Molecule template method for precise synthesis of Mo-based alloy clusters and electrocatalytic nitrogen reduction on partially reduced PtMo alloy oxide cluster

Abstract

Alloy clusters are attractive electrocatalysts that have adjustable activity through the synergistic effects of alloy components. However, the synthesis of atomically-precise alloy clusters is still a challenge. Here, we report a molecular template method in which phosphomolybdic acid adsorbs foreign noble metal ions, and then anneals into a series of Mo-based alloy oxide clusters (PtMo, IrMo, AuMo and PdMo), where oxygen is the terminal oxygen outside the cluster. The as-prepared alloy clusters have tunable atomic ratio and uniform size around 1 nm. Taking PtMo clusters as an example, their electrocatalytic nitrogen reduction reaction (NRR) has been investigated in depth. Among all compositions, PtMo-6 cluster (Pt:Mo atomic ratio 1:2) exhibits the highest NRR activity with a Faradaic efficiency of 14.37% and a NH 3 yield rate of 65.3 μg h −1 mg −1 cat. in 0.1 M KOH, surpassing the known Mo-based catalysts. The combination of operando X-ray absorption spectroscopy and DFT calculations reveals that the oxide cluster in working state is the partially reduced. An unusual synergy is discovered, namely that Pt acts as a proton donor, providing *H to promote the hydrogenation of N 2 on the adjacent Mo atom. This work provides a simple and universal method for the precise synthesis of alloy clusters and new guidance for designing highly efficient NRR catalysts. A molecule template method is developed to prepare Mo-based alloy clusters (PtMo, IrMo, AuMo and PdMo) with uniform particle size of 1–2 nm and controllable atomic ratio. Among all PtMo compositions, PtMo-6 cluster exhibits the highest electrocatalytic activity towards nitrogen reduction reaction. The combination of X-ray absorption spectroscopy and DFT calculations reveals the synergistic mechanism of NRR on PtMo-6 clusters, that is, Pt acts as a proton donor, providing *H (* represents active site) to promote the hydrogenation of N 2 on nearby Mo atoms. • A molecule template method is developed to prepare Mo-based alloy clusters. • Partially oxidized PtMo cluster exhibits high electrocatalytic activity towards nitrogen reduction reaction. • Operando observation of nitrogen reduction reaction on PtMo cluster by X-ray absorption spectroscopy. • An unusual synergy is discovered, that is, Pt providing *H to promote the hydrogenation of N 2 on Mo.