A Synergistic Hybrid of Sr3B2O6-SryTi0.6Fe0.4O3-δ (y < 1) as a Cathode for High-Performance Electrochemical Ammonia Synthesis via Protonic Ceramic Electrolysis Cells

Abstract

The electrochemical nitrogen reduction reaction (e-NRR) presents a promising approach for environmentally friendly ammonia synthesis. However, the efficiency of ammonia synthesis can be hindered by competitive hydrogen evolution reactions (HER). Therefore, the development of a catalyst capable of suppressing HER is essential. In this study, a synergistic hybrid catalyst Sr(Ti_0.6Fe_0.4)_0.8B_0.2O_3-δ [S(TF)B_0.2], composed of Sr₃B₂O₆ (SB) and Sr_yTi_0.6Fe_0.4O_3-δ (S_yTF, y<1) is synthesized and used as an electrocatalyst for electrochemical ammonia synthesis via protonic ceramic electrolysis cells, in which SB is utilized as a proton acceptor, thereby inhibiting HER and promoting proton-coupled electron transfer (PCET) for the ammonia synthesis. The formation of SB results in a deficiency of A-site cations in S_yTF, leading to an increased number of oxygen vacancies in S(TF)B_0.2. DFT calculation indicates that oxygen vacancies facilitate ammonia generation and desorption, adhering to the enzymatic pathway for NH₃ synthesis. Additionally, the grain boundary (GB) between S_yTF and SB introduces further defects, which contribute to the enhancement of the eNRR. Research indicates that utilizing S(TF)B_0.2 as a catalyst enhances both the ammonia synthesis rate and Faradaic efficiency. This study presents a straightforward and efficient approach for the fabrication of eNRR catalysts.