Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is © The Royal Society of Chemistry 2020

Electronic Supplementary Information

Highly efficient overall water splitting ruthenium-cobalt alloy

electrocatalyst across a wide pH range via electronic coupling with

carbon dots

Tanglue Feng,‡a Guangtao Yu,‡bc Tao,a Shoujun Zhu,a Ruiqi Ku,c Ran Zhang,c Qingsen Zeng,a Mingxi Yang,a Yixin Chen,a Weihua Chen,d Wei Chen*bc and Bai Yang*ae

a State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, University, , 130012, .

b College of Chemistry and Materials Science, Fujian Normal University, Fuzhou, 350007, China c Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, , Changchun, 130023, China. d State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, University of Science and Technology of China, Changchun, 130022, China. e Key Laboratory of Preparation and Application of Environmental Friendly Material (Jilin Normal University), Ministry of Education, Changchun, 130103, China.

‡ These authors contributed equally to this work. Experimental Section

Chemicals

Cobalt gluconate (C12H22CoO14·xH2O) was purchased from Alfa Aesar. Tryptophan

(AR, 99%), RuCl3·xH2O (35.0-42.0% Ru) were purchased from Aladdin. Gluconic acid aqueous solution (50%) were obtained from Macklin.

The synthesis of materials

The synthesis of carbon dots Cobalt gluconate (0.25 g) and tryptophan (0.3 g) were dissolved in 10 mL water, followed by ultrasonication for 30 min. Then the mixture was transferred to a poly (tetrafluoroethylene) (Teflon)-lined autoclave, and was hydrothermally treated at 200oC for 6 h. The as-prepared production was naturally cooled down to room temperature and filtered through a 0.22 μm filter membrane to remove large particles. As a result, the brown solution was obtained. After removing solvent,the pale yellow powder was obtained and stored at 4oC. The as-obtained CDs samples can be redispersed in DI water for further characterization. The synthesis of RuCo@CDs and control catalysts

In a typical synthesis, 0.1 g RuCl3·xH2O was dissolved in the above CDs solution, followed by ultrasonication for 30 minutes to get an entirely homogeneous solution. The as-prepared solution was dried at 60°C for 24 h. The obtained powder was then annealed at 900°C for 4 h under argon atmosphere in the tube furnace with a heating rate of 5oC·min-1. The resulting sample was denoted as RuCo@CDs. For comparison with RuCo@CDs, other control catalysts (Co@CDs, RuCo@C and Ru@CDs ) were synthesized by following procedure. The Co@CDs catalyst was obtained by pyrolysis for Co-CDs at 900oC for 4 h under argon atmosphere. The RuCo@C sample was synthesized by pyrolysis of a mixture powder (cobalt gluconate

o of 0.25 g, tryptophan of 0.3 g and 0.1 g RuCl3·xH2O) at 900 C for 4 h under argon atmosphere. The preparation of Ru@CDs catalyst followed the almost same procedure as RuCo@CDs except for replacing cobalt gluconate of 0.250 g into gluconic acid (50 wt% aqueous solution) of 436 mg.

Characterization

Transmission electron microscopy (TEM) image were measured on JEM-2100F microscope operated at 200 kV. HAADF-STEM images were recorded employing spherical aberration correction transmission electron microscope (JEM-ARM300F) at 300 kV equipped with a probe corrector. UV-vis absorption spectra were acquired using UV-3101PC spectrophotometer (Shimadzu), and PL spectra were measured by 5301PC spectrometer. Element analysis were carried out by element analyzer (Vario micro cube, Elementar). Fourier Transfer infrared (FT-IR) spectra were gained from fourier transform infrared spectrometer (VERTEX 80V, Brucker). X-Ray photoelectron spectroscopy (XPS) were measured by X-ray photoelectron spectroscopy (HP 5950A), and the deconvolution processing of XPS spectra were carried out on XPSPEARK Version 4.1 software. The XRD pattern were obtained by X-ray diffractometer (Empyrean, PANalytical B.V.), and the Raman spectra were measured by Raman Spectrometer (LabRAM HR Evolution, Horiba) with a laser of

