Deep eutectic solvent stabilised Co-P films for electrocatalytic oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid

Article abstract of DOI:10.1039/d0nj01426e

The electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) has been studied extensively. However, the short lifetime of catalytic electrodes remains a challenge for the electrocatalytic HMF oxidation reaction, and the high pH of the electrolyte causes denaturation of HMF during the reaction. Herein, deep eutectic solvents (DES) are employed for the preparation of efficient and durable catalytic electrodes for HMF oxidation. The catalytic electrode made up of DES avoided the complexity of multiple alkylations leading to 99% HMF conversion affording FDCA in 85.3% yield with high durability, due in part to the lower pH of the electrolyte.

Full text of DOI:10.1039/d0nj01426e

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Deep Eutectic Solvent Stabilised Co-P film for Electrocatalytic
Oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic
Acid
66Received 00th January 20xx
Accepted 00th January 20xx
Myung Jong Kang, Hye Jin Yu, Hyun Sung Kim b,* and Hyun Gil Cha a,*
a
a,b
DOI: 10.1039/x0xx00000x
The electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) has been studied
extensively. However, the short lifetime of catalytic electrodes remains a challenge for the electrocatalytic HMF oxidation
reaction, and the high pH of the electrolyte causes denaturation of HMF during reaction. Herein, deep eutectic solvents (DES)
employed in the preparation of efficient and durable catalytic electrodes for HMF oxidation. The catalytic electrode made
in DES avoided the complexity of multiple alkylations, giving 99% HMF conversion and 85.3% of FDCA yield obtained with
high durability, due in part to the lower pH of the electrolyte.
monomer that can be used for the synthesis of bio-based
polymers such as polyamides, polyesters, and polyurethanes.14
For this reason, FDCA has been rated as one of the top twelve
Introduction
Deep eutectic solvents (DES), developed by Abbot et al.,
consist of two or more interacting components linked by
hydrogen bonding, which results in a mixture with a lower
melting point than the individual precursor components.1-3 DES
are non-toxic, low cost, and stable against moisture compared
to many known ionic liquids. DES have several superior
properties such as ease of preparation, availability at fairly low
cost, biodegradability with relatively low toxicity, and even be
recycled more easily than pristine traditional solvents.
Therefore, DES have been shown to be useful for the
electrodeposition of metals and alloys such as cobalt, nickel,
value-added chemicals by the U.S. Department of Energy
15
(DOE).
Till date, most reported strategies for the conversion of HMF
into FDCA require harsh conditions, demanding high energy and
2
costly production, such as high O or air pressure, toxic chemical
oxidants, and elevated temperature with expensive catalytic
16, 17
materials.
In this manner, the electrochemical oxidation of
HMF into FDCA, which driven by electrochemical potential
applied to an electrode, is an emerging approach with the
advantage of eliminating O
2
or other chemical oxidants during
1
8-20
the reaction.
Additionally, it can offer ideal conditions for
4
-6
zinc, and tin. As an alternatives for traditional solvent system,
usage of DES systems has been investigated in various fields
such as material preparation, metal electrodeposition, solvent
extraction, and lignocellulose pre-treatment.7 Recently, an
efficient approaches on synthesizing DES for quaternary
ammonium salts (i.e., choline chloride) and hydrogen bond
donors (i.e., ethylene glycol and urea) was developed using twin
screw extrusion or ball milling, which makes it possible to
extend DES applications to industrial scale.10, 11
HMF oxidation into FDCA by utilising noble metal-based
catalysts such as Pt, Au, Pd and to reduce expenses, Co, Ni or
bimetallic alloys and metal oxides/hydroxides are also used
-9
2
1-23
frequently.
Cu is also used frequently, however, using
transition metal like Cu, Co and Ni as an electrocatalysts has
huge drawback that it easily oxidise into metal oxide in alkaline
24
conditions for HMF oxidation. To prevent it, homo/hetero
junction between transition metal and metal oxides electrodes
applied in electrochemical HMF oxidation reaction, leading
oxygen vacancy formation on the surface of metal oxide for
Biomass is the only accessible and renewable nonfossil-based
carbon source, whose utilisation will not alter the current
balance of the carbon in ecosystem as biomass stores
One of the most attractive building
block chemicals is 2,5-furandicarboxylic acid (FDCA), which
produced from 5-hydroxymethylfurfural (HMF). FDCA is a
2
5-27
better catalytic properties.
