Green Ammonia Production through Nitrate Reduction on Defect-Rich NiO Nanoparticles

Ammonia is an essential compound for sustaining modern agriculture and food production, yet its industrial synthesis through the Haber–Bosch process remains highly energy-intensive and contributes significantly to global greenhouse gas emissions, accounting for nearly 2% of total CO₂ release. At the same time, the widespread use of ammonia-based fertilizers has generated a serious environmental concern, as excessive application leads to nitrate accumulation and contamination in aquatic ecosystems. Developing alternative and sustainable strategies for ammonia synthesis that also mitigate water pollution is therefore a pressing challenge. In this context, the electrochemical nitrate reduction reaction (E-NO₃RR) has emerged as a particularly attractive solution, offering the dual advantage of removing harmful nitrates while enabling decentralized ammonia generation under mild conditions.
Here, we investigate nickel oxide (NiO) nanoparticles as low-cost, earth-abundant electrocatalysts for E-NO₃RR. NiO was synthesized via a scalable precipitation route in which different ethanol/water solvent ratios were employed to deliberately tune defect density, porosity, and crystallinity. The resulting materials were thoroughly characterized using thermal, spectroscopic, and structural analyses. Electrochemical measurements reveal that higher ethanol content during synthesis increases the degree of defectiveness, which directly correlates with enhanced Faradaic efficiency and higher ammonia production rates. These results demonstrate the pivotal role of synthetic parameters in tailoring the catalytic properties of NiO. Overall, this study positions defect-engineered NiO nanoparticles as a promising platform for sustainable ammonia production while simultaneously contributing to nitrate remediation, advancing the broader goal of greener chemical processes.