Mesoporous and ultrathin arrays of cobalt nitride nanosheets for electrocatalytic oxygen evolution

Accepted Manuscript Mesoporous and ultrathin arrays of cobalt nitride nanosheets for electrocatalytic oxygen evolution

Chang Liu, Gailing Bai, Xili Tong, Yunwei Wang, Baoying Lu, Nianjun Yang, Xiang-Yun Guo PII: DOI: Reference:

S1388-2481(18)30313-8 https://doi.org/10.1016/j.elecom.2018.11.022 ELECOM 6352

To appear in:

Electrochemistry Communications

Received date: Accepted date:

29 November 2018 29 November 2018

Please cite this article as: Chang Liu, Gailing Bai, Xili Tong, Yunwei Wang, Baoying Lu, Nianjun Yang, Xiang-Yun Guo , Mesoporous and ultrathin arrays of cobalt nitride nanosheets for electrocatalytic oxygen evolution. Elecom (2018), https://doi.org/10.1016/ j.elecom.2018.11.022

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ACCEPTED MANUSCRIPT Mesoporous and ultrathin arrays of cobalt nitride nanosheets for electrocatalytic oxygen evolution Chang Liu,a,b Gailing Bai,a,b Xili Tong,a,* Yunwei Wang,a Baoying Lu,c Nianjun Yang,d,* Xiang-Yun Guoa

Sciences, Taiyuan, 030001, China

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a State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of

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b University of the Chinese Academy of Sciences, Beijing, 100039, China

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c Guangxi University of Science and Technology, Liuzhou, 545000, China

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d Institute of Materials Engineering, University of Siegen, Siegen 57076, Germany

Abstract: Efficient electrocatalysts for oxygen evolution are vitally important for

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regenerative fuel cells and metal-air batteries. Herein, 3D mesoporous and ultrathin array of CoN nanosheets are synthesized on the Ni foam via thermal transformation

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of Co3O4 nanowire arrays. This array imparts enhanced active sites, mass diffusion, and electron transfer towards oxygen evolution reaction. The low overpotential of 323

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mV at 30 mA cm-2, a Tafel slope of 74 mV dec-1, and a high potential conservation in a long process of electrolysis process are achieved. It is thus one robust and efficient

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electrocatalyst for OER.

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Keywords: CoN nanosheet; Oxygen evolution reaction; Electrocatalyst

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ACCEPTED MANUSCRIPT 1. Introduction Water electrolysis has attracted extensive interest in clean hydrogen fuel generation [1]. Oxygen evolution reaction (OER) is the major bottleneck in the overall water splitting process because OER is a sluggish electrode reaction and multi electrons are involved [2]. Due to obtained low overpotentials, high current densities and long-term

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durability during OER, iridium and ruthenium oxides are the benchmark catalysts for OER to date. However, their high cost and scarcity limit their widespread applications

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[3-5].

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Recently, nanostructured CoN with vast reserves and environmental benignity has been recognized as a promising alternative to iridium and ruthenium oxides towards

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OER, originating from the optimized electronic structure of Co element in the nitrides and its large surface area [6-8]. For example, both CoN nanowires prepared by N 2

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radio frequency plasma treatment [9] and CoN nanoparticles obtained via annealing in ammonia atmosphere exhibited high activity towards OER [3, 10].

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To further improve the OER performance of CoN catalysts, we propose here a strategy

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to synthesize mesoporous and ultrathin arrays of CoN nanosheets where toxic gases and other expensive devices are not needed. Such arrays are expected to provide more effective active sites, high conductivity, and low diffusion resistance for OER. Up to

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date, their applications for OER have rarely been reported.

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2. Experimental

2.1 Catalyst synthesis The precursor solution consisting of 0.2 g Co(NO3)2·6H2O and 0.1 g CO(NH2)2 in 100 mL deionized water was used for the synthesis of catalysts. In a Teflon liner containing this solution, a piece of pre-polished and activated Ni foam (2×4 cm2) was immersed. The liner was sealed in a stainless steel autoclave and maintained at 95 ºC for 6 h. After being rinsed with deionized water and ethanol for several times, the collected products were annealed at 300 ºC in air for 2 h. The generated Co3O4 nanowires were 2

ACCEPTED MANUSCRIPT then further annealed at 800 °C with a heating rate of 2 °C min -1 in dry synthetic gas (10 % H2, 90 % N2) for 4 h, leading to the production of the array of CoN nanosheets.