Furthermore, electrochemical
oxidation can be performed at ambient temperature and
pressure. Despite these advantages, most of the reported
results rely on noble metal catalysts in a highly basic solution,
12, 13
contemporary carbon.
2
8, 29
such as 1 M KOH or NaOH.
It is difficult to find a suitable
milder electrolyte for HMF oxidation because basic conditions
are required to oxidise the 2-position aldehyde group and
activate the 5-position alcohol in HMF during its oxidation into
a.Center for Bio-based chemistry, Korea Research Institute of Chemical Technology
KRICT), Ulsan 44429, Republic of Korea. E-mail: hgcha@krict.re.kr
Department of Chemistry, Pukyong National University, Busan 48513, Republic of
Korea.
† Electronic Supplementary Information (ESI) available: Cyclic voltammetry curves
(
b.
30
FDCA.
However, an excessive amount of bases can be detrimental
for HMF over a long reaction time. For example, a recent study
reported by Strasser and co-workers on HMF oxidation by an
.
during electrodeposition, LSV curves on different concentration of P precursor, SEM
images of electrodes after reaction. See DOI: 10.1039/x0xx00000x
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electrochemical method using a Pt electrode in a pH 10 aqueous Ethaline prepared by mixture of choline chloride VainewdAerttichleyOlenlninee
solution. They found that a fraction of the HMF was converted glycol (at a molar ratio of 1:2) at 357 KDOwI:i1t0h.1s0t3i9r/rDin0gNJu0n14ti2l6aE
into 2,5-diformylfuran (DFF), while the very less conversion of homogeneous colourless liquid formed.
HMF into FDCA. To circumvent this difficulty, addition of a
31
redox mediator, 2,2,6,6,-tetramethylpiperidine 1-oxyl (TEMPO) Preparation of Co-P/CF (Co-P_H
was tried and FDCA was successfully produced in low pH
conditions. However, the choice of electrolyte for electrolysis is
important, in order to oxidise HMF into FDCA as well as support
the long-term stability of HMF and electro-catalysts. With this
perspective, finding an appropriate electrolyte that can stabilise
both the electrode and the HMF is important for the
electrochemical oxidation of HMF into FDCA.
In this manner, recently, metal boride or phosphorous have
been implied frequently as an electrocatalysts on oxidation
reaction, due to their noticeable reactivity in aqueous
atmospheres. To the best of knowledge, boride/phosphorous
form of transition metal contributed on forming oxyhydroxide
species under aqueous atmosphere, which shows catalytic
activity and performance during electrochemical oxidation
reaction. Among various kinds of boride/phosphorous,
especially, cobalt phosphorous (Co-P) has been widely applied
2
O)
2
CF (geometric area of 1 cm ) was thoroughly rinsed with
water and ethanol to remove residual organic species before
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electrodeposition. Electrodeposition of Co-P_H
performed using a three-electrode cell with an electrolyte
composed of 50 mM CoCl ∙6H O and 0.1 M NaH PO ∙H O in
2
O
was
3
2
2
2
2
2
2
water. CF, Pt wire, and Ag/AgCl (sat. A 4 M KCl) wire used as the
working electrode, counter electrode, and reference electrode,
respectively. Cyclic voltammetry (CV) for electrodeposition of
2
O performed for 15 cycles, within the range -1.2 V to -
.3 V vs. Ag/AgCl reference electrode at a scan rate of 5 mV/s.
Co-P_H
0
3
3
After deposition, the samples were rinsed with methanol and
deionised water.
Preparation of DES-stabilised Co-P/CF (Co-P_DES)
3
4
CF was rinsed using the same method described above.
Electrodeposition of Co-P_DES was performed using the same
methods as for Co-P_H O sample preparation, except that
2
ethaline at 357 K was used as the electrolyte instead of water.
Electrodeposition of Co-P_DES was performed for 15 cycles,
within the range -1.0. to 0.1 V vs. Ag wire. After deposition, Co-
P_DES was washed several times with water. The concentration
3
5, 36
for electrochemical reaction.
