Time-Resolved Fourier Transform Infrared Spectroelectrochemical Investigation of Nitrate Reduction to Ammonia
David Kumar Yesudoss, Bright Ngozichukwu, Ibrahima Gning, B.D. Ngom, Abdoulaye Djire
Abstract
High Resolution Image Download MS PowerPoint Slide This study explores the electrocatalytic nitrate reduction reaction (NO 3 – RR) using nitride-based two-dimensional Ti 2 NT x MXene (also known as MNene) synthesized via O 2 -assisted molten salt fluoride etching and its parent Ti 2 AlN MAX phase. Ti 2 NT x MNene achieved an ammonia (NH 3 ) yield rate of ∼550 μmol h –1 g –1 with a Faradaic efficiency (FE) of ∼80%. Unexpectedly, the Ti 2 AlN MAX phase exhibited an even higher NH 3 yield rate of ∼800 μmol h –1 g –1 at a comparable FE, despite its lower surface area and being traditionally considered a poor electrocatalyst. The enhanced performance of the MAX phase is likely due to −OH functionalization under alkaline conditions, leading to enhanced reaction kinetics. Postelectrolysis analyses, including Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), confirmed no significant changes in crystallinity but indicated surface chemical changes. Control experiments with blank electrolytes and isotopically labelled 15 NO 3 – substantiate that NH 3 originates exclusively from nitrate reduction on the surface terminations. Time-resolved in situ spectroelectrochemical studies identified nitrite (NO 2 – ) reduction to further intermediates as the rate-determining step. These findings not only challenge the conventional perception of MAX phases as poor electrocatalysts but also underscore the potential of nitride-based MAX and MXene materials as robust and efficient electrocatalysts for the NO 3 – RR.