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Controllable synthesis of ruthenium phosphides (RuP and RuP2) for pH-universal hydrogen evolution reaction Qingbo Chang, Jingwen Ma, Yuanzhi Zhu, Zhen Li, Danyun Xu, Wenchao Peng, Yang Li, Guoliang Zhang, Fengbao Zhang, and Xiaobin Fan ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00187 • Publication Date (Web): 17 Apr 2018 Downloaded from http://pubs.acs.org on April 17, 2018
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ACS Sustainable Chemistry & Engineering
Controllable synthesis of ruthenium phosphides (RuP and RuP2) for pH-universal hydrogen evolution reaction Qingbo Chang, † Jingwen Ma, † Yuanzhi Zhu, † Zhen Li, † Danyun Xu, † Xuezhi Duan, ‡ Wenchao Peng, † Yang Li, † Guoliang Zhang, † Fengbao Zhang † and Xiaobin Fan*,† †
State Key Laboratory of Chemical Engineering, School of Chemical Engineering and
Technology, Collaborative Innovation Center of Chemical Science and Engineering, Tianjin University, No. 135, Yaguan Road, Jinnan District, Tianjin 300354, China ‡
State Key Laboratory of Chemical Engineering, East China University of Science and
Technology, 130 Meilong Road, Shanghai, 200237, China *Corresponding author. E-mail:
[email protected] KEYWORDS: ruthenium phosphides, one-step controlled synthesis, all pH range, Pt-like activity, Hydrogen evolution reaction
ABSTRACT Metal phosphides are promising efficient non-Pt electrocatalysts for hydrogen evolution reaction (HER). Herein, we report a simple strategy to controllably synthesize pure RuP and RuP2 and evaluate their HER performances in all pH range. Different from other transition metal phosphides, the HER performance of the RuPx in all pH range obviously improves as the phosphorus content decreases. By systematic research, it has been found that the RuP-475 with more Ru had much better conductivity and more catalytically active sites than the P rich RuP2-550. In addition, the RuP-475 exhibits excellent HER performance with small overpotential at a current density of 10 mA cm–2 (46, 47, 22 mV in pH = 0, 7, and 14, respectively).
INSTRUCTION Hydrogen (H2) as a sustainable and environmentally friendly fuel provides a promising candidate to replace fossil fuels and solve problems about the increasing of global energy demand and deteriorating of climate.1 Electrocatalytic reduction of water is an effective method to produce H2 via hydrogen evolution reaction (HER).2-3 Pt, due to its low overpotential and fast kinectics during the HER, is the benchmark of HER electrocatalysts. But the high cost makes its
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application unattractive in commercial processes.4 Transition metal phosphides (TMPs), especially the P-rich metal phosphides (MPx) based on Co,5-9 Ni,10-11 Fe,12-13 Mo,14 W,15 and Cu16-17 provide a promising alternative. Previous studies have demonstrated that P atoms could attract electrons from metal atoms, and the negatively charged P could be used as a base to capture positively charged protons during HER.18 Therefore, the P-rich TMPs are highly efficient toward HER than P-deficient TMPs, and increasing the atomic percentage of P in MPx is an effective way to enhance the HER activity of TMPs. However, these TMPs electrocatalysts still cannot compare with Pt in all pH range, despite their excellent performances in acid solutions. The non-Pt noble metal phosphides with a less expensive noble metal involved may provide a trade-off solution. Among all the non-Pt noble metals, ruthenium (Ru) is the most promising one, because of its relatively low cost (~4% of Pt) and intrinsic high catalytic activity.19-24 Recently, ruthenium phosphides have been synthesized for hydrodeoxygenation,25 oxygen reduction reaction26 and HER.27 However, it is still a great challenge to synthesize different ruthenium phosphides with a controllable manner, and the influences of P content on the HER performances of ruthenium phosphides haven’t been reported. In this study, we report a simple strategy to controllably synthesize RuP and RuP2 and evaluate their HER performances in all pH range. We demonstrated that pure RuP and RuP2 could be selectively synthesized by a simple heat-treatment in H2 under different temperatures. To our surprise, the P-deficient RuP shows much higher catalytic activity than the P-rich RuP2, and superior performances of the RuP over Pt/C were also observed under neutral and alkaline conditions.
EXPERIMENTAL SECTION Materials synthesis. In a typical procedure, 300 mg of RuCl3 and NaH2PO2·H2O with a molar ratio of 1:6 were dissolved in deionized water under sonication. Then a solid mixture was obtained after evaporating the water at 80 °C and drying under vacuum at 120 °C for 3 h. Subsequently, the mixture was grinded finely and the collection was annealed at different temperature (425~600 °C) at a ramping rate of 5 °C min–1 under H2 atmosphere with 100 sccm for 2 h. After cooling to room temperature in continued H2 flow, the mixture was passivated in Ar at 200 sccm for 0.5 h. Finally, the product was grinded and washed with deionized water for three ACS Paragon Plus Environment
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times, and then freeze-dried for 48 h. General characterization. Powder X-diffractin (XRD) patterns of different samples were tested by using an X’Pert PRO diffractometer with a Cu Kα radiation. The morphologies were collected by scanning electron microscopy (SEM, Hitachi S-4800). Transmission electron microscopy (TEM) images were recorded by a JEM 2100F Transmission electron microscopy (JEOL, Japan) at an acceleration voltage of 200 kV. X-ray photoelectron spectroscopy (XPS) data were obtained using an Thermo Scientific ESCALAB 250 XI Instrument. The survey spectra were recorded in a 1 eV step sizes with a pass energy of 150 eV. Detailed scans were recorded in 0.05 eV step sizes with a pass energy of 30 eV. Nitrogen adsorption isotherms were tested on a BJBUILDER SSA-7000 adsorption analyzer at 77 K. The samples were degassed at 150 °C for 6 h to remove surface contaminants. The Brunauer-Emmett-Teller (BET) method was used to evaluate specific surface area from adsorption points in the relative pressure of 0.05
