Electrocatalyst derived from fungal hyphae and its excellent activity for electrochemical production of hydrogen peroxide

Article abstract of DOI:10.1016/j.electacta.2019.04.011

Producing hydrogen peroxide (H₂O₂) by electrochemical O₂ reduction is a promising process, although developing high-performance carbon-based electrocatalysts at a low-cost with high-volume production remains a great challe

Full text of DOI:10.1016/j.electacta.2019.04.011

Electrochimica Acta 308 (2019) 74e82
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Electrocatalyst derived from fungal hyphae and its excellent activity
for electrochemical production of hydrogen peroxide
a
,
1
b
,
1
a
,
1
a
a
Hai-Xia Zhangc , Shi-Chao Yang , Yun-Lu Wang , Jian-Chao Xi , Jing-Cheng Huang ,
a,
d,
*
, Rong Jia b
, e, **
Jiang-Feng Li , Ping Chen
School of Chemistry and Chemical Engineering, Anhui University, Hefei, Anhui, 230601, PR China
School of Life Science, Anhui University, Hefei, Anhui, 230601, PR China
Department of Chemistry, Lishui University, Lishui, 323000, PR China
Institute of Physical Science and Information Technology, Anhui University, PR China
Anhui Key Laboratory of Modern Biomanufacturing, Anhui University, Hefei, 230601, People's Republic of China
a
b
c
d
e
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 March 2019
Received in revised form
Producing hydrogen peroxide (H O ) by electrochemical O reduction is a promising process, although
developing high-performance carbon-based electrocatalysts at a low-cost with high-volume production
remains a great challenge. We report a novel method to prepare the excellent electrocatalysts for the
2
2
2
2
April 2019
H
2
O
2
production derived from the fungal hyphae (with bioconcentrated dye), which was used as the
main sources of C, N, O, and P. The optimizational electrocatalyst had a large surface area with many
nanopores, which exhibited excellent activity, selectivity, and stability towards O reduction when
producing H in an alkaline media and good activity, selectivity, and stability in neutral media. A flow
cell with the optimizational electrocatalyst as cathode and IrO as anode exhibited exceptionally high
Faradaic efficiency, H productivity, and energetic efficiency in alkaline media. This maintained the
Faradaic efficiency and H productivity when driven by commercial dry battery (1.5 V) or by solar-
energy battery (2.5 V or 3.0 V). This is helpful in developing an electrocatalyst for H production
and practical industrial application of O reduction to H O by electrocatalysis. This low-cost, simple, and
Accepted 2 April 2019
Available online 4 April 2019
2
2 2
O
Keywords:
Hydrogen peroxide
Electrocatalyst
Fungal hyphae
Electrochemical production
Oxygen reduction reaction
2
2 2
O
2 2
O
2 2
O
2
2 2
readily scalable approach offers insight for developing a novel electrocatalyst for other electrochemical
reactions, such as hydrogen evolution reactions, oxygen evolution reactions, and CO reduction reactions.
2019 Elsevier Ltd. All rights reserved.
2
©
1
. Introduction
mixture could explode [3,4]. Researchers have found a method to
produce H by means of electrochemistry, which boasts lower
energy consumption, higher productivity, and is environmentally
friendly [5]. The high yield H requires the presence of electro-
2 2
O
Hydrogen peroxide (H
2
O
2
) is used in various industries, such as
is
paper bleaching, textiles, and wastewater treatment [1,2]. H
2
O
2
2 2
O
currently commercially generated via the anthraquinone oxidation
process. This is a multi-step and complex method requiring many
large-scale devices. The waste organic byproducts produced during
this process, the storage, and the transportation of large-scale
products are problematic [2]. Another alternative route is to syn-
catalysts with high performances, such as high selectivity and ac-
tivity. Developing the catalysts remains an essential challenge in
this field [6e12].
Previous reports have used the noble metal nanomaterials (for
example: platinum (Pt), palladium (Pd) and gold (Au)) and their
thesize H
2
O
2
directly from hydrogen and oxygen with the help of
2 2
alloys (Pd-Hg and Pd-Au) as electrocatalysts for the H O genera-
catalysts. This is potentially hazardous, as the hydrogen/oxygen
tion, demonstrating that these catalysts are efficient and boast
excellent electrocatalytic properties (such as small overpotential
and high selectivity to H O ) [13e15]. The scarcity and high cost of
2 2
*
Corresponding author. School of Chemistry and Chemical Engineering, Anhui
University, Hefei, Anhui, 230601, PR China.
