Conductive Leaflike Cobalt Metal-Organic Framework Nanoarray on Carbon Cloth as a Flexible and Versatile Anode toward Both Electrocatalytic Glucose and Water Oxidation

Article abstract of DOI:10.1021/acs.inorgchem.8b01106

Transition metal-organic frameworks (MOFs), on account of their unique inherent properties of large pore volume, high specific surface area, tunable pores, and good catalytic activity, have been highly regarded as superior catalysts recently for water electrolysis, supercapacitors, batteries, sensors, and so on. Herein, we report on a cobalt MOF phase with 3D well-aligned nanosheets array architecture on carbon cloth (Co-MOF NS/CC), fabricated by a facile ambient liquid-phase deposition, could serve as a self-standing Janus catalytic electrode toward both glucose and water oxidation. It shows good glucose-sensing performance with low determination limit and large detection range. Also, it exhibits high water-oxidation efficiency with low overpotential and good durability. This work demonstrates the potential of utilizing transition-metal based well-aligned MOF nanoarrays for electrocatalytic oxidation.

Full text of DOI:10.1021/acs.inorgchem.8b01106

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Conductive Leaflike Cobalt Metal−Organic Framework Nanoarray
on Carbon Cloth as a Flexible and Versatile Anode toward Both
Electrocatalytic Glucose and Water Oxidation
Ziyi Wei,†,⊥ Wenxin Zhu,†,⊥ Yinge Li,† Yiyue Ma,† Jing Wang,† Na Hu,‡ Yourui Suo,‡
and Jianlong Wang*,†
†College of Food Science and Engineering, Northwest A&F University, 22 Xinong Road, Yangling 712100, Shaanxi, China
‡Qinghai Key Laboratory of Qinghai-Tibet Plateau Biological Resources, Northwest Institute of Plateau Biology, Chinese Academy
of Sciences, 23 Xinning Road, Xining 810008 Qinghai, China
S
* Supporting Information
ABSTRACT: Transition metal−organic frameworks
(MOFs), on account of their unique inherent properties of
large pore volume, high specific surface area, tunable pores,
and good catalytic activity, have been highly regarded as
superior catalysts recently for water electrolysis, super-
capacitors, batteries, sensors, and so on. Herein, we report
on a cobalt MOF phase with 3D well-aligned nanosheets array
architecture on carbon cloth (Co-MOF NS/CC), fabricated
by a facile ambient liquid-phase deposition, could serve as a
self-standing Janus catalytic electrode toward both glucose and
water oxidation. It shows good glucose-sensing performance
with low determination limit and large detection range. Also,
it exhibits high water-oxidation efficiency with low overpotential and good durability. This work demonstrates the potential of
utilizing transition-metal based well-aligned MOF nanoarrays for electrocatalytic oxidation.
performance,1,4 relatively prohibitive cost and low-abundance
INTRODUCTION
■
of these materials limit their large-scale applications.3 Develop-
Diabetes is a group of metabolic diseases characterized by high
ment of non-noble metal based nonenzymatic electrochemical
blood glucose, which will lead to systemic damage and
glucose sensors have thus garnered significant interest in recent
dysfunction of tissues and organs, rapidly growing to a global
years.3,7−11
epidemic.1,2 The diagnosis and management of diabetes
Metal−organic frameworks (MOFs), as a class of organic−
inorganic hybrid materials with well-ordered tunable porous
structures, high internal surface area, and good thermal and
demands analysis of blood glucose level several times a day,
which calls for the development of highly sensitive and efficient
glucose sensors. Among different sensing methods, electro-
chemical glucose detection based on the principle of
chemical stability, have drawn much attention in gas storage,
separation, energy storage and conversion, and sensors.12−22
electrocatalytic glucose oxidation is highly regarded as an
effective means.3 Currently, commercial glucose sensing
equipment is basically based on glucose oxidase (GOD)-
Although MOFs have abundant intrinsic molecular metal sites,
they are generally recognized as poor electrode materials due
to the natures of poor conductivity and relatively small pore
assisted biorecognition and oxidation of glucose molecules in
size.17,23,24 Some recently proposed effective strategies to
resolve these problems could be mainly divided into five
aspects: (i) High-temperature calcinations of MOFs to be
more porous metal alloys/C, metal oxides, or metal oxides/
