Ruthenium nanoparticles modified oxidized, N-doped carbon substrates: Hydrogen generation electrocatalysts in alkaline and acidic conditions

Accepted Manuscript Ruthenium nanoparticles modified oxidized, N-doped carbon substrates: Hydrogen generation electrocatalysts in alkaline and acidic conditions Ya Zhang, Fangfang Wen, Ming Zhu, Zhifeng Zhou, Jing Tan, Honggui Wang PII:

S0254-0584(18)30771-5

DOI:

10.1016/j.matchemphys.2018.09.020

Reference:

MAC 20949

To appear in:

Materials Chemistry and Physics

Received Date: 14 March 2018 Revised Date:

17 August 2018

Accepted Date: 2 September 2018

Please cite this article as: Y. Zhang, F. Wen, M. Zhu, Z. Zhou, J. Tan, H. Wang, Ruthenium nanoparticles modified oxidized, N-doped carbon substrates: Hydrogen generation electrocatalysts in alkaline and acidic conditions, Materials Chemistry and Physics (2018), doi: 10.1016/ j.matchemphys.2018.09.020. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Ruthenium nanoparticles modified oxidized, N-doped carbon

substrates:

hydrogen

generation

electrocatalysts in alkaline and acidic conditions

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Ya Zhang,a* Fangfang Wen,a Ming Zhu,a Zhifeng Zhou,a Jing Tan,a Honggui Wanga,b,c*

a. School of Environmental Science and Engineering, Yangzhou University, Yangzhou, Jiangsu, 225127, P.R. China.

b. Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for

(26116120), Yangzhou, Jiangsu, 225009, P.R. China.

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Agrifood Safety and Quality, Ministry of Agriculture of China, Yangzhou University

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c. Jiangsu Key Laboratory of Zoonosis, Yangzhou University, Yangzhou, Jiangsu, 225009, P.R. China.

* Corresponding authors. Tel: +8651487979528, E-mail addresses: [email protected] (Y.

Abstract

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Zhang), [email protected] (H.G. Wang)

Various Ru nanoparticles modified porous carbon substrates were prepared as hydrogen evolution electrocatalysts via chemical reduction in this work. Before

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obtaining the Ru-based catalysts, different carbon substrates, including lignin, straw and shaddock peel, were selected. The carbon substrates were oxidized and

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nitrogen-doped under ammonia gas to further increase the physicochemical properties. Then, the nitrogen doped lignin, straw and shaddock peel were used as substrates to fabricate various Ru-based composites, which were denoted as Ru@o-NL, Ru@o-NS and Ru@o-NSP. The HER performances of Ru@o-NL, Ru@o-NS and Ru@o-NSP were fully investigated in both acidic and alkaline conditions. Experimental results indicated that all the Ru-based composites could catalyze the hydrogen evolution reaction. Ru@o-NL showed better HER activity than that of the Ru@o-NS and Ru@o-NSP. The dosage of Ru could affect the HER activity. The Ru@o-NL with 8.0 wt% Ru loading has the best HER performance. The overpotentials (@ 10 mA cm-2)

ACCEPTED MANUSCRIPT of the Ru@o-NL in 0.5 M H2SO4 and 1.0 M KOH were 42 and 14 mV, respectively. The corresponding Tafel slopes were 32 and 59 mV dec-1. It also had large exchange current density and good long term stability.

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Keywords: carbon substrates; hydrogen evolution electrocatalysts; oxidation;

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ruthenium nanoparticles.

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1. Introduction

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Fossil fuels consumption has resulted in resources shortage and greenhouse gas

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increasing. With ever increasing demand of sustainable development, renewable and

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environmentally friendly energy sources are urgently needed. Hydrogen, as a clean

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and efficient energy source, has been found to be an excellent candidate for traditional

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energy sources. Hydrogen can be harvested directly from water through the

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water-splitting reactions (hydrogen evolution and oxygen evolution reactions) [1-3].

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As one of the most effective ways to harvest hydrogen, electrochemically induced

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hydrogen evolution reaction (HER) has drawn great attention in recent years because

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no environmentally harmful by-products are generated. To achieve the best HER

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efficiency and lower the overpotentials of HER (1.23 V) [4], high-performance and

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durable electrocatalysts play a vital role.

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In recent years, researchers have paid lots of attention to produce HER catalysts.

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Transition metal compounds, including metal sulfides [5-8], carbides [9,10], oxides

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[11-13] and phosphides [14-18], have displayed their possibility to be the candidates

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as HER catalysts. However, platinum-based catalysts are still regarded as the superior

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HER catalysts as the Pt possesses favorable bond strength with hydrogen, which

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causes the fastest hydrogen evolution reaction rate [19]. Recently, to reduce the price

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of platinum-based HER catalysts and enlarge their application, platinum group metals

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have been investigated widely. As a cheaper platinum group metal, ruthenium (Ru)

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has been used as alternative to platinum. It has been reported that Ru nanoparticles

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and its oxides are good OER catalysts [20]. However, the Ru-based HER catalysts are

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not much investigated. Recent results have confirmed that Ru-based nanomaterials

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have the potential to be good candidates as new generation HER catalysts. For

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example, Lačnjevac et al. reported Ru/Ti2AlC composite as a cathode for hydrogen

