Selim Shababa, Francàs Laia, García-Tecedor Miguel, Corby Sacha, Blackman Chris, Gimenez Sixto, Durrant James R, Kafizas Andreas
Imperial College London , Department of Chemistry , South Kensington , London , SW7 2AZ , UK . Email:
Institute of Advanced Materials (INAM) , Universitat Jaume I , 12006 , Castelló de la Plana , Spain.
Chem Sci. 2019 Jan 16;10(9):2643-2652. doi: 10.1039/c8sc04679d. eCollection 2019 Mar 7.
The four hole oxidation of water has long been considered the kinetic bottleneck for overall solar-driven water splitting, and thus requires the formation of long-lived photogenerated holes to overcome this kinetic barrier. However, photogenerated charges are prone to recombination unless they can be spatially separated. This can be achieved by coupling materials with staggered conduction and valence band positions, providing a thermodynamic driving force for charge separation. This has most aptly been demonstrated in the WO/BiVO junction, in which quantum efficiencies for the water oxidation reaction can approach near unity. However, the charge carrier dynamics in this system remain elusive over timescales relevant to water oxidation (μs-s). In this work, the effect of charge separation on carrier lifetime, and the voltage dependence of this process, is probed using transient absorption spectroscopy and transient photocurrent measurements, revealing sub-μs electron transfer from BiVO to WO. The interface formed between BiVO and WO is shown to overcome the "dead-layer effect" encountered in BiVO alone. Moreover, our study sheds light on the role of the WO/BiVO junction in enhancing the efficiency of the water oxidation reaction, where charge separation across the WO/BiVO junction improves both the yield and lifetime of holes present in the BiVO layer over timescales relevant to water oxidation.
长期以来，水的四价态氧化一直被认为是整个太阳能驱动水分解的动力学瓶颈，因此需要形成长寿命的光生空穴来克服这一动力学障碍。然而，光生电荷容易发生复合，除非它们能够在空间上分离。这可以通过将具有交错导带和价带位置的材料耦合来实现，从而为电荷分离提供热力学驱动力。这一点在WO/BiVO结中得到了最恰当的证明，其中水氧化反应的量子效率可以接近100%。然而，在与水氧化相关的时间尺度（微秒至秒）上，该系统中的载流子动力学仍然难以捉摸。在这项工作中，利用瞬态吸收光谱和瞬态光电流测量，研究了电荷分离对载流子寿命的影响以及该过程的电压依赖性，揭示了从BiVO到WO的亚微秒级电子转移。结果表明，BiVO和WO之间形成的界面克服了单独使用BiVO时遇到的“死层效应”。此外，我们的研究揭示了WO/BiVO结对提高水氧化反应效率的作用，即在与水氧化相关的时间尺度上，通过WO/BiVO结的电荷分离提高了BiVO层中空穴的产率和寿命。
