Improved Ammonia Synthesis and Energy Output from Zinc-Nitrate Batteries by Spin-State Regulation in Perovskite Oxides
Hele Guo, Yazhou Zhou, Kaibin Chu, Xueying Cao, Jingjing Qin, Nan Zhang, Maarten B. J. Roeffaers, Radek Zbořil, Johan Hofkens, Kläus Müllen, Feili Lai, Tianxi Liu
Abstract
High Resolution Image Download MS PowerPoint Slide 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 0.2 Pr 0.2 Nd 0.2 Ba 0.2 Sr 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 [CoO 5 ] structural motifs compared to conventional LaCoO 3 . Consequently, this material exhibits a significantly improved electrocatalytic performance toward ammonia (NH 3 ) 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 LaCoO 3 at the optimal potential. Furthermore, the LPNBSC-based Zn-nitrate battery reaches a maximum FE of 82% and an NH 3 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, *HNO 3 + H + + e – → *NO 2 + H 2 O. 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.