633 nm as the excitation line. The N2 absorptiondesorption isotherm were obtained using by surface absorption analyzer (ASAP 2020 ) at 78 K. The metal content was obtained using inductively coupled plasma-optical emission spectrometry (ICP-OES) analyzer (ELAN 9000/DRC). Specifically, in order to insure the accuracy of ruthenium content in catalyst, the 50 mg catalyst was added into 2 mL of chloroazotic acid, and was transferred to a poly (tetrafluoroethylene) (Teflon)-lined autoclave followed by treating at 230oC for 6 h to completely dissolve ruthenium.

Electrochemical measurements

4.0 mg of the catalyst powder was dispersed in 500 µL water/ethanol (v/v=3:7) mixed solution containing 35 μL Nafion solution of 2 wt%, and the mixed solution was sonicated for 40 min. Then 8 μL of the mixed solution was loaded on a glassy carbon electrode (GCE; a diameter of 3 mm; electrode area of 0.0707 cm2). Thus, the catalyst loading amount was calculated to be 0.905 mg·cm-2. All the electrochemical measurements were carried out on an electrochemical workstation (CHI660C). A glassy carbon electrode served as the working electrode, and the graphite rod were used as counter electrode. All electrocatalytic polarization curves, cyclic voltammetry (CV) curves, electrochemical impedance spectroscopy (EIS) spectra were measured using the Hg/Hg2C2 electrode as counter electrode, while all stability tests were tested

employing the Hg/Hg2SO4 electrode, Hg/Hg2Cl2 electrode, Hg/HgO electrode as counter electrode under acidic, neutral and alkaline media, respectively. All measurements were performed at room temperature. The electrocatalytic polarization curves of the samples were obtained by using linear sweep voltammetry (LSV) with a scan rate of 2 mV·s-1 at room temperature. EIS measurements were performed in the frequency range from 100 mHz to 100 kHz with AC amplitude of 10 mV. The stability tests were performed by long-term chronoamperometry (i-t curves) and long- term chronopotentiometry under constant constant voltage and current density, respectively. The Tafel slope was obtained by linear fitting according the tafel equation (η = a+b*log j, where η is overpotential, b is Tafel slope and j is current

density). The electrochemical double-layer capacitance (Cdl) and corresponding electrochemically active surface area (ECSA) of samples were estimated using a simple CV method. To be specific, the current density were measured from 5 to 45

mV·s-1 with the interval of 5 mV·s-1 in which the CV voltage windowfor HER was

chosen from -0.1 V to 0 V (E vs. Hg/Hg2Cl2), -0.5 V to -0.4 V (E vs. Hg/Hg2Cl2), -1.0

V to -0.9 V (E vs. Hg/Hg2Cl2) under 0.5 M H2SO4, neutral 1.0 M PBS, 1.0 M KOH solution, respectively, and the CV voltage window for OER is chosen from 0.7 V to

0.8 V (E vs. Hg/Hg2Cl2), 0.15 V to 0.25 V (E vs. Hg/Hg2Cl2), 0.05 V to 0.15 V (E vs.

Hg/Hg2Cl2) under 0.5 M H2SO4, neutral 1.0 M PBS,1.0 M KOH solution, respectively. The linear curves were fitted from the capacitive currents at the middle potential against different scan rates, and the slope was the Cdl value. All measured potentials in this work were converted to the reversible hydrogen electrode (RHE) by a equation (ERHE=ESCE+0.0591 pH+0.241 V for Hg/Hg2Cl2 electrode, ERHE = E+0.0591 pH+0.616 V for Hg/Hg2SO4 electrode, ERHE = E+0.0591pH+0.098 V for Hg/HgO electrode).