The formation of Co-P follows
3
7
the net reaction for spontaneous reaction:
2
+
−
2
+
−
퐶표 ꢀ 퐻 푃푂 ꢀ ꢁ퐻 ꢀ 3푒 → 퐶표 ꢂ 푃 ꢀ ꢁ퐻 푂
2
2
The Co-P deposited by pristine methods has limitations on
durability, which the phosphorous is easily leaching out as the
electrochemical reaction proceeds.38
Therefore, following the results of a Co-P electrodes for HMF
oxidation to FDCA reported by Jiang et al.,39 we prepared two
different kinds of Co-P electrodes. Co-P on copper foam
fabricated by a modified potentiodynamic deposition method
of Co species, altering the reaction solvent to a DES and water.
Subsequently, electrochemical oxidation of HMF to FDCA investigated using field emission scanning electron microscopy
performed in lower pH (0.5 M NaHCO solution at a pH of 12 to (FE-SEM, Tescan, Mira 3) at an accelerating voltage of 20 kV. The
2 2 2
of NaH PO ∙H O varied from 0.05 M to 0.2 M for comparison of
Co-P_DES electrodes with different Co-P load amounts.
Characterisation
40
The surface morphologies of the prepared samples were
3
reduce HMF degradation during reaction. The reaction atomic ratios of the samples were measured using an energy-
efficiency and the stability of the electrodes were compared in dispersive X-ray spectrometer (EDS, Noran System Seven,
this study.
Thermo Fischer) at an accelerating voltage of 5 kV. X-ray
photoelectron spectroscopy (XPS, Kratos Axis Ultra) analysis
was performed using an Al K-alpha source. The binding energies
was calibrated by using the residual carbon 1s peak at 284.6 eV.
Transmission electron microscopy (TEM, Zeiss Libra 200 FE)
measurements were performed at 200 kV.
Experimental
Materials
Cobalt(II) sulfate heptahydrate (CoSO
4
∙7H
PO ∙H
OH), ethylene chloride,
), and potassium hydroxide were
2
O), sodium
hypophosphite monohydrate (
chloride ( 99%, (CH N(Cl)CH
sodium bicarbonate (NaHCO
purchased from Aldrich and used as received. 5-hydroxy-
methylfurfural (HMF), 2-formyl-5-furancarboxylic acid (FFCA),
≥
99%, NaH
CH
2
2
2
O), choline
HMF stability test in different pH of solution
≥
3
)
3
2
2
To evaluating HMF stability in different pH of solution, 1.0 M
KOH solution (pH 13.6) and 0.5 M NaHCO solution (pH 12) was
3
3
prepared. The 5 mM of HMF dissolved in each solutions and
solution stirred gently at the room temperature. The 10 μL of
solution taken from solution in every 2 h and analysed using
high-performance liquid chromatography. The concentration of
remained HMF was calculated and plotted by using standard
calibration curves.
2
,5-furandicarboxylic acid (FDCA), and 5-Hydroxy-methyl-2-
furancarboxylic acid (HMFCA) were purchased from Aldrich and
used as received. 2,5-Diformylfuran (DFF) was purchased from
TCI Chemical. Copper foam (CF) purchased from MTI
Corporation. A Millipore Milli-Q Integral 10 System used for
deionized water (18 MΩ/cm).
Electrochemical HMF oxidation and product analysis
Preparation of ethaline as a deep eutectic solvent (DES)
To investigate the catalytic abilities of both Co-P_H O and Co-
2
P_DES, linear sweep voltammetry (LSV) was measured under
2
| J. Name., 2012, 00, 1-3
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with and without HMF conditions. The electrochemical cell
consisted of a three-electrode system with undivided cell
prepared samples for the working electrode, Pt wire for the
View Article Online
DOI: 10.1039/D0NJ01426E
(
counter electrode, and Ag/AgCl (4M KCl) electrode for the
reference electrode) were used. The applied potential
controlled by a potentiostat/galvanostat (VSP, Biologics). A 0.5
M NaHCO
3
solution (pH 12) with or without 5 mM HMF were
prior to use, to
used as the electrolyte, which purged with N
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remove dissolved oxygen. The potential was swept from the
open-circuit potential (Voc) to the positive direction at 10 mV/s
with stirring. The measurement results plotted against the
reversible hydrogen electrode (RHE) using the equation:
Fig. 1. Concentration change of HMF in two electrolytes with different pH conditions over
time.
0
E (V vs. RHE) = E (V vs. Ag/AgCl) + 0.197 V + 0.059 × pH
This allows facile comparison of the data against the
thermodynamic water oxidation potential under the pH
conditions used in this study. The geometric area of the working
electrode used for calculating all current densities reported in
this study.
