Characterization of early transition metal carbides and nitrides by NEXAFS

Kapoor, Rajat; Oyama, S. Ted; Friihberger, B.; DeVries, B.; Chen, J. G.

doi:10.1007/bf00808333

Cited by 39 publications

(34 citation statements)

References 20 publications

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“…Such difference between theory and experiments can also be observed in other nitrides, e.g. in CrN, VN and NbN theoretical values of 10Dq are 0.8, 1.1 and 2 eV [63,64], respectively, whereas experimental values were about 3 eV for CrN [55,65], 2.7 eV for VN [66] and 3.5 eV for NbN [67]. Therefore, combing the resemblance of our N K-edge spectra in CoN together with that of ZB-FeN and to the simulated spectra for ZB-CoN, it appears that the structure of CoN in our samples is closer to ZB-type.…”

Section: Resultsmentioning

confidence: 83%

X-ray absorption spectroscopy study of cobalt mononitride thin films

et al. 2019

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We present a comprehensive study to resolve the debate about the structure of cobalt mononitride (CoN). In contradiction with theoretical predictions, experimentally CoN has been claimed to synthesize in a rock-salt (RS) and in a zincblende (ZB)-type structure under ambient pressure and temperature. Utilizing X-ray absorption near-edge spectroscopy (XANES) at Co and N K-edges and extended X-ray absorption fine structure (EXAFS) at Co K-edge, we investigated the structure of CoN in detail. The presence of a strong pre-edge feature at the Co K-edge and the absence of t 2 feature at the N K-edge indicate towards the tetrahedral coordination that is expected in the ZB-type structure of CoN. Theoretical simulations of XANES spectra unambiguously confirm the ZB-type structure in CoN. Also from EXAFS data, we found that CoN and Co-Co bond distances match well with ZB-CoN. Magnetic properties of CoN were examined using polarized neutron reflectivity and bulk magnetization measurements. It was found that CoN sample exhibits a paramagnetic behaviour as expected in ZB-CoN. Obtained results clearly demonstrate that CoN indeed crystalizes in the ZB-type structure, and the possibility of the RS-type CoN can be ruled out under ambient pressure and temperature. It is anticipated that the information about the structure of CoN can be utilized for its usage in emerging areas such as low-cost catalyst in oxygen and hydrogen evaluation reactions, high capacity anode in ion batteries and in photovoltaic applications.

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Section: Resultsmentioning

confidence: 83%

X-ray absorption spectroscopy study of cobalt mononitride thin films

et al. 2019

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“…2e, f, respectively. It can be observed that two typical L 3 and L 2 peaks of Co L-edge at about 779.3 and 794.9 eV exhibit a positive shift after P/W doping 40 , while those of N Kedge spectra show negative shift accordingly 41 , which further reveals the possibly existed interfacial charge transfer effect upon doping observed in XPS results. To disclose the coordination environment of PW-Co 3 N NWA/ NF, we further conducted the extended X-ray absorption fine structure (EXAFS) characterization.…”

Section: Synthesis and Characterization Of Pw-co 3 N Nanowire Arraysmentioning

confidence: 75%

Manipulating dehydrogenation kinetics through dual-doping Co3N electrode enables highly efficient hydrazine oxidation assisting self-powered H2 production

et al. 2020

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Replacing sluggish oxygen evolution reaction (OER) with hydrazine oxidation reaction (HzOR) to produce hydrogen has been considered as a more energy-efficient strategy than water splitting. However, the relatively high cell voltage in two-electrode system and the required external electric power hinder its scalable applications, especially in mobile devices. Herein, we report a bifunctional P, W co-doped Co 3 N nanowire array electrode with remarkable catalytic activity towards both HzOR (−55 mV at 10 mA cm −2) and hydrogen evolution reaction (HER, −41 mV at 10 mA cm −2). Inspiringly, a record low cell voltage of 28 mV is required to achieve 10 mA cm −2 in two-electrode system. DFT calculations decipher that the doping optimized H* adsorption/desorption and dehydrogenation kinetics could be the underlying mechanism. Importantly, a self-powered H 2 production system by integrating a direct hydrazine fuel cell with a hydrazine splitting electrolyzer can achieve a decent rate of 1.25 mmol h −1 at room temperature.

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“…Furthermore, a broad peak at about 406 eV is found, which can be assigned to the σ* excitation of C−N bonds . In addition, a broad peak at 414.5 eV can be observed (except for the MoP@NCHSs‐750 sample), which is assigned to the transition of N 1s electrons to an orbital that involves contributions from 2p and 3p orbitals of nitrogen and the d and s states of metals . From the detailed spectra of N K‐edge XANES spectra, we can see the intensity ratios of pyridinic N peak (peak a) to the peaks of the other three configurations (peak b) are 1.18, 1.77, 1.78, and 2.26 for MoP@NCHSs‐700, MoP@NCHSs‐800, MoP@NCHSs‐960, and MoP@NCHSs‐900, respectively.…”

Section: Resultsmentioning

confidence: 95%

Synergistically Interactive Pyridinic‐N–MoP Sites: Identified Active Centers for Enhanced Hydrogen Evolution in Alkaline Solution

Zhao,

Sun,

Cheong

et al. 2019

Angewandte Chemie

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Fore lectrocatalysts for the hydrogen evolution reaction (HER), encapsulating transition metal phosphides (TMPs) into nitrogen-doped carbon materials has been known as an effective strategy to elevate the activity and stability.Y et still, it remains unclear how the TMPs work synergistically with the N-doped support, and which Nc onfiguration (pyridinic N, pyrrolic N, or graphitic N) contributes predominantly to the synergy.H ere we present aH ER electrocatalyst (denoted as MoP@NCHSs) comprising MoP nanoparticles encapsulated in N-doped carbon hollows pheres,w hich displays excellent activity and stability for HER in alkaline media. Results of experimental investigations and theoretical calculations indicate that the synergy between MoP and the pyridinic Ncan most effectively promote the HER in alkaline media.

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Characterization of early transition metal carbides and nitrides by NEXAFS

Cited by 39 publications

References 20 publications

X-ray absorption spectroscopy study of cobalt mononitride thin films

X-ray absorption spectroscopy study of cobalt mononitride thin films

Manipulating dehydrogenation kinetics through dual-doping Co3N electrode enables highly efficient hydrazine oxidation assisting self-powered H2 production

Synergistically Interactive Pyridinic‐N–MoP Sites: Identified Active Centers for Enhanced Hydrogen Evolution in Alkaline Solution

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