Calculation of the turnover frequency (TOF)

The TOF (s-1) was calculated from below equation:

-1 TOF (H2 s )=j*S / (2Fn) (1)

-1 TOF (O2 s )=j*S / (4Fn) (2)

Where j (A·cm-2) is current density during linear sweeping, S (cm-2) is the surface area of electrode, F (C/mol) is the faraday constant of 96500. n (mol) is the number of active sites, and all Ru and Co are assumed to be active sites. Furthermore, 1/2 (1/4) represent that two (four) electron were used to form a hydrogen (oxygen) molecule.

Density functional theory (DFT) simulation

The density functional theory (DFT) computations have been performed by employing the generalized gradient approximation (GGA) with the Perdew-Burke-

Ernzerhof exchangecorrelation functional1 within the frame of Vienna ab initio

simulation package (VASP).2, 3 In all computations, the projector-augmented plane

wave (PAW) is used to describe the electronion interactions,4, 5 a 450-eV cutoff is employed for the plane-wave basis set and a semiempirical van der Waals (vdW)

correction is used for the dispersion interactions.6, 7 5×5×5 Monkhorst-Pack grid k- points are employed for the geometric optimization of the correlative bulk systems. Additionally, 3×3×1 k-points are used for the related computations to the slab models for the Ru and Ru-Co systems as well as the structural model for the Ru-Co nanoparticle adsorbed on the graphene. For all computations, the convergence

threshold is set as 10-4 eV in energy and 0.02 Ǻ/eV in force, respectively. The symmetrization is switched off and the dipolar correction is included for the related computation based on the slab model.

Moreover, the dissociation energy (Ed) of H2O on the different surfaces can be computed according to the following formula:

Ed = Esurf-OH + 1/2EH2 - Esurf-H2O (3)

where EH2 means the energy of a single hydrogen molecule, while Esurf-H2O and Esurf-OH

represent the total energies of the adsorbed structures with H2O molecule and OH species, respectively.

Experimental data consistent with the structure model are provided as below: In view of the more exposure (shown in HR-TEM, AR-TEM image) in experimentally as-synthesized RuCo@CDs catalyst as well as strongest diffraction intensity of [002] plane at around 44 degree (displayed in XRD pattern) in both pure bulk Ru and RuCo@CDs, the correlative (002) surfaces were theoretically employed in the structural models for the pure Ru, Co-doped Ru and RuCo@GNO model. The atom ratios of Ru to Co was constructed as 3:1 in RuCo-(002) structure in full consideration of the experimental results (molar ratio of 2.29: 1 for Ru: Co in the optimized RuCo@CDs catalyst) and the reasonable operability of theoretically calculated procedures. Thus, we constructed a theoretical model of the RuCo cluster based on the RuCo-(002) structure. What’s more, the chemical bonding information and electronic structures of catalysts among contained elements (C, N, O, Ru and Co) were characterized by XPS. As presented in Fig. 2d-f, there are chemical bonding of N-C=O, C-O,C-N and C=C/C-C in carbon substrate, and it is suggested that the chemical bonding of Ru-O and Co-N-C between carbon substrate and RuCo alloy. Finally, for the carbon dots substrate, because the carbon dots is a graphene-like structure with exposure of nitrogen, oxygen-containing edge sites, the N-doped graphene oxide monoatomic layer containing 129 atoms were construct to represent CDs substrate. Thus, we constructed a theoretical model of the RuCo cluster based on the RuCo-(002) structure, and then deposited it on a N-doped graphene oxide monoatomic layer through chemical bonding interaction (denoted as RuCo@GNO, Fig. 5c) to model the experimentally synthesized composite system (RuCo@CDs catalyst). For the theoretical slab models of Ru (002) and RuCo (002), all the atoms at the upper two layers were fully relaxed without any symmetry or direction restrictions, while the remaining atoms were kept frozen during the computational process.