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evolution under acidic medium [21]. Besides, MoO2, MoS2 and N-graphene modified

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Ru nanomaterials show well HER activity in both acidic and alkaline conditions

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[22-24]. It is obvious that the substrates play an important role in Ru nanoparticle

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separation. Therefore, novel substrates are still needed to prepare highly efficient

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It is well known good substrates can provide larger surface area, which will not only

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accelerate charge transfer rate but also stabilize noble metal nanoparticles. Various

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substrates have been reported, including polymer template [25], carbon material [26],

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metal [27] and metal oxides [22,28]. Among all the substrates, nanocarbon materials

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(carbon nanotubes [29], graphite [30], graphene (oxide) [31-33], hollow porous

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carbons [34] and carbon nanofiber [35]) have been widely investigated as their large

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surface area, excellent electrochemical stability and conductivity.

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In this work, various carbon substrates, including lignin, straw and shaddock peel, are

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selected. In order to further increase the physicochemical properties of the lignin,

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straw and shaddock peel, they are oxidized by nitric acid and nitrogen-doped under

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ammonia gas firstly. Then, the nitrogen doped lignin, straw and shaddock peel are

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used as substrates to fabricate various Ru-based composites, which are denoted as

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Ru@o-NL, Ru@o-NS and Ru@o-NSP. The HER performances of Ru@o-NL,

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Ru@o-NS and Ru@o-NSP are fully investigated in both alkaline and acidic

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conditions. Experimental results indicate all the Ru-based composites can catalyze the

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hydrogen evolution reaction. Ru@o-NL shows better HER activity than that of the

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Ru@o-NS and Ru@o-NSP. The dosage of Ru can affect the HER activity. The

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Ru@o-NL with 8.0 wt% Ru loading has the best HER performance. The

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overpotentials (@ 10 mA cm-2) of the Ru@o-NL in 0.5 M H2SO4 and 1.0 M KOH are

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42 and 14 mV, respectively. The corresponding Tafel slopes are 32 and 59 mV dec-1.

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The exchange current density and long term stability are also compared and

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presented.

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2. Experimental

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2.1 Reagents

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Lignin and straw were kindly provided by Yongfeng Yu life paper (Yangzhou) Co.,

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Ltd. (Jiangsu, China). Ruthenium trichloride (RuCl3), sodium borohydride (NaBH4),

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sodium hydroxide (KOH), nitric acid (HNO3), sulfuric acid (H2SO4) and other

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chemicals were of analytical grade and purchased from Sinopharm Chemical Reagent 2

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Co., Ltd.

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2.2 Preparation of o-NL, o-NS and o-NSP

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The NL, NS and NSP were all prepared by a two-step heat treatment process as our

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previous work reported [36]. Before the heat treatment, the untreated lignin, straw and

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shaddock peel were firstly cleaned with deionized (DI) water and dried at 110 °C for 2

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hours in an oven. After that, the dried biomass were placed in the porcelain boats and

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carbonized at 800 °C for 2 hours with the flowing of nitrogen gas. Then the obtained

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carbonized materials were further treated at 800 °C for 1 hour under the atmosphere

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of ammonia. After cooled to room temperature, the obtained NL, NS and NSP were

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oxidized in the 2.0 M nitric acid and heated at 40 °C for 6 hours in the water bath,

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then the products were cleaned with DI water thoroughly and dried at 60 °C overnight

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to yield o-NL, o-NS and o-NSP.

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2.3 Synthsis of Ru@o-NL, Ru@o-NS and Ru@o-NSP

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To prepare the Ru-based HER catalysts, 100 mg of NL, o-NL, o-NS and o-NSP were

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respectively dispersed in 50 mL RuCl3 solution (2.0 mM) and sonicated with a

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ultrasonic cleaning machine (42 KHz, 300 W) for 20 min. Then 10 mL NaBH4 (0.1

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M) was added dropwise into the RuCl3 solution under magnetic stirring. After

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vigorously stirred for 2 hours, the black precipitates were collected by centrifuge,

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cleaned with DI water for more than three times and dried at 60 °C for 12 hours. The

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products were recorded as Ru@NL, Ru@o-NL, Ru@o-NS and Ru@o-NSP,

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respectively. Ru@o-NL composites with different contents of Ru were synthesized

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with 25 mL and 75 mL RuCl3 solution, recorded as Ru@o-NL-1 and Ru@o-NL-3,

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respectively. The Ru@o-NL represents the Ru@o-NL-2 in the following work if

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otherwise stated. The detailed schematic of the formation and application of

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Ru@o-NL is shown in Fig. 1.

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2.4 Characteration

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Transmission electron microscopy (TEM) was performed on a Tecnai 12 transmission 3

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microscopy (HRTEM), High angle annular dark field scanning transmission electron

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microscopy (HAADF-STEM) and Energy Dispersive X-Ray Spectroscopy (EDX)

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were conducted with a Tecnai G2 F30 S-TWIN transmission electron microscopes.

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XPS measurements were recorded by using an ESCALAB 250 Xi photoelectron

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spectrometer using Al Kα radiation (Thermo-Fisher Scientific, US). The Raman

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spectra were obtained by a In Via laser confocal Raman spectrometer (Renishaw,

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Britain). The nitrogen adsorption-desorption measurement was conducted by a

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specific surface area and pore size analyzer (Beckman Coulter SA3100).

