Improved Ammonia Synthesis and Energy Output from Zinc-Nitrate Batteries by Spin-State Regulation in Perovskite Oxides

Electrocatalytic nitrate reduction to ammonia (eNRA) is a promising route toward environmental sustainability and clean energy. However, its efficiency is often limited by the slow conversion of intermediates due to spin-forbidden processes. Here, we introduce a novel A-site high-entropy strategy to develop a new perovskite oxide (La_0.2Pr_0.2Nd_0.2Ba_0.2Sr_0.2)CoO_3-δ (LPNBSC) for eNRA. The LPNBSC possesses a higher concentration of high-spin (HS) cobalt-active centers, resulting from an increased concentration of [CoO₅] structural motifs compared to conventional LaCoO₃. Consequently, this material exhibits a significantly improved electrocatalytic performance toward ammonia (NH₃) production, resulting in a 3-fold increase in yield rate (129 μmol h^-1 mg_cat.^-1) and a 2-fold increase in Faradaic efficiency (FE, 76%) compared to LaCoO₃ at the optimal potential. Furthermore, the LPNBSC-based Zn-nitrate battery reaches a maximum FE of 82% and an NH₃ yield rate of 57 μmol h^-1 cm^-2. Density functional theory calculations reveal that A-site high-entropy management in perovskites facilitates nitrate activation and potentially optimizes the thermodynamic rate-determining step of the eNRA process, namely, *HNO₃ + H⁺ + e^- → *NO₂ + H₂O. This work presents an efficient concept for modulating the spin state of the B-site metal in perovskites and offers valuable insights for the design of high-performance eNRA catalysts.