C.25−28 (ii) Hybridization MOFs with other conductive
materials like graphene, MoS2, atomically dispersed metals,
metal hydroxides, or polymers.29−33 (iii) Turning MOFs into
ultrathin 2D nanosheets with coordinately unsaturated metal
sites and fast electron-transfer kinetics.34−36 (iv) Topological
conversion of MOFs into more porous and conductive metal
the global market.4 In spite of the fact that enzyme-based
glucose sensors have high sensitivity and excellent selectivity,5
they suffer from some natural vulnerabilities like the high cost
of the enzymes used, a complex enzyme-immobilization
process, instability resulting from the denaturation of the
enzymes, and low conductivity on account of indirect electron
transfer.1,4 By contrast, nonenzymatic glucose sensors based on
direct electrocatalytic oxidation has received increasing
attention due to their direct electron-transfer-shuttle-free
sensing style.5 This kind of sensors have attractive superiorities
of high sensitivity, good reproducibility and low cost.4,6
Although conventional nonenzymatic sensors based on the
precious metals and their alloys have excellent glucose sensing
Received: April 22, 2018
© XXXX American Chemical Society
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phosphides and chalcogenides.37−41 (v) Fabrication of well-
aligned 3D MOFs architectures with more exposed active sites,
larger electrolyte/catalyst contact area, and faster trans-
portation of active species than powder ones.17,23,42−46
However, considering that the calcination and topological
conversion may sacrifice MOFs’ intrinsic molecular metal
active sites and combination with other materials may block
the intrinsic micropores,17,23,24 synthesis of MOFs with
ultrathin 2D or well-aligned 3D nanostructures are thus
considered ideal solutions to endow MOFs with more active
sites and faster electron transfer. Moreover, it should be noted
that ultrathin 2D MOF nanosheets still need the time-
consuming post-coating procedures with polymeric binders
during the electrode preparation, which would inevitably
reduce the active surface area and cause potential peeling off of
catalysts during long-time gas evolution.47 In comparison,
direct growth of well-aligned open-shelled MOF nanoarrays on
current collectors, as a facile binder-free synthetic scheme,
could guarantee the sufficient catalysts/electrolyte contact,
favorable electric conductivity, and mechanical stability.25
Carbon cloth is a type of cheap and commercially available
textile with high conductivity, excellent flexibility, robust
corrosion resistance, and strong mechanical strength, repre-
senting an ideal 3D substrate to integrate catalysts for
electrocatalysis.48
Besides, as a typical subclass of MOFs with a tetrahedral
network structurally similar to the aluminosilicate zeolites,
zeolitic imidazolate frameworks (ZIFs) that consist of
transition-metal cations (M) and imidazole-based ligands
(Im) have been widely used in hydrogen storage, CO2
capture/conversion, and heterogeneous catalysis, due to their
good thermal and chemical stability, microporous structure,
large surface area, and tunable pore aperture.49 Among
different kind of ZIFs, ZIF-67, which is composed of Co2+
and 2-methylimidazole, has caused particular interest in the
design of electrode materials for electrocatalysis or batteries.49
However, there are limited reported works on using ZIF-67
directly as electrodes,50−52 and all the catalysts are in the form
of powders with sodalite topology and a space group of I43m.53
Another kind of 2D ZIF-67, ZIF-L, with a leaf-like structure
and confirmed good photocatalytic activity,53 has not been
even reported as electrode materials.
With these understandings, we verified here that a leaf-like
ZIF-L nanosheet array assembled on the carbon cloth
(denoted as Co-MOF NS/CC) synthesized by a facile ambient
liquid-phase deposition could act as a versatile electrocatalyst
for glucose and water oxidation. Experimental results indicate
that it not only exhibits good glucose-sensing performance
with low determination limit and large detection range, but has
high water-oxidation efficiency with low overpotential and
good durability. These good performances could be ascribed to
the enlarged catalyst/electrolyte contact area and exposed
enough active sites enabled by the 3D well-aligned nanoarray,
as well as the native good catalytic activity of Co-MOFs.
