- Email: [email protected]
Enhanced oxygen evolution reaction activity of FeNi3N nanostructures via incorporation of FeNi3
Inorganic Chemistry Communications 113 (2020) 107802
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Enhanced oxygen evolution reaction activity of FeNi3N nanostructures via incorporation of FeNi3
T
Xiaoguo Fua, Jiasen Zhub, Bingyun Aoa, Xinyue Lyuc, Jian Chenc,
⁎
a
Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang 621908, Sichuan, PR China School of Chemical Engineering and Technology, Sun Yat-sen University, Guangzhou 510275, PR China c School of Materials Science and Engineering, Instrumental analysis and Research Center, Sun Yat-sen University, Guangzhou 510275, PR China b
GRAPHICAL ABSTRACT
ABSTRACT
Herein, the oxygen evolution reaction (OER) catalytic activity of FeNi3N is significantly improved through the incorporation of FeNi3 as a result of the controllable composition of the Fe source. The as-prepared FeNi3N/FeNi3 achieves overpotential of 254 mV at a current density of 10 mA cm−2, which is superior to those of pristine FeNi3N, owing to the synergistic effect between FeNi3N and FeNi3.
1. Introduction Metal nitrides have not only gained significant attention as efficient electrocatalysts for hydrogen evolution reaction (HER) but also in oxygen evolution reaction (OER) [1–5]. Among the commonly reported metal nitrides, mixed metal nitride, especially FeNi3N usually achieved impressive catalytic performance both in HER and OER [6–8]. With enormous performance improvement of FeNi3N as HER electrocatalysts [9–12], their performance is quite inferior during OER [13–16]. One of the common strategies to enhance the catalytic properties of electrocatalysts is hybridization [17–20]. However, the hybridization of FeNi3N with other active materials towards achieving efficient OER is rarely reported. In this communication, we significantly enhanced the OER
⁎
performance of FeNi3N nanostructure by hybridizing with FeNi3. The as-prepared FeNi3N/FeNi3 hybrid was achieved by simply tuning the composition Fe source. FeNi3N/FeNi3 showed excellent OER performance with 20 mA cm−2 overpotential of 254 mV and a Tafel slope of 76 mV, which outshine that of its counterpart. This present work creates more opportunities for the development of transition metal nitrides as effective electrocatalysts for OER. 2. Experimental 4.0 cm2 of Carbon cloth purchased from Fuel Earth, USA was rinsed with conc. HNO3, ethanol and distilled water. 10 mmol of FeCl3·6H2O, 15 mmol of NiCl2·6H2O, 0.15 M of urea were dissolved in 30 mL of distilled water and uniformly stirred for 15 min including the carbon
Corresponding author. E-mail address: [email protected] (J. Chen).
https://doi.org/10.1016/j.inoche.2020.107802 Received 1 December 2019; Received in revised form 19 January 2020; Accepted 19 January 2020 Available online 21 January 2020 1387-7003/ © 2020 Elsevier B.V. All rights reserved.
Inorganic Chemistry Communications 113 (2020) 107802
X. Fu, et al.
cloth. The solution was allowed to react in an electric oven at 120 °C for 8 h and then naturally to cool to ambient temperature. The sample was then dried and annealed in NH3 gas at 450 °C for 3 h to form FeNi3N/ FeNi3. To obtain FeNi3N, the composition of FeCl3·6H2O was changed to 5 mmol FeCl3·6H2O while NiCl2·6H2O remains fixed. The characterization of both FeNi3N and FeNi3N/FeNi3 were studied using scanning electron microscopy (FESEM, Quanta 400/INCA/ HKL) and transmission emission microscopy (FEI Tecnai G2 F30) for the morphology and X-Ray diffraction spectroscopy (Rigaku SmartLab X) for the phase identification. OER measurements were carried out using FeNi3N and FeNi3N/ FeNi3 as the working electrode, Ag/AgCl as the reference electrode and carbon rod as the counter electrode. The geometric area of working electrode determined the active area. The working electrode on carbon cloth used for electrochemical tests was sealed with epoxy resin, leaving a square with 1.0 cm2 in area for measuring and a small area at the other end for ohmic contact. The linear seep voltammetry (LSV) profile was measured at a scan rate of 1 mV s−1 between 1.0 and 2.0 V (vs. RHE) and the Tafel plots were derived from the LSV profiles using the electrochemical workstation (CHI 760E). Electrochemical impedance spectroscopy (EIS) was a performance at the frequency range of 100,000 Hz–0.01 Hz, 5 mV AC amplitude and 20 mA cm−2 current density. The stability test was measured under stirring for 50 h.
