1

Supplementary Information

Potential-driven surface active structure rearrangement over

FeP@NC towards efficient electrocatalytic hydrogen evolutionFumin Tang,1 Hui Su,1 Xu Zhao,1 Hui Zhang,1 Fengchun Hu,1 Peng Yao,2 Qinghua Liu1, and Weiren Cheng1,*

1National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, Anhui, P. R. China2Department of Electronic Science and Technology, University of Science and Technology of China, Hefei 230027, Anhui, P. R. China

*E-mail: weiren@ustc.edu.cn

Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics.This journal is © the Owner Societies 2019

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S1. Calibration of potential vs Ag/AgCl to RHE.1

the relation between Ag/AgCl and RHE potential can be calibrated in

the high purity H2 saturated 0.5 M H2SO4 electrolyte with a Pt wire as the

working electrode. With a scan rate of 1 mV/s, the average potential,

where the current density started to came across X axis (becoming zero)

in CV curves, was regarded as the thermodynamic potential for the

hydrogen electrode reactions (Figure S2).

S2. Calculation of jECSA and TOF (Figure S9).2,3

(1);𝐸𝐶𝑆𝐴=

𝐶𝑑𝑙𝐶𝑠

(2);𝑗𝐸𝐶𝑆𝐴=

𝑗 × 𝑆𝐸𝐶𝑆𝐴

(3).𝑇𝑂𝐹=

𝑗 × 𝑆2𝑛𝐹

ECSA is short for electrochemical active surface area;

Cdl and Cs is double layer capacitance and specific capacitance of samples,

and Cs is assumed to 35 μC/cm2 according to previous report3.

j, S, F and n is the current density under given overpotential, the surface

area of the electrode, Faraday constant and the mole number of active

metal atoms for the electrode.

3

Figure S1. LSV curves in 0.5 M H2SO4 for FeP@NC synthesized under

different temperatures.

4

-0.30 -0.25 -0.20 -0.15 -0.10

-0.004

-0.003

-0.002

-0.001

0.000j (

A)

Potential (V vs Ag/AgCl)

-0.18 V

Figure S2. CV curve of Pt wire in 0.5 M H2SO4 electrolyte.

Figure S3. Details of the device in in-situ XAS measurement.

5

5 nm200 nm

(a) (b)

0.24 nm

Figure S4. SEM and HRTEM images of FeP particles.

0 2 4 6 8 10 12 14 16-2

-4

-6

-8

-10

-12

-14

FeP@NC FeP particles

j (m

A/c

m2 )

Time (h)

Figure S5. Chronopotentiometric measurements with an initial current

density of 10 mA/cm2 for FeP@NC at -0.135 VRHE and for FeP particles

at -0.495 VRHE.

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0 1000 2000 3000

300

600

900

1200 FeP particles FeP@NC

- Im

Z (

)

Re Z ()

Figure S6. Nyquist plots of FeP particles and FeP@NC at -0.15 VRHE in a

large scale.

406 404 402 400 398 396 394

Inte

nsity

(a.u

.)

Energy (eV)

Pyridinic-N

N 1s Pyrrolic-N

Figure S7. Deconvolution of N 1s XPS spectra for FeP@NC.

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-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04m

A/c

m2

V vs Ag/AgCl

20 mV/s 40 mV/s 80mV/s 120 mV/s 160 mV/s

-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15

-0.8-0.6-0.4-0.20.00.20.40.60.8 160 mV/s

120 mV/s80mV/s

20 mV/s

mA

/cm

2

V vs Ag/AgCl

40 mV/s

(a) (b)

Figure S8. Cyclic voltammetry curves of (a) FeP particles and (b)

FeP@NC.

