Capping agent-free synthesis of surface engineered Pt nanocube for direct ammonia fuel cell

Abstract

Direct ammonia fuel cells (DAFCs), wherein the ammonia oxidation reaction (AOR) occurs at the anode and oxygen reduction at the cathode, are a promising clean energy production system using easily liquefied ammonia because they exhibit high energy density. However, only a few catalysts are, thus far, available for the AOR because of its sluggish six-electron-based reaction kinetics. Pt (100) is considered an optimal catalyst for the AOR; however, the synthesis of pristine Pt (100) is difficult because it requires the use of strong capping agents for faceting particles. Moreover, the capping agents block surface active sites, thereby deaccelerating electrochemical reactions. Herein, we report a novel synthetic method (hot separation) to achieve pristine Pt (100) by precisely controlling the formation kinetics of Pt nanocubes, wherein the further treatment for surface capping agent removal is not required. Hot separation prevents particle aggregation and overgrowth through the rapid separation of the Pt nanocubes and reaction solution and preserves the Pt (100) surface. Furthermore, the characterization of the pristine surface of Pt nanocubes was conducted to compare the properties of the Pt nanocubes with those of the particles prepared from conventional methods. The Pt nanocubes showed better mass activity toward the AOR and 2.3 times higher DAFC performance than those of commercial Pt.