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2.5 Preparation of working electrode and electrocatalytic measurements

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Usually, 4 mg of the sample was dispersed in the mixed solution of DI water (0.8 mL)

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and ethanol (0.2 mL), and then a 5 wt% 50 µL of Nafion was added into the

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dispersion and sonicated for more than 30 min. Finally, 5 µL of the above uniform

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dispersion was dropped onto the well-polished glass carbon working electrode (GCE,

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Φ=3 mm) and dried at ambient temperature to obtain the modified working electrode.

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The loading of the catalysts on the GCE was about 0.27 mg cm-2. Deoxygenated KOH

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(1.0 M) and sulfuric acid (0.5 M) were employed as supporting electrolytes.

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Electrochemical impedance spectroscopy (EIS) was conducted with Autolab 302 N

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electrochemical workstation. The linear sweep voltammetry (LSV), cyclic

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voltammetry (CV) and chronoamperometry measurements were performed on a

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three-electrode system containing a modified GCE, a platinum wire counter electrode

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and a saturated calomel reference electrode (SCE) using CHI 660E electrochemical

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workstation. All potentials were converted to the potentials relative to reversible

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hydrogen electrode (ERHE=ESCE+0.059pH+0.242V). The iR compensation was used to

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correct the polarization curves.

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3. Results and discussion

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3.1 Characterization

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Before investigating the HER activity of the as-obtained samples, they were fully 4

ACCEPTED MANUSCRIPT characterized by TEM, Raman spectra and XPS. The morphology of samples was

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recorded by both TEM and HRTEM. For comparison, the image of unmodified NL is

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presented in Fig. S1a, which displays a stacked-sheets structure. After oxidation,

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wrinkled and porous structure can be observed (Fig. S1b), which gives more area to

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grow Ru particles. It can be seen from Fig. 2a-c and S1c, Ru particles can well

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disperse on all the carbon substrates. For comparison, the images of Ru@o-NL with

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different Ru loading are presented in Fig. S1d and e. As can be seen in Fig. S1e, the

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aggregation of Ru in Ru@o-NL-3 is serious, which may result in HER activity

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degradation. From the HRTEM images of Ru@o-NL in various resolutions (Fig.

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3a-d), the diameters of the Ru nanoparticles are 2~3 nm with distinct lattice fringes

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(lattice spacing: 0.22 nm). Interestingly, the o-NL displays a fingerprint lattice fringes

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with interplanar distance of 0.39 nm (Fig. 3d). This interplanar distance of o-NL is

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slightly higher than that of graphite (0.34 nm), which may result from nitrogen doping

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in lignin and the low graphitization degree [37]. The HAADF-STEM and elemental

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mapping shown in Fig. 3e-i indicate that C, N, O and Ru elements coexist in the

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Ru@o-NL nanocomposite. EDX result indicates the presence of Ru and the

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corresponding composition is 8.0 wt% in Ru@o-NL. Specific surface area and porous

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structure of the obtained o-NL were characterized by N2 adsorption-desorption

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isotherm (Fig. S1f). The BET specific surface area of o-NL is 680.4 m2 g-1, and the

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isotherm curve belongs to type IV with a hysteresis loop, indicating that the o-NL

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possesses mesopores and macropores [38]. The pore size distribution was measured

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by the Barrett-Joiner-Halenda method. Two regions can be identified: (1) mesopores

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(2-50 nm) with a maximum peak at 5.8 nm; and (2) macropores (>50 nm) with a

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maximum peak at 87.1 nm. Therefore, the obtained o-NL with large surface area and

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high porosity is considered as a promising template for further construction of

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Ru/o-NL hybrids, and is beneficial for electrolyte permeation and efficient ion

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diffusion, thus facilitating the HER electrocatalytic performance.

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The Raman spectra of different carbon substrates with and without Ru nanoparticles

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modification are summarized in Fig. 4a. In all curves, two main bands at about 1344

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(D band) and 1607 cm-1 (G band) can be clearly observed, which are attributed to the

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ACCEPTED MANUSCRIPT presence of defects in the oxidized and N-doped carbon substrates and the vibration of

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carbon atoms, respectively [39]. The ID/IG (intensity ratio of the D and G band)

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indicates the degree of disorder in carbon materials. From Fig. 4a, the ID/IG values of

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o-NL based catalysts are smaller than that of o-NS and o-NSP based catalyst.

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However, when composited with Ru, the ID/IG value of o-NL increases. This result

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suggests the increase of disordered/defective carbon [39,40] or the decrease of

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graphitization in o-NL based catalysts [41], which is consistent with the results of

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HRTEM (Fig. 3d).

