Nickel Sulfide Freestanding Holey Films as Air-Breathing Electrodes

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Energy Conversion and Storage; Plasmonics and Optoelectronics

Nickel Sulfides Freestanding Holey Films as AirBreathing Electrodes for Flexible Zn-Air Batteries Kyle Marcus, Kun Liang, Wenhan Niu, and Yang Yang J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.8b00925 • Publication Date (Web): 09 May 2018 Downloaded from http://pubs.acs.org on May 9, 2018

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The Journal of Physical Chemistry Letters

Nickel Sulfides Freestanding Holey Films as Air-Breathing Electrodes for Flexible Zn-Air Batteries Kyle Marcus,1,# Kun Liang,1,# Wenhan Niu,1,# Yang Yang1,* 1

NanoScience Technology Center, Department of Materials Science and Engineering, University

of Central Florida, Orlando, FL 32826, USA *

Corresponding author: [email protected]

#

These authors contributed equally to this work.

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Abstract: In this work, a combination of the bottom-up electrochemical deposition and topdown electrochemical etching strategies followed by a subsequent sulfuration treatment were employed to rationally synthesize a nickel sulfides (NiSx) freestanding holey film (FHF). Owing to the holey structure along with the optimal electrochemically active surface area and active sites, the as-prepared NiSx FHF showed an impressive bifunctional electrocatalytic performance toward both oxygen evolution and reduction reactions. The holey and freestanding features provide the NiSx FHF with promising characteristics to be used as an ideal air-breathing cathode in flexible Zn-air batteries (ZABs). As a proof-of-concept, the rationally designed NiSx FHF achieved remarkable rechargeability and flexibility in a ZAB configuration.

Keywords: freestanding; holey film; bifunctional electrocatalyst; flexible; Zn-air batteries

TOC Graphic

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Considerable attention has been devoted to the progression of research in renewable energy conversion and storage systems in an attempt to meet the growing energy crisis and the rapid development of small electronic devices.1-3 There is a remarkable demand for the facile fabrication methods that can produce flexible electrodes for wearable electronic devices (WEDs) with high-performance and commercially scalable properties.4-8 Due to the high theoretical capacity and environmentally benign nature, Zn-air batteries (ZABs) have become one of the most promising energy conversion/storage technologies that are more close to large-scale commercialization when compared to other metal-air batteries such as lithium-air batteries.9-10 However, the idea of making ZABs wearable and flexible remains a challenge, primarily due to the rigid nature of the existing cathodes used in ZABs. Although the traditional method of spraying the powder-like catalysts onto carbon cloth could be an alternative fabrication method to produce flexible cathodes, the carbonaceous additives (conducting carbons and polymer binders) in the cathodes greatly limit the performance and practicability of ZABs. More specifically, the negative effects of these carbonaceous additives on the electrocatalytic performance of powder catalysts have been widely investigated. Firstly, powder catalysts are gradually poisoned and deactivated due to the active site coverage by the insoluble intermediates within the alkaline electrolytes.11 Secondly, the carbonaceous additives isolate the active sites of the powder catalysts in the cathodes.12 Thirdly, the decomposition of the carbonaceous additives leads to the detachment of a catalyst from the current collectors.13 Hence, there is a strong demand for the facile preparation of freestanding and additive-free holey film electrocatalysts with bifunctional ORR/ oxygen evolution reactions (OER) properties for practical ZABs application. Transition metal compound-based films have demonstrated impressive electrocatalytic performances for water splitting reactions.14-16 However, the