(Fig. 1c and inset), indicating that tuning modifying the composition of Fe does not have an effect on the morphology of the hybrid sample. The electrocatalytic properties of the FeNi3N and FeNi3N/FeNi3 electrocatalysts were tested in a three electrode system as mentioned above. NiFe-LDH was also introduced for comparison. The linear sweep voltammetry (LSV) curves of the three catalysts are shown in Fig. 2a. According to Fig. 2a, FeNi3N/FeNi3 electrocatalyst achieved a current density of 20 mA cm−2 at an overpotential of 254 mV, which is the same with that of commercially purchased NiFe-LDH but 53 mV lower than that of pristine FeNi3N (307 mV at 20 mA cm−2). This performance is also comparable to some of the recently reported FeNi3N nitride and nitride-based electrocatalysts [6,7,13,21]. Information on the kinetics of these electrocatalysts was studied using Tafel plots [22,23]. As shown in Fig. 2b, the Tafel slope obtained at a current density of 20 mA cm−2 for FeNi3N/FeNi3 electrocatalyst is 76 mV dec−1, which is slightly higher than that of NiFe-LDH (79 mV dec−1) and significantly superior to that of the pristine sample (98 mV dec−1). The Tafel plots result indicates that FeNi3N/FeNi3 electrocatalyst displayed the most rapid electron transportation owing to the synergistic effect between FeNi3N and FeNi3. The composite of FeNi3N and FeNi3 leads to electronic interaction and the formation of hybrid interface between the two materials, which have been proven by our previous literature [24–26]. The synergistic effect between FeNi3N and FeNi3 contributes to the most rapid electron transportation in OER. More information on the kinetics was further studied using electrochemical impedance spectroscopy (EIS). Fig. 2c shows the Nyquist plot obtained from the EIS measurements. The semi-circle represents the charge transfer resistance (Rct) and the smaller the Rct, the better the catalytic kinetics [21]. As depicted in Fig. 2c, the Rct of FeNi3N/FeNi3 electrocatalyst is smaller than that of its FeNi3N counterparts and NiFeLDH, further affirming the superior kinetics of the hybrid samples. We have compared the performance of FeNi3N/FeNi3 on carbon cloth with that of various catalysts (Table 1). The OER activity of as-prepared FeNi3N/FeNi3 is superior to the recently and previously reported Ni-Fe hybrid catalysts on non-metal substrates. Stability is one of the most important factors of a good electrocatalyst [31]. Hence, we studied the stability test of our FeNi3N/FeNi3 hybrid electrocatalyst using Chronopotentiometric measurements at a constant current of 20 mA cm−2 for 50 h (Fig. 3a). The hybrid electrocatalyst shows excellent stability with 92% capacity retention after 50 h. After 50 h stability test, the LSV curves remain nearly the same with the initial one, further indicating excellent stability (Fig. 3b). Moreover, the SEM image collected after stability test affirmed that the nanoparticle morphology of the hybrid electrocatalyst was wellpreserved (Fig. 3c), further confirming its excellent structural and morphological stability. To have a better understanding of the excellent performance of our FeNi3N/FeNi3 hybrid nanoparticles, the catalytic mechanism was carried by transmission electron microscopy (TEM) after stability test. The TEM images of FeNi3N/FeNi3 (Fig. 3d) after electrolysis confirmed that a layer of nickel oxyhydroxide around 1–2 nm thick formed on the surface of the FeNi3N/FeNi3 nanoparticles. Previous reports have shown that the surfaces of metal nitride-based catalysts are usually coated with a thin layer of oxide/hydroxide during water oxidation, which serves as the main active sites [32,33]. In our work, the TEM image of FeNi3N/FeNi3 after stability test shows the nanoparticle morphology (Fig. 3d inset). After the electrolytic process, a layer of NiOOH was formed at the surface of FeNi3N/FeNi3. In conclusion, the OER catalytic performance of FeNi3N has been an significantly enhanced by incorporating FeNi3 through the tuning of the Fe source. As a result of synergistic effect between FeNi3N and FeNi3, the as-obtained FeNi3N/FeNi3 nanoparticles on carbon cloth exhibited an impressive OER performance with overpotential of 254 mV at a current density of 20 mA cm−2, smaller Tafel slope of 76 mV dec−1 and attractive durability at a fixed current density of 20 mA cm−2. This work opens more opportunities for the development of mixed transition metal nitrides hybrids.
