The role of phase impurities and lattice defects on the electron dynamics and photochemistry of CuFeO2 solar photocathodes
The role of phase impurities and lattice defects on the electron dynamics and photochemistry of CuFeO2 solar photocathodes
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DOI：
10.1007/s12274-019-2493-6
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发表时间：
2019-08
期刊：
影响因子：
9.9
通讯作者：
E. Fugate;S. Biswas;Mathew C. Clement;Minkyu Kim;Dongjoon Kim;A. Asthagiri;L. R. Baker
中科院分区：
文献类型：
--
作者：
E. Fugate;S. Biswas;Mathew C. Clement;Minkyu Kim;Dongjoon Kim;A. Asthagiri;L. R. Baker
CuFeO2是一种很有前途的析氢和二氧化碳还原反应的光电阴极。为了更好地了解这种材料中复杂的缺陷化学和杂质相的作用以及它们对光化学性能的影响，我们用可见光暂态吸收光谱和密度泛函理论(DFT)计算方法研究了电化学沉积的CuFe氧化物薄膜的电子动力学。载流子寿命的动力学分析表明，对弛豫有快速的亚ps贡献，随后长寿命状态的持续时间延迟大于2 ns。长寿命态的幅度增加与快速初始弛豫速率相关，这可以用电荷载流子捕获和电荷分离之间的竞争来解释。CuFeO2中的电荷分离是通过从O2p到Cu3d价带态的空穴热化而发生的，导致电子和空穴在CuFeO2晶格中跨层分离。瞬时吸收测量和密度泛函理论计算之间的关联表明，铜空位通过促进电荷分离动力学来增强光化学性能。相反，预测O间隙改变了O2p和Cu3d价带态的相对位置，从而抑制了带间空穴热化导致的电荷分离。最后，我们没有发现从CuFeO2到CuO的电子注入的证据，这表明这种异质结构界面上的电荷分离不会对所研究的催化剂的载流子寿命或光化学性能产生影响。
CuFeO2is a promising photocathode for H2evolution and CO2reduction reactions. To better understand the complex defect chemistry and role of impurity phases in this material and their effect on the photochemical performance, we employ visible light transient absorption spectroscopy and density functional theory (DFT) calculations to investigate the electron dynamics in electrochemically deposited Cu-Fe oxide thin films. Kinetic analysis of carrier lifetime shows a fast, sub-ps contribution to relaxation followed by persistence of a long-lived state to time delays greater than 2 ns. Increasing amplitude of the long-lived state is shown to correlate with the rate of fast initial relaxation, and this is explained in terms of a competition between charge carrier trapping and charge separation. Charge separation in CuFeO2occurs via hole thermalization from O 2p to Cu 3d valence band states leading to segregation of electrons and holes across layers in the CuFeO2lattice. Correlation between transient absorption measurements and DFT calculations suggest that Cu vacancies enhance photochemical performance by facilitating charge separation kinetics. In contrast, O interstitials are predicted to switch the relative positions of O 2p and Cu 3d valence band states, which would inhibit charge separation by inter-band hole thermalization. Finally, we find no evidence for electron injection from CuFeO2to CuO suggesting that charge separation at this heterostructure interface does not play a role in the carrier lifetime or photochemical performance of the catalysts studied here.