Moreover, for the calculation of dissociation energy (Ed) of H2O, all the possible

adsorption sites for H2O are considered, including the top site over Ru atom or Ru/Co

atom (TRu/TCo) as well as the Ru-Ru bridge bond and ring sites.

Fig. S1. The (a, b) TEM images of the Co-CDs.

Fig. S2. The optical properties of the as-prepared Co-CDs. (a) UV-vis spectra and (b) photoluminescence spectra. The as-prepared Co-CDs exhibit typical spectral features similar to other reported CDs. Typically, the UV-vis spectrum present two absorption bands located at 270, 342 nm assigned to π→π* transition corresponding to the C=C bond, and n→π* transition related to the C=O/C=N bond, respectively. The photoluminescenct spectra show representative excitation-dependent properties due to abundant surface binding group. Fig. S3. The XRD pattern of the Co-CDs. Fig. S4. The FT-IR spectrum of the Co-CDs.

Fig. S5. The high resolution (a) C 1s, (b) N 1s, (c) O 1s and (d) Co 2p XPS spectra of the Co-CDs. Fig. S6. The TEM and HR-TEM image of Ru@CDs catalyst.

Fig. S7. The TEM and HR-TEM image of RuCo@C catalyst. Fig. S8. TOF values of RuCo@CDs and other recently reported HER electrocatalysts in alkaline media (1.0 M KOH solution). (Ref. Ru-RuO2/CNTs,8 Ru@MoS2,9

RuSx@S-GO,10 Ni3N-NiMoN,11 N,P-doped Mo2C@C,12 NiCo2Px13 and Ni5P4 NPs14). Fig. S9. EIS Nyquist plots of RuCo@CDs, Co@CDs, RuCo@C and Ru@CDs catalysts during HER process under 1.0 M KOH solution.

Fig. S10. The CV curves at different scan rates (5-45 mV·s-1 with the interval of 5 mV·s-1) of (a) RuCo@CDs, (b) Co@CDs, (c) RuCo@C and (d) Ru@CDs catalysts during HER process under 1.0 M KOH solution. Fig. S11. Capacitive currents against scan rate and corresponding Cdl value of RuCo@CDs, Co@CDs, RuCo@C and Ru@CDs catalysts during HER process under 1.0 M KOH solution.

Fig. S12. Normalized HER activity of RuCo@CDs and control catalysts by ECSA in 1.0 M KOH solution. Fig. S13. Durability characterizations of RuCo@CDs catalyst during HER process under 1.0 M KOH solution. (a) The XRD pattern before and after 1000th CV cycles, and (b) TEM image of RuCo@CDs after 1000th CV cycles.

Fig. S14. HER stability test of RuCo@CDs electrocatalysts in (a , b) 0.5 M H2SO4 and (c, d) neutral 1.0 M PBS solution: (a, c) chronopotentiometry and (b, d) chronoamperometry curves. Fig. S15. LSV curves of Ru@CDs catalyst during OER process under (a) 0.5 M

H2SO4, (b) 1.0 M KOH and (c) neutral 1.0 M PBS solution.

Fig. S16. Tafel plots of RuCo@CDs catalyst during OER process under (a) 0.5 M H2SO4, (b) 1.0 M KOH and (c) neutral 1.0 M PBS solution.

Fig. S17. The CV curves at different scan rates (5-45 mV·s-1 with the interval of 5 mV·s-1) of (a) RuCo@CDs, (b) Co@CDs, (c) RuCo@C and (d) Ru@CDs catalysts during OER process under acid media. Fig. S18. The CV curves at different scan rates (5-45 mV·s-1 with the interval of 5 mV·s-1) of (a) RuCo@CDs, (b) Co@CDs, (c) RuCo@C and (d) Ru@CDs catalysts during OER process under alkaline media.

Fig. S19. The CV curves at different scan rates (5-45 mV·s-1 with the interval of 5 mV·s-1) of (a) RuCo@CDs, (b) Co@CDs, (c) RuCo@C and (d) Ru@CDs catalysts during OER process under neutral media.

