Boosting Electrocatalytic Activities of Pt-Based Mesoporous

May 1, 2019 - The overall water splitting tests were performed with a two-electrode setup. .... The stability of the PtNiP MNs/C for overall water spl...
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Research Article Cite This: ACS Sustainable Chem. Eng. 2019, 7, 9709−9716

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Boosting Electrocatalytic Activities of Pt-Based Mesoporous Nanoparticles for Overall Water Splitting by a Facile Ni, P CoIncorporation Strategy Chunjie Li, You Xu,* Dandan Yang, Xiaoqian Qian, Xingjie Chai, Ziqiang Wang, Xiaonian Li, Liang Wang,* and Hongjing Wang*

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State Key Laboratory Breeding Base of Green-Chemical Synthesis Technology, College of Chemical Engineering, Zhejiang University of Technology, No. 18 Chaowang Road, Hangzhou, Zhejiang 310014, P.R. China S Supporting Information *

ABSTRACT: The exploration of highly efficient catalysts for electrochemical hydrogen and oxygen production via water splitting is very significant for providing affordable clean energy and reducing the reliance on conventional fossil fuels. Herein, we develop an efficient method to boost the electrocatalytic performance of Pt mesoporous nanoparticles (Pt MNs) for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by a facile Ni, P co-incorporation strategy. The co-incorporation of Ni and P atoms in a Pt crystal structure can effectively modify its electronic structure, which contributes to the superior catalytic ability toward HER. We also demonstrate that the as-fabricated PtNiP MNs could occur surface partial oxidation under oxidizing potentials to in situ form OER electroactive oxides/hydroxides species. The unique mesoporous structure and metal−nonmetal ternary alloyed composition make the PtNiP MNs a promising HER−OER bifunctional electrocatalyst for overall water splitting in alkaline media. KEYWORDS: PtNiP mesoporous nanoparticles, Bifunctional electrocatalysts, Overall water splitting, Hydrogen evolution reaction, Oxygen evolution reaction

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INTRODUCTION Electrocatalytic splitting of water into hydrogen (H2) and oxygen (O2) is considered to be a promising approach for producing high-purity molecular H2.1−5 The water splitting reaction is thermodynamically unfavorable and requires highly efficient electrocatalysts to accelerate the intrinsic sluggish kinetics of the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Currently, a variety of catalyst materials have been developed for HER and OER. However, integrating different HER and OER electrocatalysts into an overall water electrolyzer for practical use is difficult due to the mismatching pH ranges in which these electrocatalysts function best.6−8 On the other hand, the preparation of different HER and OER electrocatalysts usually requires different material precursors, equipment, and processes, which complicate the catalyst manufacturing and increase the cost of water-splitting technology.9−11 Therefore, the development of bifunction electrocatalysts with excellent activity for catalyzing both HER and OER in the same electrolyte is significant yet still challenging. Pt and Pt-based materials represent state-of-the-art HER electrocatalysts; however, they are relatively less studied for overall water splitting due to their poor OER performance. Alloying or incorporation of Pt with other earth-abundant transition metals (e.g., Co, Ni, Cu, Fe) or nonmetal elements © 2019 American Chemical Society

(e.g., P, B, S) is a frequently used strategy for modifying the electronic properties of Pt to thus improve the intrinsic electrocatalytic performance.12−24 In addition, many Pcontaining materials, such as metal phosphides, have recently demonstrated their promising potentials for electrochemical overall water splitting.8,25−27 The related studies revealed that, apart from the intrinsic HER activity, these P-containing catalysts could be in situ converted into OER-active components under electrochemical conditions and thus could serve as HER−OER bifunctional electrocatalysts.28−32 These advances inspire us to co-introduce an earth-abundant transition metal and P into Pt or Pt-based materials to boost their OER property, therefore applied to overall water splitting. Apart from the enhancement of intrinsic electrocatalytic activity by introducing suitable foreign element atoms, another noteworthy pathway to boost the catalytic performance of Pt and Pt-based catalysts is to increase exposed catalytically active sites by structure engineering.18,33−40 In this regard, catalysts with nanoporous or mesoporous features can provide abundant exposed active sites, enhanced accessibility of reactants, and fast mass transport, which largely favor electrocatalysis reactions.41−45 However, the simultaneous Received: March 15, 2019 Revised: April 19, 2019 Published: May 1, 2019 9709

