Electrocatalytic nitrate reduction using iron single atoms for sustainable ammonium supplies to increase rice yield

Increasing food production and ensuring drinking water safety have always been a focus of attention, especially for people in underdeveloped regions of the world. Traditional excessive fertilizer applications have increased crop yield but also caused groundwater nitrate pollution. Agricultural irrigating water is an important reservoir for nitrogen (N) (e.g., nitrate) accumulation after fertilization. Ammonium (NH₄⁺-N) is a more readily absorbed N form by rice than nitrate (NO₃^--N). In this study, we proposed a strategy using iron single-atom catalysts (Fe-SAC) to selectively reduce NO₃^--N to NH₄⁺-N from the real paddy field irrigating water to provide sustainable NH₄⁺-N supplies for rice uptakes, thereby highlighting decreasing N fertilizer applications and mitigating NO₃^--N pollution. Then, we constructed a solar-energy-driven electrochemical reactor for NO₃^--N reduction, with the Fe single atom as the core catalyst, and achieved an average NH₄⁺-N selectivity of 80.2 ± 2.6% with no additional energy input. Sustainable NH₄⁺-N supplies resulted in a 30.4 % increase in the 100-grain weight of the cultivated rice and a 50% decrease of fertilizer application than those of the fertilization group in the pot experiment, which were one of the best values ever reported. Furthermore, the ¹⁵N isotope tracing results indicated a N use efficiency (NUE) from ¹⁵NO₃^--N of 71.2 ± 3.2%. Sustainable NH₄⁺-N supplies played a key role in promoting rice root development which contributed to the high NUE. Our study shares unique insights in increasing grain yield, reducing fertilizer applications, and preventing nitrate leaching into groundwater.