Post on 09-Feb-2019
Electronic Supporting Information
Synthesis of Amorphous Boride Nanosheets by Chemical Reduction of Prussian Blue
Analogs for Efficient Water Electrolysis
Ting He, a Jean Marie Vianney Nsanzimana, b Ruijuan Qi, c Jun-Ye Zhang, a Mao Miao, a Ya Yan, d Kai Qi, a
Hongfang Liu, a and Bao Yu Xia a,*
a Key laboratory of Material chemistry for Energy Conversion and Storage (Ministry of Education), School
of Chemistry and Chemical Engineering, Wuhan National Laboratory for Optoelectronics, Huazhong
University of Science and Technology (HUST), 1037 Luoyu Road, Wuhan 430074, PR China
b School of Chemical and Biomedical Engineering, Nanyang Technological University, 50 Nanyang Avenue,
Singapore 639798, Singapore.
c School of Information Science and Technology, East China Normal University, 500 Dongchuan Road,
Shanghai 200241, PR China
d School of Materials Science and Engineering, University of Shanghai for Science and Technology, 516
Jungong Road, Shanghai 200093, PR China
Corresponding author: byxia@hust.edu.cn (B. Y. Xia)
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2018
Experimental Section
1、Material
Cobalt chloride hexahydrate, sodium citrate, sodium borohydride, and commercial Platinum (20%) on
graphitized carbon (20% Pt/C) were purchased from Sigma-Aldrich. Potassium hydroxide from J. T. Baker
and Nafion 5% in lower aliphatic alcohols and water was purchased from Sigma-Aldrich. All chemical
reagents were used in the experiments directly without further treatment.
2、Method
Synthesis of Co-Ni PBA stacked nanoplates: In a typical procedure, 1.6 mmol of cobalt chloride hexahydrate
and 0.6 mmol of sodium citrate were dissolved in 40 mL of DI water to form solution A. 0.8 mmol of
potassium tetracyanonickelate (II) was dissolved in 40 mL of DI water to form solution B. Next, blend
solutions A and B under magnetic stirring for 5 min. The obtained homogeneous solution was aged for 24 h
at room temperature. After collected by centrifugation and washed several times with water and ethanol, the
precipitates were dried at 60 oC overnight.
Synthesis of metal boride(oxide): The as-obtained CNBO-NS were prepared by chemical reduction of the
as-prepared PBA stacked nanoplates at room temperature. In a typical synthesis, 60 mg Co-Ni PBA was
dissolved in 20 mL DI water under a continuous and vigorous stirring to form a homogeneous mixture.
Afterward, 20 mL of sodium borohydride (NaBH4) solution (0.1 mol L-1) was added and the mixture was
maintained at room-temperature for 1.5 hours under stirring. The final products were collected by centrifuging
and washing with DI water for several times, and then dried overnight for further characterizations. Different
metal borides were synthesized by at a range of reduction times.
Characterizations. The crystal phase of metal borides was characterized by X-ray diffraction (XRD) patterns
on Empyrean (PANalytical B.V. with Cu-Kα radiation). The scanning electron microscopy (SEM) was carried
out on JEOL JSM-7100F at an accelerating voltage of 15 kV. Transmission electron microscopy (TEM) was
performed on TecnaiG2 20 (Philips) at an accelerating voltage of 200 kV assembled with a linear scanning
EDX spectrum. X-ray photoelectron spectroscopy (XPS) experiment was implemented on a Kratos AXIS
Ultra DLD-600W XPS system with a monochromatic Al Kα (1486.6 eV) X-ray source.
Electrochemical Measurements: All the electrochemical tests were carried out in a three-electrode system
on an electrochemical workstation (Autolab 302N). In the three-electrode configurations, a glassy carbon
electrode was served as the working electrode, while the calibrated Hg/HgO electrode (1.0 M KOH) and a
graphite rod were used as the reference electrode and the counter electrode, respectively. All measured
potentials were converted to the reversible hydrogen electrode (RHE), according to the equation; ERHE =
EHg/HgO + 0.098 + 0.059*pH. A homogeneous catalyst ink dispersion was obtained by sonicating the samples
(5 mg) and Nafion/alcohol mixed solution (500 μL). The prepared ink (10 μL) was dropped onto the working
electrode and dried at room temperature naturally, the mass loadings of the catalyst were about 0.5 mg cm-2.