Fig. S20. Capacitive currents against scan rate and corresponding Cdl value of RuCo@CDs, Co@CDs, RuCo@C and Ru@CDs catalysts during OER process in (a) acid, (b) alkaline and (c) neutral media. Fig. S21. Normalized OER activity of RuCo@CDs and control catalysts by ECSA in (a) acid, (b) alkaline and (c) neutral media.

Fig. S22. TOF values of RuCo@CDs with other recently reported OER electrocatalysts in alkaline media (1.0 M KOH solution).(Ref. Fe-CoP,15 a-

Co4Fe(OH)x,16 NiCo2Se4,17 CoOx nanoplates,18 Co3O4 nanomeshes19 and Ru-

RuO2/CNTs8 )

Fig. S23. OER stability characterization of RuCo@CDs electrocatalyst in (a , b) 1.0 M KOH and (c, d) neutral 1.0 M PBS solution: (a, c) chronopotentiometry and (b, d) chronoamperometry curves.

Fig. S24. Durability characterizations of RuCo@CDs catalyst during OER process under 0.5 M H2SO4 solution. (a) XRD pattern and (b) XPS Ru 3p spectra of RuCo@CDs catalyst before and after 2500 CV cycles. (c) TEM and (d) HR-TEM image of RuCo@CDs catalyst after after 2500 CV cycles.

Fig. S25. Overall water splitting (a, c, e) polarization curves and (b, d, f) current densitytime stability curves of RuCo@CDs electrocatalyst in (a, b) 0.5 M H2SO4, (c, d) 1.0 M KOH and (e, f) neutral 1.0 M PBS solution. Fig. S26. The geometry structures as well as energy comparison for three possible Co-doped Ru bulk configurations (I~III). Note that cyan and orange spheres represent Ru and Co atoms, respectively. The three computed lattice parameters of bulk metal Ru are about 2.698, 2.698 and 4.263 Å, respectively, all of which are very close to the corresponding experimental values (2.706, 2.706 and 4.282 Å from PDF# No.06- 0663).

. Fig. S27. The geometry structures for the adsorption and dissociation of H2O on the different surfaces: (a) Ru-site on Ru (002); (b) Co-site on RuCo (002), (c) Ru-site on

RuCo (002); (d) Ru1-site on RuCo@GNO, (e) Ru2-site on RuCo@GNO, (f) Ru3-site on RuCo@GNO, (g) Ru4-site on RuCo@GNO, (h) Co-site on RuCo@GNO. Note that cyan, orange, grey, blue, red and white spheres represent Ru, Co, C, N, O and H atoms, respectively. Table S1. The fitting results of electrochemical element parameters from electrochemical impedance spectroscopy (EIS) for RuCo@CDs and control catalysts.

Sample Rs (Ω) Rct (Ω) CPE (Ω)

RuCo@CDs 12.6 58.2 0.570

Co@CDs 15.1 419 0.813

RuCo@C 12.7 66.2 0.706

Ru@CDs 12.0 312 0.455

Rs shows the resistance of the electrolyte and intrinsic resistance of the active materials on the electrode. Rct represents charge transfer resistance, which determines the interfacial electron.

Table S2. Comparison of Cdl, CDL, electrochemical surface areas (ECSA) and roughness factors (RF) between RuCo@CDs and control catalysts.

