Titanium nitride is an excellent surface coating for high-hardness materials and has also attracted recent interest as an electrocatalyst for the oxygen reduction reaction (ORR). However, preparations for titanium nitride and other transition metal nitrides require extremely high temperatures in flowing ammonia gas or expensive high-vacuum deposition techniques, and nano-sized nitrides in particular remain elusive. We have explored anhydrous, solution-based ammonolysis as an alternative to such procedures. Titanium(IV) tetrakisdialkylamido complexes react with ammonia to produce air-sensitive precipitates that decompose in vacuum or argon atmospheres to rocksalt titanium nitride with measurable carbon content. The particles assume a platelet morphology and are 80-120 nm in diameter. We have observed a dependence of the carbon content on the identity of the ligand and the solvent, with low molecular weight ligands and weakly-coordinating solvents favoring lower percentages of carbon by-product. The method is additionally amenable to preparing niobium nitride from pentakisdimethylamidoniobium (V). The addition of a weak base (2,6-lutidine) to the synthesis affords products with carbon contents as low as 14 wt %. We have demonstrated single-step ammonolysis for the preparation of titanium-niobium nitride alloys with niobium content as high as 30%. Electrodes of selected materials have been prepared via suspension with Nafion and their electrochemical activity for oxygen reduction – an important reaction for hydrogen fuel cells – has been measured. TiN electrodes showed an onset potential for reduction at ~0.8 V vs. RHE and a peak current density of 0.07 mA/cm<sup>2</sup>, comparable to previously published nitride electrocatalysts. Full physical characterization of the transition metal nitrides by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy will be presented, along with the results of electrochemical measurements.

Tiny TiN: Solution ammonolysis reactions towards nanoparticulate titanium nitride and titanium-niobium nitride alloys

251st National Meeting (2016)

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