2.2 Catalyst Characterization X-ray diffraction (XRD) was acquired using a MiniFlex diffractometer equipped with

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Cu Kα radiation (λ = 0.154nm). Raman spectra were collected on the HORIBA HR800 with a laser wavelength of 532 nm. X-ray photoelectron spectroscopy (XPS)

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measurements were carried out on the Thermo Scientific ESCALAB 250Xi equipped

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with Al (Kα = 1486.6 eV) X-ray as the excitation source. Field-emission scanning electron microscopy (FE-SEM) images were obtained on the JSM-7001 FESEM.

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Atomic force microscopy (AFM) images were recorded on an ambient AFM. Transmission electron microscopy (TEM), selected area electron diffraction (SAED),

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high-resolution TEM (HR-TEM), high angle annular dark field transmission scanning electron microscopy (HAADF-STEM), and corresponding energy dispersive

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spectrometer (EDS) were executed on the Tecnai G2 F20 S-Twin field-emission TEM

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at an acceleration voltage of 200 kV. The amount of produced O2 was analyzed using a GC-960 gas chromatograph. Electrochemical measurements were performed on the CHI 760D electrochemical workstation (CH Instruments, China) with a three-

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electrode setup in 50 mL 1 M KOH aqueous solution. The platinum foil and saturated Hg/HgO electrode were used as the counter and reference electrodes, respectively. The

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obtained CoN or Co3O4/Ni foam (geometric area: 0.12 cm2) was directly used as the working electrode. All potentials were corrected to reversible hydrogen electrode (RHE) according to the Nernst equation, ERHE = EHg/HgO + EΦHg/HgO (0.098V) + 0.059 pH.

2.3 Catalyst performance Linear sweep voltammograms (LSV) and cyclic voltammograms (CVs) were measured at the scan rate of 5 mV s-1 and 10 mV s-1, respectively. These 3

ACCEPTED MANUSCRIPT voltammograms were redrawn by taking the potential loss (iR drop) into account, namely using the equation of Ecorrected = Euncorrected - iRs [11]. The resistance of the solution was measured using electrochemical impedance spectroscopy (EIS). The Tafel slopes were obtained by fitting linear portions of the Tafel plots derived from LSVs. EIS measurements were carried out on the Zahner workstation at the potential

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where the current density was 50 mA cm -2. The frequency range was from 100 kHz to 0.01 Hz and the amplitude was 5 mV. CVs were recorded at different scan rates in

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non-faradaic range to derive double-layer capacitance (Cdl) for the calculation of

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electrocatalytic active surface areas (EASA). Faradaic efficiency was obtained by comparing the amount of produced O2 with that of calculated O2 at the current density

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of 100 mA cm-2. The stability of these catalysts was tested by chronoamperometry

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with multi-step current densities.

3. Results and discussion

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Prior to OER using Co3O4 and CoN catalysts, they were characterized using XRD and

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Raman spectroscopy. As shown in Fig. 1a, both catalysts show three identified diffraction peaks associated with (111), (200) and (220) planes of Ni foam. For Co3O4, other diffraction peaks at 2θ values of 31.3°, 36.8°, 44.8°, 59.4° and 65.2° are indexed

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to the planes (220), (311), (400), (511) and (440) of cubic Co 3O4, respectively (JCPDS card no.43-1003). With respect to CoN, additional diffraction peaks appeared at

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36.19°, 42.2°, 61.3°, 73.3° and 76.8° are attributed to (111), (200), (220), (311) and (222) planes of cubic CoN, respectively (JCPDS card no.16-0116). In the Raman spectrum of the Co3O4 catalyst (Fig. 1b), four Raman bands centered at 482, 512 and 619, as well as 682 cm-1 correspond to the Eg, F2g, and A1g vibration modes of Co3O4 crystalline phase, respectively [12, 13]. After thermal treatment, new bands appear at 482, 546, 661 and 754 cm-1, resulting from the characteristic vibration mode of CoN [14, 15].

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Figure 1. (a) XRD patterns and (b) Raman spectra of Co3O4 and CoN catalysts; (c) O

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1s and Co 2p XPS spectra of Co3O4; (d) N 1s and Co 2p XPS spectra of CoN.