For quantification of oxidation products, including yield and
Faraday efficiency (FE), electrochemical HMF oxidation
performed while applying a constant potential until 50 C of
charge passed. The FE of FDCA product was calculated as follow:
푚표푙 표푓 퐹퐷퐶퐴 푝푟표푑푢푐푒푑
FE (%) =
× 100 %
푚표푙 표푓 푡표푡푎푙 푒푙푒푐푡푟표푛푠 푝푎푠푠푒푑
6
For the electrochemical oxidation, a three- electrode system
was used in which Co-P electrodes were used as the working
electrode, Pt wire was used as the counter electrode and
Ag/AgCl (4 M KCl) was used as the reference electrode,
respectively, and 1.45 V vs. RHE of potential were applied. A 0.5
M sodium bicarbonate solution (pH 12) used as the electrolyte
with 5 mM HMF. 10 μL of solution were taken from the cell
during and after reaction, and analysed using high-performance
liquid chromatography (HPLC, YL 9100, Younglin Instrument Ltd.)
with a 265 nm wavelength set ultraviolet-visible detector.
Sulfuric acid (5 mM) used as the mobile phase in isocratic mode,
with a 0.5 mL/min flow rate at 338 K, was injected into the Hi-
Plex H column. The quantification and qualification of products
were performed by calibration curves (correlation coefficient =
Fig. 2. SEM image of (a) Co-P_DES and (b) Co-P_H
elemental analysis of Co and P.
2
O electrodes; (c) table of SEM-EDS
As shown in Fig. 1, under the high pH condition of 1.0 M KOH
pH 13.6), HMF degrades quickly and only 50% of the initial
(
concentration remains after 6h. Using 0.5 M NaHCO
pH 12) does not completely prevent HMF from degradation,
but almost 80% of HMF still remains in solution. Thus, in this
work, we used 0.5 M NaHCO (pH 12) solution as the electrolyte
during electrochemical HMF oxidation into FDCA.
Co-P_DES and Co-P_H O prepared by an electrodeposition
method by cycling the designated potential ranges for 15 cycles.
The CV curves during Co-P deposition in DES and H O shown in
3
electrolyte
(
3
2
2
0
.999) by applying a standard solution of known concentration.
Fig. S1. As the reaction media changed for electrochemical
deposition of Co-P on Cu foam, the morphology of the
deposited Co-P showed noticeable changes, as shown in Fig. 2.
Using Co-P_DES, more fine particles attached to the surface of
All presented data are an average of triplicate experiments. The
produced FDCA was confirmed by nuclear magnetic resonance
spectroscopy (NMR, Bruker AVANCE III).
2
the Cu foam, while with Co-P_H O, highly aggregated irregular
Results and discussion
particles attached to the Cu foam. Furthermore, SEM-EDS
analysis results show that a higher amount of phosphorous is
loaded when the electrodeposition of Co-P on CF is in DES
Previous studies on the oxidation of HMF to FDCA have been
performed under strong basic conditions because this activates
the 5-position alcohol and oxidises the 2-position aldehyde
group to produce FDCA, which has carboxyl groups at the 2- and
5-positions of the furan ring. However, excessive bases initiates
nucleophilic attack for condensation reactions between HMF
molecules, forming linkages at the alpha position or
substitutions at the beta position of HMF, resulting in
degradation and denaturation of HMF.41, 42
2
rather than in H O (Fig. 2c).
The higher amount of loaded P in Co-P_DES also led to
enhanced electrochemical efficiency of the HMF oxidation
reaction, as shown by the LSV curves of different concentrations
of P precursors (Fig. S2).
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Fig. 4. HMF conversion and product yield curves vs. charge passed for (a) Co-P_DES and
(b) Co-P_H O electrodes
2
Six kinds of peaks are observed for both electrodes, which
correspond to Co 2p3/2 (778.2 eV), Co-O (780.8 eV), satellite
786.6 eV), Co 2p1/2 (793.3 eV), Co-O (796.7 eV), and satellite
802.8 eV), respectively. In the case of the P 2p spectra,
elemental P (129.7 eV) and P from Co-P (133.2 eV) are observed
in both Co-P_DES (Fig. 3 d) and Co-P_H O (Fig. 3 e),
(
(
26
2
43
respectively.