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The elemental compositions of the Ru@o-NL were further determined by XPS and

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shown in Fig. 4b-f. As shown in the full survey spectrum (Fig. 4b), C, N, O and Ru

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are present and the weight percentage of Ru is 8.0%, which are in good accordance

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with the result of elemental mapping and EDX, respectively. In the high-resolution C

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1s spectrum (Fig. 4c), the peaks at 284.8, 285.7 and 288.9 eV correspond to C=C,

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C-O and –O-C=O, respectively [42]. The band located at 292.0 eV is assigned to the

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π–π* interband, a common feature in graphitic carbon XPS spectra [43]. With regard

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to the Ru 3d XPS peak, the fitted peak at 280.6 eV can be assigned to Ru (0) 3d5/2

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(Fig. 4c). the presence of Run+ at 281.9 eV probably results from the oxidation of Ru

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nanoparticles upon exposure to air [44,45]. The high resolution N 1s and O 1s spectra

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are presented in Fig. 4d and e. In the N 1s spectrum, three main peaks located at about

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397.4, 399.2 and 404.0 eV are related to pyridine-type, pyrrolic-type and

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graphite-type N, respectively [24]. As shown in Fig. 4e, three kinds of surface oxygen

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species could be distinguished in the O 1s spectrum. The peaks at about 530.0 , 531.2

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and 532.2 eV can be assigned to the lattice oxygen, –O-C=O and C-O, respectively

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[46,47]. In the spectrum of Ru 3p shown in Fig. 4f, two distinct peaks located at

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462.4 and 484.9 eV are detected, which correspond to Ru 3p3/2 and Ru 3p1/2,

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respectively. The component peaks at 461.7 and 484.2 eV could be ascribed to Ru0

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[48]. The peaks at 464.5, 486.6 eV and 467.9, 489.7 eV are related to Ru oxide

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species, respectively [49,50].

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3.2 HER performance

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The as-prepared Ru-based nanocomposites and commercial Pt/C were evaluated as

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ACCEPTED MANUSCRIPT catalysts for HER via linear sweep voltammetry (LSV) measurement in both alkaline

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and acidic conditions. Before testing, iR correction (Fig. S2) has been done in both

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media to obtain the true kinetic activity. Fig. 5a and b show the polarization curves of

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the Ru-based nanocomposites with various carbon substrates and commercial Pt/C in

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1.0 M KOH and 0.5 M H2SO4, respectively. Compared with the Ru@o-NL,

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Ru@o-NS and Ru@o-NSP, Pt/C displays superior HER activity in 0.5 M H2SO4, but

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does inferior in 1.0 M KOH. All the Ru-based materials do acceptable jobs as HER

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catalysts. According to the Tafel plots (Fig. 5c and d) derived from the corresponding

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polarization curves (Fig. 5a and b), the Ru@o-NL shows lower Tafel slopes (59 and

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32 mV dec-1 in 1.0 M KOH and in 0.5 M H2SO4, respectively) than that of Ru@o-NS

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and Ru@o-NSP. The Volmer, Heyrovsky and Tafel are three widely accepted

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reactions for HER [51,52] and the corresponding Tafel slopes are 120, 40 and 30 mV

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dec-1, respectively [51,52]. Therefore, the Ru@o-NL catalyzed HER takes place by

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the Volmer−Heyrovsky mechanism in alkaline and Heyrovsky-Tafel mechanism in

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acid, respectively. The corresponding pathways are as follows:

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In alkaline condition:

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H2O + e− + Ru@o-NL →Ru@o-NL-Hads + OH−

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H2O + e− + Ru@o-NL-Hads →Ru@o-NL + OH− + H2

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In acid condition:

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H3O+ + e + Ru@o-NL-Hads → Ru@o-NL + H2 + H2O

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Ru@o-NL-Hads + Ru@o-NL-Hads → Ru@o-NL + H2

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Note that the Tafel slopes of Ru@o-NL are lower or comparable than that of Pt/C,

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which suggests that superior catalytic activity of Ru@o-NL.

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As important parameters to evaluate HER catalysts, the overpotentials (@ 10 mA cm-2)

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and exchange current densities of Ru@o-NL, Ru@o-NS, Ru@o-NSP and Pt/C are

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summarized in Fig. 5c and d. In alkaline condition, Ru@o-NL has the lowest

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overpotential of 14 mV, indicating its excellent HER activity. Besides, it has the

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highest exchange current density (5.8 mA cm-2), which is much higher than that of

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Ru@o-NS (4.1 mA cm-2), Ru@o-NSP (2.9 mA cm-2) and Pt/C (3.4 mA cm-2). In

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acidic condition, the overpotentials of Ru@o-NL, Ru@o-NS, Ru@o-NSP and Pt/C

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(Volmer-reaction) (Heyrovsky-reaction)

(Heyrovsky-reaction) (Tafel-reaction)

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ACCEPTED MANUSCRIPT are 42, 54, 60 and 30 mV, respectively. The Ru@o-NL holds the highest exchange

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current density of 2.1 mA cm-2. In a word, for considering the overpotential (@ 10

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mA cm-2) and exchange current density, the Ru@o-NL performs better in alkaline

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condition. As the substrate, o-NL is superior to o-NS and o-NSP.

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It is well known the noble metal nanoparticles play important roles in catalytic system.

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Therefore, the effect of Ru dosage on HER activity are considered and shown in Fig.

