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1 Supporting Information Intercalation Synthesis of Prussian Blue Analog Nanocone and Their Conversion into Fe Doped Co x P Nanocone for Enhanced Hydrogen Evolution Xiaosong Guo, Xiaoguang Yu, Zijia Feng, Jun Liang, Qinglin Li, Zezhong Lv, Bingjie Liu, Chuncheng Hao*,,, Guicun Li*, College of Materials Science and Engineering, Qingdao University of Science and Technology, No.53 Zhengzhou Road, Qingdao, Shandong, , People's Republic of China State Key Laboratory of Electrical Insulation and Power Equipment, Xi an Jiaotong University, No.28, Xianning West Road, Xi'an, Shaanxi, , People's Republic of China * clx@qust.edu.cn; guicunli@qust.edu.cn. Fax: Tel: The supporting information contains: Number of pages: 12 Number of Figures: 16 Number of Tables: 1 S1

2 All chemicals of analytical grade were purchased from Macklin Ltd (Shanghai, China). They were used without further purification. Synthesis of DS -Co(OH) 2 NCs: Sodium dodecyl sulfate (SDS, 99.0%, 7 mmol), urea (99.0%, 17.5 mmol) and CoCl 2 6H 2 O (99.9%, 2.5 mmol) were added into a three-neck flask and dissolved in 250 ml deionized water. The solution was heated to 95 C and keep it for 8 h under mechanical stirring and nitrogen-protection. The resulting product was washed with water and absolute ethanol, and dried in air at 60 C for 6 h. Synthesis of Fe-Co, Fe-Co 1 and Fe-Co 2 PBA NCs: 0.1 g of obtained DS -Co(OH) 2 NCs were transferred into a flask contained with 1.0 g potassium ferricyanide (K 3 Fe(CN) 6, 99.5%), 50 ml H 2 O and 50 ml ethanol at 26 C and stirred for 9 h under nitrogen protection. The brown Fe-Co PBA NCs were collected by centrifugation, rinsed with water several times, and dried at 60 C. Fe-Co 1 and Fe-Co 2 PBA NCs were obtained by using 0.3 g and 1.5 g of K 3 Fe(CN) 6, respectively. Synthesis of Fe-Fe PBA NPs: 50 ml 0.1 M K 3 Fe(CN) 6 solution is poured into 50 ml 0.1 M FeCl 3 H2O solution under stirring at room temperature for 9 h. The product was collected by centrifugation, rinsed with water several times, and dried at 60 C. Synthesis of Mo-Co NCs: 0.1 g of obtained DS -Co(OH) 2 NCs were transferred into a flask contained with 1.2 g sodium molybdate dihydrate (Na 2 MoO 4 2H 2 O, 99.0%), 50 ml H 2 O and 50 ml S2

3 ethanol at 26 C and stirred for 9 h under nitrogen protection. The brown product was collected by centrifugation, rinsed with deionized water several times, and dried at 60 C. Synthesis of Co 3 O 4, Fe-Co 3 O 4, Fe-Co 3 O 4 1, Fe-Co 3 O 4 2, Mo-Co 3 O 4 NCs and Fe 2 O 3 NPs: The DS Co(OH) 2, Fe-Co, Fe-Co 1, Fe-Co 2, Mo Co NCs and Fe-Fe PBA NPs were annealed at 450 C with a heating rate of 2 C min -1 for 1 h in air to transform into Co 3 O 4, Fe-Co 3 O 4, Fe-Co 3 O 4 1, Fe-Co 3 O 4 2, Mo Co 3 O 4 NCs and Fe 2 O 3 NPs, respectively. After cooling down to room temperature, the obtain products were collected and washed with deionized water and ethanol for 3 times to remove impurities. Synthesis of Co x P, Fe-Co x P, Fe-Co x P 1, Fe-Co x P 2 NCs and FeP NPs: The obtained Co 3 O 4 NCs and NaH 2 PO 2 were weighed by mass ratio of 1:15 and put at two separate positions in a porcelain boat with NaH 2 PO 2 at the upstream side of the furnace, heated at 350 C for 2 h in nitrogen atmosphere with a ramping rate of 5 C min -1. After cooling down to room temperature, the obtain Co x P NCs were collected and washed with deionized water and ethanol for 3 times, respectively. In order to obtain Fe-Co x P, Fe-Co x P 1, Fe-Co x P 2 NCs and FeP NPs, Co 3 O 4 NCs were simple replaced by Fe-Co 3 O 4, Fe-Co 3 O 4 1, Fe-Co 3 O 4 2 NCs and Fe 2 O 3 NPs, respectively. Synthesis of β-co(oh) 2 platelets: 2.5 mmol CoCl 2 6H 2 O and 17.5 mmol urea were added into a three-neck flask and S3