3. Results and discussion FeNi3N/FeNi3 nanoparticles can be prepared by a simple hydrothermal method and annealing in NH3 gas. Compared to FeNi3N that is usually prepared by a mixture of 1:3 ratios of NiCl2 and FeCl3, FeNi3N/ FeNi3 can be obtained by simply increasing tuning the NiCl2 and FeCl3 ratio to 3:3. X-ray diffraction (XRD) pattern was carried on both FeNi3N and FeNi3N/FeNi3 to determine their phase composition. As shown in Fig. 1a, the peaks around 41.3° and 48.2° attributed to cubic FeNi3N (corresponding to JCPDF No: 50-1434) were observed in both samples. In FeNi3N/FeNi3, new peaks around 44.1° and 51.4° were formed which are attributed to the cubic Awaruite phase also termed FeNi3, justifying the formation of the FeNi3N/FeNi3 hybrids. However, these FeNi3 phase peaks are totally absent in the pristine FeNi3N sample. Scanning electron microscopy (SEM) analyses were carried out to study the morphology of both FeNi3N and FeNi3N/FeNi3 samples. As shown in Fig. 1b and inset, FeNi3N are nanoparticles in nature. Moreover, the SEM images of FeNi3N/FeNi3 sample also are nanoparticles in nature
Fig. 1. (a) XRD pattern of both FeNi3N and FeNi3N/FeNi3 samples. SEM images of (b) FeNi3N and (c) FeNi3N/FeNi3 samples. Insets are their corresponding low magnification SEM images. 2
Inorganic Chemistry Communications 113 (2020) 107802
X. Fu, et al.
Fig. 2. (a) LSV profiles, (b) Tafel plots and (c) Nyquist plots of FeNi3N, FeNi3N/FeNi3 and NiFe-LDH electrocatalysts.
CRediT authorship contribution statement
Table 1 Comparison of OER activity for various catalysts.
Xiaoguo Fu: Conceptualization, Writing - original draft. Jiasen Zhu: Resources, Data curation. Bingyun Ao: Visualization. Xinyue Lyu: Investigation. Jian Chen: Supervision, Writing - review & editing.
Catalysts
Overpotentials at 10 mA cm−2 (mV)
Tafel slope (mV dec−1)
FeNi3N/FeNi3 on carbon cloth FeNi3N on carbon cloth NiFe-LDH on carbon cloth NiFeS on nickel foam [27] NiFe LDH on nitrogen-doped graphene framework [28] NiFe on iron foam [29] NiFe-LDH on glassy carbon electrode [30] IrO2 [27] RuO2 [30]
220 280 232 280 337
76 98 79 56.3 45
211 290
31.8 51
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
380 345
108 65
Acknowledgments
Declaration of Competing Interest
This work was supported by the Natural Science Foundation of China (51973244).
Fig. 3. (a) Stability test of FeNi3N/FeNi3 at a constant current of 20 mA cm−2 for 50 h. (b) LSV profiles of FeNi3N/FeNi3 before and after stability. (c) SEM and (d) TEM images of FeNi3N/FeNi3 after stability test. Insets are low morphological images. 3
