Mutually-dependent kinetics and energetics of photocatalyst/co-catalyst/two-redox liquid junctions
Mutually-dependent kinetics and energetics of photocatalyst/co-catalyst/two-redox liquid junctions
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DOI：
10.1039/c9ee02910a
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发表时间：
2020-01-01
影响因子：
32.5
通讯作者：
Hu, Shu
中科院分区：
文献类型：
--
作者：
Pan, Zhenhua;Yanagi, Rito;Hu, Shu
近年来，光催化颗粒裂解水因其大规模生产可再生氢-2的潜力而受到广泛关注。然而，光催化剂/助催化剂/水界面上的能量学与其界面电荷转移动力学之间的相关性仍然难以捉摸，特别是当能量学沿着液结界面在空间上变化时。首先，我们推导了光催化剂颗粒与两氧化还原电位H+/H-2和O-2/H2O接触的动力学模型，即半导体/两氧化还原液体结。我们采用了单氧化还原液体结的详细平衡原理，并将该原理扩展到含有多个氧化还原电位的局部不平衡电解质，这是光催化剂的典型条件。为了验证该模型，我们建立了一个表征框架，通过光电极模拟光催化剂的操作。开路条件模拟操作光催化剂表面；用欧姆背触点探测的（准）费米能级表示电荷分离效率。定量数据拟合进一步验证了双氧化还原动力学模型。这些表征将局部能量学与多电子电荷转移动力学联系起来，显示出由h -2和o- 2气体混合物组成和助催化剂选择性控制的可调分支比。与传统的光电极/电解质界面不同，用Pt共催化剂修饰的SrTiO3模型颗粒具有具有指定还原和氧化位点的空间变化能量的液结界面。结果表明，对于光催化剂，局部动力学控制的能量在单个粒子的光催化剂/助催化剂/水界面上发生空间变化，并敏感地影响电荷分离效率。在al掺杂SrTiO3和Ta3N5两种实际光催化体系中，证实了局部动力学和空间变化动力学之间的相互依赖行为。本研究举例说明了开发高效光催化剂的设计原则。
Water-splitting by photocatalyst particles has attracted much attention recently for its potential to produce renewable H-2 at scale. However, the correlation between the energetics at photocatalyst/co-catalyst/water interfaces and their interfacial charge-transfer kinetics is still elusive, especially when the energetics are expected to vary spatially along the liquid-junction interface. First, we derived a kinetic model for photocatalyst particles in contact with two-redox potentials, H+/H-2 and O-2/H2O, i.e., a semiconductor/two-redox liquid junction. We adopted the principle of detailed balance proven for one-redox liquid junctions and extended this principle to a locally out-of-equilibrium electrolyte containing multiple redox potentials, the condition typical for photocatalysts. To validate the model, we established a characterization framework to simulate photocatalyst operation by using photoelectrodes. The open-circuit conditions mimicked operating photocatalyst surfaces; and the (quasi-) Fermi levels, probed by ohmic back contacts, indicated charge-separation efficiency. Quantitative data fitting further validated the two-redox kinetic model. These characterizations correlated local energetics with multi-electron charge-transfer kinetics, which exhibit tuneable branching ratios controlled by H-2-and-O-2 gas-mixture compositions and co-catalyst selectivity. Unlike the conventional photoelectrode/electrolyte interfaces, SrTiO3 model particles decorated with Pt co-catalysts were found to bear liquid-junction interfaces of spatially varying energetics with designated reductive and oxidative sites. It is shown that, uniquely for photocatalysts, the local kinetic-controlled energetics vary spatially across photocatalyst/co-catalyst/water interfaces of individual particles, and affect charge-separation efficiency sensitively. The mutually dependent behaviour between local kinetics and spatially varying energetics were confirmed for two practical photocatalytic systems, Al-doped SrTiO3 and Ta3N5. This study exemplified and elucidated the design principles for developing efficient photocatalysts.