Crystalline Red Phosphorus Nanoribbons: Large-Scale Synthesis and Electrochemical Nitrogen Fixation

Two dimensional (2D) nanoribbons constitute an emerging nanoarchitecture for advanced microelectronics and energy conversion due to the stronger size confinement effects compared to traditional nanosheets. Triclinic crystalline red phosphorus (cRP) composed by a layered structure is a promising 2D phosphorus allotrope and the tube-like substructure is beneficial to the construction of nanoribbons. In this work, few-layer cRP nanoribbons are synthesized and the effectiveness in the electrochemical nitrogen reduction reaction (NRR) is investigated. An iodine-assisted chemical vapor transport (CVT) method is developed to synthesize circa 10 g of bulk cRP lumps with a yield of over 99 %. With the aid of probe ultrasonic treatment, high-quality cRP microcrystals are exfoliated into few-layer nanoribbons (cRP NRs) with large aspect ratios. As non-metallic materials, cRP NRs are suitable for the electrochemical nitrogen reduction reaction. The ammonia yield is 15.4 μg h^-1  mg_cat. ^-1 at -0.4 V vs. reversible hydrogen electrode in a neutral electrolyte under ambient conditions and the Faradaic efficiency is 9.4 % at -0.2 V. Not only is cRP a promising catalyst, but also the novel strategy expands the application of phosphorus-based 2D structures beyond that of traditional nanosheets.