Peanut Shell-Derived Biochar Loaded with Iron Phosphide as a Catalyst for Effective Electrocatalytic Ammonia Synthesis from Nitrite

Abstract

Electrocatalytic nitrite reduction for ammonia synthesis offers a novel green pathway to overcome limitations of the Haber–Bosch process, though it remains constrained by issues such as sluggish adsorption/desorption kinetics of reaction intermediates. This study employs waste peanut shells as feedstock to synthesize FeP2/PS nanocatalysts in situ via single-step high-temperature calcination. This catalyst enhances the active surface area through the incorporation of a biochar support and phosphorus (P) elements. Simultaneously, the introduction of phosphorus atoms and their electronegativity induces a directed electron transfer from iron to phosphorus within FeP2. The resulting FeP2/PS exhibits a Faradaic efficiency of 98.94% in the nitrite reduction reaction (NO2–RR), with an ammonia yield of 308.459 μmol h–1 cm–2. Performance remained stable after 15 cycles. Based on density functional theory (DFT) calculations, the P sites in FeP2/PS act as bridges for electron and proton transport, effectively mediating electron transfer and charge supply to the Fe active sites, and optimizing the electronic structure of the Fe sites, thereby greatly enhancing the catalyst’s adsorption of nitrite (NO2–) and key reaction intermediates, lowering the reaction energy barrier, and accelerating the NO2– reduction kinetics, which significantly improves the yield of electrocatalytic ammonia synthesis.