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Both catalysts were then characterized using XPS. For Co3O4 (Fig. 1c), the fitted XPS spectrum of O 1s (black line) shows three peaks (color lines), corresponding to typical

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Co-O bond (529.73 eV), the adsorbed hydroxyl group (531.08 eV), and water (531.9 eV), respectively [16]. The best de-convolution of Co 2p was fitted into Co 2p3/2

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(780.78 eV) and Co 2p1/2 (796.58eV), referring to Co3+ and Co2+, respectively. Their location and weakly satellite peaks agree well with phonon symmetries of Raman peaks caused by lattice vibrations of spinel structure [17]. For CoN (Fig. 1d), the fitted XPS spectrum of N 1s (black line) shows five peaks (color lines), assigned to pyridinic N (399.43 eV), pyrrolic N (400.23 eV), oxidized pyridinic N (403.28 eV), nitro (405.48 eV) and N-Co bond (396.73 eV), respectively. These fittings confirm the coupling of cobalt with nitrogen [18, 19]. The best de-convolution of Co 2p was fitted into Co-N bond (779.93 eV) and Co3+ peak (796.63 and 781.43 eV), but accompanied with a stronger satellite feature compared with Co 3O4. Therefore, Co3+ presents the 5

ACCEPTED MANUSCRIPT major species in CoN [20]. This is extremely important since Co3+ is highly active for OER. The appearance of sharp satellite peaks for the CoN originates from the

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breakdown of the spinel structure [9].

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Figure 2. (a, d) SEM, (b, c) TEM, and (c, f) HRTEM of (a, b, c) Co 3O4 and (d, e, f) CoN catalysts; (g) HAADF-STEM image and corresponding EDS mappings; (h) AFM

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patterns.

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image and the line profile of CoN catalyst. The insets in (b) and (e) are related SAED

Both catalysts were further examined by FE-SEM and TEM. As shown in Fig. 2a, the surface of Ni foam is uniformly covered by tapered Co 3O4 nanowires. These nanowires are interconnected with each other at the bottom and self-assembled into a sheet structure. Single Co3O4 nanowire (with a diameter or size is about 100 nm) actually possesses a smooth surface (Fig. 2b). The related SAED pattern (the inset in Fig. 2b) reflects (111), (220), (311), (400), (422), (440), and (840) planes of polycrystalline spinel Co3O4. The lattice fringes of 0.244 and 0.467 nm (Fig. 2c) are corresponded to (311) and (111) planes of spinel Co3O4, respectively. In contrast to 6

ACCEPTED MANUSCRIPT Co3O4 catalyst, the CoN catalyst shows an array of nanosheets on the surface of Ni foam where almost no nanowires are visible (Fig. 2d), indicating aggregation and further thermal conversion of Co3O4 nanowires at high temperatures. The sizes of these nanosheets are in the range of 10-15 nm. The diameters of mesopores in between are about 4-10 nm (Fig. 2e). The related SEAD pattern (the inset in Fig. 2e) reveals

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that the polycrystalline laminated CoN has diffraction rings, originating from the (111), (200), and (220) planes. For the (200) and (111) planes of CoN, the lattice fringes are

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0.214 and 0.248 nm (Fig. 2f), respectively. The elements of Co and N are also well

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resolved in their EDS elemental mappings where they are uniformly distributed on the whole surface of the CoN catalyst (Fig. 2g). From its AFM image (Fig. 2h), the

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average thickness was measured to be only 2.5 nm. Therefore, the CoN catalyst is expected to feature enhanced amount of catalytic active sites for OER and thus

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facilitate mass and electron diffusion during OER process. Figure 3 shows LSVs of OER on the catalysts of Co 3O4, CoN, Ni foam, and Ru/Ni

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foam. Compared with Co3O4 and Ni foam, the CoN catalyst exhibits the highest catalytic activity, judging from the overpotential and limiting current density. The

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overpotential on the CoN catalyst at 30 mA cm -2 is 323 mV, which is 72 mV lower than that on Co3O4 and 145 mV lower than that on bare Ni foam that had treated at the

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same synthetic conditions without the precursors. Although the onset potential of OER on CoN is more positive than that on the Ru catalysts, this CoN catalyst exhibits

