pH-Dependent Degradation of Layered Black Phosphorus: Essential Role of Hydroxide Ions

The practical application of layered black phosphorus (LBP) is compromised by fast decomposition in the presence of H₂ O and/or O₂ . The role of H₂ O is controversial. Herein, we propose a hydroxide ion (OH^- )-initiated degradation mechanism for LBP to elucidate the role of H₂ O. We found that LBP degraded faster in alkaline solutions than in neutral or acidic solutions with or without O₂ . Degradation rates of LBP increased linearly from pH 4 to 10. Density functional theory (DFT) calculations showed that OH^- initiated the decomposition of LBP through breaking the P-P bond and forming a P-O bond. The detection of hypophosphite, generated from OH^- reacting with P atoms, confirmed the hypothesis. Protons acted in a way distinctive from OH^- , by inducing deposition/aggregation or forming a cation-π layer to protect LBP from degradation. This work reveals the degradation mechanism of LBP and thus facilitates the development of effective stabilization technologies.