Electrochemical nitrate reduction to ammonia using laser-processed Nb2AlC: the role of effective Al etching

Abstract

Electrocatalytic nitrate reduction reaction to ammonia (NH₃) is a promising approach for generating NH₃ compared with the widely used Haber–Bosch process. It offers the advantage of zero carbon emission and helps in recycling nitrate waste. However, the challenge remains in the synthesis and engineering of proficient electrocatalytic materials with high faradaic efficiency and yield rate. Herein, we report a unique laser-processed niobium oxide-graphene (NbO_x-Gr) electrode attached to a conductive support of graphene for NH₃ generation. The two-step fabrication process started with spatially and temporally controlled pulsed laser writing on an Nb₂AlC-coated polymer surface followed by simple electrochemical etching to remove excess Al. Electrochemical analysis elucidated that the NbO_x-Gr electrode exhibited improved activity for ammonia generation. Moreover, theoretical studies provide insights into the nitrate reduction reaction mechanism, confirming that the electrochemical active site was located on the Nb atom of the NbO_x-Gr electrode. Laser processing is a cost-effective, less chemically hazardous, versatile, and efficient approach to utilize MAX phases for multiple energy storage and conversion applications.