Synthesis and electrocatalytic applications of flower-like motifs and associated composites of nitrogen-enriched tungsten nitride (W₂N₃)

We have sought to improve the electrocatalytic performance of tungsten nitride through synthetic control over chemical composition and morphology. In particular, we have generated a thermodynamically unstable but catalytically promising nitrogen-rich phase of tungsten via a hydrothermal generation of a tungsten oxide intermediate and subsequent annealing in ammonia. The net product consisted of three-dimensional (3D) micron-scale flower-like motifs of W₂N₃; this architecture not only evinced high structural stability but also incorporated the favorable properties of constituent two-dimensional nanosheets. From a performance perspective, as-prepared 3D W₂N₃ demonstrated promising hydrogen evolution reaction (HER) activities, especially in an acidic environment with a measured overpotential value of −101 mV at a current density of 10 mA/cm². To further enhance the electrocatalytic activity, small amounts of precious metal nanoparticles (such as Pt and Au), consisting of variable sizes, were uniformly deposited onto the underlying 3D W₂N₃ motifs using a facile direct deposition method; these composites were applied towards the CO₂ reduction reaction (CO₂RR). A highlight of this series of experiments was that Au/W₂N₃ composites were found to be a much more active HER (as opposed to either a CO₂RR or a methanol oxidation reaction (MOR)) catalyst. [Figure not available: see fulltext.]