DOI: 10.1021/acssuschemeng.9b01484 ACS Sustainable Chem. Eng. 2019, 7, 9709−9716

Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. Schematic illustration for the synthesis of the PtNiP MNs. performed by a D8 ADVANCE (Bruker AXS, Germany) diffractometer using a Cu−Kα source (λ = 1.540598 Å). Inductively coupled plasma mass spectrometry (ICP-MS) measurements were conducted on an Elan DRC-e machine. X-ray photoelectron spectroscopy (XPS) analysis was operated on an ESCALAB MK II spectroscope (VG Scientific, U.K.) using Al−Kα radiation. A nitrogen adsorption−desorption test was taken by a BELSORP-mini (BEL) machine to estimate the Brunauer−Emmett−Teller (BET) surface area and pore-size distribution of the sample. Electrochemical Investigations. The electrochemical HER and OER measurements were investigated with a CHI 660D (Chenhua Co., Shanghai, China) electrochemical workstation using a standard three-electrode device. A graphite rod counter electrode, a Hg/HgO (1.0 M KOH) reference electrode, together with a glassy carbon electrode (GCE, 3 mm in diameter) modified by catalysts as the working electrode were used for constructing the three-electrode system. For the preparation of the catalyst-modified working electrode, PtNiP MNs, PtNi MNs, and PtP MNs were mingled with commercial carbon black to ensure that the percentage of Pt was 20 wt %. A certain amount of the prepared catalyst suspension (containing 10 μg of catalyst) was transferred to the GCE surface and dried at 50 °C. Then, it was coated with 5 μL of Nafion (0.5 wt %) and dried again to form the working electrode. The electrolyte used for electrochemical measurements is a 1.0 M KOH aqueous solution. All electrochemical tests were operated at room temperature. Cyclic voltammograms (CVs) were first performed at a scan rate of 50 mV s−1 for 20 cycles from 0.2 to −0.5 V (vs. RHE) until a stable CV curve was obtained. Linear sweep voltammetry (LSV) polarization curves were recorded with a scan rate of 5 mV s−1. The test potential ranges from 0.2 to −0.5 V (vs. RHE) for HER and from 0.8 to 1.8 V (vs. RHE) for OER. For comparison in HER tests, we kept the loading amount of Pt the same for various tested catalysts, and the total loading amount of the catalysts were kept the same during OER tests due to the use of RuO2 as the benchmark catalyst. The ohmic potential drop (iR) losses were all corrected through the electrochemical impedance spectroscopy (EIS) technique. Chronopotentiometry tests were operated at the constant current density of 10 mA cm−2. The overall water splitting tests were performed with a twoelectrode setup. For the preparation of catalyst-modified electrodes, the catalyst ink was loaded on a commercial Ni foam substrate (1 cm × 1 cm) to make the catalyst loading amount ∼0.8 mg cm−2. The asobtained catalysts/Ni foam electrodes were utilized both as the cathode and anode. For comparison, Pt/C and RuO2 were loaded on the Ni foam and served as the cathode and anode, respectively.

implementation of desired P-doping or P-incorporation for enhanced intrinsic electrocatalytic activity and well-defined mesoporous nanostructures with abundant exposed catalytically active sites is rarely explored in the development of highperformance HER−OER bifunctional Pt-based electrocatalysts. Motivated by the above discussion, we herein report the fabrication of well-distributed PtNiP mesoporous nanoparticles (PtNiP MNs) by a facile Ni, P co-incorporation strategy using Pt mesoporous nanopaticles (Pt MNs) as the starting materials. The co-incorporation of Ni facilitates the introduction of P in the Pt structure under mild reaction conditions using NaH2PO2 as the P source and is free of high phosphating temperature and dangerous organophosphorus reagents. As expected, the resultant PtNiP MNs exhibited enhanced HER activity in comparison with the PtNi MNs, PtP MNs, and commercial Pt/C. More significantly, we found the cointroduction of Ni and P will largely boost the OER activity of starting Pt MNs, which is even superior to the well-known RuO2 catalysts. These advantages make the as-obtained PtNiP MNs to be a promising HER−OER bifunctional electrocatalyst for overall water splitting in alkaline media.