The Co 2p and P 2p XPS spectra of Co-P_DES and Co-P_H
2
O
are consistent with previously reported results for Co-P, which
means that Co-P is well deposited on CF using either solvent
usage. However, a higher phosphorous ratio in Co-P_DES led
to a more distinct peak of larger intensity for the P 2p spectrum
2
compared to that of Co-P_H O, which agrees well with the
44
Fig. 3. (a) LSV curves of Co-P_DES and CoP_H
O, XPS Co 2p spectra of (b) Co-P_DES, (c) above SEM-EDS analysis results.
2
Co-P_H
2
O, XPS P 2p spectra of (d) Co-P_DES, and (e) CoP_H
2
O
According to the LSV results presented in Fig. 3a, 1.45 V vs.
RHE is the optimal potential for both electrodes, which favours
As the P precursor concentration increased, the onset the HMF oxidation reaction over the water oxidation reaction.
potential (Vonset) shifted to a lower potential. Finally, the
electrode deposited at 0.2 M P precursor showed the same
V
onset of the metallic Co electrode. Accordingly, further
experiments performed using electrodes deposited using 0.2 M
P precursor. The optimal thickness of deposited Co-P layer
investigated by scanning LSV curves depends on deposition
cycles, which presented in Fig. S3. The 15 times of deposition
cycles showed the best electrochemical catalytic properties of
Co-P_DES electrode.
LSV curves of the as-deposited Co-P_DES and Co-P_H O
2
electrodes shown in Fig. 3a. The solid line corresponds to the
absence of HMF and the dashed line corresponds to its
3
presence at 5 mM concentration in 0.5 M NaHCO electrolyte.
The Vonset of the solid line is the initiation potential for water
oxidation, which was 1.5 V vs. RHE for Co-P_DES and 1.53 V vs.
2
RHE for Co-P_H O electrode.
However, when 5 mM HMF was added (dashed line), the
onset shifted to 1.34 V vs. RHE for Co-P_DES and 1.37 V vs. RHE
V
2
for the Co-P_H O electrode, indicating that where Co-P
deposited in DES solvent showed a lower Vonset than that in H
solvent.
The surface-deposited Co-P composition of both electrodes
investigated by X-ray photoelectron spectroscopy (XPS). Fig. 3b
and c show the Co 2p spectra of Co-P_DES and Co-P_H
2
O
Fig. 5. SEM images of Co-P_DES (a) before reaction and (b) after reaction, SEM images of
Co-P_H O (c) before reaction and (d) after reaction, XPS Co 2p spectra of (e) Co-P_DES
and (f) Co-P_H O after HMF oxidation reaction, P 2p spectra of (g) Co-P_DES, and (h) Co-
P_H O after HMF oxidation reaction.
2
2
O,
2
respectively.
2
4
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Fig. 6. (a) j-t plot with passed charge of Co-P_DES with repeated reaction cycles,
b) HMF conversion and Product yield profile as repeated addition of 5 mM fresh
HMF.
(
Scheme 1. Possible pathways of electrochemical HMF oxidation into FDCA
Thus, the conversion of HMF by both Co-P_DES and Co-P_H
electrodes was performed using 0.5 M NaHCO electrolyte at
1.45 V vs. RHE, with a total charge of 50 C, and the reaction
product was analysed every 10 C of charge.
At the initial stage of the reaction (<20 C), FFCA was produced
as the major product of the reaction with both Co-P_DES and
2
O
a small P peak for the Co-P (133.2 eV) is observed only for the
Co-P_DES electrode, while no phosphorous peak is observed for
the Co-P_H O electrode (Fig. 5g and h). To obtain more
2
information on the catalytic activity of Co-P_DES for the
electrochemical HMF oxidation reaction, a repeated reaction at
.45 V vs. RHE with 5 mM HMF addition was performed.
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1
2
Co-P_H O electrodes. However, after 20 C, the yield of FDCA
The Co-P_DES showed electrocatalytic properties until fourth
increased. After 50 C, the FFCA yield decreased and 85.3% yield
of FDCA was obtained with 99% of HMF conversion, and the
Faraday efficiency of HMF conversion to FDCA was 77.3% using
the Co-P_DES electrode (Fig. 4a). The detailed j-t curves during
HMF oxidation reaction by Co-P_DES and Co-P_H
on Fig. S4. In the case of the Co-P_H O electrode, a slight
increase in the FDCA yield observed, while the FFCA yield
maintained during the whole reaction, and a 46.5% yield of
FDCA obtained with 89.9% of HMF conversion. The Faraday
efficiency of HMF to FDCA conversion was 41.4% (Fig. 4b). It is
notable that the yield of HMFCA and DFF was less than 3% for
2
both the Co-P_DES and Co-P_H O electrodes.