* Corresponding author. School of Life Science, Anhui University, Hefei, Anhui,
these materials, as well as the toxicity of Hg could affect their
practical application to a certain degree. It is necessary to explore
other materials, including non-precious metals and carbon-based
materials.
*
2
30601, PR China.
E-mail addresses: chenping@ahu.edu.cn (P. Chen), ahujiarong@163.com (R. Jia).
These authors have the equal contribution to this paper.
1
Carbon materials have advantages in their resources and are
https://doi.org/10.1016/j.electacta.2019.04.011
013-4686/© 2019 Elsevier Ltd. All rights reserved.
0

H.-X. Zhang et al. / Electrochimica Acta 308 (2019) 74e82
75
cheaper than the noble-metal materials [16e18]. The ingredient
and structure of these materials have a decisive impact on the
2.2.2. Preparation of the N-, O- and P-tridoped nanoporous carbon
derived from fungal hyphae
electrosynthesis of H
2
O
2
. Some studies regarding heteroatom-
2
The dried fungal hyphae with dye were calcined in the N at-
ꢀ
ꢁ ꢁ ꢁ
mosphere (at 750 C, 800 C, and 850 C) for 1 h at a heating rate of
doped carbon materials that use N-doped carbons with high 2e
selectivity as oxygen reduction electrocatalysts have been reported.
The presence of heteroatom influences the chemical structure of
ꢁ
ꢁ
5 C/min and a cooling rate of 5 C/min. The N-, O-, and P-tridoped
nanoporous carbon derived from fungal hyphae were obtained.
They were denoted as N-O-P-C-750, N-O-P-C-800, and N-O-P-C-
850. We also prepared the N-, O- and P-tridoped nanoporous car-
bon derived from fungal hyphae without the dye according to the
same steps as typical N-, O-, and P-tridoped nanoporous carbon.
The fungal hyphae did not have dye. The material was N-O-P-C-
800-C.
the catalyst, which improves the H
2 2
O productivity and selectivity
[
6,8,19,20]. The carbon-based materials have become more popular,
thanks to their super high surface area and numerous exposed
active sites. Many methods aim to achieve enough surface area,
although these methods are not perfected [21e24]. Fungal hyphae
is the typical biomass material that is formed by the germination of
fungal spores. Fungus hyphae is cheap, obtained easily, and does
not generate pollution. Growth of fungus hyphae requires essential
nutrients, such as carbon and nitrogen sources, making it a candi-
date for preparing heteroatom-doped carbon materials. Irpex lac-
teus is a cosmopolitan fungus that is widespread in Europe, North
America, and Asia [25,26]. Irpex lacteus F17 is a forest mushroom, a
type strain of lignin degrader fungus, belonging to the class Ba-
sidiomycetes. Very recently, we reported the high-quality draft
genome sequence of Irpex lacteus F17, which was isolated from a
decaying hardwood tree in the vicinity of Hefei, China [27].
Fig. 1 shows the preparation of typical N-, O-, and P-tridoped
nanoporous carbon from fungal hyphae (N-O-P-C-800).
2
.3. Characterization
SEM images were obtained on a scanning electron microscopy
SEM) with a field emission scanning electron microanalyzer
Hitachi SU8010) and energy-dispersive X-ray spectroscopy (EDX)
analytical system. The SEM samples were prepared by drop-drying
the samples from their aqueous suspensions onto silicon sub-
strates. The X-ray photoelectron spectroscopy (XPS) data was
collected using an ESCALAB MKII X-ray photoelectron spectrometer
(
(
Here, we used the fungal hyphae from Irpex lacteus F17 as
sources of N-, O-, and P to prepare the N-, O-, and P-tridoped
nanoporous carbon. The typical product exhibited excellent activ-
ity, selectivity, and stability towards oxygen reduction for produc-
(
Thermo VG Scientific Ltd., East Grinstead, Sussex, UK). The BET
surface area and the pore size distribution of all samples were
analyzed on a Micrometrics ASAP2020 analyzer (USA). The micro-
pore size distribution was calculated using the Horvath-Kawazoe
method. An inVia-Reflex spectrometer (Renishaw) was used to
obtain the Raman spectra.