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EXPERIMENTAL SECTION

Materials and Chemicals. H 2 PtCl 6 ·6H 2 O, NiCl 2 ·6H 2 O, NaH2PO2, NaBH4, KBr, and RuO2 were ordered from Aladdin (Shanghai, China). Pluronic F127 (PEO100PPO65PEO100) and Lascorbic acid (AA) were obtained from Sigma. Pt/C (20 wt %) was purchased from Alfa Aesar. Synthesis of PtNiP MNs. To fabricate the PtNiP MNs, Pt MNs were first synthesized according to the literature reported previously.46 Briefly, KBr (200 mg), Pluronic F127 (30 mg), deionized water (2 mL), and H2PtCl6 solution (0.04 M, 0.75 mL) were mixed together to create a homogeneous solution. Then, AA solution (0.1 M, 2 mL) was added, and the resultant mixed solution was maintained at 70 °C in a water bath for 12 h. The product was separated by centrifugation and washed with water several times. For the preparation of PtNiP MNs, the as-made Pt MNs were dispersed in water (2 mL) again. Next, NiCl2 solution (0.02 M, 0.2 mL) and NaH2PO2 solution (7 mg mL−1, 1 mL) were added into the above Pt MNs dispersion, and the mixture was stirred for 2 min at room temperature, followed by the addition of freshly prepared NaBH4 solution (0.1 M, 2 mL). After that, the mixture was stirred for another 20 min at room temperature. The final product was collected by centrifugation and washed with water three times. PtNi MNs and PtP MNs were prepared with a similar procedure, but NaH2PO2 (for PtNi MNs) or NiCl2 (for PtP MNs) was not added. Materials Characterization. Scanning electron microscopy (SEM) images were taken by a ZEISS SUPRA 55 microscope, along with the energy-dispersive X-ray spectroscopy (EDX) analysis. The transmission electron microscopy (TEM) test was recorded with a JEM-2100 microscope. X-ray diffraction (XRD) characterization was

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RESULTS AND DISCUSSION The preparation procedure of PtNiP MNs was illustrated in Figure 1. Pt MNs were first synthesized by a one-step wetchemical method according to previous literature.46 As revealed by SEM and TEM, the as-produced Pt MNs are uniform and monodispersed with obvious mesoporous surfaces (Figure S1). The average particle size of the Pt MNs is determined to be 53 nm (Figure S2). These Pt MNs further 9710

DOI: 10.1021/acssuschemeng.9b01484 ACS Sustainable Chem. Eng. 2019, 7, 9709−9716

Research Article

ACS Sustainable Chemistry & Engineering

Figure 2. (a) SEM and (b, c) TEM images of the PtNiP MNs. The inset in (b) is the SAED pattern. (d) HRTEM of PtNiP, and the inset in (d) are the lattice fringes in the square area and the corresponding FFT pattern. (e) HAADF-STEM image of a single PtNiP MN and corresponding elemental mapping images.

uniformly distributed among the nanoparticle shape, demonstrating the formation of the ternary PtNiP alloyed structure. In addition, the EDX spectrum further verifies the presence of the Pt, Ni, and P elements (Figure S4). The quantitative analysis by ICP-MS reveals that the molar ratio of Pt/Ni/P in the PtNiP MNs is approximately 64.6/10.2/25.2. For comparison in materials characterization and electrochemical measurements, the PtNi MN counterparts without P incorporation were also prepared (Figure S5). XRD analysis is further carried out to test the crystallinity of the PtNiP MNs and PtNi MNs (Figure 3a). The five characteristic diffraction peaks in the XRD patterns of PtNiP MNs and PtNi MNs correspond to the (111), (200), (220), (311), and (222) planes of the Pt-based fcc crystal structure, respectively. Compared with standard pure Pt (JCPDS no. 040802), the diffraction peaks for PtNi MNs shift positively, indicating that Pt atoms are partially displaced by the smaller Ni atoms, which lead to the shrink of the lattice distance. In the case of PtNiP MNs, the representative diffraction peaks show a slightly negative shift relative to PtNi MNs, which is ascribed to the introduction of P atoms resulting in the expansion of the lattice.47 These results indicate that Ni and P atoms have entered into the Pt crystal structure and lead to the