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utilization of these catalyst films in other energy conversion/storage applications, including fuel cells and metal-air batteries, is still not realized because of their gas-impermeability and rigid structures. Moreover, these pristine transition metal compound-based films generally suffer from poor conductivity. Although, it has been reported that the transition metal sulfides can improve the conductivity of electrodes. Jin et al reported MoOx/MoS2 core-shell structure showed better conductivity than that of MoOx.17 Additionally, Zheng et al reported NiS2 polyhedrons presented excellent conductivity to be employed as dye-sensitized solar cells.18 Therefore, the rational preparation of flexible catalyst films with air-permeable pores for a freestanding and additivefree cathode in flexible ZABs will be a tremendous challenge and can promote the expansion of catalyst film applications. In this work, we report a rational strategy for the fabrication of NiSx flexible holey film (FHF) via a combination of bottom-up and top-down methods. The as-prepared NiSx FHF with freestanding structure was demonstrated to be a bifunctional and additive-free catalyst, and interior NiSx/Ni layer for the enhanced electron transfer ability. Additionally, as a proof-ofconcept, the freestanding NiSx FHF was implemented as the air-breathing cathode in the flexible ZABs. A typical fabrication process is schematically represented in Figure 1a. A Ni film was electrodeposited (bottom-up) onto a stainless steel (SS) substrate, which acts as a low cost, reusable and easily removable substrate.19 The Ni deposit layer was subsequently removed from the SS substrate, leaving a freestanding Ni thin film to be further processed. Then, the freestanding Ni thin film was subjected to electrochemical etching (top-down) to form a holey structure. For this process, the electrochemical etching can lead to an increase in electrocatalytically active surface area (EASA). Therefore, the holey structures ultimately create

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more readily active sites to take part in ORR/OER. Finally, sulfuration was employed to transfer Ni film to highly active NiSx film (denoted as NiSx FHF). The inset of the photograph in Figure 1a demonstrates the flexibility of NiSx FHF. Scanning electron microscopy (SEM) was used to identify the NiSx FHF structure and morphology. From top-view SEM images (Figure 1b and Figure S1), the NiSx FHF shows a very holey arrangement with pores that fully extend through the entire thin film layer. The crosssectional SEM image in Figure 1c shows a 2 µm thick NiSx FHF. Moreover, the cross-section of an electrochemically etched pore structure can also be observed (Figure 1c, dotted yellow line), where complete pore formation from top to bottom is evident. This is an important factor when considering it as an air-permeable electrode in ZABs because it allows for unabated gas diffusion. Energy dispersive X-ray spectroscopy (EDX) was employed to better understand the elemental distribution of the NiSx FHF. Figure 1d shows a uniform allocation of Ni and S across the material surface. Dark voided regions are observed (Figure 1d) in NiSx mapping overlay, which affirms that the holey structures extend through the film layer. Transmission electron microscopy (TEM) was employed to provide insight into the location of active materials within the NiSx FHF. The cross-sectional TEM image in Figure 1e illustrates a partially formed pore with clear separation of residual Ni (yellow dotted line) and the active NiSx FHF layer (white dotted line). EDX of two separate NiSx active layer locations within the partially formed pore cross-section (Figure S2) identifies the presence of Ni and S elements. High-resolution TEM (HRTEM) images in Figures 1f and 1g identify the 100 (0.29 nm), 111 (0.32 nm) and 101 (0.41 nm) d-spacings for hexagonal α-NiS, cubic NiS2, and hexagonal Ni3S2 phases, respectively,20-21 which confirms the result of the following XRD analysis.

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The NiSx FHF phases were further characterized by X-ray diffraction (XRD) as shown in Figure 2a, where a multiphase composition of Ni3S2, NiS2, and α-NiS are clearly recognized. Location of peaks present at 21.8o, 38.3o, 50.1o, and 55.2o are designated to the hexagonal (101), (021), (211), and (122) planes of Ni3S2 (JCPDS# 44-1418).22 Diffraction peaks at 27.4o, 31.6o, 35.1o, 38.8o, 53.6o, 58.8o can be attributed to the (111), (200), (210), (211), (311), and (230) cubic planes of NiS2 (JCPDS # 11-0099).4 For the α-NiS phase, peaks at 30.2o, 34.7o, 46.0o, and 60.3o correspond to the (100), (101), (102), and (103) hexagonal planes of NiS (JCPDS# 021280).20 Presence of all three NiSx phases was further confirmed by Raman spectroscopy (Figure 2b). More specifically, vibrational modes at 345.1, 228.7, 197.7, and 173.1 cm-1 correspond to the Ni3S2 phase, while peak locations at 474.3, 282.9, 275.8 cm-1 can be attributed to NiS2, and peaks belonging to NiS can be found at 301.7, 248.2, 155.1 cm-1.23 Chemical composition was examined by X-ray photoelectron spectroscopy (XPS), in which the survey in Figure S3 confirmed the presence of Ni and S elements on the surface. Highresolution XPS profiles for Ni 2p3/2 can be found in Figure 2c, where peaks at 857.0, 854.7, and 851.1 eV can be attributed to the presence of Ni3+, Ni2+, and Ni species, respectively.21 A satellite Ni 2p3/2 peak can also be found at 860 eV.24 Moreover, S 2p high-resolution XPS profiles in Figure 2d show peaks corresponding to S 2p1/2 and S 2p3/2 orbitals found at 164 and 162.8 eV, which are consistent with S elemental XPS profiles in nickel sulfides.19,

