Engineering of local electron properties optimization in single-atom catalysts enabling sustainable photocatalytic conversion of N2 into NH3

Photocatalytic synthesis of ammonia (NH 3 ) from nitrogen (N 2 ) offers a promising strategy for carbon neutrality, as it avoids the energy-intensive and carbon-emitting industrial processes. The exploration of high-efficiency N 2 photofixation systems for photocatalytic N 2 reduction reaction (pNRR) is critical but it remains a challenge since the lack of rational structural design and atomic-level insights into molecular N 2 activation mechanism. Herein, an atomically dispersed single-atom palladium (Pd) active sites decorated oxygen-deficient molybdenum oxide (Pd/MoO 3-x ) was creatively designed for assessing pNRR performance. Interestingly, the integration of single-atom Pd active sites in MoO 3-x can significantly weaken the N≡N bond of adsorbed N 2 and effectively lower the activation energy barrier during the pNRR process. This is attributed to the fact that the modified Pd single-atom sites of Pd/MoO 3-x play a dominant role in the N 2 spontaneous adsorption process as well as possess a remarkable photogenerated electron trapping ability, which could be assisted to inject electrons into N 2 antibonding orbital, thus significantly accelerates the reaction kinetics. Consequently, the Pd/MoO 3-x photocatalyst reaches an impressive NH 3 yield rate of 103.2 μgg cat . −1 h −1 , which is superior to that of pristine MoO 3-x (21.2 μgg cat . −1 h −1 ) and commercial MoO 3 (6.5 μgg cat . −1 h −1 ), respectively. The present study not only creates a reliable approach to expand efficient N 2 photofixation system under mild conditions through the fabrication of atomically dispersed monometallic active sites, but also offers atomic-level insights into the underlying mechanism of pNRR catalytic process.