served as the starting materials for the synthesis of PtNiP MNs. The Ni and P elements were co-introduced into the Pt crystal structure through a co-reduction of NiCl2 and NaH2PO2 by NaBH4 at room temperature in the presence of Pt MN precursors. As is clearly seen from the SEM image (Figure 2a), the as-converted PtNiP MNs maintain the original spherical shapes, nanoporous surface morphology, and size distribution of the initial Pt MNs. Figure S3 shows the nitrogen adsorption−desorption isotherms for the PtNiP MNs, further revealing the mesoporous features with a BET surface area of 29.3 m2 g−1. TEM images further confirmed the morphological and structural features of the PtNiP MNs (Figure 2b and c). The selected-area electron diffraction (SAED) image presents clear concentric ring patterns, indicative of the polycrystalline feature of the ternary PtNiP MNs (inset in Figure 2b). From the high-resolution TEM (HRTEM) image, the d-spacing of the adjacent fringes was determined to be 0.23 nm, in accordance with the (111) planes of the face-centered-cubic (fcc) crystal structure of obtained PtNiP MNs (Figure 2d). The elemental distribution of PtNiP MNs was analyzed by elemental mapping. Figure 2e displays the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image and the element mapping of one individual PtNiP MN. The Pt, Ni, and P elements are 9711

DOI: 10.1021/acssuschemeng.9b01484 ACS Sustainable Chem. Eng. 2019, 7, 9709−9716

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ACS Sustainable Chemistry & Engineering

Figure 3. (a) XRD patterns of the PtNiP MNs and PtNi MNs. XPS spectra of Pt 4f (b), Ni 2p (c), and P 2p (d) for the PtNiP MNs and PtNi MNs.

Figure 4. HER polarization curves (a) and Tafel plots (b) of the PtNiP MNs/C, PtNi MNs/C, PtP MNs/C, and Pt/C. (c) HER polarization curves of the PtNiP MNs/C before and after the durability test. (d) The chronopotentiometry curve of the PtNiP MNs/C at the cathode current density of 10 mA cm−2 for HER. The polarization curves in (a) and (c) were iR corrected.

formation of Pt-based ternary alloy, as also demonstrated by other P-containing Pt-based nanostructures.16,48,49 To probe the valence state in the surface of the as-converted PtNiP MNs, XPS analysis was conducted. As shown in Figure 3b, the main peaks for PtNiP MNs at 74.70 and 71.33 eV in the XPS spectrum of Pt can be ascribed to Pt(0).16,50 The smaller peaks in the position of 75.51 and 72.06 eV are attributed to Pt(II). Moreover, four characteristic peaks are observed in the Ni 2p spectrum (Figure 3c), which can be

assigned to Ni(II) and their shakeup satellites. The results suggest that most of the surface Ni is mainly present in the oxidized state. In PtNiP MNs, both the binding energies of Pt 4f and Ni 2p shift positively relative to the PtNi MNs. Remarkably, as shown in Figure 3d, the peaks of 129.45 and 133.10 eV in the P 2p XPS spectrum can be attributed to P0 and oxidized P species.49 The position of the P0 peak shows a negative shift compared with pure P (130.4 eV). The existence of oxidized Pt, Ni, and P species arises from the superficial 9712

DOI: 10.1021/acssuschemeng.9b01484 ACS Sustainable Chem. Eng. 2019, 7, 9709−9716

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ACS Sustainable Chemistry & Engineering

Figure 5. OER polarization curves (a) and Tafel plots (b) of the PtNiP MNs/C, PtNi MNs/C, PtP MNs/C, and commercial RuO2. (c) OER polarization curves of the PtNiP MNs/C before and after the durability test. (d) The chronopotentiometry curve of the PtNiP MNs/C at the anode current density of 10 mA cm−2 for OER. The polarization curves in (a) and (c) were iR corrected.