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The XPS

observations are in full support of XRD, Raman, and HRTEM characterization results that suggest the presence of Ni3S2, NiS2, and NiS phases within NiSx FHF samples. To evaluate the ORR electrochemical performance of NiSx FHF, cyclic voltammogram (CV) and linear sweep voltammogram (LSV) measurements were carried out. First of all, CVs tested in N2- and O2-saturated electrolyte (0.1 M KOH) were acquired to characterize the activities of

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NiSx FHF samples towards oxygen reduction. As shown in Figure 3a, the CV curve of NiSx FHF tested in the N2-saturated electrolyte displays a featureless electrical double layer within 0-1.0 V vs. RHE. In contrast, an obvious reduction peak at 0.78 V was detected in the O2-saturated electrolyte, implying the good catalytic activity of NiSx FHF toward ORR. In addition, LSV measurement was further carried out on the samples, including NiSx FHF, in the O2-saturated electrolyte. As shown in Figure 3a, the onset potential is observed at the 0.86 V for NiSx FHF electrode. Considering the low-cost and facile fabrication process, NiSx FHF is a promising candidate to replace precious-metal-based catalysts, even though it exhibits a little worse activity than the Pt/C electrode (Figure S4). The LSV curves of NiSx FHF were further investigated using rotating ring-disk electrode (RRDE) technology. As can be seen from Figure S5a, the diffusion current densities increase with increasing the electrode rotating speed, implying that the diffusion current densities are relative to the oxygen concentration in the electrolyte. Notably, a considerable increase of current density is observed at 0.82 V vs. RHE, suggesting that the NiSx FHF is favorable for the oxygen reduction. Kouteck-levich plots were used to calculate the electron-transfer number during ORR process. As shown in Figure S5b, the electron-transfer number was calculated to be ~3.25 at different potentials, reflecting a four-electron transfer pathway. An RRDE was employed using at a rotating speed of 1600 rpm to give an insight on the electrocatalytic behavior as it relates to electron transfer number (n) and peroxide yield (H2O2%). The RRDE voltammograms in Figure 3b show a low ring current with a large disk current for ORR on the NiSx FHF. In addition, the electron transfer number within 0-0.8 V vs. RHE on the NiSx FHF was calculated to be ~3.6, corresponding to HO2- yield of ~4.2%, as shown in the inset of Figure 3b. The result suggests that a good ORR activity of NiSx FHF with the desired single-step and four-electron transfer pathway is achieved. 27-28

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With respect to the OER performance for NiSx FHF, we also conducted the LSV analysis. Figure 3c shows the outstanding OER performance of NiSx FHF with a minimal potential of 1.56 V vs RHE to reach a current density of 10 mA cm-2, which is superior to that of commercial RuO2 (1.58 V) powder catalysts,29-30 and even better than those of recently reported OER powder electrocatalysts (Table S1). An oxidization peak can be found in the NiSx FHF, which is due to the oxidation of the surface NiII to NiIII.23, 29-30 The Tafel plot in Figure 3d shows a slop of 29 mV dec-1 for the NiSx FHF electrode, which is close to 27 mV dec-1 of the state-of-the-art RuO2 electrode, implying a similar OER kinetics process with 4e- transfer occurs on both NiSx FHF and RuO2 electrodes.21 Electrochemically active surface area (ECSA) was also estimated based on the electrochemical double layer capacitance (EDLC) for all samples (see Supporting Information for more experimental details). As depicted in Figure S6, the electrochemical double layer capacitance was measured to be 0.79 mF cm-2 for the NiSx FHF, which is equal to a EASA value of 20 cm2 after calculation. Such high EASA value is significantly larger than that of the non-porous Ni foil. The electrochemical etching treatment generates micro-pores that reduce the electrode mass and increase the ECSA, exposing more electrochemically accessible surface. This result confirms the crucial role of the holey structure in enlarging the active surface of the electrode and consequently enhancing the catalytic activities for both ORR and OER.33-36 Considering the excellent performance of NiSx FHF toward both ORR and OER, it is feasible to incorporate this freestanding electrode into flexible ZABs. Consequently, for a proof-ofconcept, the as-prepared freestanding NiSx FHF was not only used as the electrocatalyst and current collector but also served as the gas diffusion layer (GDL) in a ZAB system. The holey nature of the film allows for sufficient flow of oxygen gas into and out of ZAB without the need of polymer binder and other conductive supporters. A flexible ZAB was built up using NiSx FHF