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6. Fig. 6a and b show the polarization curves of the Ru@NL and o-NL-based

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nanocomposites with various Ru in 1.0 M KOH and 0.5 M H2SO4, respectively. As

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shown in Fig. 6a and b, o-NL without Ru modification has little HER activity whether

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in alkaline or acidic condition. Besides, oxidation is also important to obtain the

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porous and high efficient HER substrate. Among Ru@o-NLs, Ru@o-NL-2

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(Ru@o-NL) shows the best HER activity. The Tafel plots derived from the

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corresponding polarization curves (Fig. 6a and b) are displayed in Fig. 6c and d. the

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Ru@o-NL has the lowest Tafel slopes in both conditions. Therefore, the Ru@o-NL is

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used in the following tests as the best HER catalyst.

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EIS in both conditions are recorded in Fig. 7 to further confirm the kinetics process of

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Ru-based HER. As can be seen in Fig. 7a, Ru@NL and o-NL have much larger

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semicircle diameters than those of the Ru@o-NLs, Ru@o-NS and Ru@o-NSP, which

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suggests lowest electron transfer rate. Among the Ru@o-NLs, Ru@o-NS and

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Ru@o-NSP, Ru@o-NL has the smallest semicircle diameter, indicating the fastest

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electron transfer rate and the best HER activity [52]. These results are well consistent

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with the results shown in Fig. 6.

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Electrochemical double layer capacitance (Cdl), generally proportional to the

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electrocatalytical active surface area [11,22], was recorded and calculated using cyclic

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voltammetry (CV) measurements. Fig. 8a and b show the CVs of Ru@o-NL,

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Ru@o-NS and Ru@o-NSP with scan rate of 100 mV s−1 in 1.0 M KOH and 0.5 M

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H2SO4, respectively. The corresponding capacitive current @ 0.15 V as a function of

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scan rate for Ru@o-NL, Ru@o-NS and Ru@o-NSP in 1.0 M KOH and 0.5 M H2SO4

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is displayed in Fig. 8c and d, respectively, in which straight lines are obtained. The Cdl

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of Ru@o-NL in 1.0 M KOH and 0.5 M H2SO4 are 45 and 42 mF cm-2, respectively,

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As another important factor to evaluate the performance of HER catalyst, the

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durability of Ru@o-NL, Ru@o-NS and Ru@o-NSP in 1.0 M KOH and 0.5 M H2SO4

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were investigated by both CV cycling and chronoamperometry (Fig. 9). As displayed

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in Fig. 9a and b, slight cathodic current loss can be observed after 1000 cycles in both

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media. From the chronoamperometric curves (Fig. 9c and d), although small serrate

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fluctuations can be seen, no obvious degradation is detected after electrolysis in 1.0 M

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KOH and 0.5 M H2SO4 for 10 h, indicating the well dispersion of Ru nanoparticles

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onto the three porous carbon substrates and the strong chemical and electronic

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coupling between Ru nanoparticles and o-NL, o-NS and o-NSP. The HER

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performance of Ru-based nanomaterials is summarized in Table 1. Unlike Pt-based

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HER catalysts, Ru-based materials show good HER activity in both alkaline and

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acidic conditions. The Ru@o-NL obtained in this work shows the best HER

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performance except for Ru@C2N. Therefore, it is a promising Ru-based HER

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catalyst.

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4. Conclusion

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In this work, oxidized and nitrogen doped lignin, straw and shaddock peel are

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introduced as porous carbon substrates. Various Ru nanoparticles supported porous

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carbon substrates are prepared (Ru@o-NL, Ru@o-NS and Ru@o-NSP) as hydrogen

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evolution electrocatalysts via chemical reduction. The as-obtained nanocomposites are

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characterized. Experimental results indicate that oxidation and nitrogen-doping can

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accelerate the charge transfer rate between Ru nanoparticles and the carbon substrates.

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The HER performances of Ru@o-NL, Ru@o-NS and Ru@o-NSP in both acidic and

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alkaline conditions display all the Ru-based composites can catalyze the hydrogen

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evolution reaction. Ru@o-NL shows better HER activity than that of the Ru@o-NS

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and Ru@o-NSP, which dues to the more porous structure. The Ru@o-NL with 8.0 wt%

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Ru loading has the best HER performance. The overpotentials (@ 10 mA cm-2) of the

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Ru@o-NL in 0.5 M H2SO4 and 1.0 M KOH are 42 and 14 mV, respectively. The

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corresponding Tafel slopes are 32 and 59 mV dec-1. The Ru@o-NL also shows large

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exchange current density and excellent long term stability under acidic and alkaline

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media, which is quite comparable to the Ru-based HER catalysts reported.

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Acknowledgments

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This work was supported by the National Natural Science Foundation of China (No.

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21307104), Natural Science Foundation of Jiangsu Province, China (No.

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BK20171281), Postgraduate Research & Practice Innovation Program of Jiangsu

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Province

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Foundation of Yangzhou University (No. 2016CXJ046), the Open Project Program of

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Jiangsu Key Laboratory of Zoonosis (No. R1705), Innovative Research Team and

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Teaching and Research Award Program for Young Academic Leaders of Yangzhou

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University.

