The surface stabilities of vanadium hydrides were studied by the first principles calculations. The surface phase diagram for a wide hydrogen partial pressure range was constructed based on the calculated formation energies. The results show that V2H is stable when \(- 33.5 \le \ln p_{{H_{2} }} \le - 13.8\) at 300 K (or \(- 20.1 \le \ln p_{{H_{2} }} \le - 1.6\) at 500 K). However, as the hydrogen partial pressure increases, V2H has a tendency to transform into VH. Among all the investigated surfaces of V2H, H-terminated (101) has the lowest surface energy, and the order of surface energies is (101)-H2 < (110) < (111) < (100) < (001). And V2H is the only stable vanadium hydride at 800 K. When the hydrogen partial pressure continues to increase beyond the above critical pressure, that is, \(- 13.8 \le \ln p_{{H_{2} }} \le - 7.6\) at 300 K or \(\ln p_{{H_{2} }} \ge - 1.6\) at 500 K, VH has higher stability than V2H. The surface energies of VH follow the sequence (111)-H < (110)-H < stoi-(111)-VH < (100)-H < (010)-H < (001)-H < (101) < (011). Under a high s ( \(\ln p_{{H_{2} }} \ge - {7}{\text{.6}}\) at 300 K), VH2 becomes a new stable phase. The stoi-(111)-VH of VH2 has the lowest surface energy, which is 1.10 J/m2. And VH2 is no longer a stable phase at 500 K. The energies of non-stoichiometric surfaces were determined in relation to hydrogen partial pressure and temperature. Additionally, the Gibbs-Wulff model was employed to predict the morphology evolution of vanadium hydrides.
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