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 H2O and/or O-2. The role of H2O is controversial. Herein, we propose a hydroxide ion (OH-)-initiated degradation mechanism for LBP to elucidate the role of H2O. We found that LBP degraded faster in alkaline solutions than in neutral or acidic solutions with or without O-2. 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-pi layer to protect LBP from degradation. This work reveals the degradation mechanism of LBP and thus facilitates the development of effective stabilization technologies.