Inorganic Chemistry Communications 113 (2020) 107802
X. Fu, et al.
References
[17] Y. Hu, H. Yang, J. Chen, T. Xiong, M.S.J.T. Balogun, Y. Tong, ACS Appl. Mater. Inter. 11 (2019) 5152–5158. [18] H. Jin, X. Liu, Y. Jiao, A. Vasileff, Y. Zheng, S.-Z. Qiao, Nano Energy 53 (2018) 690–697. [19] Y. Yu, Y. Liu, S. Ju, X. Shen, Z. Ji, L. Kong, G. Zhu, Inorg. Chem. Commun. (2019) 107674. [20] H. Yang, L.Q. He, Y.W. Hu, X. Lu, G.R. Li, B. Liu, B. Ren, Y. Tong, P.P. Fang, Angew. Chem. Int. Ed. 54 (2015) 11462–11466. [21] F. Yan, Y. Wang, K. Li, C. Zhu, P. Gao, C. Li, X. Zhang, Y. Chen, Chem.-Eur. J. 23 (2017) 10187–10194. [22] B. Zhang, C. Xiao, S. Xie, J. Liang, X. Chen, Y. Tang, Chem. Mater. (2016). [23] Q. Wang, L. Shang, R. Shi, X. Zhang, G.I.N. Waterhouse, L.-Z. Wu, C.-H. Tung, T. Zhang, Nano Energy 40 (2017) 382–389. [24] M.-S. Balogun, H. Yang, Y. Luo, W. Qiu, Y. Huang, Z.-Q. Liu, Y. Tong, Energy Environ. Sci. 11 (2018) 1859–1869. [25] Y. Huang, H. Yang, T. Xiong, D. Adekoya, W. Qiu, Z. Wang, S. Zhang, M.S. Balogun, Energy Storage Mater. (2019). [26] X.-R. Wang, J.-Y. Liu, Z.-W. Liu, W.-C. Wang, J. Luo, X.-P. Han, X.-W. Du, S.-Z. Qiao, J. Yang, Adv. Mater. 30 (2018) 1800005. [27] B.-Q. Li, S.-Y. Zhang, C. Tang, X. Cui, Q. Zhang, Small 13 (2017) 1700610. [28] C. Tang, H.-S. Wang, H.-F. Wang, Q. Zhang, G.-L. Tian, J.-Q. Nie, F. Wei, Adv. Mater. 27 (2015) 4516–4522. [29] X. Yang, Q.-Q. Chen, C.-J. Wang, C.-C. Hou, Y. Chen, J. Energy Chem. 35 (2019) 197–203. [30] H. Zhong, T. Liu, S. Zhang, D. Li, P. Tang, N. Alonso-Vante, Y. Feng, J. Energy Chem. 33 (2019) 130–137. [31] H. Yang, Y. Hu, D. Huang, T. Xiong, M. Li, M.S. Balogun, Y. Tong, Mater. Today Chem. 11 (2019) 1–7. [32] Y. Zhang, B. Ouyang, J. Xu, G. Jia, S. Chen, R.S. Rawat, H.J. Fan, Angew. Chem. Int. Ed. 55 (2016) 8670–8674. [33] S. Jin, ACS Energy Lett. 2 (2017) 1937–1938.
[1] M.-S. Balogun, Y. Huang, W. Qiu, H. Yang, H. Ji, Y. Tong, Mater. Today 20 (2017) 425–451. [2] J. Xie, Y. Xie, Chem.-Eur. J. 22 (2016) 3588–3598. [3] N. Han, P. Liu, J. Jiang, L. Ai, Z. Shao, S. Liu, J. Mater. Chem. A 6 (2018) 19912–19933. [4] X. Peng, C. Pi, X. Zhang, S. Li, K. Huo, P.K. Chu, Sustain. Energy Fuels 3 (2019) 366–381. [5] N. Wang, X. Li, Inorg. Chem. Commun. 92 (2018) 14–17. [6] Y. Wang, C. Xie, D. Liu, X. Huang, J. Huo, S. Wang, ACS Appl. Mater. Inter. 8 (2016) 18652–18657. [7] X. Jia, Y. Zhao, G. Chen, L. Shang, R. Shi, X. Kang, G.I.N. Waterhouse, L.-Z. Wu, C.H. Tung, T. Zhang, Adv. Energy Mater. 6 (2016) 1502585. [8] H. Huang, Y. Li, W. Li, S. Chen, C. Wang, M. Cui, T. Ma, Inorg. Chem. Commun. 103 (2019) 1–5. [9] Z. Liu, H. Tan, J. Xin, J. Duan, X. Su, P. Hao, J. Xie, J. Zhan, J. Zhang, J.-J. Wang, H. Liu, ACS Appl. Mater. Inter. 10 (2018) 3699–3706. [10] H. Yang, Z.H. Wang, Y.Y. Zheng, L.Q. He, C. Zhan, X. Lu, Z.Q. Tian, P.P. Fang, Y. Tong, J. Am. Chem. Soc. 138 (2016) 16204–16207. [11] Q. Liu, J. Shen, X. Yu, X. Yang, W. Liu, J. Yang, H. Tang, H. Xu, H. Li, Y. Li, J. Xu, Appl. Catal. B-Environ. 248 (2019) 84–94. [12] H. Tang, R. Wang, C. Zhao, Z. Chen, X. Yang, D. Bukhvalov, Z. Lin, Q. Liu, Chem. Eng. J. 374 (2019) 1064–1075. [13] Q. Chen, R. Wang, M. Yu, Y. Zeng, F. Lu, X. Kuang, X. Lu, Electrochim. Acta 247 (2017) 666–673. [14] H. Huang, Y. Li, N. Wang, S. Chen, C. Wang, T. Ma, Inorg. Chem. Commun. 101 (2019) 23–26. [15] D. Li, H. Wang, H. Tang, X. Yang, Q. Liu, ACS Sustain. Chem. Eng. 7 (2019) 8466–8474. [16] J. Wu, J. Wang, Y. Lv, X. Wang, Inorg. Chem. Commun. 106 (2019) 128–134.
