Crystallinity-tuned Cu3P nanoparticles constructed through solvothermal phosphidization of metal–organic frameworks for electrocatalytic nitrate reduction to ammonia

Abstract

Electrocatalytic nitrate reduction to ammonia (NO₃RR) offers a promising alternative to the Haber–Bosch process, and nitrate-based voltaic cells enable simultaneous energy conversion and value-added ammonia production. Herein, Cu₃P nanoparticles with different degrees of crystallinity (Cu₃P-H, Cu₃P-L, and Cu₃P-a) are synthesized via a solvothermal reaction between Cu-1,3,5-benzenetricarboxylic acid metal organic frameworks and white phosphorus. Amorphous Cu₃P-a exhibits the best NO₃RR performance, achieving a faradaic efficiency (FE) of 90.95%, an ammonia selectivity of 83.62% at –0.3 V (vs. reversible hydrogen electrode, RHE), and an ammonia yield of 542.54 μg h⁻¹ cm⁻² at –0.5 V (vs. RHE). Structural characterizations after eight NO₃RR cycles reveal severe crack propagation and particle agglomeration, accounting for the reduced ammonia yield. While the ammonia yield decreases due to structural changes, the FE remains reasonably stable over cycling. Moreover, a Zn–NO₃⁻ battery using Cu₃P-a as the cathode delivers a peak power density of 2.79 mW cm⁻² and an FE of 91.07%. This study highlights the importance of crystallinity control in Cu₃P and broadens the application of Cu₃P in electrocatalysis.