Boron doping induced charge transfer switching of a C3N4/ZnO photocatalyst from Z-scheme to type II to enhance photocatalytic hydrogen production
Boron doping induced charge transfer switching of a C3N4/ZnO photocatalyst from Z-scheme to type II to enhance photocatalytic hydrogen production
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DOI：
10.1016/j.apcatb.2020.119538
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发表时间：
2021-03-01
影响因子：
22.1
通讯作者：
Yong, Kijung
中科院分区：
文献类型：
--
作者：
Kim, Donghyung;Yong, Kijung
异质结光催化剂由于其在光驱动电荷产生和分离方面的高效率而在太阳能制氢方面具有很大的应用前景。C3 N4/ZnO异质结构纳米复合材料从UV和可见光区域收集广泛的太阳光，并且由于其Z-方案能带结构而保持高的氧化还原电位。然而，由于C3 N4和ZnO都具有足够高的导带能量来驱动氢光还原，因此II型异质结更有利于提高当前系统中的制氢效率。在这项研究中，我们首先证明了电荷转移机制切换从Z-方案的II型简单的硼（B）掺杂的C3 N4/ZnO。用低电负性硼掺杂C3 N4使其费米能级增加0.4 V，使其甚至高于ZnO。结果表明，B掺杂的C3 N4与ZnO的费米能级对准导致C3 N4/ZnO结处的能带弯曲方向相反。通过UPS和ESR分析证实了所产生的电荷转移从Z-方案（C3 N4/ZnO）切换到II型（B-掺杂的C3 N4/ZnO）。II型B掺杂的C3 N4/ZnO的光催化析氢速率稳定、急剧增加，比未掺杂的C3 N4/ZnO高出约2.9倍。B掺杂的C3 N4/ZnO的带隙能量的降低也有助于通过增强的光捕获而额外提高效率。我们的工作提出了一个简单而有效的策略，设计高性能的异质结光催化剂，通过电荷转移开关与掺杂的方法。
Heterojunction photocatalysts are very promising for solar hydrogen production due to their high efficiency in photo-driven charge generation and separation. A C3N4/ZnO heterostructure nanocomposite harvests a wide range of solar light from the UV and visible regions and retains a high redox potential due to its Z-scheme band structure. However, since both C3N4 and ZnO have sufficiently high conduction band energies to drive hydrogen photoreduction, a type II heterojunction is more beneficial for enhancing the hydrogen production efficiency in the current system. In this study, we first demonstrated the charge transfer mechanism switching from the Z-scheme to type II by simple boron (B) doping of C3N4/ZnO. The doping of C3N4 with low-electronegativity boron increases its Fermi level by 0.4 V, making it even higher than that of ZnO. As a result, the Fermi level alignment of B-doped C3N4 with ZnO causes a reversed band bending direction at the C3N4/ZnO junction. The resultant charge transfer switching from the Z-scheme (C3N4/ZnO) to type II (B-doped C3N4/ZnO) was confirmed by UPS and ESR analysis. Type II B-doped C3N4/ZnO shows a stable, drastic increase in the photocatalytic hydrogen evolution rate, approximately 2.9 times higher than that of undoped C3N4/ZnO. The decreased bandgap energy of B-doped C3N4/ZnO also contributes to an additional improvement in efficiency through enhanced light harvesting. Our work presents a simple but effective strategy to design highly capable heterojunction photocatalysts via charge transfer switching with a doping method.