Supporting Information

A Novel Nickel-based Honeycomb Electrode with Microtapered Holes and Abundant Multivacancies for Highly Efficient Overall Water Splitting

Fan Zhanga†, Renjie Jia†*, Yonghong Liua,b*, Yuan Panc, Baoping Caia, Zhijian Lia, Zheng Liua, Shuaichen Lua, Yating Wanga, Hui Jina, Chi Maa, Xinlei Wua

a College of Mechanical and Electronic Engineering, China University of Petroleum (East China), Qingdao, Shandong, 266580, PR China.

b Key Laboratory of Unconventional Oil & Gas Development, China University of Petroleum (East China), Ministry of Education, Qingdao, PR China.

c State Key Laboratory of Heavy Oil Processing, Key Laboratory of Catalysis, China University of Petroleum (East China), Qingdao 266580, PR China.

* Corresponding authors. Email: jirenjie@163.com (Renjie Ji), liuyhupc@126.com (Yonghong Liu)

† These authors contributed equally to this work and should be considered as the co-first authors.

Supplementary Figures

Figure S1 a) Schematic illustration of the fabrication equipment. b) The schematic illustration of

fabricating the NHEMH. c) The simplified mechanism of the NHEMH preparation process. d) The

images of samples.

According to the schematic diagram of NHEMH electrodeposition mechanism shown in

Figure S1a,b, a constant potential is provided for the preparation process. When the anode rod is

close to the cathode, a local high current density area will be generated on the cathode plate. The

deposition rate in this direction is further accelerated by the rapid circulation of solution, and finally

the skeleton structure is electrodeposited. In the electrodeposition process, due to the high current

density, a large number of hydrogen bubbles would be generated in the cathode. Through the role of

the template of hydrogen bubbles (Figure S1c), a large number of pores would be generated on the

inner surface of the framework during the preparation process, and the bubbles would be rapidly

separated from the framework with the flow of the solution. With the continuous deposition of the

framework, the honeycomb skeleton with microtapered holes will eventually be formed. The

samples of NHEMH, nickel foam and carbon paper are shown in Figure S1d. The picture indicates

that the color of NHEMH is darker than that of nickel foam, but, lighter than carbon paper. The

detailed analysis is explained below.

Figure S2 a) HRTEM image of NHEMH. b) HRTEM of lattice defect NiO in NHEMH.

Figure S3 a,b) EDS mapping of NHEMH; c) EDS pattern of NHEMH with atom and weight ratio

for elements (inset).

Figure S4 The wetting ability test and the bubble contact angles under electrolyte of a,b) NF and

c,d) CP, respectively. (The CP is adopted after hydrophilic treatment to promote the electrocatalytic

reaction.)

Figure S5 a,b) The digital photos demonstrating the bubble releasing behaviors on the surface of

NF and CP. c,d) The figures are the size distribution statistics of releasing bubbles on the surface of

NF and CP.

Figure S6 SEM image of honey electrode without microtapered holes

Figure S7 Electrode OER and HER performance without IR compensation. a) polarization curves

of NHEMH, stainless steel, NF and carbon paper for OER; b) polarization curves of NHEMH,

stainless steel, NF and carbon paper for HER.

Figure S8 a) XRD pattern of NHEMH. b) XPS survey spectra of NHEMH.

Figure S9 Ni K-edge XANES spectra for NHEMH, Ni and NiO.

Table S1 Local structure parameters around Ni estimated by EXAFS analysis.

Sample Path N[a] R (Å)[b] σ2×103 (Å2)[c] ΔE (eV) R factor

Ni foil Ni-Ni 12* 2.48±0.002 6.0±0.2 7.5±0.4 0.001

NiONi-O 6.2±1.0 2.09±0.01 5.6±2.3 -0.2±2.0

0.009Ni-Ni 12.8±2.0 2.95±0.01 7.6±1.0 -3.3±1.2

NHEMH Ni-Ni 2.6±0.2 2.48±0.005 4.9±0.6 8.2±1.0 0.010

PNHEMH Ni-Ni 1.1±0.1 2.48±0.005 3.8±0.5 6.8±0.8 0.003

[a] N=coordination number;

[b] R=distance between absorber and backscatter atoms;

[c] σ2=Debye-Waller factor；

* =fixed coordination number.

