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 Ti3C2Tx 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 Ti3C2Tx surface via metal & horbar;O and metal & horbar;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.