Electro-triggered Joule heating method to synthesize single-phase CuNi nano-alloy catalyst for efficient electrocatalytic nitrate reduction toward ammonia

Abstract

Electrochemical nitrate reduction reaction (NO3RR) has great potential for ammonia (NH3) synthesis benefiting from its environmental friendliness and sustainability. Cu-based alloys with elemental diversity and adsorption tunability are widely used as electrocatalyst to lower the reaction overpotential for NO3RR catalysis. However, phase separation commonly found in alloys leads to uneven distribution of elements, which limits the possibility of further optimizing the catalytic activity. Herein, an electro-triggered Joule heating method, possessing unique superiority of flash heating and cooling that lead to well-dispersed nanoparticles and uniform mixing of various elements, was adopted to synthesize a single-phase CuNi nano-alloy catalyst evenly dispersed on carbon fiber paper, CFP-Cu1Ni1, which exhibited a more positive NO3RR initial potential of 0.1 V versus reversible hydrogen electrode (vs. RHE) than that of pure copper nanoparticles at 10 mA·cm−2 in 0.5 mol·L−1 Na2SO4 + 0.1 mol·L−1 KNO3 solution. Importantly, CFP-Cu1Ni1 presented high electrocatalytic activity with a Faradaic efficiency of 95.7% and NH3 yield rate of 180.58 µmol·h−1·cm−2 (2550 µmol·h−1·mg cat −1 ) at −0.22 V vs. RHE. Theoretical calculations showed that alloying Cu with Ni into single-phase caused an upshift of its d-band center, which promoted the adsorption of NO 3 − and weakened the adsorption of NH3. Moreover, the competitive adsorption of hydrogen ions was restrained until −0.24 V. This work offers a rational design concept with clear guidance for rapid synthesis of uniformly dispersed single-phase nano-alloy catalyst for efficient electrochemical NO3RR toward ammonia.