2 2
ing H O in both alkaline and neutral media.
2
. Experimental section
.1. Chemicals
2 5
SO , C H OH, KOH, and fuchsin basic were purchased from
2
2
.4. Rotating ring-disk electrode (RRDE) measurements
K
2
4
We prepared the catalyst ink according to pervious literature
Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). The above
chemicals were analytical reagent and used without further
purification.
[
3
16,21]. For each catalyst, the powder (15 mg) was dispersed in
mL of mixed solvent (1:3 v/v isopropanol/deionized water) with
Nafion (wt.0.8%). The obtained mixture was ultrasonicated for
0 min to obtain the catalyst ink. The ink (10- L volume) was
3
m
uniformly deposited onto the glassy carbon ring-disk (Pine
Research Instrumentation, Durham, NC, USA) and air dried. A glassy
carbon ring-disk was used as the working electrode, a platinum
2
.2. Preparation of the N-, O- and P-tridoped nanoporous carbon
derived from fungal hyphae
2.2.1. Preparation of the fungal hyphae with dye
Irpex lacteus F17 was isolated from a decayed wood chip pile in
Hefei, China, which was then stored in the China Center for Type
Culture Collection (CCTCC AF 2014020). The fungus was cultured on
a PDA solid medium (200 g/L of potato extract, 20 g/L of glucose,
ꢁ
and 20 g/L of agar) for 5 days at 28 C. Then the grown mycelial mat
was dug up from the agar-plate and was inoculated into 120 ml
liquid PDA medium for the formation of mycelial pellets. Incubation
ꢁ
was carried out at 28 C on a rotary shaker at 120 rpm for 6 days.
These mycelial pellets were used for the subsequent experiments.
To ensure inoculum size of the fungus was the same, 1 mL of the
mycelia suspension obtained by crushing the mycelial pellets in a
Waring blender was inoculated into a Erlenmeyer flask containing a
ꢁ
new liquid PDA medium, and grown at 28 C in a constant tem-
perature shaker. When new mycelial pellets occurred in the flasks
after 5 days, 0.6 mL fuchsin basic solution (6 mg/mL) was added and
incubated continuously for 2 days. The control group did not have
the fuchsin basic solution. After the culture, separation, deionized
water washing to fastness, and freeze-drying, the dried fungal hy-
phae with dye were obtained. The experiments were performed in
ꢁ
the sterile operation and all media were sterilized at 121 C for
Fig. 1. Illustrated diagram of the N-O-P-C-800 preparation. (a) fungal hyphae; (b)
2
0 min before inoculation.
fungal hyphae containing dye; (c) dried fungal hyphae with dye; and (d) N-O-P-C-800.

76
H.-X. Zhang et al. / Electrochimica Acta 308 (2019) 74e82
plate was used as counter electrode, and an Ag/AgCl was used as
reference electrode in an O -saturated 0.1 M KOH and in an O
saturated 0.1 M K SO solution.
The working electrode was scanned at a rate of 5 mVs with a
rotating speed of 1600 rpm. The ring current (i ) was achieved
using a Pt ring electrode separately in the alkaline and neutral
media. The selectivity for H yield was evaluated using the RRDE
voltammogram of each sample, according to the following equation
6,16]:
calculated for the chronoamperometric measurements by deter-
mining the charge required to produce the measured product
concentration and dividing the, by the total charge passed. The
2
2
-
2
4
ꢀ
1
2 2
productivity of the produced H O was calculated by the produced
R
hydrogen peroxide concentration in 100 mL solution. The reaction
time and the area of the GDE was supported by the catalyst. The
energetic efficiency (E.E.) of the flow cell was calculated by the
following equation:
2 2
O
[
0
E
FEH2
O
H
2
O
2
2
h
¼
(4)
IR=N
ID þ IR=N
energetic;H
2
O
2
%
ðH O Þ ¼ 200 ꢂ
(1)
Vin
2
2
where E0
2 2
is the standard thermodynamic potential of H O ,
H
2
O
2
where i
D
denotes the disk current, i
R
is the ring current, and N stand
2 2
FEH2O2 is the faradaic efficiency of H O , and Vin is the total cell
voltage.
for the current collection efficiency of the Pt ring. N was 0.33 from
the reduction of K Fe[CN] and the corresponding result (the RRDE
3
6
voltammograms for the determination of current collection effi-
ciency) is shown in Fig. S1.
