Aqueous Kilogram-Scale Electrosynthesis of Reagent-Grade Cystine Enabled by Asymmetric N, P-Coordinated Ni Single Atoms.

The scalable and selective oxidative coupling of organothiols to disulfides remains a challenge in sustainable chemical manufacturing, as conventional routes rely on stoichiometric chemical oxidants and generate substantial waste. Here, we report a simple, "green" aqueous electrosynthesis route for the kilogram-scale production of reagent-grade cystine, featured by the electrooxidation of cysteine (CysER) in a membrane-free single-cell electrolyzer with 1 M KCl electrolyte. This electrosynthesis efficiency is mainly enabled by an asymmetric N,P-dual-coordinated Ni single-atom electrocatalyst (Ni-N3P/C), which lowers the onset potential for CysER, suppresses the competing oxygen evolution reaction, and accelerates the CysER reaction kinetics. The electrolysis at industrially relevant currents of even 10 A yields over one kilogram of cystine with >99% purity without complicated separation and purification procedures, owing to the cystine product spontaneously precipitating due to its low water solubility. Techno-economic analysis estimates a ∼70% reduction in production cost compared to the conventional chemical route. This work establishes a practical and scalable electrocatalytic strategy for the green synthesis of high-value disulfides based on an asymmetric single-atom electrocatalyst.