4 dissolved in 250 ml deionized water. The solution was heated to 95 C for 8 h under mechanical stirring and nitrogen-protection. The resulting product was washed with water and absolute ethanol, and dried in air at 60 C for 6 h. Synthesis of Fe-β-Co(OH) 2 platelets: 0.05 g of obtained β-co(oh) 2 platelets were transferred into a flask contained with 0.5g K 3 Fe(CN) 6, 25 ml H 2 O and 25 ml ethanol at 26 C and stirred for 9 h under nitrogen protection. The brown product was collected by centrifugation, rinsed with water several times, and dried at 60 C. Characterization Scanning electron microscope (SEM) images and Energy dispersive X-ray spectrometry (EDS) was employed on the FESEM equipment to analyze the composition and element distribution of CoP hollow microspheres (JSM 6700F, JEOL Japan). Transmission electron microscopy (TEM) images were taken on a Transmission Electron Microscope (JEOL JEM 2100F). The phase composition of the samples were determined by X-ray diffraction (XRD, Rigaku D-max-γA XRD with Cu K α radiation, λ = Å) from 5 to 80. The X-ray photoelectron spectroscopy (XPS) analysis was performed on a Perkin Elmer PHI 550 spectrometer with Al K ( ev) as the X-ray source. Fourier-transformed infrared spectroscopy (FTIR) was determined on a Nicolet Magna IR-750 spectrophotometer using KBr pressed disk. Thermogravimetric analysis (TGA, Netzsch STA449C) was performed in air over temperatures ranging from the room temperature to 700 C, at a heating rate of 5 C min -1. The atomic compositions of the present materials were probed with S4

5 inductively coupled plasma mass spectrometry (ICP-MS, Agilent 7700ce). All the electrochemical measurements were conducted by using an electrochemical workstation (AUTOLAB PGSTAT302N, Metrohm, Switzerland). Electrochemical measurement All the electrochemical measurements were conducted by using the AUTOLAB electrochemical workstation in a typical three-electrode, a graphite rod as the counter electrode, a glassy carbon electrode coated with catalysts as the working electrode and a saturated calomel electrode (SCE) as the reference electrode. Firstly, the electrode was polished with polishing powder, washed with deionized water, and then dried with cold air. Subsequently, 4 mg Fe-Co x P NCs powder, 2 mg carbon black were mixed in 750 µl deionized water, 250 µl ethanol, 30 µl 5 wt.% Nafion solution, forming a mixed solution, which was put in ultrasound for at least 30 minutes. 5 µl the prepared solution was dropped onto the polished electrode eventually. Linear sweep voltammetry (LSV) was performed at a scan rate of 5 mv s -1 in 0.5 M H 2 SO 4. The electrochemical surface area (ECSA) was compared by estimating the electrochemical double layer capacitances (C dl ) with cyclic voltammetry (CV). CV curves were performed at a potential range of V vs RHE. The capacitive currents at 0.05 V vs RHE were plotted against the scan rate. S5

6 Figure S1. HRTEM image of the staggered stacking of nanosheets. Figure S2. Optical photographs of (a) Co(OH) 2 NCs, (b) Fe-Co PBA NCs and (c) Mo-Co NCs. Figure S3. Low-magnification SEM image of Fe-Co PBA NCs. S6

7 Figure S4. SAED pattern of Fe-Co PBA NCs. Figure S5. TGA of (a) Co(OH) 2 NCs and (b) Fe-Co PBA NCs at a temperature ramp of 5 C min -1 in air. Figure S6. FT-IR spectroscopy of Co(OH) 2 and Mo-Co NCs. S7

8 Figure S7. EDS images of Co(OH) 2 and Mo-Co NCs. Figure S8. SAED pattern of Mo-Co NCs. Figure S9. High-magnification TEM image of NC bottom edge. S8

9 Figure S10. (a) SEM and (b) TEM images of β-co(oh) 2 platelets; (c) SEM and (d) TEM images of Fe-β-Co(OH) 2 platelets. Figure S11. XRD patterns of β-co(oh) 2 and Fe-β-Co(OH) 2. S9

10 Figure S12. EDS images of Fe-Co x P NCs. Figure S13. HRTEM image of Fe-Co x P NCs. S10

11 Figure S14. SEM images of (a) Fe-Co 1 PBA NCs, (b) Fe-Co x P 1 NCs, (c) Fe-Co 2 PBA NCs and (d) Fe-Co x P 2 NCs. Figure S15. XRD pattern of Fe-Fe PBA NPs. S11

12 Figure S16. SEM images of (a), (b) Fe-Fe PBA NPs; (c), (d) Fe 2 O 3 NPs obtained after calcination process; (e), (f) FeP NPs obtained after phosphorization process. S12

13 Table S1. The atomic ratio of Co to Fe element obtained from ICP-MS data for Fe-Co, Fe-Co 1 and Fe-Co 2 PBA NCs. S13