The electrochemical measurements were investigated in 1.0 M KOH medium. Linear sweep voltammetry
(LSV) measurements were performed at the scan rate of 5 mV s-1 at a potential range 0 V to -0.4 V for
cathodic hydrogen evolution and from 1.3 V to 1.7 V for anodic oxygen evolution. The overall electrochemical
water splitting was detected by LSV measurements at the potential from 1.2 to 2.0 V. The stability test was
performed at a current density of 10 mA cm-2 for 24 h. All the data presented were corrected for iR losses and
background current. Electrochemical impedance spectroscopy (EIS) detection was conducted in the frequency
range from 100 kHz to 0.01 Hz with an ac perturbation of 5 mV when the potential was 1.55 V vs RHE. The
electrochemical double-layer capacitance was determined from the CV curves measured in a potential range
without redox processes according to the following equation: Cdl = Ic/ν, where Cdl, Ic, and ν are the double-
layer capacitance (mF cm-2) of the electroactive materials, charging current (mA cm-2), and scan rate (mV s-
1). Hence, cyclic voltammogram (CV) cycles used for Cdl determination was performed in the potential range
from 0.22 V to 0.12 V at the scan rate of 20, 40, 60, 80, 100, 200 mV s-1, respectively. And the drainage
method is applied in faradaic efficiency test. The faradaic efficiency calculation efficiency is: F=(m*n*F)/Q,
m denotes the moles of product, n denotes transferred electrons, F is faradaic constant and Q is the consumed
Figure and Captions
Figure S1. (a) SEM and (b) XRD of Co-Ni PBA precursor.
Figure S2. XRD patterns of amorphous metal borides annealed at different temperatures.
.
Figure S4. (a) TEM image and corresponding, inset of (a) is HRTEM, (b) EDX spectrum accompanying the
atomic ratio of corresponding elements.
Figure S5. XPS spectra of Ni 2p (a) and Co 2p (b) of Co-Ni PBA precursor.
Figure S6. XPS spectra of Ni 2p (a), Co 2p (b), B 1s (c) and O 1s (d) of CNBO-NS product obtained at 3h
reduction time.
Figure S7. (a) Polarization curves, (b) corresponding Tafel plots and (c) Nyquist plot EIS of CNBO-NS
obtained at different reaction time.
Figure S8. Polarization curves of CNBO-NS and their annealed samples at different temperatures.
Figure S9. Electrochemical capacitance measurements to determine the surface area of the obtained electrodes
in 1.0 M KOH electrolyte. The capacitive current density on CNBO-NS obtained at 1.5h (a) and 3h (b) from
double layer charging can be measured from cyclic voltammograms in a potential range where no Faradic
reaction occur, and (c) the measured capacitive current plotted as a function of scan rate.
Figure S10. Electrochemical capacitance measurements to determine the surface area of the obtained
electrodes in 1.0 M KOH electrolyte. The capacitive current density on CNBO-NS obtained at 1.5h (a) and
PBA precursor (b) from double layer charging can be measured from cyclic voltammograms in a potential
range where no Faradic reaction occur, and (c) the measured capacitive current plotted as a function of scan
rate.
Figure S11. (a) Polarization curves and (b) corresponding Tafel plots of the amorphous boride of different
reaction time in 1.0 M KOH solution.
Figure S12. Tafel plots of the amorphous boride and Co-Ni PBA in 1.0 M KOH solution.
Figure S13. Faradic efficiency of hydrogen evolution.
Figure S14. (a) LSV of CNBO-NS couple (without iR corrected), PBA couple and Pt/C//IrO2. (b)
Chronopotentiometry test during 24h electrolysis by the CNBO-NS pair. Inset is the photograph of CNBO-
NS couple assembled electrolysis cell.
Table S1. OER activity of recent reported catalysts.
