A Schottky-Barrier-Free Plasmonic Semiconductor Photocatalyst for Nitrogen Fixation in a "One-Stone-Two-Birds" Manner

Plasmonic photocatalysis has received much attention owing to attractive plasmonic enhancement effects in improving the solar-to-chemical conversion efficiency. However, the photocatalytic efficiencies have remained low mainly due to the short carrier lifetime caused by the rapid recombination of plasmon-generated hot charge carriers. Although plasmonic metal-semiconductor heterostructures can improve the separation of hot charge carriers, a large portion of the hot charge carriers are lost when they cross the Schottky barrier. Herein, a Schottky-barrier-free plasmonic semiconductor photocatalyst, MoO_{3- x} , which allows for efficient N₂ photofixation in a "one-stone-two-birds" manner, is demonstrated. The oxygen vacancies in MoO_{3- x} serve as the "stone." They "kill two birds" by functioning as the active sites for the chemisorption of N₂ molecules and inducing localized surface plasmon resonance for the generation of hot charge carriers. Benefiting from this unique strategy, plasmonic MoO_{3- x} exhibits a remarkable photoreactivity for NH₃ production up to the wavelength of 1064 nm with apparent quantum efficiencies over 1%, and a solar-to-ammonia conversion efficiency of 0.057% without any hole scavenger. This work shows the great potential of plasmonic semiconductors to be directly used for photocatalysis. The concept of the Schottky-barrier-free design will pave a new path for the rational design of efficient photocatalysts.