3. Results and discussion
2 2
2.5. H O production in a flow electrochemical cell
Fig. 2aeb shows the typical product (N-O-P-C-800) with a sheet
shape. The elemental mapping (Fig. 2def and Fig. S3) exhibited four
types of elements C, N, O, and P that were uniformly dispersed in
the carbon nanosheets. The EDS data proved the existence of C, N,
O, and P elements. Fig. S4 shows the SEM images of the N-O-P-C-
Catalyst-coated gas diffusion electrode (GDE) was prepared by
depositing 150 of catalyst ink onto pre-cut strip
pro-
duction for the samples were investigated by a three-electrode and
two-electrode method on a CHI750e electrochemical workstation
m
L
a
(
2.0 cm ꢂ 2.0 cm) of GDE and was immediately dried. H
2 2
O
750, N-O-P-C-850, and N-O-P-C-800-C.
Fig. 3aeb shows the results of the BET of the N-O-P-C-800,
(
Shanghai Chenhua Instrument Co., Shanghai, China). The experi-
where the typical product had a large quantity of nanopores
mesopores and micropores). The BET specific surface area, total
pore volume, and micropore volume of the N-O-P-C-800 was
ments were performed in a flow electrochemical cell with two
compartments separated by a Nafion 117 membrane. (The experi-
mental device was shown in Fig. S2). On the side of the cell there
(
2
ꢀ1
3
ꢀ1
3 ꢀ1
3
50 m g , 0.30 cm g , and 0.12 cm g . Table S1 shows the de-
2 4 2
was the electrolyte of 0.1 M KOH or K SO . The GDE, a IrO /C, and an
tails of the element content ratio, the BET surface area, the total
pore volume, and the micropore volume of the samples. Fig. S5 and
Table S1 show that with the increased annealing temperature, the
BET surface area became higher and the pore size distribution
changed. The BET specific surface area, the total pore volume, and
Ag/AgCl electrode were used as the working electrode, counter
electrode, and reference electrode. Before the measurement, the
cathodic compartment of the cell was saturated with high-purity
2 2
O (99.999%) for at least 30 min. The O was continuously
2
ꢀ1
bubbled into the cathodic chamber at a rate of 40 mL/min during
the reduction.
the micropore volume of N-O-P-C-800-C were 281 m g
,
3
ꢀ1
3 ꢀ1
0
.18 cm g , and 0.12 cm g . The N-O-P-C-800 had higher BET
specific surface area and total pore volume than the N-O-P-C-800-
C. During the preparation of N-, O-, and P-tridoped nanoporous
carbon, the bioconcentrated dye (fuchsin basic) in fungal hyphae
was helpful in promoting the BET specific surface area and total
pore volume.
2
.6. Determination of the H
2
O
2
concentration
Determination of the H
O concentration was measured by ultravioletevisible (UVeVis)
2 2
2
O
2
concentration was as follows: the
H
4
þ
spectrophotometry according to the yellow Ce
solution that
2. A UV-3600 UVeVis
spectrophotometer (Shimadzu Scientific Instruments Inc., Kyoto,
Table S1 shows that the N-O-P-C-800 had an atomic content of
C, N, O, and P of 74.7 at%, 2.7 at%, 18.9 at%, and 3.7 at%. Fig. 3cef
exhibit the high-resolution C1s, N1s, O1s, and P2p XPS spectra of
the N-O-P-C-800. Fig. 3c shows a strong peak at 284.8eV and two
weak peaks at 285.9eV and 287.8eV. The peak of 284.8 eV repre-
3
þ
2
could be reduced to colorless Ce by H O
Japan) was used. The H
2
O
2
concentration was calculated according
to the reduced Ce4 amount and equations (2) and (3) [6].