4
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Enhanced oxygen evolution reaction activity of FeNi3N nanostructures via incorporation of FeNi3
T
Xiaoguo Fua, Jiasen Zhub, Bingyun Aoa, Xinyue Lyuc, Jian Chenc,
⁎
a
Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang 621908, Sichuan, PR China School of Chemical Engineering and Technology, Sun Yat-sen University, Guangzhou 510275, PR China c School of Materials Science and Engineering, Instrumental analysis and Research Center, Sun Yat-sen University, Guangzhou 510275, PR China b
GRAPHICAL ABSTRACT
ABSTRACT
Herein, the oxygen evolution reaction (OER) catalytic activity of FeNi3N is significantly improved through the incorporation of FeNi3 as a result of the controllable composition of the Fe source. The as-prepared FeNi3N/FeNi3 achieves overpotential of 254 mV at a current density of 10 mA cm−2, which is superior to those of pristine FeNi3N, owing to the synergistic effect between FeNi3N and FeNi3.
1. Introduction Metal nitrides have not only gained significant attention as efficient electrocatalysts for hydrogen evolution reaction (HER) but also in oxygen evolution reaction (OER) [1–5]. Among the commonly reported metal nitrides, mixed metal nitride, especially FeNi3N usually achieved impressive catalytic performance both in HER and OER [6–8]. With enormous performance improvement of FeNi3N as HER electrocatalysts [9–12], their performance is quite inferior during OER [13–16]. One of the common strategies to enhance the catalytic properties of electrocatalysts is hybridization [17–20]. However, the hybridization of FeNi3N with other active materials towards achieving efficient OER is rarely reported. In this communication, we significantly enhanced the OER
⁎
performance of FeNi3N nanostructure by hybridizing with FeNi3. The as-prepared FeNi3N/FeNi3 hybrid was achieved by simply tuning the composition Fe source. FeNi3N/FeNi3 showed excellent OER performance with 20 mA cm−2 overpotential of 254 mV and a Tafel slope of 76 mV, which outshine that of its counterpart. This present work creates more opportunities for the development of transition metal nitrides as effective electrocatalysts for OER. 2. Experimental 4.0 cm2 of Carbon cloth purchased from Fuel Earth, USA was rinsed with conc. HNO3, ethanol and distilled water. 10 mmol of FeCl3·6H2O, 15 mmol of NiCl2·6H2O, 0.15 M of urea were dissolved in 30 mL of distilled water and uniformly stirred for 15 min including the carbon
Corresponding author. E-mail address: [email protected] (J. Chen).
https://doi.org/10.1016/j.inoche.2020.107802 Received 1 December 2019; Received in revised form 19 January 2020; Accepted 19 January 2020 Available online 21 January 2020 1387-7003/ © 2020 Elsevier B.V. All rights reserved.