The produced FDCA was purified and confirmed by NMR
spectroscopy. The two peaks was observed which first one is
from aromatic singlet protons (denoted as H
from hydroxyl protons (denoted as H ), with chemical shifts of
7.3 ppm and 13.6 ppm, respectively (Fig. S5). The measured
NMR spectrum was in a good accordance with previously
reported NMR spectrum of FDCA.
To determine the reason why different FDCA yields observed
even when they were both Co-P deposited Cu foam electrodes,
SEM images of each electrode after the reaction were analysed.
In the image of the Co-P_DES electrode after the reaction,
surface-attached Co-P particles are pulverised into smaller
particles, maintaining the original shape of Co-P (Fig. 5 a and b).
times of repeated continuous reaction (Fig. 6a). The HMF
conversion and product yield profile as repeated addition of 5
mM of fresh HMF (Fig. 6b). As repeated reaction cycle increases,
distribution of HMF oxidation products was maintained, which
means that Co-P_DES electrode is stable, with in a good
accordance with above XPS analysis results.
The electrochemical oxidation of HMF into FDCA follows the
two pathway which shown as Scheme 1. The first pathway is
HMF oxidize into 2,5-Furandicarboxaldehyde (DFF) (route A).
The other pathway is HMF oxidize into 5-hydroxymethyl-2-
furancarboxylic acid (HMFCA) (route B). Both pathways are
converge into 5-formyl-2-furancarboxylic acid (FFCA) and FDCA
obtained as final product. Under the base condition, HMF
rapidly converted into HMFCA by nucleophilic addition of
hydroxide ion, forming a geminal diol and then, proton transfer
from water to the intermediate of alkoxy ion forms FFCA.14
According to the above analysis results, the decreased
2
O presented
2
A
) and the other is
B
2
efficiency of Co-P_DES and Co-P_H O electrodes derived from a
45
loss of phosphorous atoms during the reaction, converting
surface-attached Co-P particles into cobalt oxides. Since the
hydrogen evolution reaction occurs as by-reaction during
2
O, stability of surface electrodeposited
Co-P decreases in H O atmosphere. Additionally, DES have
typical properties such as good ionic conductivity and good
solubility of metal salts, and do not degrade products. In these
reasons, Co-P synthesised in DES shows better electrochemical
preparation of Co-P_H
2
2
Conversely, in the case of the Co-P_H O electrode, the
morphology of the particles dramatically changed from a round-
type particle to a hexagonal plate shape, which proves that the
surface-deposited Co-P changed into cobalt oxides or
oxyhydroxides (Fig, 5 c and d). To reveal the changed surface
state of both electrodes after the HMF oxidation reaction, Co 2p
and P 2p XPS analyses performed. Both the metallic Co 2p1/2 and
Co 2p3/2 peaks (binding energies of 793.3 and 778.2 eV,
46
properties.
Conclusions
In summary, electrodeposited Co-P on Cu foam in different
solvents of water and DES, and these applied as electodes for
the electrochemical HMF oxidation reaction to FDCA. The Co-P
synthesised in DES solvent showed 99% HMF conversion with
5.3% FDCA yield, a remarkably increased performance
compared with Co-P synthesised under H O as the reaction
2
respectively) disappear for Co-P_DES and Co-P_H O after
reaction. Only Co-O peaks (796.7 eV and 780.8 eV) and their
satellite peaks (786.8 eV and 802.8 eV) observed (Fig. 5e and f).
However, in the case of the P 2p spectra of both electrodes,
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solvent, also demonstrated long-term stability. Referring to the
previously reported advantages of DES as a reaction solvent
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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such as good ionic conductivity, easily prepared, nontoxic, low- 17.
cost, and biodegradable, this work shows that DES also
contributes to the stability of synthesised metal-phosphorous-
based electrodes. Thus, this work suggests the usability of DES
to replace water as a reaction solvent for preparing electrodes
by electrodeposition, with enhanced sustainability and better
efficiency of electrodes.
X. Han, C. Li, Y. Guo, X. Liu, Y. Zhang and YV.ieWw Aarnticgl,e OAnplpinle.
Catal. A, 2016, 526, 1-8.
