Ti3C2Tx (T = F, OH) MXene nanosheets: conductive 2D catalysts for ambient electrohydrogenation of N2 to NH3

Abstract

The Haber–Bosch process for industrial-scale NH₃ production suffers from high energy consumption and serious CO₂ emission. Electrochemical N₂ reduction is an attractive carbon-neutral alternative for NH₃ synthesis but is severely restricted due to N₂ activation needing efficient electrocatalysts for the N₂ reduction reaction (NRR) under ambient conditions. Here, we report that Ti₃C₂T_x (T = F, OH) MXene nanosheets act as high-performance 2D NRR electrocatalysts for ambient N₂-to-NH₃ conversion with excellent selectivity. In 0.1 M HCl, such catalysts achieve a large NH₃ yield of 20.4 µg h⁻¹ mg_cat.⁻¹ and a high faradic efficiency of 9.3% at −0.4 V vs. reversible hydrogen electrode, with high electrochemical and structural stability. Density functional theory calculations reveal that N₂ chemisorbed on Ti₃C₂T_x experiences elongation/weakness of the NN triple bond facilitating its catalytic conversion to NH₃ and the distal NRR mechanism is more favorable with the final reaction of *NH₂ to NH₃ as the rate-limiting step.