Figure S10 a) OER and b) HER polarization curves of PNHEMH under different heat rates with

0.3 g NaH2PO2·H2O.

Figure S11 a) OER and b) HER polarization curves of PNHEMH under different masses of

NaH2PO2·H2O with a 5 /min heat rate.℃

Figure S12 EDS pattern of PNHEMH with atom and weight ratio for elements (inset).

Table S2 Elements components of solution by ICP-OES. Ni (wt%) B (wt%) Ca (wt%) Na (wt%) Al (wt%) Fe (wt%)

Solution 94.94 4.99 0.04463 0.02203 0.00024 0.00022

Table S3 Comparison of OER performance.

Catalysis Electrolyte Overpotential@10mA/cm2 Reference

PNHEMH 1.0M KOH 220mV This work

Ni2P 1.0M KOH 290mV S1

Ni/NiO 1.0M KOH 340mV S2

Ni2P nanoplates 1.0M KOH 300 mV S3

Multishelled Ni2P

Hollow Microspheres

1.0M KOH 270 mV S4

NiCoP microspheres 1.0M KOH 340 mV S5

Ni2P@ N-doped carbon 1.0M KOH 320 mV S6

FeMnP films 1.0M KOH 320 mV S7

Co-P film 1.0M KOH 345 mV S8

Ni5P4/Ni foil 1.0M KOH 290mV S9

NiCo LDH 1.0M KOH 367mV S10

NiO@Ni@Carbon

fiber

1.0M KOH 300mV S11

Ni(OH)2/NF 1.0M KOH 330mV S12

Figure S13 TOF of PNHEMH for OER.

The turnover frequency for OER and HER was estimated following the equation: TOF= jM/4Fm

and TOF= jM/2Fm, where j is the current density, F is Faraday's constant (96485.3C/mol), M is the

molar mass, m is the loading mass, and numbers 4 and 2 means 4 and 2 electrons per mole of O2

and H2, respectively.

Figure S14 Characterizations of PNHEMH after OER durability. a) SEM image. b) XRD pattern.

c) XPS spectra of Ni 2p; d) XPS spectra of P 2p; e) XPS spectra of O 1s. f) EPR spectrum.

Table S4 Comparison of HER performance.

Catalysis Electrolyte Overpotential@-10mA/

cm2

Reference

PNHEMH 1.0M KOH 84mV This work

Ni/NiP 1.0M KOH 130mV S2

Ni5P4/Ni foil 1.0M KOH 150mV S9

NiO@Ni@Carbon

fiber

1.0M KOH 153mV S11

Ni(OH)2/NF 1.0M KOH 172mV S12

CoP/CC 1.0M KOH 210mV S13

FeP NAS/CC 1.0M KOH 220mV S14

FeP nanorod 1.0M KOH 218mV S15

NiCuP 1.0M KOH 146mV S16

Porous NiCu-P 1.0M KOH 175mV S17

NiP2NS/CC 1.0M KOH 102mV S18

NiN3/NF 1.0M KOH 121mV S19

S-NiFe2O4/NF 1.0M KOH 138mV S20

VN-Co-P 1.0M KOH 138mV S21

Figure S15 TOF of PNHEMH for HER.

Figure S16 Characterizations of PNHEMH after HER durability. a) SEM image. b) XRD pattern.

c) XPS spectra of Ni 2p; d) XPS spectra of P 2p; e) XPS spectra of O 1s. f) EPR spectrum.

Figure S17 Polarization curves for a) OER and b) HER from the 3-time prepared sample,

respectively.

Figure S18 a) 50 h stability for the OER by chronopotentiometry at 100 mA/cm2; b) SEM image of

PNHEMH for honeycomb framework after 50 h OER.

Figure S19 a) 50 h stability for the HER by chronopotentiometry at 100 mA/cm2; b) SEM image of

PNHEMH for honeycomb framework after 50 h HER.

Figure S20 Cyclic voltammograms in the rank of 1.02-1.12 V vs RHE. a) NHEMH; b) PNHEMH;

c) P-doped NF; d) NF; e) the capacitive current of NHEMH, PNHEMH, P-doped NF, and NF at the

1.07 V vs RHE.

Figure S21 a) OER and b) HER polarization curves normalized to ECSA by the specific

capacitance.