Figure 1. Top: Schematic illustration for the fabrication of Co-MOF
NS/CC. (a) XRD pattern of Co-MOF NS/CC. (b) SEM image of the
bare CC. (c,d) Low- and high-resolution SEM images of Co-MOF
NS/CC. (e) Cross-sectional SEM image of Co-MOF NS/CC; (f)
TEM image of the scratched Co-MOF nanosheet.
pointed star),48 other peaks match well with the diffraction
pattern of reported leaf-like ZIF-67 (also denoted as ZIF-
L).53,54 The ZIF-L exhibits a different crystal structure with a
space group of Cmce compared with previously reported ZIF-
67 materials with sodalite topology and a space group of
I43m.53,54 Figures 1b and S2a show the field emission scanning
electron microscopy (FE-SEM) images of bare carbon cloth.
After deposition with Co-MOF, the skeleton of carbon fibers is
fully covered with their well-aligned nanoarrays (Figures 1c
and S2b). Closer longitudinal and cross-sectional views (Figure
1d,e) indicate these units are actually leaf-like smooth
nanosheets with the thickness of 160 nm and the height of
3.8 μm. Elemental mapping images prove the presence and
uniform distribution of Co, C, N, and O elements on the Co-
MOF NS/CC (Figure S3). Transmission electron microscope
(TEM) image (Figure 1f) of Co-MOF phase scratched from
CC further shows a well-defined nanosheet morphology. N2
adsorption/desorption isotherms and multipoint Brunauer−
Emmett−Teller (BET) plot of the scratched Co-MOF
nanosheets show that it has a BET surface area of 17.08 m2
g−1 (Figure S4a,b), consistent well with the reported value of
16.245 m2 g−1 for ZIF-L.53 This result suggests the as-
synthesized Co-MOF nanosheets have no channels owing to
the leaf-like morphology with a 2D laminated structure.54 The
surface elemental compositions and valence states of Co-MOF
NS/CC were further analyzed by the X-ray photoelectron
spectroscopy (XPS). Survey XPS spectrum proves the
existence of Co, C, N, and O elements in Co-MOF NS/CC
RESULTS AND DISCUSSION
■
The fabrication process of Co-MOF NS/CC is illustrated in
the top portion of Figure 1. The optical photograph of color
change from bare CC to Co-MOF NS/CC and detailed
description are shown in the Supporting Information. Figure
1a shows the X-ray diffraction (XRD) pattern of Co-MOF NS/
CC. Except for the two typical broad peaks located at about 26
and 43° ascribing to the substrate of CC (marked with the five-
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(Figure S5a), consistent with above-mentioned elemental
mapping results. Figure S5b,c show the high-resolution XPS
spectra of Co 2p and N 1s. The XPS spectrum of Co 2p shows
Co 2p3/2 and Co 2p1/2 peaks centered at 781.2 and 796.7 eV,
respectively, along with two shakeup satellites (identified as
“Sat.”) at 786.3 and 802.5 eV, indicating that the Co2+ state is
predominant in Co-MOF phase.55 The N 1s spectrum shows
two peaks centered at about 398.8 and 400.3 eV, which could
be well assigned to the pyridinic N and pyrrolic N,
respectively.56
The glucose-sensing performances of Co-MOF NS/CC, Co-
MOF NS powder/CC and bare CC were investigated via cyclic
voltammetry (CV) in 0.1 M NaOH in the absence and
presence of 1.0 mM glucose at a scan rate of 50 mV s−1 (Figure
2a). In the absence of glucose, there is no any redox peak for
bare CC (black dotted line). In contrast, a pair of redox peaks
for both the Co-MOF NS/CC (violet dotted line) and Co-
MOF NS powder/CC (green dotted line) can be obviously
observed. When 1.0 mM glucose was added in above
electrolyte, bare CC causes a negligible oxidation current
density (black solid line), while significant increases in anodic
peak current density for both the Co-MOF NS/CC (violet
solid line) and Co-MOF NS powder/CC (green solid line)
could be clearly seen. This phenomenon suggests the Co-MOF
phase possesses high electrocatalytic activity for glucose
oxidation. Besides, from the bar chart of comparison of
current density increments for different electrodes (inset in
Figure 2a), we could concluded that the Co-MOF NS/CC has
a higher glucose-oxidation performance than Co-MOF NS
powder/CC, indicating that the integrated nanoarray structure
is beneficial to the improved catalytic performance of Co-MOF
NS/CC. In addition, the cyclic voltammetric curves (CVs) of
Co-MOF NS/CC in 0.1 M NaOH containing 1.0 mM glucose
at different scan rates were also acquired, as depicted in Figure
S6a. It can be seen that the anodic peak shows a slightly
positive shift and the cathodic peak shifts negatively with the
increase of scan rate. Figure S6b exhibits that both the anodic
and cathodic peak current densities increase linearly with the
scan rates in the range of 30−100 mV s−1. The good linear
relationship between peak current densities and scan rates
implies a diffusion-controlled electrochemical process of
glucose oxidation on the surface of Co-MOF NS/CC.8,57
To further study the sensing performance of Co-MOF NS/
CC electrode toward nonenzymatic glucose detection, CVs of
the Co-MOF NS/CC electrode in 0.1 M NaOH containing
different concentrations of glucose were recorded here (Figure
2b). As observed, the anodic peak current densities increase
with the increase of glucose concentration in the range of 0−
2.5 mM. A good linear correlation between glucose
concentrations and anodic peak current densities in the
whole concentration range (0−2.5 mM) can be obtained
(Figure S7). These results indicate the excellent catalytic
performance of Co-MOF NS/CC for glucose oxidation.