þ
2
sents the sp hybridized graphite carbon. The peaks at 285.9 eV and
Ce4 þ H
þ
O
2
/2Ce þ2Hþ þO
3þ
(2)
(3)
2
2
2
287.8 eV corresponded to the carbon-oxygen single bond (CeOH)
and the carbon doubly bound to oxygen (C¼O) [23]. Fig. 3d shows
that the three types of nitrogen atoms (pyridinic nitrogen, pyrrolic
nitrogen and graphite nitrogen) were doped in the carbon mate-
rials. The peak at 398.3 eV belonged to the pyridinic nitrogen, the
peak at 399.7 eV was pyrrolic nitrogen, and the peal at 401.0 eV was
attributed to the graphitic nitrogen with the highest peak area [16].
Content of graphitic-, pyrrolic- and pyridinic- N in different sam-
ples was shown in Table S2. Fig. 3e shows the O]CeO bond (cor-
responding to the peak of 531.8 eV), O]C bond (corresponding to
the peak of 532.8 eV), and the CeOeC bond (corresponding to the
peak of 533.4 eV) in N-O-P-C-800. Content of different type oxygen
in different samples was listed in Table S3. Fig. 3f shows that the N-
O-P-C-800 contained the PeC bond (corresponding to a peak of
132.8 eV), the PeN bond (corresponding to a peak of 133.6 eV), and
the PeO bond (corresponding to a peak of 134.4 eV) [21]. The XPS
spectra of N-O-P-C-750, N-O-P-C-850 and N-O-P-C-800-C were
M ¼ 2.5 ꢂ MCe4þ
where M denotes the concentration of H
molarity of consumed Ce
2
O
2
(M) and M Ce4þ was the
4
þ
.
4
þ
A standard curve for measurement of the Ce concentration
was established by various concentrations of the corresponding
Ce(SO
trolysis used a 1 mL sample that was mixed with 4 mL of the
standard solution and the selected Ce(SO standard solution was
transferred to the quartz glass UV cell for testing.
4 2
) standard solution. The sample in the potentiostatic elec-
4 2
)
2.7. Calculations for productivity, faradic efficiency of the produced
2 2
H O
and energetic efficiency of the flow cell
2 2
The faradaic efficiency (F.E.) for the produced H O was

H.-X. Zhang et al. / Electrochimica Acta 308 (2019) 74e82
77
Fig. 2. (a) SEM image of N-O-P-C-800; (bef) STEM image and mapping of C, N, O, and P of N-O-P-C-800.
Fig. 3. (a-b) Nitrogen adsorption-desorption isotherm curve and pore distribution of N-O-P-C-800. (cef) high-resolution C1s, N1s, O1s, and P2p XPS spectra of the N-O-P-C-800.
also tested (Figs. S6-S8). The C, N, O, and P contents in the N-O-P-C-
00-C were 73.6 at%, 3.0 at%, 19.3 at%, and 4.1 at%. These materials
0.1 M KOH are shown in Fig. 4a. The N-O-P-C-800 exhibited the
highest overall catalytic reactivity for oxygen reduction (disk cur-
8
2
ꢀ
2
specific
had C, N, O, and P elements, with various elements existing in the
same form. We also tested the Raman spectra of the samples. Fig. S9
shows that the samples have two strong peaks at the G band and D
band, the positions of the two main peaks concentrated around
rent density, jdisk, up to ꢀ2.5 mA/cm ), and the largest HO
2
productivity (ring current, iring, up to 0.73 mA/cm ) at 0.3 V (Fig. 4a).
The H
Fig. 4b. The H
2
O
2
selectivity from the RRDE voltammograms are shown in
selectivity depended on the applied potential. The
2 2
O
ꢀ1
ꢀ1
1
335 cm and 1593 cm , with one weak 2D peak appearing at
N-O-P-C-800 revealed that the selectivity was around 93.0e97.0%
at potentials ranging from 0.25 V to 0.68 V (vs RHE), indicating that
it followed the 2-electron reduction pathway. As a control, the N-O-
2
850 cm [16]. According to the above results and discussion, the N-,
O-, and P-tridoped nanoporous carbon was prepared using the
fungal hyphae (from Irpex lacteus F17) as N-, O-, and P- sources.