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superior activity to Ru and other CoN catalysts, especially when the current density is higher than 400 mA cm-2 [21, 22]. Moreover, the current density of OER on CoN is four times greater than that on Co3O4, indicating CoN has a larger amount of catalytic centers, namely Co3+ [25]. To further confirm the catalytic centers, the cyclic voltammograms of the catalysts of Ni foam, Co3O4 and CoN were recorded. No clear redox behavior of Ni foam is found (green line in the inset of Fig. 3a). The disappearance of traditional redox peaks of Ni metal is probably caused by the deactivation of Ni redox activity or the formation of an inert layer on the surface of Ni 7

ACCEPTED MANUSCRIPT metal during thermal treatment. For the catalysts of Co 3O4 (blue line in the inset of Fig. 3a) and CoN (red line in the inset of Fig. 3a) loaded on Ni foam, a pair of much pronounced redox waves are clearly seen. There waves originate from the redox activity of Co3+/Co4+ redox couple, as confirmed from the obtained XPS results in Figure 2 as well as other reported cobalt catalysts [23, 24]. However, the conductive

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and porous Ni foam might contribute to electrocatalytic OER and even the synergistic interaction between Ni foam and CoN nanosheets towards OER might occur, although

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these contributions might be omitted on our case. Therefore, the CoN catalyst plays

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the key role towards OER and exhibits superior OER activity.

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ACCEPTED MANUSCRIPT Figure 3. (a) iRs-corrected LSVs and CVs (inset), (b) corresponding Tafel plots, and (c) Nyquist plots and equivalent circuit mode of OER on the catalysts of Co3O4, CoN, Ni foam, and Ru/Ni foam; (d) current density variation on the catalysts of Co3O4, CoN and Ni foam as a function of the scan rates; (e) multi-step current variation of OER obtained at the catalysts of Co3O4 and CoN as a function of running time; (f) volume

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comparison of experimental and theoretical values of generated O2 on the CoN

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catalyst.

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Moreover, the Tafel slope of OER on the CoN catalyst (Fig. 3b) is only 74 mV dec -1. It is smaller than that obtained on the catalyst of Ru (87 mV dec-1), Co3O4 (127 mV

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dec-1), and Ni foam (146 mV dec-1). This comparison clearly indicates the array of CoN nanosheets is one of the most efficient Co-based OER catalysts.

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To investigate the OER kinetics process, the recorded Nyquist plots were fitted by the Randles equivalent circuit model (Fig. 3c) where shows that the OER on the CoN catalyst is controlled by a charge-transfer process. Its charge-transfer resistance (Rct)

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is only 5.58 Ω, lower than that of the catalysts of Co3O4 (12.15 Ω) and Ni foam (28.02

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Ω). It thus has the fastest charge-transfer process towards OER. To analyze quantitatively the efficiencies of OER, EASAs were assessed by Cdl based

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on non-faradaic ion adsorption and desorption processes (Fig. 3d). The CoN catalyst provides the maximum Cdl (223 mF cm-2), much larger than that of Co3O4 (18 mF cm) and Ni foam (3 mF cm-2). Such a large capacitance of this CoN catalyst mainly

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results from its large surface area due to its mesoporous and ultrathin nanostructure. The difference of the normalized capacitances of these catalysts also contributes to the variation of these obtained capacitances. Provided that their normalized capacitances are in the same order of magnitude, the CoN catalyst thus supplies more sufficient active sites for OER. The durability of the catalysts of Co3O4 and CoN towards OER was testified (Fig. 3e). In the chronoamperometeric measurements, the current densities were sequentially 9

ACCEPTED MANUSCRIPT altered from 10, 20, to 50 mA cm-2. The test time was 15000 s. The corresponding potentials on the CoN catalyst remain stable in the whole process even at high current densities, while those on the Co3O4 catalyst shift a positive direction. This demonstrates superior stability of the CoN catalyst than the Co3O4 one towards OER. The measurement of faradaic efficiencies on the CoN catalyst was finally performed

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via comparing the volume of theoretically calculated and experimentally produced O2 (Fig. 3f). The former one was based on the consumed electric energies. The faradaic

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efficiency is above 97 %. This indicates that no side reaction occurs and extremely

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high energy utilization rate is achieved during OER on the CoN catalyst.

