The dual active site Ni <sub>3</sub>Sn <sub>2</sub>-NiSnO <sub> <i>x</i> </sub> alloy-oxide catalysts via Sn-Modulated Ni coordination for efficient ammonia synthesis
Shaoshuang Zhu, Kaiyu Liu, Zhe Feng, Huimin Jiang, Jianjian Lin
Abstract
As promising non-precious catalysts for the nitrogen reduction reaction (NRR), the nickel (Ni)-based materials have attracted considerable attention due to their unique electronic structure and catalytic activity, nevertheless, the efficiency is hindered by inefficient nitrogen (N<sub>2</sub>) adsorption and activation due to insufficiently flexible coordination environments. Here in this work, we develop the dual active site Ni<sub>3</sub>Sn<sub>2</sub>-NiSnO<em><sub>x</sub></em> alloy-oxide catalysts with succulent-plant-like nanostructure as catalysts via a facile electrochemical deposition strategy. Intriguingly, the Ni<sub>3</sub>Sn<sub>2</sub>-NiSnO<em><sub>x</sub></em> catalysts exhibit outstanding NRR performance with a Faradaic efficiency (FE) of 54.36 ± 1.2% and an ammonia yield of 83.33 ± 1.0 μg·h<sup>–1</sup>·cm<sup>–2</sup> in 0.1 M KOH. Meanwhile, the catalysts retain 90% initial activity after 4200 minutes continuous operation at -0.7 V (<em>vs.</em> RHE), showcasing remarkable durability in the alkaline medium. We demonstrate that the introduced high-valent Sn modulates the electronic structure and coordination environment of Ni, effectively reduces its d-band center, and attenuates hydrogen adsorption. We further reveal that the synergistic Ni-Sn interaction in the nanoalloy cooperatively localizes electrons at the Ni-Sn interface via surface oxide-mediated charge redistribution through the combined <em>in-situ</em> spectroscopic measurements and theoretical simulations. These changes collectively suppress the competing hydrogen evolution reaction (HER), thereby boosting the FE for NRR. This work presents a simple synthesis method for alloy-oxide catalyst fabrication and offers mechanistic insights as well as design principles for the development of Ni-based materials NRR electrocatalysts with dual active sites in alkaline environments.