Phase‐Controlled Synthesis of Nickel‐Iron Nitride Nanocrystals Armored with Amorphous N‐Doped Carbon Nanoparticles Nanocubes for Enhanced Overall Water Splitting

Abstract

deemed as an effective and prospective route for mass production of clean H 2 fuels to alleviate global energy crisis and environmental issues. [1] Nevertheless, its oxygen evolution reaction (OER) occurring at the anode suffers from sluggish kinetics while the hydrogen evolution reaction (HER) occurring at the cathode confronts with large energy barriers in alkaline media, both of which restrict the efficiency of hydrogen production and the development of OWS technology. [2] Although noble metal-based oxides (e.g., Ru/Ir oxides) and commercial Pt/C show high electrocatalytic activity toward OER and HER, respectively, their low natural reserves and high cost as well as poor durability severely hinder their widespread applications. [3] To overcome those limitations, great efforts have been put into the design and development of nonprecious metal catalysts, including transition metal carbides, [4] borides, [5] oxides or oxyhydroxides, [6] chalcogenides, [7] and phosphides or phosphorsulfides [8] nanostructures. Unfortunately, most reported catalysts are usually only applicable to OER or HER, which is unadvantageous to the further development and commercial application of OWS. Hence, exploring and designing costeffective and highly active bifunctional catalysts are imperative but remain a great challenge owing to the diverse reaction mechanisms for OER and HER. Transition metal nitrides (TMNs) nanostructures possess distinctive electronic, optical, and catalytic properties, showing great promise to apply in clean energy, optoelectronics, and catalysis fields. Nonetheless, phase-regulation of NiFe-bimetallic nitrides nanocrystals or nanohybrid architectures confronts challenges and their electrocatalytic overall water splitting (OWS) performances are underexplored. Herein, novel pure-phase Ni 2+x Fe 2−x N nanocrystals armored with amorphous N-doped carbon (NC) nanoparticles nanocubes (NPNCs) are obtained by controllable nitridation of NiFe-Prussian-blue analogues derived oxides/NC NPNCs under Ar/NH 3 atmosphere. Such Ni 2+x Fe 2−x N/NC NPNCs possess mesoporous structures and show enhanced electrocatalytic activity in 1 m KOH electrolyte with the overpotential of 101 and 270 mV to attain 10 and 50 mA cm -2 current toward hydrogen and oxygen evolution reactions, outperforming their counterparts (mixed-phase NiFe 2 O 4 /Ni 3 FeN/NC and NiFe oxides/NC NPNCs). Remarkably, utilizing them as bifunctional catalysts, the assembled Ni 2+x Fe 2−x N/NC||Ni 2+x Fe 2−x N/NC electrolyzer only needs 1.51 V cell voltage for driving OWS to approach 10 mA cm -2 water-splitting current, exceeding their counterparts and the-state-of-art reported bifunctional catalysts-based devices, and Pt/C||IrO 2 couples. Additionally, the Ni 2+x Fe 2−x N/ NC||Ni 2+x Fe 2−x N/NC manifests excellent durability for OWS. The findings presented here may spur the development of advanced TMNs nanostructures by combining phase, structure engineering, and hybridization strategies and stimulate their applications toward OWS or other clean energy fields.

Constructing Air-Stable and Reconstruction-Inhibited Transition Metal Sulfide Catalysts via Tailoring Electron-Deficient Distribution for Water Oxidation

“…By further investigating the vibration modes of N–NiS 2 NSs and NiS 2 NSs through Raman spectroscopy, Figure d, the peaks located at 492.7 and 999.6 cm –1 ascribed to the vibrations of NiS 2 can be observed in the NiS 2 NSs, while in the N–NiS 2 NSs, both of these peaks shift to the relatively lower wavenumbers under the effect of lattice distortion caused by N introduction, which is consistent with the XRD results. In addition, the N–NiS 2 NSs further exhibited two peaks at 225.0 and 284.1 cm –1 , which originated from the Ni–N vibration. , The appearance of Ni–N Raman peaks reveals that the N atoms introduced in the N–NiS 2 NSs will bridge with the Ni center and form Ni–N coordination. Moreover, both N–NiS 2 NSs and NiS 2 NSs exhibit two slight peaks at 1590 and 1359 cm –1 , corresponding to the G band and D band of carbon, respectively, demonstrating the existence of residual carbon from the GO template.…”

“…In addition, the N− NiS 2 NSs further exhibited two peaks at 225.0 and 284.1 cm −1 , which originated from the Ni−N vibration. 55,56 The appearance of Ni−N Raman peaks reveals that the N atoms introduced in the N−NiS 2 NSs will bridge with the Ni center and form Ni−N coordination. Moreover, both N−NiS 2 NSs and NiS 2 NSs exhibit two slight peaks at 1590 and 1359 cm −1 , corresponding to the G band and D band of carbon, respectively, demonstrating the existence of residual carbon from the GO template.…”

Modulating the electronic structure of hollow Cu/Cu3P hetero‐nanoparticles to boost the oxygen reduction performance in long‐lasting Zn‐air battery

“…Compared with Cu NPs@N-C-900, the binding energy of Cu 0 peak in Cu/Cu 3 P@NP-C-900 (Figure 3E) is negatively shifted by 0.5 eV, evidencing the charge transfer from Cu 3 P to the metallic Cu, interpreting the strong electronic interaction between Cu and Cu 3 P species. 50 This result was further evidenced by valence band (VB) spectra (Figure 3F) and Mott-Schottky (M-S) plots (Figure 3G). The work functions (Φ) of Cu NPs@N-C-900 and Cu/Cu 3 P@NP-C-900 are calculated to be 6.33 and 6.17 eV by VB spectra via the equation ΔV = Φ À φ, where ΔV is the distance between the two inflection points and φ $ 4.55 eV is the work function of the instrument.…”

“…While after phosphating, most of the Cu 0 was changed to Cu 2+ along with satellite peaks in Cu/Cu 3 P@NP‐C‐900. Compared with Cu NPs@N‐C‐900, the binding energy of Cu 0 peak in Cu/Cu 3 P@NP‐C‐900 (Figure 3E) is negatively shifted by 0.5 eV, evidencing the charge transfer from Cu 3 P to the metallic Cu, interpreting the strong electronic interaction between Cu and Cu 3 P species 50 …”

An oxygen vacancy-modulated bifunctional S-NiMoO4 electrocatalyst for efficient alkaline overall water splitting

“…2a, the peaks at 873.74 eV and 855.97 eV corresponded to Ni 2p 1/2 and Ni 2p 3/2 , respectively, and the peaks located at 879.67 eV and 861.47 eV are Ni 2+ satellite peaks. 17 After S-doping, two characteristic peaks of Ni δ+ (0 < δ < 2) species at 870.57 eV and 853.23 eV appeared, 18,19 implying the formation of a low oxidation state of Ni. Similarly, a low oxidation state of Mo also occurred in S-NiMoO 4 .…”