Calcium manganese oxide films were prepared by cosputter deposition from Mn and CaMnO₃ targets and evaluated for their suitability as catalysts for the oxygen evolution reaction (OER). Scanning electron microscopy (SEM) revealed a compact morphology for the as-deposited films and the formation of nanorodlike features on the surfaces after annealing at 600 °C. X-ray-photoelectron-spectroscopy analysis showed that the surface oxidation state is close to +III (as in Mn₂O₃) for the as-deposited films and increases slightly to a mixture of III and IV after annealing occurs in dry air at 400–600 °C. Glancing-incidence X-ray diffraction (GIXRD) suggested that the CaMn_xO_y films are amorphous even when heated to 600 °C. However, transmission electron microscopy (TEM) showed that there is actually a polycrystalline component of the film, which best matches Mn₃O₄ (hausmannite with the average Mn oxidation state of ∼+2.7) but may have a slightly expanded unit cell because of the incorporation of Ca. Electrochemical analyses revealed that the as-deposited CaMn_xO_y films were OER-inactive. In contrast, annealing at 400 or 600 °C resulted in an increase of ∼15-fold in the current densities, which reached j ≅ 1.5 mA·cm^–2 at OER overpotentials of η ≈ 550 mV in cyclic voltammetry (CV) sweeps. For the same η, annealed CaMn_xO_y electrodes also showed good electrochemical stabilities during 2 h of electrolysis, as rather constant steady-state current densities of j ≅ 0.4–0.5 mA·cm^–2 were observed. The thicknesses and surface morphologies of the CaMn_xO_y films did not change during the electrochemical measurements, indicating that corrosion was negligible. In comparison with a previous study in which Ca-free thin layers of MnO_x were evaluated, the results demonstrate that Ca²⁺ incorporation can enhance the OER activity of MnO_x electrocatalysts prepared by sputter deposition. This work provides guidance for designing new electrodes for water oxidation on the basis of the abundant and nontoxic elements manganese and calcium.

中文翻译：

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共溅射钙氧化锰电极用于水氧化

通过共溅射从Mn和CaMnO ₃靶材制备钙锰氧化物膜，并评估其作为氧释放反应（OER）催化剂的适用性。扫描电子显微镜（SEM）揭示了沉积态薄膜的致密形态，并在600°C退火后在表面上形成了纳米棒状特征。X射线光电子能谱分析表明，沉积态薄膜的表面氧化态接近+ III（在Mn ₂ O _3中），并在干燥空气中于110℃退火后略微增加至III和IV的混合物。 400–600°C。掠入射X射线衍射（GIXRD）表明CaMn _x O _y即使加热到600°C，薄膜也是无定形的。然而，透射电子显微镜（TEM）显示，薄膜中实际上存在多晶成分，与Mn ₃ O ₄最佳匹配（菱锰矿的平均Mn氧化态为+2.7），但由于Ca的掺入。电化学分析表明，所沉积的CaMn _x O _y膜不具有OER活性。在电流密度，达到与此相反，退火在400或600℃下导致增加的〜15倍Ĵ ≅1.5毫安·厘米^-2在η的OER超电势≈550毫伏在循环伏安法（CV）扫描。对于相同的η，退火的CaMn _x O_ÿ电解的2小时期间电极也表现出良好的电化学稳定性，作为相当恒定的稳态电流密度Ĵ ≅0.4-0.5毫安·厘米^-2观察。CaMn _x O _y膜的厚度和表面形貌在电化学测量过程中没有变化，表明腐蚀可以忽略不计。与以前的评估MnO _x的无钙薄层的研究相比，结果表明掺入Ca ²⁺可以增强MnO _x的OER活性。通过溅射沉积制备的电催化剂。这项工作为基于锰和钙的丰富且无毒的元素设计用于水氧化的新电极提供了指导。