S. R. Kubota and K.-S. Choi, ChemSusChem, 2018, 11, 2138-
145.
B. J. Taitt, D.-H. Nam and K.-S. Choi, ACS Catal., 2019, 9,
60-670.
DOI: 10.1039/D0NJ01426E
1
1
2
8.
9.
0.
2
6
N.-T. Suen, S.-F. Hung, Q. Quan, N. Zhang, Y.-J. Xu and H. M.
Chen, Chem. Soc. Rev., 2017, 46, 337-365.
L. Gao, Y. Bao, S. Gan, Z. Sun, Z. Song, D. Han, F. Li and L.
Niu, ChemSusChem, 2018, 11, 2547-2553.
W.-J. Liu, L. Dang, Z. Xu, H.-Q. Yu, S. Jin and G. W. Huber,
ACS Catal., 2018, 8, 5533-5541.
H. Chen, J. Wang, Y. Yao, Z. Zhang, Z. Yang, J. Li, K. Chen, X.
Lu, P. Ouyang and J. Fu, ChemElectroChem, 2019, 6, 5797-
0
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21.
Conflicts of interest
There are no conflicts to declare.
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2.
3.
2
5801.
Acknowledgements
This work was supported by Basic Science Research Program
24.
D.-H. Nam, B. J. Taitt and K.-S. Choi, ACS Catal., 2018, 8,
1197-1206.
Z. Zhou, C. Chen, M. Gao, B. Xia and J. Zhang, Green Chem.,
2019, 21, 6699-6706.
M. J. Kang, H. Park, J. Jegal, S. Y. Hwang, Y. S. Kang and H.
G. Cha, Appl. Catal. B, 2019, 242, 85-91.
X. Huang, J. Song, M. Hua, Z. Xie, S. Liu, T. Wu, G. Yang and
B. Han, Green Chem., 2020, 22, 843-849.
H. M. Pham, M. J. Kang, K.-A. Kim, C. G. Im, S. Y. Hwang and
H. G. Cha, Korean J. Chem. Eng., 2020, 37, 556-562.
L. Gao, Z. Liu, J. Ma, L. Zhong, Z. Song, J. Xu, S. Gan, D. Han
and L. Niu, Appl. Catal. B, 2020, 261, 118235.
M. Sajid, X. Zhao and D. Liu, Green Chem., 2018, 20, 5427-
5453.
K. R. Vuyyuru and P. Strasser, Catal., 2012, 195, 144-154.
H. G. Cha and K.-S. Choi, Nat. Chem., 2015, 7, 328-333.
S. Barwe, J. Weidner, S. Cychy, D. M. Morales, S. Dieckhöfer,
D. Hiltrop, J. Masa, M. Muhler and W. Schuhmann, Angew.
Chem. Int. Ed., 2018, 57, 11460-11464.
D. K. Zhong and D. R. Gamelin, J. Am. Chem. Soc., 2010, 132,
4202-4207.
M. W. Kanan and D. G. Nocera, Science, 2008, 321, 1072-
1075.
K. W. Cho and H. S. Kwon, Catal. Today, 2007, 120, 298-304.
F. H. Saadi, A. I. Carim, E. Verlage, J. C. Hemminger, N. S.
Lewis and M. P. Soriaga, J. Phys. Chem. C, 2014, 118, 29294-
29300.
W. Li, X. Gao, D. Xiong, F. Xia, J. Liu, W.-G. Song, J. Xu, S. M.
Thalluri, M. F. Cerqueira, X. Fu and L. Liu, Chem. Sci., 2017,
8, 2952-2958.
N. Jiang, B. You, R. Boonstra, I. M. Terrero Rodriguez and Y.
Sun, ACS Energy Lett., 2016, 1, 386-390.
R. Hallaj, K. Akhtari, A. Salimi and S. Soltanian, Appl. Surf.
Sci., 2013, 276, 512-520.
G. Tsilomelekis, M. J. Orella, Z. Lin, Z. Cheng, W. Zheng, V.
Nikolakis and D. G. Vlachos, Green Chem., 2016, 18, 1983-
1993.
H. Ait Rass, N. Essayem and M. Besson, ChemSusChem,
2015, 8, 1206-1217.
(
NRF-2019R1C1C1004210) and (NRF-2019R1F1A1058695) 25.
through the National Research Foundation of Korea (NRF) grant
funded by the Ministry of Science, ICT and Korea Research
Institute of Chemical Technology (KRICT) core project (SS2042-
26.