Scientific

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Innovation

Foster

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(KYCX17-1882),

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ACCEPTED MANUSCRIPT

Ru/Ti2AlC Ru–MoO2

Ru/MoS2/CP

Ru@NG-4

1.0 M KOH 1.0 M H2SO4

16.16

1.0 M KOH 1.0 M KOH 0.5 M H2SO4 1.0 M KOH 1.0 M H2SO4 0.5 M H2SO4

nanosponges

0.5 M KOH

N/A

N/A

49.2

EP

Pt53Ru39Ni8

0.5 M H2SO4

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Ru@C2N

5-20

0.5 M H2SO4

0.5 M H2SO4

Co80Ru15Pt5

8.0

0.1 M PBS (pH=7) 0.5 M H2SO4 0.5 M H2SO4 1.0 M KOH

39

5 15 28.7

-2

Tafel slope -1

Cdl

Reference

@ 10 mA cm

(mV dec )

(mF cm-2)

42

34

42

14

59

45

~60

0.82-3.38

[21]

N/A

[22]

SC

0.5 M H2SO4

Ru/SiNWs-42.9

Ru/MeOH/THF

loading (wt%)

Overpotential (mV)

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Noble metal

Electrolytes

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Table 1 Comparison of HER performances of Ru-based electrocatalysts.

-126 - -97

(@100 mA cm-2)

This work

55

44

29

31

13

60

25

96

N/A

N/A

40

76

44

60

41

11.2

200

81

N/A

[27]

37

34

40

46

N/A

[50]

83

46

83

80

N/A

[53]

73.1 (@ 4 mA cm-2)

30.4

N/A

[54]

13.5

30

17.0

38

N/A

[55]

[23]

[24]

ACCEPTED MANUSCRIPT Figure captions Fig. 1 Schematic of the formation and application of Ru@o-NL. Fig. 2 TEM of images Ru@o-NL (a), Ru@o-NS (b) and Ru@o-NSP (c). Fig. 3 HRTEM images of Ru@o-NL in low magnification ((a), (b)) and high

results of elements: (f) C, (g) N, (h) O, (i) Ru.

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magnification ((c), (d)); (e) HAADF-STEM images of the Ru@o-NL; Mapping

Fig. 4 (a) Full survey spectrum of Ru@o-NL; XPS spectra: (b) C 1s, (c) N 1s, (d) O 1s and (e) Ru 3p of Ru@o-NL. (f) Raman spectra of o-NL, Ru@o-NL-1, Ru@o-NL-2,

SC

Ru@o-NL-3, o-NS, Ru@o-NS, o-NSP and Ru@o-NSP.

Fig. 5 Polarization curves of Ru@o-NL, Ru@o-NS, Ru@o-NSP and Pt/C in 1.0 M

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KOH (a) and 0.5 M H2SO4 (b), respectively; Tafel plots obtained from the polarization curves in 1.0 M KOH (c) and 0.5 M H2SO4 (d), respectively; Overpotentials at 10 mA cm-2 (left) and exchange current densities (right) of Ru@o-NL, Ru@o-NS, Ru@o-NSP and Pt/C in 1.0 M KOH (e) and 0.5 M H2SO4 (f), respectively. Fig. 6 Polarization curves of o-NL, Ru@NL, Ru@o-NL-1, Ru@o-NL-2 and

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Ru@o-NL-3 in 1.0 M KOH (a) and 0.5 M H2SO4 (b), respectively; Tafel plots obtained from the polarization curves in 1.0 M KOH (c) and 0.5 M H2SO4 (d), respectively.

EP

Fig. 7 Nyquist plots of o-NL, Ru@NL, Ru@o-NL-1, Ru@o-NL-2, Ru@o-NL-3, Ru@o-NS and Ru@o-NSP recorded in 1.0 M KOH (a) at 40 mV and 0.5 M H2SO4 (b)

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at 70 mV, respectively.

Fig. 8 CVs of Ru@o-NL, Ru@o-NS and Ru@o-NSP with scan rate of 100 mV s−1 in 1.0 M KOH (a) and 0.5 M H2SO4 (b), respectively; The capacitive current at 0.15 V as a function of scan rate for Ru@o-NL, Ru@o-NS and Ru@o-NSP in 1.0 M KOH (c) and 0.5 M H2SO4 (d), respectively. Fig. 9 Polarization curves of Ru@o-NL, Ru@o-NS and Ru@o-NSP initially (solid) and after 1000 cycles (dash) in 1.0 M KOH (a) and 0.5 M H2SO4 (b), respectively; (c) Time-dependent current density curve of Ru@o-NL, Ru@o-NS and Ru@o-NSP in 1.0 M KOH under a static overpotential of 14, 26, 40 mV, respectively; (d)

ACCEPTED MANUSCRIPT Time-dependent current density curve of Ru@o-NL, Ru@o-NS and Ru@o-NSP in

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0.5 M H2SO4 under a static overpotential of 59, 67, 73 mV, respectively.

ACCEPTED MANUSCRIPT

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Fig. 1 Schematic of the formation and application of Ru@o-NL.

ACCEPTED MANUSCRIPT

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Fig. 2 TEM images of Ru@o-NL (a), Ru@o-NS (b) and Ru@o-NSP (c).

ACCEPTED MANUSCRIPT Fig. 3 HRTEM images of Ru@o-NL in low magnification ((a), (b)) and high magnification ((c), (d)); (e) HAADF-STEM images of the Ru@o-NL; Mapping

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results of elements: (f) C, (g) N, (h) O, (i) Ru.

