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 mu m 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. This study unveils a pioneering FeCoNiCuMn high-entropy alloy (HEA) obtained from high-entropy Prussian blue-analogs via combining calcination and pulsed laser irradiation in liquids. The HEA demonstrates outstanding performance, efficiently converting low-level NO2- with 79.77% Faradaic efficiency and 61.49% N-selectivity. Notably, it exhibits remarkable durability in NO2--reduction, showcasing versatility and efficacy, as elucidated by advanced X-ray absorption and in-situ Raman techniques. image