Hollow Nanoreactors Modulate Mass Transfer and Dual-Species Spillover to Boost Nitrate-to-Ammonia Reduction in Real Wastewater.

Abstract

Copper-based materials are promising catalysts for electrocatalytic nitrate reduction to ammonia (NH₃), while their use in real wastewater with low nitrate concentrations is hindered by poor mass transfer and high energy barrier. To overcome these limitations, we design a hollow Cu/MoS₂-550 nanoreactor, consisting of hollow MoS₂ support loaded with Cu single atoms and clusters. At the mesoscale, the hollow MoS₂ support features a heat-exchanger-fin-like structure that accelerates mass transfer, thereby promoting local enrichment of NO₃ ^-. At the microscale, precise modulation of sulfur vacancy concentration in MoS₂ triggers dual-species spillover, namely reverse hydrogen spillover and *NO spillover from Cu single atoms to Cu clusters, which lowers the energy barrier of deep hydrogenation step. As a result, the Cu/MoS₂-550 nanoreactor achieves an NH₃ Faradaic efficiency (FE) of 98.14% and a yield rate of 27.46 mg h^-1 mg_cat ^-1. Furthermore, when assembled into an Al-NO₃ ^- battery operating in real wastewater containing only ∼ 0.76 mM NO₃ ^-, the battery runs stably for 120 h, delivers an NH₃ FE of 53.20%, and maintains a nitrate removal rate of 91.17%. This work provides cross-scale modulation strategies to overcome mass-transfer bottlenecks and energy barriers in multi-electron transfer reactions, offering a potential pathway for environmental applications.