ACCEPTED MANUSCRIPT Fig. 4 (a) Raman spectra of o-NL, Ru@o-NL-1, Ru@o-NL-2, Ru@o-NL-3, o-NS, Ru@o-NS, o-NSP and Ru@o-NSP. (b) Full survey spectrum of Ru@o-NL; XPS spectra: (c) C 1s, (d) N 1s, (e) O 1s and (f) Ru 3p of Ru@o-NL.

(b)

o-NSP Ru@o-NS o-NS Ru@o-NL-3 Ru@o-NL-2

N 1s

o-NL

1500

2000

200

2500

-1

285.7 eV 288.9 eV 292.0 eV

285

290

390

531.2 eV

532.2 eV

AC C 525

530

700

N 1s

535

Binding Energy (eV)

540

404.0 eV

400

405

410

Binding Energy (eV)

(f) Ru 3p

461.7 eV 484.2 eV

Counts (s)

EP

Counts (s)

O 1s

530.0 eV

600

399.2 eV

395

Binding Energy (eV)

(e)

500

(d)

295

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280

400

Counts (s)

Counts (s) 275

300

397.4 eV

284.8 eV

281.9 eV

Ru 8.02 1.08

Ru 3p

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C 1s

280.6 eV

O 15.43 13.13

Binding Energy (eV)

Raman shift (cm )

(c)

N 5.97 5.8

O 1s

Ru@o-NL-1

1000

C 70.58 79.99

SC

500

Element Weight % Atomic %

Ru@o-NSP

ID/IG=1.14 ID/IG=1.17 ID/IG=1.12 ID/IG=1.08 ID/IG=1.03 ID/IG=1.02 ID/IG=0.96

Counts (s)

Intensity (a. u.)

ID/IG=1.53

C 1s

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(a)

486.6 eV

464.5 eV 467.9 eV

489.7 eV

450

460

470

480

490

Binding Energy (eV)

500

510

ACCEPTED MANUSCRIPT

Fig. 5 Polarization curves of Ru@o-NL, Ru@o-NS, Ru@o-NSP and Pt/C in 1.0 M KOH (a) and 0.5 M H2SO4 (b), respectively; Tafel plots obtained from the polarization curves in 1.0 M KOH (c) and 0.5 M H2SO4 (d), respectively; Overpotentials at 10 mA

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cm-2 (left) and exchange current densities (right) of Ru@o-NL, Ru@o-NS, Ru@o-NSP and Pt/C in 1.0 M KOH (e) and 0.5 M H2SO4 (f), respectively.

(b) j (mA cm )

-20

0

Ru@o-NL Ru@o-NS Ru@o-NSP Pt/C

-2

-30

-90

1.0 M KOH

-0.1

0.0

0.1

E (V) vs. RHE

(d) 80

Ru@o-NL Ru@o-NS Ru@o-NSP Pt/C

-1

73 mV dec

30

TE D

40

-1

67 mV dec

20

-1

10

59 mV dec

-1

83 mV dec

0 0.4

0.6

1.0

-1

52 mV dec

-1

32 mV dec

40

-1

25 mV dec

0.5 M H2SO4

0.8

(f) 80

8

-2

4

20

2

10

S L SP /C -N o-N -N Pt @ o u@ u@ o R Ru R

1.2

1.4

1.6

2.5

0

2.0

60

-2

6

j0 (mA cm )

30

1.0

0.5 M H2SO4

1.0 M KOH

Overpotential (mV)

AC C

0.6

-2

40

L NS SP /C -N -N Pt @ o u@ o @ o u Ru R R

-1

55 mV dec

log j (mA cm )

50

0

0.1

Ru@o-NL Ru@o-NS Ru@o-NSP Pt/C

60

20

1.2

-2

60

0.0

1.0 M KOH

0.8

log |j (mA cm )|

(e)

-0.1

E (V) vs. RHE

EP

Overpotential (mV)

50

-0.2

j0 (mA cm )

-0.2

0.5 M H2SO4

-120 -0.3

Overpotential (mV)

-80 -0.3

(c)

-60

M AN U

Ru@o-NL Ru@o-NS Ru@o-NSP Pt/C

-40

-60

Overpotential (mV)

SC

0

-2

j (mA cm )

(a)

1.5 40 1.0 20

0

0.5

L NS SP C -N Pt/ o-N o@ u@ u@o R Ru R

L S SP /C o-N o-N o-N Pt @ u@ @ Ru Ru R

0.0

ACCEPTED MANUSCRIPT Fig. 6 Polarization curves of o-NL, Ru@NL, Ru@o-NL-1, Ru@o-NL-2 and Ru@o-NL-3 in 1.0 M KOH (a) and 0.5 M H2SO4 (b), respectively; Tafel plots obtained from the polarization curves in 1.0 M KOH (c) and 0.5 M H2SO4 (d),

(a)

(b)

0

RI PT

respectively.

