samples (A) survey and (B) high-resolution XPS spectra of the selected peaks in A, (a) N 1s and (b) P 2p fine spectra
of NPC@AC-0.7; (c) N 1s fine spectrum of NC@AC and (d) P 2p fine spectrum of PC@AC, respectively.
graphitization degree. This tendency could also be conrmed by carbon ring could change the spin density and atomic charge
the Raman analysis results. As shown in Fig. S1B,† the Raman distribution of carbon atoms in the graphitic layers, which
spectra of the AC-based catalysts all display two wide peaks at effectively weakened the O–O bonding energy, thus facilitated
ꢀ1327 cmꢁ1 (D-band) and ꢀ1594 cmꢁ1 (G-band). The intensity ORR catalytic activity.40,41 The ne P 2p spectra of the NPC@AC
ratios of D band to G band (ID/IG) which reects the average (Fig. 4Bb) and PC@AC (Fig. 4Bd) can be tted into two bands
graphitization degree of different catalysts are calculated and at ꢀ131.8 and 133.6 eV, which were ascribed to P–C and P–O
summarized in Table 1. Aer doped carbon modication, the states, respectively. It was reported that P-doping could
ID/IG value of the AC-based catalysts decreased, demonstrating enhance the charge delocalization of the carbon atoms and
increase in the average graphitization degree. Moreover, the N produce carbon structures with many edge sites.42 These
and P co-doped NPC@AC-0.7 show lower ID/IG value than mono- electrical and physical alternations of carbon substrate caused
doped NC@AC and PC@AC, thus conrms the higher average by N, P co-doping would be more favorable for the reduction of
graphitization degree in the NPC@AC-0.7, indicating the posi- the oxygen on the carbon surface, thus probably give rise to
tive effect of phosphorus doping on the graphitization of the high ORR catalytic activity.
carbon layers.36
N2 adsorption–desorption isotherm curves (Fig. S2A†) show
To conrm the incorporation of heteroatom (N and/or P) that the NPC@AC-0.7 preserve a high specic surface area of
doped carbons to the AC, XPS analysis was conducted and the 649.2 m2 gꢁ1 and a total pore volume of 0.656 cm3 gꢁ1
spectra are shown in Fig. 4A, and the textural parameters are (Table 1), which is about 70% specic surface area and pore
summarized in Table 1. As expected, the XPS spectrum of volume of the pristine AC (943.5 m2 gꢁ1 and 0.919 cm3 gꢁ1).
conrms the presence of the O, N, and P heteroatom in the The relatively lower specic surface area the NPC@AC-0.7 is
NPC@AC-0.7 with N and P content of 4.54% and 2.21%, likely due to the occupancy of partial pores of the AC by the
respectively. The ne N 1s spectra of the NPC@AC-0.7 deposition of NPC during pyrolysis process. Barrett–Joyner–
(Fig. 4Ba) and NC@AC (Fig. 4Bc) can be tted into three Halenda (BJH) pore size distribution curves of the as-prepared
bands at ꢀ398.6, 401.3 and 402.5 eV, which correspond to catalysts (Fig. S2B†) conrm the presence of mesopores with
pyridinic (N-6), pyrrolic (N-5) nitrogen and pyridine-N-oxide diameters <10 nm, which would be in favor for electrocatalytic
groups (N-Q), respectively.37–39 The incorporation of N atom to applications.
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Fig. 5 (A) LSV and (B) V–t curves of MFC equipped with air-cathodes using catalysts of NPC@AC, NC@AC, PC@AC and pristine AC. The media is
50 mM PBS (pH ¼ 7.0) containing 1 g Lꢁ1 acetate. Scan rate is 1 mV sꢁ1
.
3.3 Performance of the electrocatalyst in the air-cathode of
MFCs
The practical performance of different catalysts in MFCs, air-
cathodes with various ORR catalysts were prepared by rolling
method as reported previously.28,35 The LSV curves in Fig. 5A
demonstrate that all the air-cathodes with doped carbon modi-
ed AC catalysts exhibit higher current response than that of
pristine AC catalyst. Comparing to the NC@AC and PC@AC, the
NPC@AC-0.7 displays the highest current density. As shown in
Fig. 5B, air-cathode MFC using NPC@AC-0.7 ORR catalyst is able
to generate a stable voltage of 0.668 V across an external resistor
of 1000 U, which is much higher than that of using the NC@AC
(0.583 V), PC@AC (0.517 V) and pristine AC (0.432 V) catalysts,
respectively. These results imply that modication by doped
carbon is an effective method to enhance the ORR activity of the
AC. Moreover, the NPC@AC-0.7 prepared by N and P co-doped
carbon modication outperforms the NC@AC and PC@AC by
mono-doped carbon modication, when using as ORR catalyst in
the air-cathode of MFC.
