Photocatalytic fixation of nitrogen to ammonia: state-of-the-art advancements and future prospects

Abstract

The burgeoning development of ammonia (NH₃) synthesis technology addresses the urgency of food intake required to sustain the population growth of the last 100 years. To date, NH₃ has mostly been synthesized by the Haber–Bosch process in industry. Under the ever-increasing pressure of the fossil fuel depletion crisis and anthropogenic global climate change with continuous CO₂ emission in the 21st century, research targeting the synthesis of NH₃ under mild conditions in a sustainable and environment friendly manner is vigorous and thriving. Therefore, the focus of this review is the state-of-the-art engineering of efficient photocatalysts for dinitrogen (N₂) fixation toward NH₃ synthesis. Strenuous efforts have been devoted to modifying the intrinsic properties of semiconductors (i.e. poor electron transport, rapid electron–hole recombination and sluggish reaction kinetics), including nanoarchitecture design, crystal facet engineering, doping and heterostructuring. Herein, this review provides insights into the most recent advancements in understanding the charge carrier kinetics of photocatalysts with respect to charge transfer, migration and separation, which are of fundamental significance to photocatalytic N₂ fixation. Subsequently, the challenges, outlooks and future prospects at the forefront of this research platform are presented. As such, it is anticipated that this review will shed new light on photocatalytic N₂ fixation and NH₃ synthesis and will also provide a blueprint for further investigations and momentous breakthroughs in next-generation catalyst design.