MNs/C. To further explore the effect of composition on the electrocatalytic activity, we compare the HER performance of various PtNiP samples with diverse compositions. The results demonstrate that the PtNiP MNs prepared in typical conditions possess preferable activity (Figure S7 and Table S1). The catalytic stability of the catalysts was assessed by recording the LSV curves before and after accelerated CV cycling tests between −0.2 to 0.1 V. After 2000 cycles, the polarization curve for PtNiP MNs/C almost coincided with that of the initial result (Figure 4c). However, the overpotential needed to afford a current density of 10 mA cm−2 increased obviously for PtNi MNs/C, PtP MNs/C, and Pt/C after durability tests (Figure S8). The chronopotentiometry curve for PtNiP MNs/C was also recorded with the fixed current density of 10 mA cm−2. As seen in Figure 4d, there is only a negligible increase of the overpotential after 30 h, implying that the PtNiP MNs/C exhibits excellent catalytic stability and durability for HER, attributed to the introduction of P element. The OER activities of the catalysts were also tested under the same conditions with different potential ranges. The PtNi MNs/C, PtP MNs/C, and commercial RuO2 catalyst were investigated as well for comparison. As shown in Figure 5a, the PtNiP MNs/C possesses the lowest overpotential (320 mV) at a current density of 10 mA cm−2 relative to PtNi MNs/C (358 mV), PtP MNs/C (420 mV), and RuO2 (353 mV). The Tafel slope is used to explore OER kinetics. The smaller Tafel slope for PtNiP MNs/C (49.8 mV dec−1) compared with PtNi MNs/C (78.7 mV dec−1), PtP MNs/C (103.4 mV dec−1), and RuO2 (95.5 mV dec−1) implies rapid OER kinetics (Figure 5b). Moreover, the OER performance of PtNiP MNs/C is also more excellent than that of the Ni−P nanoparticles (NPs)/C (Figure S9), indicating that the enhanced OER ability is a result from the synergistic effect of Pt, Ni, and P components. Catalytic durability tests are also conducted for PtNiP MNs/C toward OER. From the LSV polarization curves before and

oxidation of the PtNiP MNs due to exposure to the air, which was also reported in the literature.49−51 These provide strong evidence of electronic interaction between the three elements, suggesting the electron transfer from Pt and Ni to P. Accordingly, the above results could demonstrate that both Ni and P atoms are incorporated into the starting Pt MNs, forming a tricomponent metal−nonmetal alloyed structure, and the electronic structure of Pt is modified due to electronic interactions between Pt, Ni, and P atoms. Such a Ni, P cointroduction strategy can be carried out at ambient temperature, thus avoiding the use of a high phosphating temperature or dangerous organophosphorus reagents. In consideration of its favorable mesoporous nanostructure and ternary Pt−Ni−P compositions, we investigated the electrocatalytic activity of the PtNiP MNs toward HER under alkaline conditions. For comparison, the catalytic activities of PtNi MNs, PtP MNs (see Figure S6 for the SEM image), and commercial Pt/C catalyst were also tested. Before electrochemical measurements, the PtNiP MNs, PtNi MNs, and PtP MNs were uniformly loaded onto a commercial carbon black to ensure that the percentage of Pt was 20 wt %. The carbon-supported PtNiP MNs, PtNi MNs, and PtP MNs are denoted as PtNiP MNs/C, PtNi MNs/C, and PtP MNs/C, respectively. Figure 4a displays the HER polarization curves of the electrocatalysts in a 1.0 M KOH aqueous solution at room temperature. It is obvious that the PtNiP MNs/C shows superior catalytic performance relative to PtNi MNs/C, PtP MNs/C, and Pt/C catalyst. The required overpotential to yield a current density of 10 mA cm−2 for PtNiP MNs/C is 54.4 mV, which is distinctly lower than that for PtNi MNs/C (74.4 mV), PtP MNs/C (72.0 mV), and Pt/C (74.6 mV), suggesting the improved HER ability on PtNiP MNs/C. The Tafel slope for the PtNiP MNs/C is 39.3 mV dec−1, which is a smaller value compared with that for PtNi MNs/C (45.9 mV dec−1), PtP MNs/C (52.6 mV dec−1), and Pt/C (53.3 mV dec−1) (Figure 4b), implying the faster HER kinetics catalyzed by PtNiP 9713

DOI: 10.1021/acssuschemeng.9b01484 ACS Sustainable Chem. Eng. 2019, 7, 9709−9716

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ACS Sustainable Chemistry & Engineering

Figure 6. (a) Polarization curves of the catalysts in a two-electrode system at the scan rate of 5 mV s−1. (b) The corresponding voltages of the catalysts at the current density of 10 mA cm−2. (c) Photograph during the overall water splitting. (d) Long-term durability test of the PtNiP MNs/ C at the constant current density of 10 mA cm−2 for the overall water splitting.