We investigated the electrocatalytic activity of the samples to-
2 2
P-C-800-C showed lower H O selectivity (14.5e29.5% from 0.25 V
to 0.68 V). The N-O-P-C-800 had the best performance. In addition,
for further comparison, the dye has been carbonized under the
ward oxygen reduction to H
and neutral media. The RRDE voltammograms in the O
2
O
2
by RRDE measurements in alkaline
-saturated
ꢁ ꢁ
optimal conditions (800 C, 5 C/min) and the product was denoted
2

78
H.-X. Zhang et al. / Electrochimica Acta 308 (2019) 74e82
Fig. 4. (a-b) Polarization curves (solid lines), simultaneous H
rotational speed of 1600 rpm); (c-d) Polarization curves (solid lines), simultaneous H
.1 M K SO solution (rotational speed of 1600 rpm).
2
O
2
detection currents at the ring electrode (dashed lines) and H
2
O
2
selectivity of the samples in the 0.1 M KOH solution
selectivity of samples in
(
0
2
O
2
detection currents at the ring electrode (dashed lines) and H O
2 2
2
4
as dye-800. The activity of dye-800 tested by RRDE (Fig. S10)
indicated that there is not ideal performance for oxygen reduction
2 2
P-C-800 catalyst exhibited the both high H O production rate and
high faradaic selectivity. Previous literature revealed that the cat-
alytical activity of the N-O-P-C-800 was superior to most of the
reported catalysts, including nitrogen-doped carbon, transition-
metal-based, and metal catalysts (Table S4) [6,11,28e30]. Fig. 5a
shows that the N-O-P-C-800 catalyst exhibited excellent stability in
to H
rated 0.1 M K
catalytic reactivity for oxygen reduction. When the potential was
2
O
2
. Fig. 4c shows the RRDE voltammograms in the O
2
-satu-
2
SO . The N-O-P-C-800 exhibited the highest overall
4
2
0
V (vs RHE), the jdisk reached up to ꢀ2.2 mA/cm and the iring
2
ꢀ
2
specific pro-
approached 0.30 mA/cm , revealing the largest HO
ductivity. In 0.1 M K SO4, the H selectivity of the samples
the successive H
ideal durability, which is considered one of the most important
issues [6,7,31,32]. Fig. 5ced shows the H production rate of
at 0.1 V and faradaic selectivity of up to 65.0%
was obtained in the 0.1 M K SO solution, which indicated the N-O-
2 2
O production. The electrocatalyst should have
2
2 2
O
depended on the applied potential. N-O-P-C-800 showed the
selectivity of 53.1e60.4% from ꢀ0.14 V to 0.41 V (vs RHE), indicating
the N-O-P-C-800 had the best performance in the neutral media
than other samples. The results in acidic media are shown in
Fig. S11, the electrochemical performance in acid solution was not
ideal compared to alkaline and neutral solutions (the selectivity of
N-O-P-C-800 catalyst was only less than 50%).
2 2
O
ꢀ
1
ꢀ1
435 mmol gcatalyst
h
2
4
P-C-800 catalyst exhibited good catalytical activity and stability in
the neutral solution. The results indicated that the N-O-P-C-800
2 2
catalyst was a promising electrocatalyst for H O production by the
ORR process. In the alkaline solution, the N-O-P-C-800 catalyst
ꢀ
1
ꢀ1
To further investigate the catalytical activity, the H
2
O
2
faradaic
exhibited the H
2
O
2
production rate (0.25 V, 1470 mmol gcatalyst
h
)
selectivity and productivity during bulk electrolysis were tested by
a flow cell with a GDE (containing N-O-P-C-800) cathode and a GDE
and faradaic selectivity (97.0%), which was remarkably higher than
ꢀ1
ꢀ1
the 0.1 M K
2
SO
4
(0.10 V, 435 mmol gcatalyst
h
, faradaic selectivity
could be
(
containing IrO
ductivity were both important factors to evaluate the performance
of the catalyst. The H faradaic selectivity was calculated ac-
cording to the real amount of H produced in the reduction re-
action. The amount of H was tested by a photometric method.
