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Transition-metal dichalcogenide NiTe2: an ambient-stable material for catalysis and nanoelectronics

Recently, transition-metal dichalcogenides hosting topological states have attracted considerable attention for their potential implications for catalysis and nanoelectronics. The investigation of their chemical reactivity and ambient stability of these materials is crucial in order to assess the suitability of technology transfer. With this aim, an international team of researchers from Italy, Russia, China, USA, India, and Taiwan has studied physicochemical properties of NiTe2 by means of several experimental techniques and density functional theory. Surface chemical reactivity and ambient stability were followed by x-ray photoemission spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) experiments at the BACH beamline, while the electronic band structure was probed by spin- and angle-resolved photoelectron spectroscopy (spin-ARPES) at the APE-LE beamline
High-resolution XPS spectra of Ni-3p and Te-4d core levels for the as-cleaved NiTe2 and the same surface modified by the exposure to 2·10L of CO, H2O and O2 are reported in Fig. 1. Specifically, the Ni-3p (Fig. 1a) core level was recorded at a binding energy (BE) of 66.8 (J=3/2) and 68.5 (J=1/2) eV. No change was observed upon CO dosage, thus proving the absence of CO poisoning, confirmed by vibrational experiments by high-resolution electron energy loss spectroscopy. Upon O2exposure, the intensity of the Ni-3p level was reduced by 42% with the emergence of a new doublet with a J=3/2 component at 67.6 eV, which is associated with Ni(II) species, evidently related to Ni-O bonds. Correspondingly, the Te-4d (Fig. 1b) core level for as-cleaved NiTe2 showed two doublets with J=5/2 components at 39.9 and 40.1 eV, which arise from surface and bulk contributions, respectively. The NiTe2 surface did not show any reactivity toward H2O and CO, enabling the possibility to fabricate CO-tolerant electrodes for electrocatalysis, which would be stable in an aqueous environment. Conversely, the Te-4d spectrum drastically changed after O2exposure, which induces oxidation of Te.

Figure 1.    a) Ni-3p and b) Te-4d XPS core-level spectra collected from as-cleaved NiTe2 (black curves) and from the same surface exposed to 2·10L of CO (red curves), H2O (green curves) and O2 (blue curves). Adapted from "S. Nappini et al., Adv. Funct. Mater. 30, 2000915 (2020); DOI: 10.1002/adfm.202000915" with permission from Wiley (Copyright 2020) with license 4873681106527


The as-cleaved NiTe2 was also directly exposed to the atmosphere with the aim to assess its ambient stability. Ni-3p and Te-4d core-level spectra were measured as a function of exposure time to the atmosphere to study the aging of NiTe2. A passivation layer of TeO2 with a thickness ~7 Å was formed after only 5 minutes of air exposure and it saturates after 30 minutes. 
The presence of low-energy type-II Dirac fermions in this sample was also unveiled by spin-ARPES experiments (Fig. 2). Notably, the bulk Dirac point in NiTe2was found in close proximity to the Fermi energy (EF), contrarily to the case of PdTe2 and PtTe2. Exactly, Dirac point is located at 20 meV above EF, making NiTe2the most prominent transition-metal dichalcogenide for the potential exploitation of Dirac fermiology. In addition, several surface states were also observed. 
The performance of this material in hydrogen and oxygen evolution reactions (HER and OER) was also investigated by direct electrocatalytic tests by measuring the linear sweep voltammetry (LSV) curve in 1.0 M KOH. Concerning HER, the overpotential was quite high, though it was compensated by a low onset potential, typical of a good intrinsic HER activity. In the case of OER, the overpotential was much lower, indicating promising OER activity in alkaline medium. The Tafel slope of NiTe2 single crystal towards HER ad OER was estimated to be 188.3 and 106.9 mV dec-1, respectively, validating the high efficiency of NiTe2-based electrodes. Finally, a good durability of the current density was determined for both reactions, ranging from 15 h for HER up to 45 h for OER.  

In addition, the suitability in the field of nanoelectronics was assessed by fabricating nanodevices with active channels of NiTe2, which exhibited high stability in air even without encapsulation. Specifically, a NiTe2-based high-frequency receiver was implemented. At an operational frequency of 40 GHz, the nanodevice showed responsivity of ~5 A/W with signal-to-noise ratio of ~103, with negligible changes in their performance after air exposure for more than one month. Remarkably, NiTe2also enables integration in future communication or imaging systems in both the GHz and THz range of the electromagnetic spectrum.

Figure 2.    Band dispersion of NiTe2 measured along the Γ-K direction using a photon energy of 22 eV. Adapted from "S. Nappini et al., Adv. Funct. Mater. 30, 2000915 (2020); DOI: 10.1002/adfm.202000915" with permission from Wiley (Copyright 2020) with license 4873681106527



This research was conducted by the following research team:

Silvia Nappini1, Danil W. Boukhvalov2,3, Gianluca D’Olimpio4, Libo Zhang5, Barun Ghosh6, Chia-Nung Kuo7, Haoshan Zhu8, Jia Cheng9, Michele Nardone4, Luca Ottaviano4, Debashis Mondal1, Raju Edla1, Jun Fuji1, Chin Shan Lue7, Ivana Vobornik1, Jory Yarmoff8, Amit Agarwal6, Lin Wang5, Lixue Zhang9, Federica Bondino1, and Antonio Politano4,10


Consiglio Nazionale delle Ricerche (CNR)- Istituto Officina dei Materiali (IOM) , Trieste, Italy

College of Science, Institute of Materials Physics and Chemistry, Nanjing Forestry University, Nanjing, P. R. China
Theoretical Physics and Applied Mathematics Department, Ural Federal University,  Ekaterinburg, Russia 

Department of Physical and Chemical Sciences, University of L’Aquila, L’Aquila , Italy

State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, China
Department of Physics, Indian Institute of Technology Kanpur, India
Department of Physics, National Cheng Kung University, Tainan, Taiwan

Department of Physics and Astronomy, University of California, Riverside, United States

College of Chemistry and Chemical Engineering, Qingdao University, Shandong, China
10 CNR-IMM Istituto per la Microelettronica e Microsistemi, Catania, Italy

Contact persons:

Antonio Politano, e-mail: antonio.politano@univaq.it;
Silvia Nappini, e-mail: nappini@iom.cnr.it
Federica Bondino, e-mail: bondino@iom.cnr.it



S. Nappini, D. W. Boukhvalov, G. D’Olimpio, L. Zhang, B. Ghosh, C.-N. Kuo, H. Zhu, J. Cheng, M. Nardone, L. Ottaviano, D. Mondal, R. Edla, J. Fuji, C. S. Lue, I. Vobornik, J. A. Yarmoff, A. Agarwal, L. Wang, L. Zhang, F. Bondino and A. Politano, Transition-metal dichalcogenide NiTe2: an ambient-stable material for catalysis and nanoelectronics, Adv. Funct. Mater. 2000915 (2020). https://doi.org/10.1002/adfm.202000915, https://onlinelibrary.wiley.com/doi/pdf/10.1002/adfm.202000915  
Last Updated on Thursday, 20 August 2020 11:46