detected for 30 h. From the chronopotentiometry curve in Figure 6d, there is simply a slight degradation of the potential at the current density of 10 mA cm−2, suggesting the admirable stability of PtNiP MNs/C toward the splitting of water. According to above results, it can be concluded that the assynthesized PtNiP MNs exhibit superior bifunctional electrocatalytic abilities for both HER and OER, leading it to be a promising candidate in catalyzing the splitting of water. The enhanced catalytic performance for the overall water splitting of the PtNiP MNs can be attributed to the geometry and electronic effect. On the one hand, the interconnected and open pore structure of the nanoparticles will render the full access of the catalysts and the electrolyte. The mesoporous structure provides abundant active sites and facilates the transfer of reactants. On the other hand, after the coincorporation of Ni and P atoms, the electronic state of Pt could be modified, which contributed to the superior catalytic ability toward HER. When used for OER catalysis, the surface of PtNiP MNs can be partially oxidized to form OER active oxide species due to the existence of Ni and P components, which is in favor of the improved OER electrocatalytic performance of the Pt-based structure.

after accelerated CV cycling tests and the chronopotentiometry curves for PtNiP MNs/C at the current density of 10 mA cm−2, it can be seen that there are only slight changes after the tests (Figure 5c and d), suggesting the remarkable stability and durability of the PtNiP MNs/C toward OER. In order to probe into the origin of enhanced OER performance on PtNiP MNs, we collected the catalyst samples after more than 30 h of OER testing and carried out XPS analysis. It was found that the surface of the original PtNiP MNs was partially oxidized under oxidizing potentials as evidenced by the disappearance of P characteristic peaks and the increase of oxygen characteristic peaks (Figure S10). The disappearance of P component from the catalyst surface might be caused by the transformation of P at the catalyst surface into phosphates during the OER and their further dissolution in the electrolyte.52,53 These in-situ formed surface oxides/hydroxides species are regarded as electroactive sites to drive significantly improved OER activity, as also reported for other metal phosphide-derived OER catalysts.54,55 On account of their high electrocatalytic performance for HER and OER, the PtNiP MNs are expected to be an excellent candidate as a bifunctional electrocatalyst for the overall water splitting. A two-electrode system was assembled with the synthesized catalysts loaded on the Ni foam substrate which served as both the anode and cathode. Commercial Pt/C and RuO2 were loaded on the Ni foam and acted as the cathodic and anodic catalysts for comparison. The water electrolyzer composed of PtNiP MNs catalysts exhibits high performance with the need of a cell voltage of 1.590 V to deliver a watersplitting current density of 10 mA cm−2 (Figure 6a and b). The cell voltages for Pt/C + RuO2 composite and blank Ni foam are 1.631 and 1.910 V, respectively. In the process of overall water splitting, O2 and H2 were produced at the anode and cathode, respectively, at the same time owning to the electron transfer from the anode to the cathode (Figure 6c). The stability of the PtNiP MNs/C for overall water splitting was

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CONCLUSION In summary, a simple and practicable strategy was presented to synthesize highly ordered PtNiP MNs. The proposed method can be performed in a mild condition, free of high phosphating temperature, dangerous organophosphorus reagents, and complex procedures. The resultant PtNiP MNs exhibited superior activity and durability toward HER, OER, and overall water splitting, benefiting from its modified electronic structure and superb composition. The significantly enhanced electrocatalytic property and stability strongly supported that the coincorporation of Ni and P elements would be an effective way to prepare high-efficiency Pt-based electrocatalysts with reduced Pt-loading. More meaningfully, the proposed method 9714

DOI: 10.1021/acssuschemeng.9b01484 ACS Sustainable Chem. Eng. 2019, 7, 9709−9716

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ACS Sustainable Chemistry & Engineering

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is equally applicable to the preparation of other P-containing multicomponent alloy or heterostructure materials.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.9b01484. SEM images; TEM images, elemental mapping images; EDX spectrum; XPS spectra; histogram of particle size distribution; N2 adsorption−desorption isotherms; HER and OER polarization curves; and (Table S1) summary of the adding amounts of precursors and the HER performance for various PtNiP MNs (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Liang Wang: 0000-0001-7375-8478 Hongjing Wang: 0000-0003-0641-3909 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (21601154, 21776255, and 21701141).

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DOI: 10.1021/acssuschemeng.9b01484 ACS Sustainable Chem. Eng. 2019, 7, 9709−9716