PDF《Supporting Information》

5 mV s-1. Onset overpotentials were determined based on the beginning of the linear regime in the Tafel plot. The time dependency of catalytic currents during electrolysis for the catalyst was tested in 0.5 M H2SO4 at η =

150 mV after equilibrium. Electrochemical impedance spectroscopy (EIS, PARSTAT 2273, Princeton Applied Research, USA) measurements were carried out in the frequency range of

100 kHz-0.1 Hz. Potentials were referenced to a reversible hydrogen electrode (RHE) by adding a value of (0.197 + 0.059pH) V.[3] S5 Figure S1 SEM images of PB microcubes (A, B) and HFe3O4@C microcubes (C, D). TEM images of HFe3O4@C microcubes (E, F). S6

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70 80 a: PB Microcubes b: HFe3 O4 @C Microcubes JCPDS card No: 65-2595 FeP JCPDS card No: 65-3107 Fe3 O4 JCPDS card No: 73-0687 Fe4 (Fe(CN)6 )3 c: HMFeP@C Microcubes Intensity (a. u.) 2Theta?(Degree) Figure S2 XRD patterns of PB microcubes, HFe3O4@C microcubes and HMFeP@C. S7

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8 Element At % Fe 40.2 P 42.1 O 12.0 C 5.7 Fe P Fe O Concenta (a. u.) Energy(keV) C Figure S3. EDX of HMFeP@C. S8 Figure S4. EDX mapping on SEM for HMFeP@C. S9

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70 FePNPs Fe3 O4 NPs Intensity (a. u.) JCPDScard No: 65-2595 FeP JCPDScard No: 65-3107 Fe3 O4 2Theta?(Degree) Figure S5. XRD patterns of Fe3O4 NPs and FeP NPs. S10 Figure S6. SEM images of Fe3O4 NPs (A) and FeP NPs (B). S11 0.0 0.2 0.4 0.6 0.8 1.0

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100120140 0.000 0.004 0.008 0.012 0.016 dV/dlog (D) Pore size (nm) Volume absorbed (cm

3 g -1 ) Relative pressure (P/P0) Figure S7. Nitrogen adsorption-desorption isotherms of porous FeP NPs. Inset: the BJH pore-size distribution of the nanocomposite calculated from the desorption branch of N2 isotherm. S12

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712 714 Fe 2p3/2 Intensity (a.u.) Binding energy(eV) A

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140 P 2p P-O P2p1/2 B Intensity (a.u.) Binding energy(eV) P2p3/2 Figure S8. XPS spectrum of Fe (2p3/2) (A) and regions for FeP NPs (B). S13 -1.5 -1.0 -0.5 0.0 0.5 1.0 0.0 0.1 0.2 0.3 HMFeP@C FeP NPs Overpotential (V vs. RHE) log [ j (mAcm-2) ] Figure S9. Tafel plots used for calculating j0 of the HMFeP@C and FeP NPs. The exchange current density (j0) was calculated using extrapolation methods. When the overpotential value is 0, the log j values for HMFeP@C and FeP NPs are - 0.72 and -1.60, respectively. Based on Tafel equations, j0 for HMFeP@C and FeP NPs was calculated to be 0.191 mA cm-2 and 0.025 mA cm-2, respectively. S14 Table S1. Comparison of HER performance in acidic media of HMFeP@C with other non-noble metal electrocatalysts (a catalysts directly grown on current collectors;

rGO: reduced graphene oxide;

--: not given;

NRs: nanorod arrays NAs: nanowire arrays,........