Inorganic Chemistry Communications 113 (2020) 107802
X. Fu, et al.
cloth. The solution was allowed to react in an electric oven at 120 °C for 8 h and then naturally to cool to ambient temperature. The sample was then dried and annealed in NH3 gas at 450 °C for 3 h to form FeNi3N/ FeNi3. To obtain FeNi3N, the composition of FeCl3·6H2O was changed to 5 mmol FeCl3·6H2O while NiCl2·6H2O remains fixed. The characterization of both FeNi3N and FeNi3N/FeNi3 were studied using scanning electron microscopy (FESEM, Quanta 400/INCA/ HKL) and transmission emission microscopy (FEI Tecnai G2 F30) for the morphology and X-Ray diffraction spectroscopy (Rigaku SmartLab X) for the phase identification. OER measurements were carried out using FeNi3N and FeNi3N/ FeNi3 as the working electrode, Ag/AgCl as the reference electrode and carbon rod as the counter electrode. The geometric area of working electrode determined the active area. The working electrode on carbon cloth used for electrochemical tests was sealed with epoxy resin, leaving a square with 1.0 cm2 in area for measuring and a small area at the other end for ohmic contact. The linear seep voltammetry (LSV) profile was measured at a scan rate of 1 mV s−1 between 1.0 and 2.0 V (vs. RHE) and the Tafel plots were derived from the LSV profiles using the electrochemical workstation (CHI 760E). Electrochemical impedance spectroscopy (EIS) was a performance at the frequency range of 100,000 Hz–0.01 Hz, 5 mV AC amplitude and 20 mA cm−2 current density. The stability test was measured under stirring for 50 h.
(Fig. 1c and inset), indicating that tuning modifying the composition of Fe does not have an effect on the morphology of the hybrid sample. The electrocatalytic properties of the FeNi3N and FeNi3N/FeNi3 electrocatalysts were tested in a three electrode system as mentioned above. NiFe-LDH was also introduced for comparison. The linear sweep voltammetry (LSV) curves of the three catalysts are shown in Fig. 2a. According to Fig. 2a, FeNi3N/FeNi3 electrocatalyst achieved a current density of 20 mA cm−2 at an overpotential of 254 mV, which is the same with that of commercially purchased NiFe-LDH but 53 mV lower than that of pristine FeNi3N (307 mV at 20 mA cm−2). This performance is also comparable to some of the recently reported FeNi3N nitride and nitride-based electrocatalysts [6,7,13,21]. Information on the kinetics of these electrocatalysts was studied using Tafel plots [22,23]. As shown in Fig. 2b, the Tafel slope obtained at a current density of 20 mA cm−2 for FeNi3N/FeNi3 electrocatalyst is 76 mV dec−1, which is slightly higher than that of NiFe-LDH (79 mV dec−1) and significantly superior to that of the pristine sample (98 mV dec−1). The Tafel plots result indicates that FeNi3N/FeNi3 electrocatalyst displayed the most rapid electron transportation owing to the synergistic effect between FeNi3N and FeNi3. The composite of FeNi3N and FeNi3 leads to electronic interaction and the formation of hybrid interface between the two materials, which have been proven by our previous literature [24–26]. The synergistic effect between FeNi3N and FeNi3 contributes to the most rapid electron transportation in OER. More information on the kinetics was further studied using electrochemical impedance spectroscopy (EIS). Fig. 2c shows the Nyquist plot obtained from the EIS measurements. The semi-circle represents the charge transfer resistance (Rct) and the smaller the Rct, the better the catalytic kinetics [21]. As depicted in Fig. 2c, the Rct of FeNi3N/FeNi3 electrocatalyst is smaller than that of its FeNi3N counterparts and NiFeLDH, further affirming the superior kinetics of the hybrid samples. We have compared the performance of FeNi3N/FeNi3 on carbon cloth with that of various catalysts (Table 1). The OER activity of as-prepared FeNi3N/FeNi3 is superior to the recently and previously reported Ni-Fe hybrid catalysts on non-metal substrates. Stability is one of the most important factors of a good electrocatalyst [31]. Hence, we studied the stability test of our FeNi3N/FeNi3 hybrid electrocatalyst using Chronopotentiometric measurements at a constant current of 20 mA cm−2 for 50 h (Fig. 3a). The hybrid electrocatalyst shows excellent stability with 92% capacity retention after 50 h. After 50 h stability test, the LSV curves remain nearly the same with the initial one, further indicating excellent stability (Fig. 3b). Moreover, the SEM image collected after stability test affirmed that the nanoparticle morphology of the hybrid electrocatalyst was wellpreserved (Fig. 3c), further confirming its excellent structural and morphological stability. To have a better understanding of the excellent performance of our FeNi3N/FeNi3 hybrid nanoparticles, the catalytic mechanism was carried by transmission electron microscopy (TEM) after stability test. The TEM images of FeNi3N/FeNi3 (Fig. 3d) after electrolysis confirmed that a layer of nickel oxyhydroxide around 1–2 nm thick formed on the surface of the FeNi3N/FeNi3 nanoparticles. Previous reports have shown that the surfaces of metal nitride-based catalysts are usually coated with a thin layer of oxide/hydroxide during water oxidation, which serves as the main active sites [32,33]. In our work, the TEM image of FeNi3N/FeNi3 after stability test shows the nanoparticle morphology (Fig. 3d inset). After the electrolytic process, a layer of NiOOH was formed at the surface of FeNi3N/FeNi3. In conclusion, the OER catalytic performance of FeNi3N has been an significantly enhanced by incorporating FeNi3 through the tuning of the Fe source. As a result of synergistic effect between FeNi3N and FeNi3, the as-obtained FeNi3N/FeNi3 nanoparticles on carbon cloth exhibited an impressive OER performance with overpotential of 254 mV at a current density of 20 mA cm−2, smaller Tafel slope of 76 mV dec−1 and attractive durability at a fixed current density of 20 mA cm−2. This work opens more opportunities for the development of mixed transition metal nitrides hybrids.
