CO₂ Laser-Stabilized Ni-Co Dual Single-Atomic Sites for Energy Generation and Ammonia Harvesting.

Abstract

Dual single-atom catalysts (DSACs) hold immense potential in electrochemical nitrate (NO₃ ^-) reduction (EcNR) as a sustainable replacement to the Haber-Bosch process for the production of ammonia (NH₃). However, challenges such as synthesis complexity, low purity, scalability, and stability have hindered their practical application. Herein, a rapid and scalable method is introduced to stabilize low-cost 3d transition metals (Ni and Co) as DSACs on Ti₃C₂T_x MXene in 10 min using continuous-wave CO₂-laser irradiation. Ni²⁺ and Co²⁺ ions are chelated and stabilized as single atoms onto an L-tryptophan-modified Ti₃C₂T_x surface via metal─O and metal─N bonds, forming Ni-single atom catalyst (SAC)/MXene, Co-SAC/MXene, and NiCo-DSAC/MXene. This approach enhances MXene properties, enabling the synthesis of efficient atomic-level electrocatalysts. Potential-resolved in situ Raman spectroelectrochemistry and density functional theory reveal that EcNR proceeds through NO₃ ^- reduction to ^*NO₂, ^*NO, ^*NH, and ^*NH₂ intermediates, ultimately forming NH₃ via final protonation step. This process exhibits a low limiting potential of -0.37 V, with ^*NO₂ protonation identified as the critical step. NiCo-DSAC/MXene exhibited superior EcNR performance for NH₃ production in 1.0 M potassium hydroxide with sustained multiple cyclic stability. Furthermore, this catalyst is integrated into a Zn-NO₃ ^- a battery that simultaneously removes NO₃ ^-, generates energy, and synthesizes NH₃.