85 135 1850

2

4

6

8

10

12

14

FeP particles

TOF

(10-3

·s-1

)

Overpotential (mV)

0

50

100

150

200

250

300

350

400 FeP@NC

TOF

(10-3

·s-1

)85 135 185

0

4

8

12

16

20

24

j EC

SA (m

A/c

m2 )

Overpotential (mV)

FeP@NC FeP particle

(a) (b)

Figure S9. (a) JECSA, and (b) TOF comparison of FeP@NC and FeP

particles under different overpotentials in 0.5 M H2SO4.

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-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

2.5 mA/cm2

0 mA/cm2

AfterBefore

Pote

ntia

l (V

vs R

HE)

Test SequenceDuring

0 mA/cm2

Figure S10. Working condition of work electrode during in-situ XAS

measurement.

7112 7113 7114 7115 7116 7117

-0.04

-0.02

0.00

0.02

0.04

0.06

2nd d

eriv

ativ

e

Energy (eV)

Before HER After HER During HER

7120 7140 7160 71800.0

0.2

0.4

0.6

0.8

1.0

1.2

XA

NES

Energy (eV)

Before HER After HER During HER

Figure S11. (a) XANES and (b) 2nd derivative curves of pre-edge region.

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0 2 4 6 8 10

-6

-4

-2

0

2

4

6

1s

Ener

gy (e

V)

D.O.S

3dz2

Figure S12. DOS calculation of 3dz2 orbits in different surface structure.

100 nm

(a) (b)

30 35 40 45 50 55 60 65

Inte

nsity

2(Degree)

FeP pdf.78-1443

Before HER

After HER

(c)

5 nm

Figure S13. (a) TEM, (b) HRTEM images and XRD patterns of

FeP@NC after long-time HER measurement.

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536 534 532 530 528

Inte

nsity

(a.u

.)

Binding Energy (eV)

Before HER

After HERAfter HER

H2O/OH Fe-OP-O

C-OO 1s

Figure S14. XPS comparison of O 1s for FeP@NC.

Table S1. The EXAFS fitted results for structure parameters around Fe

atoms.

Paths N σ2 (10-3) ΔE(eV) ΔR(Å)

Before HER

Fe-P 5.6 6.4 -1.84 0.024

Fe-O <0.05

During HER

Fe-P 5.8 5.3 -1.55 0.039

Fe-O 0.85 5.5 -2.12 -0.04

After HER

Fe-P 5.6 6.3 -1.84 0.024

Fe-O 0.23 5.0 -3.25 -0.04

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Table S2. The ratio of different bonds according to Figure S14.

Fe-O P-O C-O H2O/OH

Before HER 12.0 % 32.9 % 52.7 % 2.4 %

After HER 22.1 % 24.9 % 49.7 % 3.3 %

Table S3. Summary of HER performance for recent typical TMP electrocatalysts in 0.5 M H2SO4 electrolyte. (Stability is defined as the time when current density decays to its’ 90 %)

η@10 mA/cm2

(mV)

Tafel slope

(mV/dec)Stability Ref.

FeP@NC 135 78 >15 h This work

FeP 240 67 - Chem. Commun., 2013, 49, 6656.

FeP/NCNSs 114 64 - ACS Sustain. Chem. Eng., 2018, 6, 11587-

11594.

FeP nanowires 96 39 < 1 h Chem. Commun., 2016, 52, 2819–2822.

CoP nanorod bundle arrays/Ti

203 40 ~10 h Electrochem. Commun., 2015, 56, 56–60.

CoP@BCN-1 87 46 < 10 hAdv. Energy Mater., 2017, 7, 1601671.

Ni-P@Carbon fiber paper

98 58.8 - Adv. Funct. Mater., 2016, 26, 4067–4077.

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85 50 > 11 h J. Mater. Chem. A, 2016, 4, 10925–10932.

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172 62 < 6 h RSC Adv., 2015, 10290–10295.

MoP2 nanoparticles/Mo

143 57 - Nanoscale, 2016, 8,8500–8504 .

MoP nanosheet array

124 58 < 10 h Appl. Catal. B: Environ., 2016, 196, 193–198

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