Fig. 5aeb shows the H faradaic selectivity and the amount of
produced in alkaline (0.1 M KOH) solution by N-O-P-C-800
catalyst for 18 cycles at the applied potentials of 0.15 V, 0.25 V, and
.35 V(vs RHE). Fig. 5aeb shows that when the applied potential
shifted negatively, the H production rate increased. The H
production rate of the 1470 mmol gcatalyst
the faradaic selectivity of up to 97.0% (Fig. 5b) were obtained. N-O-
2
) anode. The H
2
O
2
faradaic selectivity and pro-
65.0%). The concentrated basic solution containing H O
2 2
used in many fields, including the pulp and paper industries [6,11].
We investigated the catalytical activity of the N-O-P-C-800
catalyst by a two-electrode method in the flow cell in an alkaline
2 2
O
2 2
O
2
O
2
solution (0.1 M KOH) and a neutral solution (0.1 M K
Faradaic efficiency and productivity during bulk electrolysis at
2 2
different cell voltage are shown in Fig. 6. Fig. 6a shows that the H O
2 4
SO ) [33]. The
2
O
2
2 2
H O
H
2
O
2
started to generate at a cell voltage of 0.73 V (with iR-free correc-
tion) and reached a current of 15.0 mA at a voltage of 1.5 V.
0
2
O
2
2
O
2
Fig. 6bec shows that the H
2
O
2
production rate of 540 mmol
at cell voltage of 1.3 V and Faradaic efficiency reached
93.1% in 0.1 M KOH. Fig. 6eeh shows the results in 0.1 M K SO
ꢀ
1
ꢀ1
ꢀ1
ꢀ1
h
at 0.25 V (Fig. 5a) and
g
catalyst
h
2
4
.

H.-X. Zhang et al. / Electrochimica Acta 308 (2019) 74e82
79
Fig. 5. (a-b) Faradaic efficiency and H
2
O
2
productivity for the N-O-P-C-800 catalyst as a function of cycle number at 0.15 V, 0.25 V, and 0.35 V(vs RHE) in 0.1 M KOH; (c-d) Faradaic
SO
efficiency and H
2
O
2
productivity for N-O-P-C-800 catalyst as a function of cycle number at ꢀ0.10, 0.10 and 0.30 V(vs RHE) in 0.1 M K
2
4
.
ꢀ
1
ꢀ1
Fig. 6e shows that the H
.18 V (with iR-free correction) and reached a current of 15.0 mA at
a voltage of 2.0 V. The H production rate of 220 mmol
at cell voltage of 2.1 V and Faradaic efficiency of up to
5% were obtained (Fig. 6eeh). The H production rate and
2
O
2
started to generate at a cell voltage of
15 min. The 804 mmol g catalyst h H
2
O
2
(Faradaic efficiency of
ꢀ1
ꢀ1
1
94.0%) and 921 mmol g catalyst
h
H O (Faradaic efficiency of
2 2
2
O
2
95.0%) was obtained in 15 min via a solar-energy battery with 2.5 V
and 3.0 V. These results revealed that the two-electrode cell was
driven by the commercial dry battery (1.5 V) and has potential
ꢀ
1
ꢀ1
g
3
catalyst
h
2 2
O
Faradaic efficiency of the flow cell in the alkaline solution were
higher than in the neutral solution. The flow cell in the alkaline
2 2 2
application in O reduction to H O via only the solar-energy bat-
tery and not by the electricity power from the fossil fuels [34].
From the above discussion, in the preparation, addition of dye
(fuchsin basic) plays an important role in the excellent activity. The
N-O-P-C-800 had higher BET specific surface area and total pore
volume than the N-O-P-C-800-C. The carbon sheets in N-O-P-C-800
had large surface areas with many nanopores, so that many cata-
lytic sites on the surface of the catalyst were exposed for the re-
action [16,21,35]. These catalysts contained the doped-nitrogen and
oxygen. From Tables S2 and S3, the content of different type ni-
trogen and oxygen of the samples are different. The addition of dye
(fuchsin basic) can also change the content of different type of N
element and the content of different type of O. Some DFT studies
have shown that the doped N or O play an important role in the
solution exhibited a high H
ciency, which was due to the cathode (excellent N-O-P-C-800
catalyst) and the anode (containing IrO ).