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4. Conclusions

3D mesoporous and ultrathin array of CoN nanosheets is proved to be a robust and

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efficient electrocatalyst for OER in alkaline media, exhibiting low overpotential, small Tafel slope and considerable durability towards OER. The performance surpasses the

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Ru and most Co-based catalysts, especially at the larger current density. This great

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performance derives from the large electrochemical active surface area, porous structure, and the enhanced electron transfer process on the CoN catalyst. In summary, the present work provides a promising approach for designing high-performance and

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low-cost OER catalyst, which is desirable for energy conversion technologies.

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Acknowledgments

This work is financial supported by Joint Funds the National Natural Science Foundation (U1710112) and the National Natural Foundation of for Young Scientists (21603259) of China.

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ACCEPTED MANUSCRIPT References [1] X. Zou, Y. Zhang, Noble metal-free hydrogen evolution catalysts for water splitting, Chem. Soc. Rev. 44 (2015) 5148-5180. [2] D.U. Lee, J. Scott, H.W. Park, S. Abureden, J.-Y. Choi, Z. Chen, Morphologically controlled Co3O4 nanodisks as practical bi-functional catalyst for rechargeable zinc–

PT

air battery applications, Electrochem. Commun. 43 (2014) 109-112. [3] Y. Wang, B. Zhang, W. Pan, H. Ma, J. Zhang, 3D porous nickel–cobalt nitrides

RI

supported on nickel foam as efficient electrocatalysts for overall water splitting,

SC

ChemSusChem 10 (2017) 4170-4177.

[4] V. Vij, S. Sultan, A.M. Harzandi, A. Meena, J.N. Tiwari, W.-G. Lee, T. Yoon, K.S.

NU

Kim, Nickel-based electrocatalysts for energy-related applications: oxygen reduction, oxygen evolution, and hydrogen evolution reactions, ACS Catal. 7 (2017) 7196-7225.

MA

[5] S. Cherevko, T. Reier, A.R. Zeradjanin, Z. Pawolek, P. Strasser, K.J.J. Mayrhofer, Stability of nanostructured iridium oxide electrocatalysts during oxygen evolution

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reaction in acidic environment, Electrochem. Commun. 48 (2014) 81-85.

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[6] Z. Chen, Y. Ha, Y. Liu, H. Wang, H. Yang, H. Xu, Y. Li, R. Wu, In situ formation of cobalt nitrides/graphitic carbon composites as efficient bifunctional electrocatalysts for overall water splitting, ACS Appl. Mater. Inter. 10 (2018) 7134-7144.

CE

[7] X. Zhang, Z. Yang, Z. Lu, W. Wang, Bifunctional CoNx embedded graphene electrocatalysts for OER and ORR: A theoretical evaluation, Carbon 130 (2018) 112-

AC

119.

[8] M.-S. Balogun, W. Qiu, W. Wang, P. Fang, X. Lu, Y. Tong, Recent advances in metal nitrides as high-performance electrode materials for energy storage devices, J. Mater. Chem. A 3 (2015) 1364-1387. [9] Y. Zhang, B. Ouyang, J. Xu, G. Jia, S. Chen, R.S. Rawat, H.J. Fan, Rapid synthesis of cobalt nitride nanowires: highly efficient and low-cost catalysts for oxygen evolution, Angew. Chem. Int. Edit. 55 (2016) 8670-8674. [10] P. Chen, K. Xu, Z. Fang, Y. Tong, J. Wu, X. Lu, X. Peng, H. Ding, C. Wu, Y. Xie, 11

ACCEPTED MANUSCRIPT Metallic Co4N porous nanowire arrays activated by surface oxidation as electrocatalysts for the oxygen evolution reaction, Angew. Chem. Int. Edit. 54 (2015) 14710-14714. [11] X. Xiong, Y. Ji, M. Xie, C. Yao, L. Yang, Z. Liu, A.M. Asiri, X. Sun, MnO 2-CoP3 nanowires array: An efficient electrocatalyst for alkaline oxygen evolution reaction

PT

with enhanced activity, Electrochem. Commun. 86 (2018) 161-165. [12] C.-W. Tang, C.-B.Wang, S.-H.Chien, Characterization of cobalt oxides studied

RI

by FT-IR, Raman, TPR and TG-MS, Thermochim. Acta 473 (2008) 68-73.

SC

[13] V.G.Hadjiev, M.N.Iliev, I.V.Vergilov, The Raman spectra of Co 3O4 , J. Phys. C: Solid State Phys. 21 (1988) L199-L201.