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as an air-breathing cathode, glass fiber as a separator and flexible zinc plate as an anode (additional information in experimental section). Galvanostatic discharge testing was first carried out to determine the stability and practicability of the flexible rechargeable ZAB. As can be seen from Figure 3e, the flexible ZAB using NiSx FHF air electrode maintains a stable discharge voltage over 1.1 V when the bending degree of flexible ZAB is increased from 0o to 180o, confirming the flexibility and practicability of ZAB using the flexible NiSx FHF electrode. Galvanostatic charge/discharge curves further confirm the performance of NiSx FHF and commercial Pt/C+RuO2 powder catalyst in ZABs. As shown in Figure 3f, the excellent performance of ZAB using NiSx FHF is demonstrated by the charge/discharge cycling test over 3000 min, outperforming the performances of ZABs using commercial Pt/C+RuO2 powder catalyst. In a close observation, the charge voltage is measured to be ~1.8 V for NiSx FHF electrode, which is lower than commercial Pt/C+RuO2 electrodes, implying the remarkable OER performance of NiSx FHF in ZAB system. The NiSx FHF pore morphology after GCD testing was viewed by SEM (Figure S7) to reassure that pores size and distribution was not significantly hindered by battery testing conditions. Remarkably, the NiSx FHF maintained its original pore structure and element contribution, indicating that the thin film could resist physical degradation as a cathode under harsh conditions, which is a problem observed in rechargeable ZABs.31 Finally, we identified the component of NiSx FHF electrode after cycling test by XRD analysis. The XRD pattern in Figure S8 confirms the NiS2 and Ni3S2 phases in final NiSx FHF electrode after cycling test, implying the NiS2 and Ni3S2 phases should be responsible for the excellent ORR performance of NiSx FHF electrode in ZAB. The disappeared NiS phase probably react with OH- from the electrolyte to form a NiOOH or Ni(OH)2 amorphous passivation layer, which

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notes only donates activity to OER but also protects NiS2 and Ni3S2 phases to achieve excellent performance.37 In summary, we developed a strategy including bottom-up and top-down methods to prepare the NiSx FHF electrode with highly efficient bifunctional activity toward OER/ORR. The suggested fabrication routes, including electrodeposition, electrochemical etching, and sulfuration, offer a facile and cost-effective approach for energy conversion and storage electrode nanomanufacturing. The unique freestanding and holey characteristics of the as-prepared NiSx FHF allows for the amalgamation of the NiSx active catalyst and current collector into a single component for flexible ZAB testing. Considering these positive attributes, the NiSx FHF fabrication process and resulting materials have emerged as a promising alternative for future energy conversion and storage systems. To our knowledge, this is for the first time to report the use of flexible, freestanding and holey metal sulfides film into flexible ZAB. Supporting Information Supplementary information is available in the online version of the paper. Correspondence and requests for materials should be addressed to Y.Y. Author contributions K.L., W.N., and K.M. contributed equally to this work. Y.Y., K.L., and K.M. designed the experiments. K.L. and K.M. performed the experiments. W.N. performed the electrochemical test and collected the data. Y.Y., K.L., W.N., and K.M. wrote the manuscript. Y.Y. oversaw all results and corrected the manuscript. All authors approve the manuscript. Competing financial interests

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The authors declare a potential conflict of interest with a patent in the application. Acknowledgments This work was financially supported by the University of Central Florida through a startup grant (No. 20080741). Reference 1.

Wu, Q.; Yang, L.; Wang, X.; Hu, Z. From carbon-based nanotubes to nanocages for

advanced energy conversion and storage. Acc. Chem. Res. 2017, 50, 435-444. 2.

Zhong, Y.; Xia, X.; Shi, F.; Zhan, J.; Tu, J.; Fan, H. J. Transition metal carbides and

nitrides in energy storage and conversion. Adv. Sci. 2016, 3, 1500286. 3.

