Polyoxometalate-Intercalated Tremella-Like CoNi-LDH Nanocomposites for Electrocatalytic Nitrite-Ammonia Conversion

The electrocatalytic reduction of NO₂^- (NO₂RR) holds promise as a sustainable pathway to both promoting the development of emerging NH₃ economies and allowing the closing of the NO loop. Highly efficient electrocatalysts that could facilitate this complex six-electron transfer process are urgently desired. Herein, tremella-like CoNi-LDH intercalated by cyclic polyoxometalate (POM) anion P₈W₄₈ (P₈W₄₈/CoNi-LDH) prepared by a simple two-step hydrothermal-exfoliation assembly method is proposed as an effective electrocatalyst for NO₂^- to NH₃ conversion. The introduction of POM with excellent redox ability tremendously increased the electrocatalytic performance of CoNi-LDH in the NO₂RR process, causing P₈W₄₈/CoNi-LDH to exhibit large NH₃ yield of 0.369 mmol h^-1 mg_cat^-1 and exceptionally high Faradic efficiency of 97.0% at -1.3 V vs the Ag/AgCl reference electrode in 0.1 M phosphate buffer saline (PBS, pH = 7) containing 0.1 M NO₂^-. Furthermore, P₈W₄₈/CoNi-LDH demonstrated excellent durability during cyclic electrolysis. This work provides a new reference for the application of POM-based nanocomposites in the electrochemical reduction of NO₂^- to obtain value-added NH₃.