The electrochemical conversion efficiency (energetic efficiency)
for H was discussed according to its standard thermodynamic
2 2
O production rate and Faradaic effi-
2
2 2
O
potential, Faradaic efficiency, and the total input cell voltage. This
measurement method accounts for the potential losses (including
the overpotentials of cathode and anode and resistance losses) and
accurately defines the overall electrochemical cell efficiency. The
energetic efficiency and current values are two key indexes in the
practical industrial application of the electrochemical cell [19,33].
As shown in Fig. 6d and h, when the cell voltage increased, the
energetic efficiency decreased, and reduction current and H
production rate increased. In the 0.1 M KOH, the overall energetic
efficiency for H reached up to 29.0% when the total current was
1 mA/cm . The exceptional energetic efficiency and total current
density values were two key advantages for the practical industrial
application of the O reduction to H [33].
We investigated the H production rate and the Faradaic ef-
2
O
2
2 2
H O production by the ORR process [6,10,20,36,37]. In addition,
the carbon sheets in the material may form an interpenetrated
network structure, which was helpful to accelerate the reactant and
the electron transport [22,23].
2 2
O
2
2
2
2 2
O
2
O
2
4. Conclusions
ficiency by the two-electrode cell driven by a commercial dry
battery (1.5 V) and a solar-energy battery (2.5 and 3.0 V) (shown in
Fig. 7aeb). Fig. 7ced shows the Faradaic efficiency of 85.0% and
We proposed fungal hyphae as the main sources of C, N, O, and P
to prepare the electrocatalyst to produce H O by the ORR process.
2 2
The electrocatalyst was the N-, O-, and P-tridoped nanoporous
carbon that had a large surface area with many nanopores. It
ꢀ1
ꢀ1
6
62 mmol gcatalysth H
2
O
2
that was achieved via a dry battery in

80
H.-X. Zhang et al. / Electrochimica Acta 308 (2019) 74e82
Fig. 6. (a) I-V curve of the flow cell with a GDE (containing N-O-P-C-800) cathode and a GDE (containing IrO
applied potentials in 0.1 M KOH; (c) H productivity and Faradaic efficiency at the different applied potentials in 0.1 M KOH; (d) energetic efficiency at the different applied
potentials in 0.1 M KOH; (e) I-V curve of the flow cell with a GDE (containing N-O-P-C-800) cathode and a GDE (containing IrO ) anode in 0.1 M K SO ; (f) I-t curves of the flow cell at
the different applied potentials in 0.1 M K SO ; (g) H productivity and Faradaic efficiency at the different applied potentials in 0.1 M K SO ; and (h) energetic efficiency at the
different applied potentials in 0.1 M K SO
2
) anode in 0.1 M KOH; (b) I-t curves of the flow cell at the different
2 2
O
2
2
4
2
4
2
O
2
2
4
2
4
.

H.-X. Zhang et al. / Electrochimica Acta 308 (2019) 74e82
81
Fig. 7. (a-b) Illustration of the H
2
O
2
production by ORR process driven by dry cells and solar cells; and (c-d) Faradaic efficiency and H
2
O
2
productivity for N-O-P-C-800 catalyst by
dry cell and solar cells (2.5 V and 3.0 V) in 0.1 M KOH.
exhibited excellent activity, selectivity, and stability towards O
reduction for producing H O in alkaline media and showed good
2 2
2
(02303203-0054), College Students' Innovation and Training Proj-
ect (201710357228).
activity, selectivity, and stability with neutral media. In the prepa-
ration, addition of dye (fuchsin basic) plays an important role in the
excellent activity. A flow cell with a GDE (containing the typical
Appendix A. Supplementary data
electrocatalyst) cathode and a GDE (containing IrO
exhibited exceptionally high Faradaic efficiency, H productivity,
and energetic efficiency in alkaline media. The Faradaic efficiency
and H productivity were maintained when it was driven by a
commercial dry battery (1.5 V) or by a solar-energy battery (2.5 V or
.0 V), which indicated that these excellent electrocatalyst may
have potential application in the O reduction to H . This work
provides insights in developing the new electrocatalyst for H
production and practical industrial application of O reduction to
by electrocatalysis.
2
) anode
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.electacta.2019.04.011.
2 2
O
2
O
2
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