Shanghai Key Lab of Chemical Assessment and Sustainability, Department of Chemistry, Tongji University , Shanghai 200092, China.
J Am Chem Soc. 2015 Mar 11;137(9):3193-6. doi: 10.1021/jacs.5b00037. Epub 2015 Feb 25.
Chloride oxidation to chlorine is a potential alternative to water oxidation to oxygen as a solar fuels half-reaction. Ag(I) is potentially an oxidative catalyst but is inhibited by the high potentials for accessing the Ag(II/I) and Ag(III/II) couples. We report here that the complex ions AgCl2(-) and AgCl3(2-) form in concentrated Cl(-) solutions, avoiding AgCl precipitation and providing access to the higher oxidation states by delocalizing the oxidative charge over the Cl(-) ligands. Catalysis is homogeneous and occurs at high rates and low overpotentials (10 mV at the onset) with μM Ag(I). Catalysis is enhanced in D2O as solvent, with a significant H2O/D2O inverse kinetic isotope effect of 0.25. The results of computational studies suggest that Cl(-) oxidation occurs by 1e(-) oxidation of AgCl3(2-) to AgCl3(-) at a decreased potential, followed by Cl(-) coordination, presumably to form AgCl4(2-) as an intermediate. Adding a second Cl(-) results in "redox potential leveling", with further oxidation to {AgCl2(Cl2)}(-) followed by Cl2 release.
氯化物氧化为氯气是一种潜在的替代水氧化为氧气的太阳能燃料半反应。Ag(I) 可能是一种氧化催化剂，但由于 Ag(II/I) 和 Ag(III/II) 电对的高电势而受到抑制。我们在这里报告，AgCl2(-) 和 AgCl3(2-) 两种配合物离子在高浓度 Cl(-) 溶液中形成，避免了 AgCl 的沉淀，并通过将氧化电荷分散在 Cl(-)配体上来提供进入更高氧化态的通道。该反应是均相催化，具有高反应速率和低过电势（起始时为 10 mV），所需的 Ag(I) 浓度低至 μM。作为溶剂，D2O 增强了催化作用，具有显著的 H2O/D2O 反动力学同位素效应，为 0.25。计算研究的结果表明，Cl(-) 氧化通过 AgCl3(2-) 的 1e(-) 氧化以降低的电势发生，随后是 Cl(-) 的配位，可能形成 AgCl4(2-) 作为中间体。添加第二个 Cl(-) 会导致“氧化还原电势平衡”，进一步氧化为 {AgCl2(Cl2)}(-)，随后释放 Cl2。