NU

[14] T. Varga, G. Ballai, L. Vásárhelyi, H. Haspel, Á. Kukovecz, Z. Kónya, Co4N/nitrogen-doped graphene: A non-noble metal oxygen reduction electrocatalyst

MA

for alkaline fuel cells, Appl. Catal. B: Environ. 237 (2018) 826-834. [15] G. Gubert, E. Ribeiro, J. Varalda, A.G. Bezerra, W.H. Schreiner, D.H. Mosca,

D

Laser irradiation of iron, cobalt, and nickel targets in liquid nitrogen: A facile approach

725 (2017) 519-525.

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for nitride nanoparticle fabrication of ferromagnetic transition metals, J. Alloy. Compd.

[16] L. Armelao, D. Barreca, S. Gross, E. Tondello, Sol-gel and CVD Co3O4 thin films

CE

characterized by XPS, Surf. Sci. Spectra 8 (2001) 14-23. [17] G. Wang, X. Shen, J. Horvat, B. Wang, H. Liu, D. Wexler, J. Yao, Hydrothermal

AC

synthesis and optical, magnetic, and supercapacitance properties of nanoporous cobalt oxide nanorods, J. Phys. Chem. C 113 (2009) 4357-4361. [18] J.R. Pels, F. Kapteun, J.A. Moulun, Q. Zhu, K.M. Thomas, Evolution of nitrogen functionalities in carbonaceous materials during pyrolysis, Carbon 33 (1995) 16411653. [19] K.R. Yoon, K. Shin, J. Park, S.H. Cho, C. Kim, J.W. Jung, J.Y. Cheong, H.R. Byon, H.M. Lee, I.D. Kim, Brush-like cobalt nitride anchored carbon nanofiber membrane: current collector-catalyst integrated cathode for long cycle Li–O2 batteries, 12

ACCEPTED MANUSCRIPT ACS Nano 12 (2018) 128-139. [20] M.D. Meganathan, S. Mao, T. Huang, G. Sun, Reduced graphene oxide intercalated Co2C or Co4N nanoparticles as an efficient and durable fuel cell catalyst for oxygen reduction, J. Mater. Chem. A 5 (2017) 2972-2980. [21] T. Gao, Z. Jin, Y. Zhang, G. Tan, H. Yuan, D. Xiao, Coupling cobalt-iron

PT

bimetallic nitrides and N-doped multi-walled carbon nanotubes as high-performance bifunctional catalysts for oxygen evolution and reduction reaction, Electrochim. Acta

RI

258 (2017) 51-60.

SC

[22] B. Weng, W. Wei, Y. Yiliguma, H. Wu, A.M. Alenizi, G. Zheng, Bifunctional CoP and CoN porous nanocatalysts derived from ZIF-67 in situ grown on nanowire

NU

photoelectrodes for efficient photoelectrochemical water splitting and CO 2 reduction, J. Mater. Chem. A 4 (2016) 15353-15360.

MA

[23] Y.-C. Liu, J.A. Koza, J.A. Switzer, Conversion of electrodeposited Co(OH) 2 to CoOOH and Co3O4 , and comparison of their catalytic activity for the oxygen

D

evolution reaction, Electrochim. Acta 140 (2014) 359-365.

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[24] M. Xie, L. Yang, Y. Ji, Z. Wang, X. Ren, Z. Liu, A.M. Asiri, X. Xiong, X. Sun, An amorphous Co-carbonate-hydroxide nanowire array for efficient and durable oxygen evolution reaction in carbonate electrolytes, Nanoscale 9 (2017) 16612-16615.

CE

[25] Y. Zhang, F. Ding, C. Deng, S. Zhen, X. Li, Y. Xue, Y.-M. Yan, K. Sun, Crystal plane-dependent electrocatalytic activity of Co 3O4 toward oxygen evolution reaction,

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Catal. Commun. 67 (2015) 78-82.

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Highlights

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Graphical abstract

Direct growth of mesoporous and ultrathin arrays of CoN nanosheets on Ni foam

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Large specific surface areas of mesoporous and ultrathin array of CoN nanosheets

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More available active sites of the CoN arrays for oxygen evolution reaction

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Robust and efficient catalysts for oxygen evolution reaction, especially at high current

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densities

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