Synthesis of Pt-M (M=Ir, Pd) Bimetallic Nanocrystals with Controlled Shape and Composition As a High-Performance Electrocatalyst for Ammonia Electrolysis

Abstract

Ammonia is a promising hydrogen storage carrier owing to its higher hydrogen capacity relative to liquid hydrogen (108 vs 71 g/L), non-flammability, well-developed technologies for synthesis and distribution.1-2 To utilize ammonia as the hydrogen storage carrier, it is essential to develop a highly efficient and durable catalyst that decomposes ammonia into hydrogen and nitrogen. Platinum (Pt) is the most effective catalyst for the electrolysis of ammonia, but it is rapidly deactivated during the reaction due to the strong adsorption of nitrogen on the surface. Thus, it is critical to develop a highly efficient and robust catalyst that surpasses Pt catalyst, enabling the utilization of ammonia as a safe and efficient hydrogen storage carrier. In this work, we synthesized nano-sized Pt-Ir (and Pt-Pd) alloy cubes as a high-performance electrocatalyst for ammonia electrolysis. During the synthesis, both elemental composition and shape of nanocrystals were systemically controlled for improving their electrocatalytic performance (Fig. 1a). Among the as-synthesized catalysts, the Pt-Ir nanocubes exhibited ~7.2 and ~4.6 times higher specific (mA/cm2) and mass (A/mg) activities, respectively, relative to a state-of-the-art commercial Pt/C catalyst (Tanaka) at 0.6 V (vs RHE, Fig. 1b). The significantly enhanced activity can be attributed to reduced adsorption strength of nitrogen, thus mitigating the deactivation of active sites of the catalyst. Hanada, N.; Hino, S.; Ichikawa, T.; Suzuki, H.; Takai, K.; Kojima, Y., Hydrogen generation by electrolysis of liquid ammonia. Chem Commun 2010, 46 (41), 7775-7777.Vitse, F.; Cooper, M.; Botte, G. G., On the use of ammonia electrolysis for hydrogen production. Journal of Power Sources 2005, 142 (1), 18-26. Figure 1