Heterogeneous 2D/2D MnO2/MXene catalyst for nitrate-to-ammonia electrochemical reduction and Zn-nitrate battery behavior

Ambient temperature electrochemical ammonia synthesis via nitrate reduction reaction (NO₃RR) is a promising alternative to the energy-intensive Haber-Bosch process but lacks effective electrocatalysts for practical applications. In this work, MnO₂ 2D-nanoflakes are anchored onto 2D-MXene Ti₃C₂T_x, forming a heterogeneous catalyst for NO₃RR with an ammonia yield of 14.06 ± 0.48 mg h^-1.mg_cat ^-1 at -1.2 V versus reversible hydrogen electrode (vs. RHE) and a Faradaic efficiency (FE) of 85.23 ± 1.62% at -1.0 vs. RHE, along with good stability over six consecutive cycles, with NH₃ FE exceeding 75% at -1.0 V vs. RHE in 0.5 M K₂SO₄ and 0.1 M KNO₃ electrolyte. As a cathode in a Zn-NO₃ ^- battery with a polished Zn plate from spent Zn-C batteries as anode, it delivers a power density of 0.323 mW cm^-2 and NH₃ FE of ∼79.9%. This study highlights a highly effective electrocatalyst for NO₃RR and its potential in self-powered NH₃ production.