The optimal application potential was further tested by
dropwise addition of 1.0 mM glucose to 0.1 M NaOH at 100 s
interval under different potentials in the range of 0.30−0.55 V,
as presented in Figure S8. When the potential is 0.50 V, the
current density reaches the top and the signal-to-noise ratio is
relatively small. No matter the potential is higher or lower than
0.50 V, the current density will decrease. Therefore, we chose
0.50 V as the optimal working potential in the follow-up
experiments. Amperometric responses to successive injection
of different glucose concentrations in constantly stirred 0.1 M
NaOH were also performed. As shown in Figure 2c,
amperometric current density response increases with the
continuous addition of glucose. The lowest response
concentration of 4 μM (determination limit, LOD) can be
seen in the inset. Figure 2d displays excellent linearity between
the steady-state current densities and glucose concentrations in
the range of 0.004−4.428 mM, and a relative-high sensitivity of
1113 μA mM−1 cm−2 calculated by the slope (inset). The limit
of detection was calculated to be 1.2 μM by using the equation
of LOD = 3.3 σ/S, where σ is the standard deviation of
intercept and S is the slope of the calibration curve.4 However,
the limit of detection just reflects theoretically the minimum
detectable concentration. In contrast, determination limit is
more reliable and meaningful that it could provide an accurate
minimum detectable concentration.4 Quantitative comparisons
in regard to linear range, LOD, and sensitivity of this electrode
with other reported superior transition-metal based glucose
Figure 2. (a) CVs of bare CC (black curves), Co-MOF NS powder/
CC (green curves), and Co-MOF NS array/CC (violet curves) in 0.1
M NaOH with and without the presence of 1.0 mM glucose at 50 mV
s−1. Inset: bar chart of comparison of current density increments for
different electrodes. (b) CVs of Co-MOF NS/CC in 0.1 M NaOH
with different glucose concentrations (0−2.5 mM) at 50 mV s−1. (c)
Amperometric responses of Co-MOF NS/CC to the successive
addition of glucose at 0.5 V vs Ag/AgCl (Inset is the i−t curve at low
glucose concentration range). (d) Corresponding linear calibration
curve. Inset is amplification of the calibration curve in the low glucose
concentration range. (e) Amperometric responses of the Co-MOF
NS/CC toward the successive addition of different concentrations of
glucose, Lac, Fru, AA, Urea, UA, DA, NaCl, and L-Cys in a stirred 0.1
M NaOH. (f) Amperometric responses of the Co-MOF NS/CC with
the successive addition of 0.05 mM glucose in 10% diluted human
blood serum sample. Inset in the top left corner: Corresponding
calibration curve. Inset in the lower right corner: amperometric
responses of this sensor with the successive addition of another
glucose concentration of 0.07 mM in a new 10% diluted serum
sample.
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sensors were presented in Table S1, proving its superiority in
glucose sensing.