Liang, K.; Li, L.; Yang, Y. Inorganic porous films for renewable energy storage. ACS

Energy Lett. 2017, 2, 373-390. 4.

An, T.; Wang, Y.; Tang, J.; Wei, W.; Cui, X.; Alenizi, A. M.; Zhang, L.; Zheng, G.

Interlaced NiS2-MoS2 nanoflake-nanowires as efficient hydrogen evolution electrocatalysts in basic solutions. J. Mater. Chem. A 2016, 4, 13439-13443. 5.

Liang, K.; Guo, L.; Marcus, K.; Zhang, S.; Yang, Z.; Perea, D. E.; Zhou, L.; Du, Y.; Yang,

Y. Overall water splitting with room-temperature synthesized NiFe oxyfluoride nanoporous films. ACS Catal. 2017, 7, 8406-8412. 6.

Liang, K.; Marcus, K.; Zhang, S.; Zhou, L.; Li, Y.; De Oliveira, S. T.; Orlovskaya, N.;

Sohn, Y. H.; Yang, Y. NiS2/FeS holey film as freestanding electrode for highKperformance lithium battery. Adv. Energy Mater. 2017, 7 (22), 1701309. 7.

Yang, Y.; Fei, H. L.; Ruan, G. D.; Tour, J. M. Porous Cobalt-Based Thin Film as a

Bifunctional Catalyst for Hydrogen Generation and Oxygen Generation. Adv. Mater. 2015, 27,

11



3175-3180. 8.

Liang, K.; Yan, Y.; Guo, L.; Marcus, K.; Li, Z.; Zhou, L.; Li, Y.; Ye, R.; Orlovskaya, N.;

Sohn, Y.-H.; et al. Strained W(SexS1–x)2 nanoporous films for highly efficient hydrogen evolution. ACS Energy Lett. 2017, 2, 1315-1320. 9.

Niu, W. H.; Li, Z.; Marcus, K.; Zhou, L.; Li, Y. L.; Ye, R. Q.; Liang, K.; Yang, Y. Surface-

modified porous carbon nitride composites as highly efficient electrocatalyst for Zn-air batteries. Adv. Energy Mater. 2018, 8, 1701642. 10.

Fu, J.; Cano, Z. P.; Park, M. G.; Yu, A. P.; Fowler, M.; Chen, Z. W. Electrically

rechargeable Zinc-air batteries: Progress, challenges, and perspectives. Adv. Mater. 2017, 29, 1604685. 11.

Yarlagadda, V.; Carpenter, M. K.; Moylan, T. E.; Kukreja, R. S.; Koestner, R.; Gu. W.;

Thompson, L.; Kongkanand, A. Boosting fuel cell performance with accessible carbon mesopores. ACS Energy Lett. 2010, 35, 9788-9794. 12.

Yang, W.; Fellinger, T.-P.; Antonietti, M. Efficient metal-free oxygen reduction in alkaline

medium on high-surface-area mesoporous nitrogen-doped carbons made from ionic liquids and nucleobases. J. Am. Chem. Soc. 2010, 133, 206-209. 13.

Zhao, Z. L.; Zhang, L. Y.; Bao, S. J.; Li, C. M. One-pot synthesis of small and uniform

Au@PtCu core-alloy shell nanoparticles as an efficient electrocatalyst for direct methanol fuel cells. Appl. Catal. B: Enviorn. 2016, 8, 7180-7188. 14.

Cai, P. W.; Huang, J. H.; Chen, J. X.; Wen, Z. H. Oxygen-containing amorphous cobalt

sulfide porous nanocubes as high-activity electrocatalysts for the oxygen evolution reaction in an alkaline/neutral medium. Angew. Chem. Int. Ed. 2017, 56, 4858-4861. 15.

Ganesan, P.; Prabu, M.; Sanetuntikul, J.; Shanmugam, S. Cobalt sulfide nanoparticles

12


Page 12 of 19

Page 13 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


grown on nitrogen and sulfur codoped graphene oxide: An efficient electrocatalyst for oxygen reduction and evolution reactions. ACS Catal. 2015, 5, 3625-3637. 16.