As shown in Fig. 6A, using the NPC@AC-0.7 catalyst, the air-
cathode MFC is able to generate a higher open circuit voltage
(OCV) of 0.753 V than that of using other catalysts. Moreover, the
electrode polarization curves in Fig. 6B show that the increase of
OCV is mainly brought by the improvement of performance at
the air-cathode. These results demonstrate that incorporation of
NPC to the AC greatly reduce the over-potential of air-cathode
towards ORR, thus lead to high OCV. The power density curves
of air-cathode MFC using different catalysts in Fig. 6A reveal that
the air-cathode MFC using the NPC@AC-0.7 ORR catalyst shows
better performance than the mono-doped carbon modied AC,
NC@AC and PC@AC, and the pristine AC. And the power
densities arranged in this order: pristine AC (595 mW mꢁ2) <
PC@AC (762 mW mꢁ2) < NC@AC (895 mW mꢁ2) < NPC@AC-0.7
(1223 mW mꢁ2). The power density from the MFC with NPC@AC-
0.7 catalyst (1223 mW mꢁ2) is two times higher than that with
pristine AC. These results demonstrate that the NPC@AC-0.7 is
an efficient ORR catalyst for air-cathode of MFCs.
4. Conclusions
Fig. 6 (A) Cell and (B) electrode polarization and (C) power density
curves of air-cathode MFCs using different AC based catalysts.
The method of doped carbon modication was employed to
improve the ORR electrocatalytic activity of the AC
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electrocatalyst. The doped carbon modication were realized by
using a facilely and scalable process including steps of coating
of PA doped polyaniline by in situ oxidative polymerization and
9 X. Zhang, S. Cheng, X. Wang, et al., Separator characteristics
for increasing performance of microbial fuel cells, Environ.
Sci. Technol., 2009, 43, 8456–8461.
¨
subsequent high-temperature pyrolysis. The NPC@AC-0.7 10 F. Zhao, F. Harnisch, U. Schroder, et al., Application of
modied by N and P co-doped carbon, inherited the large
surface area and mesoporous characteristics from the AC and
had improved degree of graphitization, thus exhibited higher
ORR electrocatalytic activity in term of both the onset potential
pyrolysed iron(II) phthalocyanine and cotmpp based
oxygen reduction catalysts as cathode materials in
microbial fuel cells, Electrochem. Commun., 2005, 7, 1405–
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and current density in neutral solution, comparing to the mono- 11 L. Deng, M. Zhou, C. Liu, et al., Development of high
doped carbon modied AC, NC@AC and PC@AC, and the
performance of co/fe/n/cnt nanocatalyst for oxygen
pristine AC. The MFC using the NPC@AC-0.7 as ORR catalyst
reduction in microbial fuel cells, Talanta, 2010, 81, 444–448.
generated a much higher open circuit voltage of 0.753 V and two 12 L. Zhang, C. Liu, L. Zhuang, et al., Manganese dioxide as an
times higher power density of 1223 mW mꢁ2, comparing to the
MFC using the pristine AC ORR catalyst. The NPC@AC-0.7
alternative cathodic catalyst to platinum in microbial fuel
cells, Biosens. Bioelectron., 2009, 24, 2825–2829.
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manganese oxide as a cathodic catalyst for enhanced
Conflicts of interest
oxygen reduction in
a microbial fuel cell fed with
There are no conicts to declare.
a synthetic wastewater, Water Res., 2010, 44, 5298–5305.
15 E. Martin, B. Tartakovsky and O. Savadogo, Cathode
materials evaluation in microbial fuel cells: a comparison
of carbon, Mn2O3, Fe2O3 and platinum materials,
Electrochim. Acta, 2011, 58, 58–66.
16 L. Feng, Y. Yan, Y. Chen, et al., Nitrogen-doped carbon
nanotubes as efficient and durable metal-free cathodic
catalysts for oxygen reduction in microbial fuel cells,
Energy Environ. Sci., 2011, 4, 1892–1899.
Acknowledgements
This research was supported by the National Natural Science
Foundation of China (grant 51678281), the Science and Tech-
nology Project of Jiangxi Province (grants 20162BCB23024,
20161BCB24005), and the project of Education Department of
Jiangxi Province (grants GJJ150296).
17 Y. Liu, H. Liu, C. Wang, et al., Sustainable energy recovery in
wastewater treatment by microbial fuel cells: stable power
generation with nitrogen-doped graphene cathode,
Environ. Sci. Technol., 2013, 47, 13889–13895.
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