The selectivity and practical feasibility in diluted human
blood serum of this sensor were further tested. Figure 2e
exhibits the amperometric response of the Co-MOF NS/CC at
0.5 V to the successive addition of different concentrations of
interferents and glucose in a stirred 0.1 M NaOH. With
stepwise addition of the same concentration (0.2 mM),
obvious current responses of these interferents could be seen
(black curve). As the glucose concentration in human serum is
generally about 30 times higher than those for other
interferents,4 the concentration ratios of these interferents
and glucose at 1:10 and 1:30 (physiological level) were applied
for comparison. It could be seen that these interfering species
(20 or 6.7 μM) cause negligible current responses, proving the
excellent selectivity of Co-MOF NS/CC for glucose under
physiological conditions. We also applied this sensor in diluted
human blood serum samples to verify its practicability for
glucose sensing. Figure 2f shows the amperometric responses
of Co-MOF NS/CC on the continuous addition of 0.05 mM
glucose in 10% diluted human blood serum sample.
Calibration curve (inset in the top left corner) shows that
the current densities increase linearly with the increase of
glucose concentrations from 0.48−0.78 mM. Furthermore, we
recorded the amperometric responses with the successive
addition of 0.07 mM glucose in another 10% diluted serum
sample (inset in the lower right corner) and found that the
glucose concentration is consistent well with the measured
value in each sample with high recoveries from 100.4−103.4%
(Table S2). The above results demonstrate this glucose sensor
is feasible in diluted serums.
Figure 3. (a) LSV curves of RuO2/CC, Co-MOF NS/CC, Co-MOF
NS powder/CC, and bare CC at 2 mV s−1 in 1.0 M KOH. (b)
Corresponding Tafel plots. (c) Multistep chronopotentiometric curve
of Co-MOF NS/CC performed in 1.0 M KOH with anodic current
densities increasing from 10 to 100 mA cm−2 (inset: response time
and LSV curves before and after 5000 s durability test). (d) OER
chronopotentiometric curve at a constant 10 mA cm−2 for Co-MOF
NS/CC in 1.0 M KOH (inset: LSV curves before and after long-term
durability test).
amperometric response toward altered potentials with just
needing less than 2 s to achieve a steady-state current density
(inset), further proving the rapid reaction kinetics and
excellent working stability of this Co-MOF NS/CC in
base.47,59,62
In addition to the glucose-sensing performance, the oxygen
evolution reaction (OER) efficiency of Co-MOF NS/CC was
also tested here to verify its good electrocatalytic-oxidation
activity. The OER performances of Co-MOF NS/CC, Co-
MOF NS powder/CC, bare CC, and RuO2/CC were tested
using linear sweep voltammetry (LSV) in a homemade three-
electrode configuration with the electrodes as the working
electrode, a graphite plate as the counter electrode, and a
saturated calomel electrode (SCE) as the reference electrode.
As shown in Figure 3a, Co-MOF NS/CC exhibits a higher
current density and more negative OER onset potential (∼1.52
V vs RHE) than Co-MOF NS powder/CC (∼1.58 V vs RHE)
and bare CC (∼1.63 V vs RHE), although there is still a gap
between RuO2/CC and Co-MOF NS/CC. Note that the Co-
MOF NS/CC has an obvious superiority over the calcined
product of Co3O4 NS/CC (Figure S9) indicating that the
calcination treatment will sacrifice this Co-MOF’s intrinsic
molecular metal active sites.23,24 In addition, this Co-MOF
NS/CC electrode shows small overpotentials of 330 and 370
mV to achieve current densities of 20 and 50 mA cm−2 with a
relative-low Tafel slope of 106.6 mV dec−1 (Figure 3a,b),
surpassing those for Co-MOF NS powder/CC and some
newly reported MOF-based catalysts and even some transition
metal based oxides, hydroxides, chalcogenides, and phosphides
(Table S3). Both the small overpotential and low Tafel slope
demonstrate this Co-MOF NS/CC possesses a high activity
and fast reaction kinetics for OER.58,59 To evaluate the stability
of the Co-MOF NS/CC toward OER, multistep chronopo-
tentiometric curve was also measured (Figure 3c). The Co-
MOF NS/CC depicts an impressive OER durability with the
polarization curve keeping almost the same after 5000 s
electrolysis (inset in Figure 3c) and exhibits a fast
The long-term durability test shown in Figure 3d indicates
the good stability of the Co-MOF NS/CC toward OER in 1.0
M KOH. The potential almost remains unchanged at the
constant current density of 10 mA cm−2, and the OER
polarization curve after 10 h electrolysis shows negligible decay
compared with the initial one (inset in Figure 3d). Of note,
considering the zeolitic imidazolate framework (ZIF)-type
MOFs are not stable in base, the Co-MOF might be converted
to corresponding hydroxide or oxyhydroxide phases in the
electro-oxidation process to sustain the stable OER catalysis.
