Nickel oxyhydroxide (NiOOH)-based anodes are among the most promising materials for the electrocatalytic production of oxygen from water under alkaline conditions. We explore the stability of the low-index facets of the catalytically active β-NiOOH phase, namely the (0001), {101̅N} surfaces, and the as yet unexplored {112̅N} surfaces, via density functional theory with a Hubbard-U like correction on Ni. We find that their relative stabilities depend strongly on the coordination number of the exposed Ni (cn_Ni) and O (cn_Ni). In the vacuum, where passivation of the surface dangling bonds is limited, the stability order is as follows: (0001) > {101̅N} ≫ {112̅N}, noting that the coordination numbers for each phase are, respectively, cn_Ni = 6, 5, and 4, and cn_O = 3–4, 2–3, and 2–3. In aqueous media, the order of stability is (0001) > {101̅N} ≈ {112̅N}, as the cn_Ni and cn_O of the latter two surface types increase due to water coordination and dissociation. Water adsorption is found to be most favorable on the {112̅N} surfaces, giving rise to fivefold-coordinated Ni (Ni^5c) or Ni^6c from Ni^4c. Our work suggests that a plethora of facets are likely to coexist on β-NiOOH crystallites with water serving to equalize the stabilities of the different surfaces.

中文翻译：

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水环境对β-NiOOH表面稳定性和化学性质的影响

羟基氧化镍（NiOOH）基阳极是在碱性条件下从水中电催化生产氧气的最有前途的材料之一。我们探讨该催化活性的β-NiOOH相，即（0001），{101的低指数晶面的稳定性Ñ }表面，并且尚未未开发{112 Ñ }表面，通过密度与Hubbard-密度泛函理论U喜欢对Ni进行校正。我们发现它们的相对稳定性在很大程度上取决于暴露的Ni（cn _Ni）和O（cn _Ni）的配位数。在真空，其中表面悬空键的钝化是有限的，稳定性顺序如下：（0001）> {101 ñ }»{112 Ñ}，请注意，每个阶段的协调数分别为cn _Ni = 6、5和4，cn _O = 3-4、2-3和2-3。在水性介质中，稳定性的顺序是（0001）> {101 ñ }≈{112 Ñ }，作为CN_的Ni和cn _ö后两者表面类型的增加，由于水的协调和离解。水吸附被发现是在{112上最有利的Ñ }面，从而产生了五倍配位的Ni（镍^5C）或Ni ^6C选自Ni ^4c中。我们的工作表明，β-NiOOH微晶可能与水共存过多面，以平衡不同表面的稳定性。