Engineering nickel dopants in atomically thin molybdenum disulfide for highly efficient nitrate reduction to ammonia

The electrocatalytic nitrate reduction reaction (NO${}_3$${}^{-}$RR) presents a promising pathway for achieving both ammonia (NH${}_3$) electrosynthesis and water pollutant removal simultaneously. Among various electrocatalysts explored, 2D materials have emerged as promising candidates due to their ability to regulate electronic states and active sites through doping. However, the impact of doping effects in 2D materials on the mechanism of NO${}_3$${}^{-}$RR remains relatively unexplored. Here, Ni-doped MoS${}_2$ (Ni-MoS${}_2$) nanosheets are investigated as a model system, demonstrating enhanced NO${}_3$${}^{-}$RR performance compared to undoped counterparts. By controlling the doping concentration, the Ni-MoS${}_2$ nanosheets achieve a remarkable faradic efficiency (FE) of 92.3% for NH${}_3$ at -0.3 V${}_{RHE}$ with excellent stability. The mechanistic studies reveal that the elevation of the NO${}_3$${}^{-}$RR performances originates from the generation of more active hydrogen and the acceleration of the reaction from nitrite (NO${}_2$${}^{-}$) to NH${}_3$ facilitated by Ni doping. Combining the experimental observations and theoretical calculations it is revealed that the appropriate Ni doping level in MoS${}_2$ can enhance *NO${}_3$ adsorption strength, thereby facilitating subsequent electrocatalytic steps. Together with the demonstration of Zn-NO${}_3$${}^{-}$ and Zn-NO${}_2$${}^{-}$ battery devices, the work provides new insights into the design and regulation of the active sites in 2D material catalysts for efficient NO${}_3$${}^{-}$RR. (© 2024 Wiley‐VCH GmbH)