The SEM image, XRD pattern, XPS survey, and Co 2p spectra
of the Co-MOF NS/CC after long-term OER test were
recorded in Figure S10. The XRD pattern only exhibits the
characteristic peaks of CC, possibly due to the conversion of
Co-MOF to amorphous Co(OH)2 or CoOOH. The recorded
SEM image shows that the surface of Co-MOF nanosheets
turns to be rough with many derived nanoparticles. XPS survey
spectrum of Co-MOF after OER test shows that only small
amounts of N element exists on the surface of this catalyst,
further indicative of the conversion of Co-MOF to Co(OH)2
or CoOOH phases. The XPS Co 2p spectrum shows that after
electrolysis the Co2+ state in the catalyst turns to a mixed
valence state of Co2+/Co3+ with Co3+ state being predominant
and demonstrates that the derived main phase is CoOOH.
Besides, the flexural property of Co-MOF NS/CC was tested
by deforming this electrode under various bending states. The
photographs in Figure S11 indicate the Co-MOF NS/CC has a
good mechanical flexibility.
The high catalytic activity toward both the OER and glucose
oxidation of Co-MOF NS/CC could be well explained by the
following four aspects of electrochemical surface area (ECSA),
D
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conductivity, unique open-shelled 3D nanoarrayed topology,
and intrinsic catalytic activity of transition-metal based MOFs.
First, the Nyquist curves in Figure 4a present that Co-MOF
Methods; optical photographs; SEM images; elemental
mappings; XPS spectra; electrochemical data; Tables
S1−S3 (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: wanglong79@nwsuaf.edu.cn.
■
ORCID
Jianlong Wang: 0000-0002-2879-9489
Author Contributions
⊥Z.W. and W.Z. contributed equally to this work and are
considered co-first authors.
Figure 4. (a) Nyquist plots of Co-MOF NS/CC, Co-MOF NS
powder/CC, and bare CC measured in 1.0 M KOH. (b) Capacitive
current density (Δj) at 0.15 V as a function of scan rate in the range
of 0.1−0.2 V vs SCE.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by Grants from National Natural
Science Foundation of China (Nos. 31701690, 21675127, and
31371813), the Fundamental Research Funds for the Central
Universities (Nos. 2452015355, 2452017147, 2014YB093, and
2452015257), and the Development Project of Qinghai Key
Laboratory (2017-ZJ-Y10).
NS/CC has a smaller charge transfer resistance than Co-MOF
NS powder/CC and bare CC, demonstrating the Co-MOF
NS/CC possesses a more rapid electron transport kinetics.25,32
Second, we compared the ECSAs of Co-MOF NS/CC, Co-
MOF NS powder/CC, and bare CC (Figure S12) by double-
layer capacitance (Cdl), which is typically used to represent
ECSA.58−65 Figure 4b indicates the Cdl value of Co-MOF NS/
CC (192.5 mF cm−2) is about 5 times larger than that for Co-
MOF NS powder/CC (43.6 mF cm−2) and 40 times larger
than that for bare CC (4.88 mF cm−2), proving the Co-MOF
NS/CC owns a much higher ECSA than Co-MOF NS
powder/CC and bare CC. Third, the well-aligned open-shelled
nanoarrays structure provides a 3D mass-transfer pathway for
electrolyte penetration and small molecules diffusion, and
allows high utilization efficiency of catalytically active
species.25,48 Besides, the intrinsic high catalytic activity of
Co-MOFs, which has been previously confirmed,34,50−52 could
also support the superior glucose and water oxidation activities
of the Co-MOF NS/CC.
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CONCLUSION
■
In summary, we demonstrated here that the well-aligned Co-
MOF NS/CC synthesized by a simple ambient liquid-phase
deposition could act as a versatile anode for both glucose and
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01106.
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