Yu, X. Y.; Feng, Y.; Guan, B. Y.; Lou, X. W.; Paik, U. Carbon coated porous nickel

phosphides nanoplates for highly efficient oxygen evolution reaction. Energy Environ. Sci. 2016, 9, 1246-1250. 17.

Jin, B.; Zhou, X.; Huang, L.; Licklederer, M.; Yang, M.; Schmuki, P. Aligned

MoOx/MoS2 core–shell nanotubular structures with a high density of reactive sites based on selfKordered anodic molybdenum oxide nanotubes. Angew. Chem. Int. Ed. 2016, 55, 1225212256. 18.

Zheng, J.; Zhou, W.; Ma, Y.; Cao, W.; Wang, C. Guo, L. Facet-dependent NiS2

polyhedrons on counter electrodes for dye-sensitized sloar cells. Chem. Commun. 2015, 51, 12863-12866. 19.

Liang, K.; Marcus, K.; Guo, L.; Li, Z.; Zhou, L.; Li, Y.; De Oliveira, S. T.; Orlovskaya,

N.; Sohn, Y. H.; Yang, Y. A freestanding NiSx porous film as a binder-free electrode for Mg-ion batteries. Chem. Commun. 2017, 53, 7608-7611. 20.

Geng, H.; Kong, S. F.; Wang, Y. NiS nanorod-assembled nanoflowers grown on

graphene: morphology evolution and Li-ion storage applications. J. Mater. Chem. A 2014, 2, 15152-15158. 21.

Jiang, N.; Tang, Q.; Sheng, M. L.; You, B.; Jiang, D. E.; Sun, Y. J. Nickel sulfides for

electrocatalytic hydrogen evolution under alkaline conditions: A case study of crystalline NiS, NiS2, and Ni3S2 nanoparticles. Catal. Sci. Technol. 2016, 6, 1077-1084. 22.

Dong, J.; Cheng, Z.; Zha, S.; Liu, M. Identification of nickel sulfides on Ni–YSZ cermet

exposed to H2 fuel containing H2S using Raman spectroscopy. J. Power Sources 2006, 156, 461-

13



465. 23.

Luo, P.; Zhang, H. J.; Liu, L.; Zhang, Y.; Deng, J.; Xu, C. H.; Hu, N.; Wang, Y. Targeted

synthesis of unique nickel sulfide (NiS, NiS2) microarchitectures and the applications for the enhanced water splitting system. ACS Appl. Mater. Interfaces 2017, 9, 2500-2508. 24.

Zhou, T.; Cao, Z.; Zhang, P.; Ma, H.; Gao, Z.; Wang, H.; Lu, Y.; He, J.; Zhao, Y.

Transition metal ions regulated oxygen evolution reaction performance of Ni-based hydroxides hierarchical nanoarrays. Sci. Rep. 2017, 7, 46154. 25.

Wang, P.; Zhang, X.; Zhang, J.; Wan, S.; Guo, S.; Lu, G.; Yao, J.; Huang, X. Precise

tuning in platinum-nickel/nickel sulfide interface nanowires for synergistic hydrogen evolution catalysis. Nat. Commun. 2017, 8, 14580. 26.

Park, G. D.; Cho, J. S.; Kang, Y. C. Sodium-ion storage properties of nickel sulfide

hollow nanospheres/reduced graphene oxide composite powders prepared by a spray drying process and the nanoscale Kirkendall effect. Nanoscale 2015, 7, 16781-16788. 27.

Niu, W. H.; Li, L. G.; Liu, X. J.; Wang, N.; Liu, J.; Zhou, W. J.; Tang, Z. H.; Chen, S. W.

Mesoporous N-doped carbons prepared with thermally removable nanoparticle templates: An efficient electrocatalyst for oxygen reduction reaction. J. Am. Chem. Soc. 2015, 137, 5555-5562. 28.

Wang, X.; Wang, J.; Wang, D.; Dou, S.; Ma, Z.; Wu, J.; Tao, L.; Shen, A.; Ouyang C.;

Liu, Q.; Wang, S. One-pot synthesis of nitrogen and sulfur co-doped graphene as efficient metalfree electrocatalysts for the oxygen reduction reaction. Chem. Commun. 2014, 50, 4839-4842. 29.

Liang, Y.; Li, Y.; Wang, H.; Zhou, J.; Wang, J.; Regier, T.; Dai, H., Co3O4 nanocrystals

on graphene as a synergistic catalyst for oxygen reduction reaction. Nat. Mater. 2011, 10 (10), 780-786.

