Ru-Ni alloy nanosheets as tandem catalysts for electrochemical reduction of nitrate to ammonia

Developing electrocatalysts that exhibit both high activity and ammonia selectivity for nitrate reduction is a significant and demanding challenge,primarily due to the complex nature of the multiple-electron reduction process involved.An encouraging approach involves coupling highly active precious metals with transition metals to enhance catalytic performance through synergy.Here,we report a ruthenium-nickel alloy catalyst with nanosheets(Ru-Ni NSs)structure that achieves a remarkable ammonia Faradaic efficiency of approximately 95.93%,alongside a yield rate of up to 6.11 g·h^(−1)·cm^(−2).Moreover,the prepared Ru-Ni NSs exhibit exceptional stability during continuous nitrate reduction in a flow reactor for 100 h,maintaining a Faradaic efficiency of approximately 90%and an ammonia yield of 37.4 mg·L^(−1)·h^(−1)using 0.05 M nitrate alkaline electrolyte.Mechanistic studies reveal that the catalytic process follows a two-step pathway,in which HONO serves as a migration intermediate.The presence of a partially oxidized Ru(002)surface enhances the adsorption of nitrate and facilitates the release of the migration intermediate by adjusting the strength of the electrostatic and covalent interactions between the adsorbate and the surface,respectively.On the other hand,the Ni(111)surface promotes the utilization of the migration intermediate and requires less energy for NH_(3)desorption.This tandem process contributes to a high catalytic activity of Ru-Ni NSs towards nitrate reduction.

Co-incorporation of hydrotalcite and starch into biochar-based fertilizers for the synthesis of slow-release fertilizers with improved water retention

The unsatisfactory nutrient slow-release and water-retention performance of traditional biochar-based compound fertilizers(BCF)severely limit their practical application.Herein,a new type of slow-release fertilizer with high water retention was fabricated via the incorporation of hydrotalcite and starch into BCF,named as HS-BCF.The waterretention and nutrient releasing performance of the prepared HS-BCF and related nutrient slow-release mechanism were investigated.The results showed that the incorporation of hydrotalcite and starch into BCF could increase the soil water-retention ratio by 5-10%points.The accumulated N,P,and K leaching amounts of HS-BCF in soil within 30 days were 49.4%,13.3%,and 87.4%of BCF at most,respectively.Kinetic analysis indicated that the release of nutrients from HS-BCF was attributed to the coupling of the diffusion-controlled and relaxation-controlled mechanism.Moreover,hydrotalcite could bind with P in HS-BCF,contributing to the enhanced durability of P in HS-BCF.Finally,pot experiments showed that the N-P-K utilization efficiencies of HS-BCF were all higher than those of BCF due to a better synchronization between the nutrient release of HS-BCF and the uptake of tomato plants.Overall,the study may provide a promising strategy for simultaneously improving the water-retention and slow-release performance of traditional biochar-based fertilizers.