0

-2

o-NL Ru@NL Ru@o-NL-1 Ru@o-NL-2 Ru@o-NL-3

-40

-60

-40 -60 -80

1.0 M KOH

-0.1

0.0

0.1

60

-1

112 mV dec

40 86 mV dec

20

-1

67 mV dec

-1

TE D

Overpotential (mV)

(d) 200

Ru@NL Ru@o-NL-1 Ru@o-NL-2 Ru@o-NL-3

-1

59 mV dec

0

1.0 M KOH

0.6

0.8

1.0

-2

EP

log j (mA cm )

AC C

-0.1

o-NL Ru@NL Ru@o-NL-1 Ru@o-NL-2 Ru@o-NL-3

0.5 M H2SO4

0.0

0.1

E (V) vs. RHE

E (V) vs. RHE

(c) 80

-0.2

M AN U

-0.2

-100 -0.3

1.2

Overpotential (mV)

-80 -0.3

SC

j (mA cm )

-2

j (mA cm )

-20 -20

160

Ru@NL Ru@o-NL-1 Ru@o-NL-2 Ru@o-NL-3

-1

89 mV dec

120

71 mV dec

80

-1 -1

68 mV dec -1

32 mV dec

40 0.3

0.5 M H2SO4 0.6

0.9

1.2 -2

log j (mA cm )

1.5

ACCEPTED MANUSCRIPT Fig. 7 Nyquist plots of o-NL, Ru@NL, Ru@o-NL-1, Ru@o-NL-2, Ru@o-NL-3, Ru@o-NS and Ru@o-NSP recorded in 1.0 M KOH (a) at 40 mV and 0.5 M H2SO4 (b)

(a)

800

RI PT

at 70 mV, respectively.

(b)

0.5 M H2SO4

1200

1.0 M KOH

o-NL Ru@NL Ru@o-NL-1 Ru@o-NL-2 Ru@o-NL-3 Ru@o-NS Ru@o-NSP

200

0

800

400

0 0

200

400

600

800

1000

Z' (ohm)

0

SC

400

-Z'' (ohm)

-Z'' (ohm)

600

400

M AN U TE D EP AC C

800

Z' (ohm)

o-NL Ru@NL Ru@o-NL-1 Ru@o-NL-2 Ru@o-NL-3 Ru@o-NS Ru@o-NSP

1200

1600

ACCEPTED MANUSCRIPT Fig. 8 CVs of Ru@o-NL, Ru@o-NS and Ru@o-NSP with scan rate of 100 mV s−1 in 1.0 M KOH (a) and 0.5 M H2SO4 (b), respectively; The capacitive current at 0.15 V as a function of scan rate for Ru@o-NL, Ru@o-NS and Ru@o-NSP in 1.0 M KOH (c) and 0.5 M H2SO4 (d), respectively. 9

(b) 6

RI PT

(a)

j (mA cm )

3

3

-2

-2

j (mA cm )

6

Ru@o-NL Ru@o-NS Ru@o-NSP

0 -3

Ru@o-NL Ru@o-NS Ru@o-NSP

0 -3

-6

0.05

0.10

0.15

0.20

SC

-6

1.0 M KOH

-9

0.5 M H2SO4

0.05

0.25

E (V) vs. RHE

0.15

0.20

0.25

M AN U

E (V) vs. RHE

(d) 10

(c) 10 -2

6 -2

34 mF cm

2

40

80

TE D

0

120

160

200

-1

AC C

EP

Scan rate (mV s )

-2

42 mF cm

6

-2

30 mF cm

-2

4

24 mF cm

2

0.5 M H2SO4

0

1.0 M KOH

0

-2

-2

38 mF cm

4

Ru@o-NL Ru@o-NS Ru@o-NSP

8

-2

45 mF cm

∆j/2 (mA cm )

Ru@o-NL Ru@o-NS Ru@o-NSP

8

∆ j/2 (mA cm )

0.10

240

0

40

80

120

160 -1

Scan rate (mV s )

200

240

ACCEPTED MANUSCRIPT Fig. 9 Polarization curves of Ru@o-NL, Ru@o-NS and Ru@o-NSP initially (solid) and after 1000 cycles (dash) in 1.0 M KOH (a) and 0.5 M H2SO4 (b), respectively; (c) Time-dependent current density curve of Ru@o-NL, Ru@o-NS and Ru@o-NSP in 1.0 M KOH under a static overpotential of 14, 26, 40 mV, respectively; (d)

RI PT

Time-dependent current density curve of Ru@o-NL, Ru@o-NS and Ru@o-NSP in 0.5 M H2SO4 under a static overpotential of 59, 67, 73 mV, respectively. (b)

-40

Ru@o-NS Ru@o-NL

-60

-60

-0.2

-0.1

0.0

0.1

AC C

EP

TE D

E (V) vs. RHE

Ru@o-NS

Ru@o-NL

-90 1.0 M KOH

-80 -0.3

Ru@o-NSP

-30

-2

j (mA cm )

Ru@o-NSP

-2

j (mA cm )

-20

0

SC

0

M AN U

(a)

-120 -0.3

-0.2

-0.1

E (V) vs. RHE

0.5 M H2SO4

0.0

0.1

ACCEPTED MANUSCRIPT Highlights N-doped carbon substrates were prepared from lignin, straw and shaddock peel. The wrinkled porous substrates were decorated with Ru nanoparticles via chemical reduction.

AC C

EP

TE D

M AN U

SC

in both acidic and alkaline conditions.

RI PT

The materials showed superior HER performances and good long-term stability