Deciphering Indirect Nitrite Reduction to Ammonia in High-Entropy Electrocatalysts Using In Situ Raman and X-ray Absorption Spectroscopies

Abstract

This research adopts a new method combining calcination and pulsed laser irradiation in liquids to induce a controlled phase transformation of Fe, Co, Ni, Cu, and Mn transition-metal-based high-entropy Prussian blue analogs into single-phase spinel high-entropy oxide and face-centered cubic high-entropy alloy (HEA). The synthesized HEA, characterized by its highly conductive nature and reactive surface, demonstrates exceptional performance in capturing low-level nitrite (NO₂ ^-) in an electrolyte, which leads to its efficient conversion into ammonium (NH₄ ⁺) with a Faradaic efficiency of 79.77% and N selectivity of 61.49% at -0.8 V versus Ag/AgCl. In addition, the HEA exhibits remarkable durability in the continuous nitrite reduction reaction (NO₂ ^-RR), converting 79.35% of the initial NO₂ ^- into NH₄ ⁺ with an impressive yield of 1101.48 µm h^-1 cm^-2. By employing advanced X-ray absorption and in situ electrochemical Raman techniques, this study provides insights into the indirect NO₂ ^-RR, highlighting the versatility and efficacy of HEA in sustainable electrochemical applications.

Keywords: X‐ray absorption; ammonia production; high‐entropy materials; in situ Raman spectroscopy; nitrite reduction reaction; pulsed laser irradiation in liquids.