3. Results and discussion FeNi3N/FeNi3 nanoparticles can be prepared by a simple hydrothermal method and annealing in NH3 gas. Compared to FeNi3N that is usually prepared by a mixture of 1:3 ratios of NiCl2 and FeCl3, FeNi3N/ FeNi3 can be obtained by simply increasing tuning the NiCl2 and FeCl3 ratio to 3:3. X-ray diffraction (XRD) pattern was carried on both FeNi3N and FeNi3N/FeNi3 to determine their phase composition. As shown in Fig. 1a, the peaks around 41.3° and 48.2° attributed to cubic FeNi3N (corresponding to JCPDF No: 50-1434) were observed in both samples. In FeNi3N/FeNi3, new peaks around 44.1° and 51.4° were formed which are attributed to the cubic Awaruite phase also termed FeNi3, justifying the formation of the FeNi3N/FeNi3 hybrids. However, these FeNi3 phase peaks are totally absent in the pristine FeNi3N sample. Scanning electron microscopy (SEM) analyses were carried out to study the morphology of both FeNi3N and FeNi3N/FeNi3 samples. As shown in Fig. 1b and inset, FeNi3N are nanoparticles in nature. Moreover, the SEM images of FeNi3N/FeNi3 sample also are nanoparticles in nature
Fig. 1. (a) XRD pattern of both FeNi3N and FeNi3N/FeNi3 samples. SEM images of (b) FeNi3N and (c) FeNi3N/FeNi3 samples. Insets are their corresponding low magnification SEM images. 2
Inorganic Chemistry Communications 113 (2020) 107802
X. Fu, et al.
Fig. 2. (a) LSV profiles, (b) Tafel plots and (c) Nyquist plots of FeNi3N, FeNi3N/FeNi3 and NiFe-LDH electrocatalysts.
CRediT authorship contribution statement
Table 1 Comparison of OER activity for various catalysts.
Xiaoguo Fu: Conceptualization, Writing - original draft. Jiasen Zhu: Resources, Data curation. Bingyun Ao: Visualization. Xinyue Lyu: Investigation. Jian Chen: Supervision, Writing - review & editing.
Catalysts
Overpotentials at 10 mA cm−2 (mV)
Tafel slope (mV dec−1)
FeNi3N/FeNi3 on carbon cloth FeNi3N on carbon cloth NiFe-LDH on carbon cloth NiFeS on nickel foam [27] NiFe LDH on nitrogen-doped graphene framework [28] NiFe on iron foam [29] NiFe-LDH on glassy carbon electrode [30] IrO2 [27] RuO2 [30]
220 280 232 280 337
76 98 79 56.3 45
211 290
31.8 51
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
380 345
108 65
Acknowledgments
Declaration of Competing Interest
This work was supported by the Natural Science Foundation of China (51973244).
Fig. 3. (a) Stability test of FeNi3N/FeNi3 at a constant current of 20 mA cm−2 for 50 h. (b) LSV profiles of FeNi3N/FeNi3 before and after stability. (c) SEM and (d) TEM images of FeNi3N/FeNi3 after stability test. Insets are low morphological images. 3
Inorganic Chemistry Communications 113 (2020) 107802
X. Fu, et al.
References
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