Figure S22 (a) Nyquist plots of the NHEMH, PNHEMH, P-doped NF, and NF at an overpotential

of 300 mV; (b) Equivalent circuit; (c) corresponding resistances of NHEMH, PNHEMH, P-doped

NF, and NF.

Figure S23 Photograph of a two electrode cell for water splitting.

Table S5 Comparison of water splitting performance.

Catalysis Electrolyte Potential@10mA/cm2 Reference

PNHEMH 1.0M KOH 1.52V This work

NiP/NF 1.0M KOH 1.61 V S2

Co-P film 1.0M KOH 1.56V S8

Ni5P4/Ni foil 1.0M KOH 1.70V S9

Fe-CoP 1.0M KOH 1.60V S22

Ni-

P(Ni11(HPO3)8(OH)6/NF

1.0M KOH 1.65V S23

NiFe/NiCo2O4 1.0M KOH 1.67 V S24

Cu3P/NF 1.0M KOH 1.67 V S25

Ni(OH)2/NF 1.0M KOH 1.68 V S26

Ni-P/CF 1.0M KOH 1.68V S27

NiS/NF 1.0M KOH 1.64V S28

NiCoP/NF 1.0M KOH 1.58V S29

NiCoP/rGO 1.0M KOH 1.59V S30

NiF/NC@NF 1.0M KOH 1.58V S31

FeCoNi@NCP 1.0M KOH 1.687V S32

NiFe@NC 1.0M KOH 1.81V S33

Co/CFNG@NF 1.0M KOH 1.69V S34

Co-Ni-P film/Ti 1.0M KOH 1.65V S35

NFe LDH/NiCoP@NF 1.0M KOH 1.57V S36

NiFeSP@NF 1.0M KOH 1.56V S37

NiCo2N@NF 1.0M KOH 1.70V S38

Figure S24 Polarization curves of a) NHEMH and b) NF with different Pt/C and IrO2 masses for

overall water splitting.

Figure S25 The amount of evolved oxygen and hydrogen gas.

From the total charge passed through the cell at various time intervals, the Faradic efficiency was

calculated by the equation, Faradic efficiency=nFm/Q, where n is 2 and 4 for HER and OER

respectively, F is Faraday's constant (96485.3C/mol), m is moles of gas evolved and Q is the total

charge passed.

Figure S26 Ni 2p XPS spectra of NHEMH after heat treatment in a) hydrogen and b) oxygen.

Figure S27 OER polarization curves of NHEMH after heat treatment in hydrogen and oxygen.

Figure S28 The optimized model of heterojunction of Ni2P/NiO.

Figure S29 the optimized model of H* on the a) Ni2P/NiO-Vni, b) Ni2P/NiO-Vo, c) Ni2P/NiO.

Table S6 All the acronyms and symbols.Acronyms and symbols Expansions

NHEMH Nickel-based honeycomb electrode with microtapered holes

PNHEMH P-doped NHEMH

OER Oxygen Evolution Reaction

HER Hydrogen Evolution Reaction

CVD Chemical Vapour Deposition

NF Nickle Foam

CP Carbon Paper

XRD X-ray Diffraction

XPS X-ray Photoelectron Spectroscopy

SEM Scanning Electron Microscope

TEM Transmission Electron Microscope

HRTEM High Resolution Transmission Electron Microscope

XANES X-ray Absorption Near Edge Structure

EXAFS X-Ray Absorption Fine Structure

EDS Energy Dispersive X-ray Spectroscopic

EPR Electron Paramagnetic Resonance

Cdl Double Layer Capacitance

ECSA Electrochemical Active Surface Areas

EIS Electrochemical Impedance Spectroscopy

TOF Turnover Frequency

PBE Perdew–Burke–Ernzerhof

GTH Goedecker-Teter-Hutter

DOS Density of States

Movie S1 The wetting ability of NHEMH

Movie S2The gas evolution performance at 10 mA/cm2

Movie S3The gas evolution performance at 50 mA/cm2 captured by a high-speed camera

Movie S4The bubble behaviors of skeleton with and without micro-tapered holes

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