2 2 Sample Cdl (mF/cm ) CDL (mF) ECSA (cm ) RF

RuCo@CDs 170.15 12.03 300.74 4253.75

Co@CDs 37.09 2.62 65.56 927.25

RuCo@C 125.82 8.90 222.39 3145.50

Ru@CDs 50.14 3.50 88.62 1253.50

CDL = Cdl * S; ECSA = CDL/Cs; RF = ECSA/S. Cdl (mF/cm2) is the electrochemical double 2 layer capacitance, S (cm ) is the surface area of electrode. Cs is specific electrochemical -2 double layer capacitance of an atomically smooth surface. Cs was assumed to be 0.04 mF cm because it could be typically 0.02-0.06 mF/cm2. Table S3. Performances comparison of the recently reported HER electrocatalysts. Related to Fig. 3g.

pH η j=10 mA·cm-2 Tafel Electrocatalysts electrode electrolytes Ref. (mV) (mV·dec-1) university

0.5 M H2SO4 51 47.8 RuCo@CDs GCE Yes This work 1.0 M KOH 11 51.3

1.0 M PBS 67 171.0

Ru@N-C GCE Yes 0.5 M H2SO4 126 - 20

RuNi@N-C GCE Yes 0.5 M H2SO4 50 36 21

Ru@N-graphene GCE Yes 0.5 M H2SO4 90 35.9 22

NiCo2Px NWs carbon felt Yes 0.5 M H2SO4 50 32.5 13

Mo2C/graphene-NC GCE Yes 0.5 M H2SO4 70 39 23

α-MoB2 Cu sheet No 0.5 M H2SO4 149 - 24

Ni3S2@Cu Cu foil Yes 0.5 M H2SO4 91.6 63.5 25 carbon fiber Co@N,O-C colth No 0.5 M H2SO4 69 49 26

Co NPs@CNTs@rGO GCE Yes 0.5 M H2SO4 87 52 27

Ru@C2N GCE Yes 1.0 M KOH 17 38 28

RuNi@N-C GCE Yes 1.0 M KOH 32 64 21

RuNi NSs GCE No 1.0 M KOH 40 23.4 29

RuP2@NC GCE Yes 1.0 M KOH 52 69 30

RuCoP GCE Yes 1.0 M KOH 23 - 31

RuCo@N-graphene GCE No 1.0 M KOH 28 31 32

IrCo@NC GCE Yes 1.0 M KOH 45 80 33 carbon fiber Ru@MoS2@CNTs paper No 1.0 M KOH 50 62 34

Mo2C/graphene-NC GCE Yes 1.0 M KOH 66 37 23

Ni3N-NiMoN carbon cloth No 1.0 M KOH 31 64 11

NiCo2Px@CNTs GCE No 1.0 M KOH 47 57 35

V-NiS2 NSs GCE No 1.0 M KOH 110 90 36

Ru@N-C GCE Yes 1.0 M PBS 100 - 20 RuNi@N-C GCE Yes 1.0 M PBS 482 - 21

NiSe@N-C GCE Yes 1.0 M PBS 300 66.2 37

Co-CoOx@CN GCE Yes neutral 280 - 38

Co/CoP NPs GCE Yes 1.0 M PBS 138 - 39

Ni3S2@Cu Cu foil Yes 2.0 M PBS 280 - 25

Table S4. Performances comparison of the recently reported OER electrocatalysts. Related to Fig. 4e, 4f.

pH η j=10 mA·cm-2 Tafel Electrocatalysts electrode electrolytes Ref. (mV) (mV·dec-1) university