27.
1
0).
2
8.
9.
Notes and references
2
1.
A. P. Abbott, G. Capper, D. L. Davies, H. L. Munro, R. K.
Rasheed and V. Tambyrajah, Chem. Comm., 2001, 2010- 30.
011.
A. P. Abbott, G. Capper, D. L. Davies, R. K. Rasheed and V. 31.
Tambyrajah, Chem. Comm., 2003, 70-71.
32.
2
2.
3.
A. P. Abbott, D. Boothby, G. Capper, D. L. Davies and R. K. 33.
Rasheed, J. Am. Chem. Soc., 2004, 126, 9142-9147.
N. M. Pereira, C. M. Pereira, J. P. Araújo and A. Fernando
Silva, J. Electroanal. Chem., 2017, 801, 545-551.
A. P. Abbott, J. C. Barron, G. Frisch, K. S. Ryder and A. F.
Silva, Electrochim. Acta, 2011, 56, 5272-5279.
X. Cao, L. Xu, Y. Shi, Y. Wang and X. Xue, Electrochim. Acta,
2
4.
5.
6.
7.
8.
34.
35.
36.
019, 295, 550-557.
X.-J. Shen, J.-L. Wen, Q.-Q. Mei, X. Chen, D. Sun, T.-Q. Yuan 37.
and R.-C. Sun, Green Chem., 2019, 21, 275-283.
B. L. Kuhn, G. C. Paveglio, S. Silvestri, E. I. Muller, M. S. P.
Enders, M. A. P. Martins, N. Zanatta, H. G. Bonacorso, C. 38.
Radke and C. P. Frizzo, New J. Chem., 2019, 43, 1415-1423.
M. R. S. J. Foreman, S. Holgersson, C. McPhee and M. S.
9.
Tyumentsev, New J. Chem., 2018, 42, 2006-2012.
W. Yu, C. Wang, Y. Yi, W. Zhou, H. Wang, Y. Yang and Z. Tan,
Cellulose, 2019, 26, 3069-3082.
D. E. Crawford, L. A. Wright, S. L. James and A. P. Abbott,
Chem. Comm., 2016, 52, 4215-4218.
39.
40.
41.
10.
11.
12.
13.
14.
P. McKendry, Bioresour. Technol., 2002, 83, 37-46.
M. Parikka, Biomass Bioenerg., 2004, 27, 613-620.
H. Yu, K.-A. Kim, M. J. Kang, S. Y. Hwang and H. G. Cha, ACS 42.
Sustainable Chem. Eng., 2019, 7, 3742-3748.
15.
T. W. G. Petersen, Top Value Added Chemicals from 43.
Biomass: Volume 1—Results of Screening for Potential
Candidates from Sugars and Synthesis Gas, Report 44.
DOE/GO-102004-1992, National Renewable Energy
H. Jung and A. Alfantazi, Electrochim. Acta, 2006, 51, 1806-
1814.
X.-y. Yan, S. Devaramani, J. Chen, D.-l. Shan, D.-d. Qin, Q.
Ma and X.-q. Lu, New J. Chem., 2017, 41, 2436-2442.
X. Han, L. Geng, Y. Guo, R. Jia, X. Liu, Y. Zhang and Y. Wang,
Green Chemistry, 2016, 18, 1597-1604.
Laboratory, 2004, 26-28.
P. Sharma, M. Solanki and R. K. Sharma, New J. Chem., 2019,
45.
16.
43, 10601-10609.
46.
A. A. C. Alcanfor, L. P. M. dos Santos, D. F. Dias, A. N. Correia
and P. de Lima-Neto, Electrochim. Acta, 2017, 235, 553-560.
6
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DOI: 10.1039/D0NJ01426E
Table of Contents Entry
Deep Eutectic Solvent Stabilised Co-P film for
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Electrocatalytic Oxidation of 5-hydroxymethylfurfural into
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,5-furandicarboxylic Acid
Myung Jong Kang, Hye Jin Yu, Hyun Sung Kimb,* and Hyun Gil Cha a,*
a
a,b
a
Center for Bio-based chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan
4
4429, Republic of Korea
b
Department of Chemistry, Pukyong National University, Busan 48513, Republic of Korea
hgcha@krict.re.kr

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The Co-P electrode synthesized in deep eutectic solution showed enhanced stability for
electrocatalytic HMF oxidation into FDCA.