Radiofrequency Plasma‐Assisted Pulsed Laser Deposited Pt/TiO_xN_y Coatings on Multi‐Walled Carbon Nanotubes as Gas Diffusion Electrodes for the Oxygen Reduction Reaction

Abstract

ance electrocatalytic activity and fuel cell costs. [1,2] Downsizing Pt to nanoparticles (NPs) is one of the practical approaches to lower its loading, while significantly enhancing its activity. However, the parallel problems are the complexity of the Pt NPs synthesis process and their aggregation during the ORR, limiting their range of practical applications. Introducing a support material for Pt can enhance the activity and stability of Pt NPs by enabling strong metal-support interactions. [3][4][5] Owing to their wealth of properties, transition metal nitrides, especially titanium nitride (TiN) and titanium oxynitride (TiO x N y ), have become essential technological materials, offering highly desirable properties such as hardness, excellent wear resistance, high melting point, thermodynamic stability, electrical conductivity, and corrosion resistance. Thin films of these materials have drawn considerable attention for use as coating materials for various applications such as cutting and drilling tools, diffusion barriers in integrated circuits, contact materials in semiconductors, and as catalyst supports for various heterogeneous reactions. [6][7][8][9][10][11] In addition, the thermodynamically-favorable formation of the native layer containing a mixture of oxide and oxynitride film on the surface of TiN makes it resistant to further oxidation. [12,13] TiN NPs are mainly produced by magnetron sputtering, atomic layer deposition, nitridation of titanium oxide by nitrogen sources such as ammonia or nitrogen at high temperature, and chemical vapor deposition (CVD) utilizing volatile precursors such as TiCl 4 . [9,[14][15][16] The latter, however, faces problems such as chlorine impurity incorporation and hightemperature requirements ( >600 °C). On the other hand, gasphase techniques are solvent-free routes toward synthesizing TiN at low temperatures. [17] With advances in continuous, highquality large-area film growth by pulsed laser deposition (PLD), more attention is directed toward using this method for thin film deposition. [18] PLD is an efficient gas-phase technique in which a focused short-pulse high-fluence laser beam is aimed at a target. The target absorbs the laser energy, and a rapid temperature increase occurs in the external layers of the target. This study reports on the fabrication and characterization of novel multilayered electrocatalyst nanostructures for the oxygen reduction reaction (ORR).Thin titanium oxynitride (TiO x N y ) coatings are deposited on a forest of multi-walled carbon nanotubes (MWCNTs), directly grown on a stainless-steel mesh, by capacitively coupled radiofrequency plasma-assisted pulsed laser deposition (RF-PAPLD) in a N 2 environment. The resulting high-surface-area binder-free electrode is further coated with a low quantity of well-dispersed Pt nanoparticles (NPs) by PLD in an inert atmosphere. High-speed imaging of the laser-induced plasma expansion provided evidence of a higher kinetics of the expanding plume at higher RF plasma powers, changing the morphology of the...

Synthesis of TiOxNy oxynitrides with a tunable nitrogen content

“…5b shows the N 1s spectra of TiO x N y , with two major peaks, 396 eV and 397.3 eV, appearing owing to Ti–O–N and Ti–N, respectively. 17,25,53,54 With the increase in reaction temperature, the peak intensity of Ti–O–N and Ti–N in the N 1s pattern also shows an increasing trend, which is consistent with the trend of the Ti 2p pattern, implying that the N content increases with the increase in temperature, consistent with the results from the elemental analysis. The low-intensity feature at 399.4 eV is assigned to the TiN satellite.…”

“…The low-intensity feature at 399.4 eV is assigned to the TiN satellite. 17 Due to the limited penetration capability of XPS, we Table 2 Results of Ti 2p level decomposition of TiO x N y synthesized at 800-1200…”

“…[1][2][3] This makes oxynitrides highly attractive as effective photocatalysts for visible light harvesting. 4 Oxynitrides have found widespread use in diverse fields, including photocatalysis, [5][6][7][8][9][10] electrocatalysis, [11][12][13][14][15] electrode materials, [16][17][18] and supercapacitors. [19][20][21][22] Titanium dioxide has been extensively studied in the field of photocatalysis, with researchers striving to extend its photocatalytic activity to the visible light range.…”

“…32 Another frequently used method for synthesizing TiO x N y oxynitrides is high-temperature treatment (600-1100 °C) of TiO 2 directly under pure NH 3 flow. 7,9,11,17,26,31,41 The nitrogen content can be increased by raising the reaction temperature and ammonia flow rate, 31 but this method is hazardous because of NH 3 . In addition to these methods, alternative techniques including atomic deposition, 8,13,42 physical vapor deposition, 20 laser deposition, 17,43,44 and anhydrous sol-gel methods 32 have also been employed to synthesize TiO x N y oxynitrides.…”

“…7,9,11,17,26,31,41 The nitrogen content can be increased by raising the reaction temperature and ammonia flow rate, 31 but this method is hazardous because of NH 3 . In addition to these methods, alternative techniques including atomic deposition, 8,13,42 physical vapor deposition, 20 laser deposition, 17,43,44 and anhydrous sol-gel methods 32 have also been employed to synthesize TiO x N y oxynitrides. Titaniumcontaining precursors such as TiCl 4 , 8,27,30 Ti(OH) 4 , 32 and Ti (SO 4 ) 2 28 have been used with nitrogen sources such as nitrogen, 43 ammonia, 12,25,27,45 and urea 32 for synthesizing TiO x N y oxynitrides.…”