0.5 M H2SO4 190 49.5 RuCo@CDs GCE Yes This work 1.0 M KOH 257 96.1

1.0 M PBS 410 147.4

Ru-N-C GCE No 0.5 M H2SO4 267 52.6 40

Cu-RuO2 GCE No 0.5 M H2SO4 188 44 41

RuO2@N,P-C GCE No 0.5 M H2SO4 220 66.8 42

RuO2@C GCE Yes 0.5 M H2SO4 220 66 43

Co-RuO2 NMs GCE Yes 0.5 M H2SO4 200 - 44

Ru@IrOx Au No 0.05 M H2SO4 282 69.1 45

RuIrOx GCE Yes 0.5 M H2SO4 233 42 46

IrO2-RuO2@Ru GCE No 0.5 M H2SO4 281 53.1 47

Pt@IrO2 GCE No 0.5 M H2SO4 320 - 48

IrO2 FTO-GCE No 1.0 M H2SO4 280 85 49

IrNiOx GCE No 0.05 M H2SO4 330 - 50

IrOx-Ir GCE No 0.5 M H2SO4 290 - 51

Cu-Ir GCE No 0.05 M H2SO4 286 43.8 52

Ir NPs graphite foam No 0.5 M H2SO4 290 46 53

IrNi nanoclusters GCE Yes 0.5 M H2SO4 330 - 54

Ir@Fe4N GCE No 0.5 M H2SO4 316 62 55 RuNi NSs GCE No 1.0 M KOH 300 - 29

Ru@N-graphene GCE No 1.0 M KOH 372 68 22

Ni3Co3@Ru GCE No 1.0 M KOH 272 56 56

N-Co3O4@NC GCE No 1.0 M KOH 266 54.9 57

CoOx nanoplates GCE No 1.0 M KOH 306 65 18

Co3O4 nanomeshes GCE No 1.0 M KOH 307 76 58

FeCo@Co4N GCE No 1.0 M KOH 280 40 59

NiCo-P NSs GCE No 1.0 M KOH 273 45 60

CoP/Co2P@N,P-CNTs carbon paper No 1.0 M KOH 300 76 61

Ag@CoxP GCE No 1.0 M KOH 310 76.4 62

NiCo2Px@CNTs GCE No 1.0 M KOH 284 50.3 35

V-NiS2 NSs GCE No 1.0 M KOH 290 45 36

Ni3Se4 Ni foam Yes PBS 480 116 63

Co2P NPs GCE No 0.1 M PBS 492 134 64

CoO/CoSe2 Ti mesh No 0.5 M PBS 510 137 65

N, S-graphitic sheets GCE Yes 1.0 M PBS 420 - 66

(FexNi1-x)2P Ni foam Yes 0.1 M PBS 396 182 67

570 Co/CoP NPs GCE Yes 1.0 M PBS - 39 @2.6 mA·cm-2 Table S5. Performances comparison of the recently reported overall water splitting electrocatalysts.

η j=10 mA·cm-2 (mV or V) pH Electrocatalysts electrolytes Ref. overall university HER OER water splitting

0.5 M H2SO4 51 191 1.49 RuCo@CDs Yes This work 1.0 M KOH 11 257 1.50

1.0 M PBS 26 410 1.64

Ru@N-graphene No 1.0 M KOH 40 372 1.65 22

RuNi nanoplates No 1.0 M KOH 40 ~300 1.58 29

NiFeRu-LDH No 1.0 M KOH 29 225 1.52 68

Ir NPs No 0.5 M H2SO4 7 290 1.55 53

IrNi nanoclusters No 0.5 M H2SO4 17 330 1.58 54

Ir@Co/NC No 1.0 M KOH 60 260 1.60 69

Co-RuIr No 0.1 M HClO4 14 235 1.52 70 ~30 0.1 M KOH - - Rh2P@C Yes 71 @5 mA·cm5.4 -2 510 0.5 M H2SO4 - @5 mA·cm-2 @5 mA·cm-2

0.5 M H2SO4 131 261 -

Co4Ni-P Yes 72 1.0 M KOH 129 245 1.59

1.0 M PBS 134 268 -

CoP@N-CNTs No 1.0 M KOH 115 310 1.64 73

NiCo2Px@CNTs No 1.0 M KOH 47 284 1.61 35

Ni3N-NiMoN No 1.0 M KOH 31 277 1.54 11

1.0 M KOH 68 247 1.56 CoN-Ni3N@N-C Yes 74

0.5 M H2SO4 35 300 -

NixCo3-xS4-Ni3S2 No 1.0 M KOH 136 160 1.60 75

V-NiS2 NSs No 1.0 M KOH 110 290 1.56 36

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