Okada Takuya, Abe Hikaru, Murakami Ai, Shimizu Tomohito, Fujii Kenta, Wakabayashi Toru, Nakayama Masaharu
Department of Applied Chemistry, Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611, Japan.
Nakabohtec Corrosion Protecting Co., Ltd, Ageo 362-0052, Japan.
Langmuir. 2020 May 19;36(19):5227-5235. doi: 10.1021/acs.langmuir.0c00547. Epub 2020 May 8.
A fluorine-doped tin oxide-coated glass electrode modified with a bilayer film of underlying α-Co(OH) and overlying Mg-intercalated and Co-doped δ-type (layered) MnO (Mg|Co-MnO) preferentially yielded oxygen with a Faradaic efficiency as high as 79% in the presence of chloride ions at high concentration (0.5 M). This noble metal-free electrode was fabricated by cathodic electrolysis of aqueous Co(NO) followed by anodic electrolysis of a mixture of Mn, Co, and cetyltrimethylammonium (CTA) ions in water. The CTA ions accommodated in the interlayer spaces of Co-doped δ-MnO were replaced with Mg by ion exchange. The upper Mg|Co-MnO could effectively block the permeation of Cl ions and allow only HO and O, while the under α-Co(OH) acted as an oxidation catalyst for the HO penetrated through the upper coating. Thus, the oxygen evolution reaction (OER) was preferred to the chlorine evolution reaction (CER). In artificial seawater (pH 8.3), the blocking effect against Cl decreased because of ion exchange of the intercalated Mg ions with Na in solution, but the OER efficiency still remained at 57%, much higher than that (28%) without the upper Mg|Co-MnO. This demonstrates that the interlayer spaces between MnO layers acted as pathways for HO molecules to reach the active sites of the underlying Co(OH). Density functional theory (DFT) calculations revealed that the most stable structure of hydrated Mg ion, in which a part of coordinated HO molecules is hydrolyzed, has less affinity toward Cl ion than that of hydrated Na ion.
一种氟掺杂氧化锡涂层玻璃电极，其修饰有由下层的α-Co(OH)和上层的镁插层且钴掺杂的δ型（层状）MnO（Mg|Co-MnO）组成的双层膜，在高浓度（0.5 M）氯离子存在的情况下，优先产生氧气，法拉第效率高达79%。这种无贵金属电极是通过对Co(NO)水溶液进行阴极电解，然后对水中的锰、钴和十六烷基三甲基铵（CTA）离子混合物进行阳极电解制备的。通过离子交换，掺杂钴的δ-MnO层间空间中容纳的CTA离子被镁取代。上层的Mg|Co-MnO可以有效地阻止Cl离子的渗透，只允许HO和O通过，而底层的α-Co(OH)则作为穿透上层涂层的HO的氧化催化剂。因此，析氧反应（OER）优先于析氯反应（CER）。在人工海水（pH 8.3）中，由于插层镁离子与溶液中的钠离子发生离子交换，对Cl的阻挡作用降低，但OER效率仍保持在57%，远高于没有上层Mg|Co-MnO时的效率（28%）。这表明MnO层之间的层间空间充当了HO分子到达底层Co(OH)活性位点的通道。密度泛函理论（DFT）计算表明，水合镁离子最稳定的结构（其中一部分配位的HO分子发生水解）对Cl离子的亲和力比水合钠离子小。