Catalysts Electrolyte Overpotential
(η10)(mV)
Tafel slope (mV dec-1)
Reference
CNBO-NS 1.0 M KOH 300 60 This work
Co2B-500 0.1 M KOH 380 45 Adv. Energy Mater. 2016, 6, 1502313
Co–Ni–B@NF 1.0 M KOH 339 131 J. Mater. Chem. A 2017, 5, 12379
Ni-Co mixed oxide cages
1.0 M KOH 381 50 Adv. Mater. 2016, 28, 4601
FeNi@single layer graphene
1.0 M KOH 280 70 Energy Environ. Sci. 2016, 9, 123
Co3O4/NiCo2O4 nanocages
1.0 M KOH 340 88 J. Am. Chem. Soc. 2015, 137, 5590-5595
Hollow Co3S4 nanosheets
0.1 M KOH 363 90 ACS Nano 2014, 8, 10909-10919
NixB-300-GC 1.0 M KOH 380 / Adv. Energy Mater. 2017, 7, 1700381
Co-Bi NS/G 1.0 M KOH 290 53 Angew. Chem. Int. Ed. 2016, 55, 2488-2492
Ni-Bi@NB 1.0 M KOH 302 52 Angew. Chem. Int. Ed. 2017, 56, 6572-6577
CoP@N-doped Graphene
1.0 M KOH 338 54 Nanoscale 2016, 8, 10902
FeB2 1.0 M KOH 296 52.4 Adv. Energy Mater. 2017, 7, 1700513
Ni3Se2-GC 1.0 M KOH 310 79.5 Energy Environ. Sci. 2016, 9, 1771
NiCoP/NF 1.0 M KOH 320 37 Nano Lett. 2016, 16, 7718
NiCo LDH 1.0 M KOH 367 / Nano Lett. 2015, 15, 1421
Table S2. HER activity of recent reported catalysts.
Catalysts Electrolyte Overpotential
(η10)(mV)
Tafel slope (mV dec-1)
Reference
CNBO-NS 1.0 M KOH 140 116 This work
(Ni,Co)Se2-GA 1.0 M KOH 127 79 ACS Catal. 2017, 7, 6394-6399
NiCoFe LDHs 1.0 M KOH 200 70 ACS Energy Lett. 2016, 1, 445
Co–Ni –B@NF 1.0 M KOH 205 / J. Mater. Chem. A. 2017, 5, 12379
NiBx film 1.0 M KOH 135 88 Nano Energy 2016, 19, 98
Ni-Co-P-300 1.0 M KOH 150 60.6 Chem. Commun. 2016, 52, 1633-1636
CoP nanowire arrays 1.0 M KOH 209 129 J. Am. Chem. Soc. 2014, 136, 7587-7590
Co2B-500 1.0 M KOH 127 92.4 Adv. Energy Mater. 2016, 6, 1502313
NiB0.54@Ni Foil 1.0 M KOH 306 / Nano Energy 2016, 19, 98
FeCoNi 1.0 M KOH 149 77 ACS Catal. 2017, 7, 469
NiCo2S4 NWs/NF 1.0 M KOH 210 58.9 Adv. Funct. Mater. 2016, 26, 4661
CP@Ni-P 1.0 M KOH 117 85.4 Adv. Funct. Mater. 2016, 26, 4067
Ni-P 1.0 M KOH 350 132.3 Chem. Commun. 2016, 52, 1633-1636
Ni3Se2 nanoforest 1.0 M KOH 203 79 Nano Energy 2016, 24, 103
Table S3. Cell voltage of different catalysts for overall water electrolysis.
Catalysts Electrolyte Cell voltage (V)
Current density (mA cm-2)
Reference
CNBO-NS 1.0 M KOH 1.69 10 This work
(Ni,Co)Se2 1.0 M KOH 1.69 10 ACS Catal. 2017, 7, 6394-6399
NiSe 1.0 M KOH 1.63 10 Angew. Chem. Int. Ed. 2015, 54, 9351
NiFe LDH/NF 1.0 M KOH 1.7 10 Science 2014, 345, 1593
NiCo2O4 hollow microcuboids
1.0 M KOH 1.65 10 Angew. Chem. Int. Ed. 2016, 55, 1
Co–Ni –B@NF 1.0 M KOH 1.72 10 J. Mater. Chem. A 2017, 5, 12379
Co/NBC-900@NF 1.0 M KOH 1.68 10 Adv. Funct. Mater. 2018, 28, 1801136
Co2B-500 3.0 M KOH 1.81 10 Adv. Energy Mater. 2016, 6, 1502313
CoMnCH 1.0 M KOH 1.68 10 J. Am. Chem. Soc. 2017, 139, 8320
FeCoNi 1.0 M KOH 1.66 10 ACS Catal. 2017, 7, 469
Ni5P4 1.0 M KOH 1.7 10 Angew. Chem. Int. Ed. 2015, 54, 12361
Ni3S2/NF 1.0 M KOH 1.76 10 J. Am. Chem. Soc. 2015, 137, 14023