The present work focuses on the anodic dissolution mechanism of molybdenum and the quantification of oxygen evolution as a possible side reaction. Molybdenum dissolution was studied in sodium nitrate solution under acidic (pH 1) and alkaline (pH 12) conditions at high current densities, which is typical for the industrial electrochemical machining process (ECM). The anodic oxygen evolution was evidenced by using the fluorescence quenching technique. The oxygen efficiency amounts to ≈1% at pH 12 and ≈7% at pH 1. These and considering previous results, lead to the assumption that a part of molybdenum does not dissolve as Mo⁶⁺. This agrees with oxidation of dissolved ions in a subsequently coupled amperometric cell at pH 12. The evolution of oxygen as well as supplementary material diagnostics clearly shows the (trans-)passive dissolution of molybdenum via the formation and dissolution of molybdenum oxide films under acidic as well as under alkaline conditions in sodium nitrate solutions. Considering all data, the authors conclude that the average valency is slightly lower than z = 5.5 at pH 1 and z = 5.9 at pH 12. The assumption of the partial dissolution of lower valent molybdenum ions is supported by the observation of a blue coloring of the remaining electrolyte on the sample surface after the experiments.

目前的工作重点是钼的阳极溶解机制和析氧作为可能的副反应的量化。在酸性 (pH 1) 和碱性 (pH 12) 条件下，在高电流密度下研究了硝酸钠溶液中的钼溶解，这是工业电化学加工过程 (ECM) 的典型特征。通过使用荧光猝灭技术证明了阳极析氧。氧气效率在 pH 12 时约为 1%，在 pH 1 时约为 7%。这些以及考虑到先前的结果，导致假设一部分钼不溶解为 Mo ⁶⁺. 这与随后在 pH 12 下耦合的安培计电池中溶解离子的氧化一致。氧气的释放以及补充材料诊断清楚地表明，通过在酸性条件下氧化钼膜的形成和溶解，钼的（跨）被动溶解，如以及在硝酸钠溶液中的碱性条件下。考虑到所有数据，作者得出结论，平均价数在 pH 1 时略低于 z = 5.5，在 pH 12 时 z = 5.9。低价钼离子部分溶解的假设得到了观察到的蓝色实验后样品表面剩余的电解液。