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.