14


Page 14 of 19

Page 15 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


30.

Frydendal, R.; Paoli, E. A.; Knudsen, B. P.; Wickman, B.; Malacrida, P.; Stephens, I. E.;

Chorkendorff, I., Benchmarking the stability of oxygen evolution reaction catalysts: the importance of monitoring mass losses. ChemElectroChem 2014, 1 (12), 2075-2081. 31.

Ouyang, C.; Wang, X.; Wang, C.; Zhang, X.; Wu, J.; Ma, Z.; Dou, S.; Wang, S.,

Hierarchically porous Ni3S2 nanorod array foam as highly efficient electrocatalyst for hydrogen evolution reaction and oxygen evolution reaction. Electrochim. Acta 2015, 174, 297-301. 32.

Zhu, W.; Yue, X.; Zhang, W.; Yu, S.; Zhang, Y.; Wang, J.; Wang, J., Nickel sulfide

microsphere film on Ni foam as an efficient bifunctional electrocatalyst for overall water splitting. Chem. Commun. 2016, 52 (7), 1486-1489.

33.

Zhang, J.; Zhang, D.; Zhang, R.; Zhang, N.; Cui, C.; Zhang, J; Jiang, B.; Yuan, B.; Wang,

T.; Li. Q. Facile synthesis of mesoporous and thin-walled Ni-Co sulfide nanotubes as efficient electrocatalysts for oxygen evolution reaction. ACS Appl. Energy Mater. 2018, 1, 495-502. 34.

Hao, J.; Yang, W.; Hou, J.; Mao, B.; Huang, Z.; Shi, W. Nitrogen doped NiS2 nanoarrays

with enhanced electrocatalytic activity for water oxidation. J. Mater. Chem. A 2017, 5, 1781117816. 35.

Chen, J. S.; Ren, J.; Shalom, M.; Fellinger, T.; Antonietti, M. Stainless steel mesh-

supported NiS nanosheet array as highly efficient catalyst for oxygen evolution reaction. ACS Appl. Mater. Interfaces 2016, 8, 5509-5516. 36.

Jin, Z.; Li, P.; Xiao, D. Enhanced electrocatalytic performance for oxygen reduction via

active interfaces of layer-by-layered titanium nitride/titanium carbonitride structures. Sci. Rep. 2014, 4, 6712.

15



37.

Yan, B.; Krishnamurthy, D.; Hendon, C. H.; Deshpande, S.; Surendranath, Y.;

Viswanathan, V. Surface restructuring of nickel sulfide generates optimally coordinated active sites for oxygen reduction catalysis. Joule, 2017, 1, 600-612.

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Figure 1. (a) Schematic image for a typical freestanding NiSx FHF fabrication process. Surface (b) and (c) cross-sectional SEM images; yellow dotted outline represents a pore included in cross-section; scale bars are 20 µm and 1 µm, respectively. (d) Surface SEM image with EDS mapping for Ni, S, and NiSx overlay, respectively; scale bar 10 µm. (e) Cross-sectional TEM image of a partially formed pore, Ni and NiSx rich areas indicated by yellow and white dotted lines; scale bar 100 nm. (e) and (f) High-resolution TEM images of NiSx FHF; scale bars are both 2 nm.

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Figure 2. (a) XRD pattern and (b) Raman spectrum of NiSx FHF; (c, d) high-resolution XPS profiles of Ni 2p3/2 and S 2p peaks, respectively.

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Figure 3. Electrochemical performance. (a) CV curves in N2- and O2-saturated 0.1 M KOH at a scan rate of 5 mV s-1. (b) RRDE LSV curve at 1600 rpm in 0.1 M KOH showing disk and ring currents. Inset is the plots of electron transfer number and HO2- yield. (c) OER on the electrode within 0.1 M KOH with a scan rate of 5 mV s-1. (d) The corresponding Tafel plots of OER. (e) Galvanostatic discharge curves of the flexible ZAB using NiS2 FHF as the air-breathing cathode at 2 mA cm-2; (f) Galvanostatic charge/discharge curves for all electrodes at 2 mA cm-2. 19


Nickel Sulfide Freestanding Holey Films as Air-Breathing Electrodes

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