Pathways Following Electron Injection: Medium Effects and Cross-Surface Electron Transfer in a Ruthenium-Based, Chromophore-Catalyst Assembly on TiO2
Pathways Following Electron Injection: Medium Effects and Cross-Surface Electron Transfer in a Ruthenium-Based, Chromophore-Catalyst Assembly on TiO2
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DOI：
10.1021/acs.jpcc.8b04837
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发表时间：
2018-06-21
影响因子：
3.7
通讯作者：
Meyer, Thomas J.
中科院分区：
文献类型：
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作者：
Brennaman, M. Kyle;Gish, Melissa K.;Meyer, Thomas J.
纳米晶 TiO2 电极上水氧化组装体 [((PO3H2)(2)bpy)(2)Ru-II(bpy-bimpy)Ru-II(tpy)-(OH2)](4+), -[Ru-a(II)-Ru-b(II)-OH2](4+) 光激发后的界面动力学，从 -已研究了-[Ru-a(II)-Ru-b(II)-OH2](4+) 或-[Ru-a(II)-Ru-b(III)-OH2](5+)。 TiO2-[Ru-a(II)-Ru-b(II)-OH2](4+) 在 0.1 M HPF6 或纯三氟乙醇中的瞬态吸收测量表明，电子注入效率很高，但在电化学时间尺度上发生的空穴向催化剂的转移受到局部环境影响的抑制。氧化发色团在微秒时间尺度上发生反向电子转移。一次氧化的组装体 TiO2-[Ru-a(II)-Ru-b(III)-OH2](5+) 在各种介质中的光激发生成 -[Ru-a(III)-Ru-b(III)-OH2](6+)。注入的电子随机迁移通过表面氧化物结构，将未反应的-[Ru-a(II)-Ru-b(III)-OH2](5+)组装体还原为-[Ru-a(II)-Ru-b(II)-OH2](4+)。在平行反应中，通过电子注入形成的-[Ru-a(III)-Ru-b(III)-OH2](6+)经历质子损失，得到-[Ru-a(II)-Ru-b(IV)=O](4+)，并可能通过电解质介导的反应转化为[Ru-a(II)-Ru-b(II)-OH2](4+)。在接下来的缓慢步骤中，通过与添加的 Fe-III/II 反应或通过空间分离的 -[Ru-a(II)-Ru-b(IV)=O](4+) 和 -[Ru-a(II)-Ru-b(II)-OH2](4+) 组件之间的跨表面电子转移发生表面重新平衡，得到 -[Ru-a(II)-Ru-b(III)-OH2](5+)，半衰期为t(1/2) 类似于 68 mu s。这些结果和分析表明，组装和跨表面反应的瞬态表面行为在用于水氧化的表面上产生和存储氧化还原当量方面发挥着重要作用。
Interfacial dynamics following photoexcitation of the water oxidation assembly [((PO3H2)(2)bpy)(2)Ru-II(bpy-bimpy)Ru-II(tpy)-(OH2)](4+), -[Ru-a(II)-Ru-b(II)-OH2](4+), on nanocrystalline TiO2 electrodes, starting from either - -[Ru-a(II)-Ru-b(II)-OH2](4+) or -[Ru-a(II)-Ru-b(III)-OH2](5+), have been investigated. Transient absorption measurements for TiO2-[Ru-a(II)-Ru-b(II)-OH2](4+) in 0.1 M HPF6 or neat trifluoroethanol reveal that electron injection occurs with high efficiency but that hole transfer to the catalyst, which occurs on the electrochemical time scale, is inhibited by local environmental effects. Back electron transfer occurs to the oxidized chromophore on the microsecond time scale. Photoexcitation of the once-oxidized assembly, TiO2-[Ru-a(II)-Ru-b(III)-OH2](5+), in a variety of media, generates -[Ru-a(III)-Ru-b(III)-OH2](6+). The injected electron randomly migrates through the surface oxide structure reducing an unreacted -[Ru-a(II)-Ru-b(III)-OH2](5+) assembly to -[Ru-a(II)-Ru-b(II)-OH2](4+). In a parallel reaction, -[Ru-a(III)-Ru-b(III)-OH2](6+) formed by electron injection undergoes proton loss giving -[Ru-a(II)-Ru-b(IV)=O](4+) with possible conversion to [Ru-a(II)-Ru-b(II)-OH2](4+) by an electrolyte-mediated reaction. In the following slow step, re-equilibration on the surface occurs either by reaction with added Fe-III/II or by cross-surface electron transfer between spatially separated -[Ru-a(II)-Ru-b(IV)=O](4+) and -[Ru-a(II)-Ru-b(II)-OH2](4+) assemblies to give -[Ru-a(II)-Ru-b(III)-OH2](5+) with a half-time of t(1/2) similar to 68 mu s. These results and analyses show that the transient surface behavior of the assembly and cross-surface reactions play important roles in producing and storing redox equivalents on the surface that are used for water oxidation.