Electron Accumulation Induces Efficiency Bottleneck for Hydrogen Production in Carbon Nitride Photocatalysts
Electron Accumulation Induces Efficiency Bottleneck for Hydrogen Production in Carbon Nitride Photocatalysts
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DOI：
10.1021/jacs.9b04556
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发表时间：
2019-07-17
影响因子：
15
通讯作者：
Durrant, James R.
中科院分区：
文献类型：
--
作者：
Yang, Wenxing;Godin, Robert;Durrant, James R.
本研究解决了光强度的光催化剂悬浮液中的电荷积累的依赖性，其电荷复合动力学和稳态H-2的进化效率的影响。氰酰胺表面功能化的瓜型氮化碳（（CNx）-C-NCN）由于其优异的电荷储存能力而被选为新兴的氮化碳光催化剂的实例。瞬态光谱研究（ps到s）表明，（CNx）-C-NCN中光生电子和空穴的双分子复合可以用随机游走模型很好地描述。值得注意的是，空穴清除剂如4-甲基苄醇的添加可以导致类似于快400倍的复合动力学（寿命缩短至类似于10 ps）。我们表明，这种加速是不是超快空穴提取的清道夫的直接结果，而是由长寿命的电子积累（CNx）-C-NCN空穴提取后引起的。色散的伪一级复合动力学变得由累积电子的密度控制。H-2的产生和稳态光谱测量表明，电子积累引起的加速复合限制了H-2的产生效率。添加可逆电子受体和介体甲基紫精（MV 2+）加速了从（CNx）-C-NCN提取电子，并且在一个太阳照射下将H-2产生效率提高了30%以上。这些结果定量地表明，虽然长寿命的电子对于在许多光催化剂中驱动光诱导的H-2产生是必不可少的，但是过度的电子积累可能导致加速的复合损失和较低的性能，并且因此突出了有效的电子和空穴提取在实现有效的水裂解光催化剂中的重要性。
This study addresses the light intensity dependence of charge accumulation in a photocatalyst suspension, and its impact on both charge recombination kinetics and steady-state H-2 evolution efficiency. Cyanamide surface functionalized melon-type carbon nitride ((CNx)-C-NCN) has been selected as an example of emerging carbon nitrides photocatalysts because of its excellent charge storage ability. Transient spectroscopic studies (from ps to s) show that the bimolecular recombination of photogenerated electrons and holes in (CNx)-C-NCN can be well described by a random walk model. Remarkably, the addition of hole scavengers such as 4-methylbenzyl alcohol can lead to similar to 400-fold faster recombination kinetics (lifetime shortening to similar to 10 ps). We show that this acceleration is not the direct result of ultrafast hole extraction by the scavenger, but is rather caused by long-lived electron accumulation in (CNx)-C-NCN after hole extraction. The dispersive pseudo-first order recombination kinetics become controlled by the density of accumulated electrons. H-2 production and steady-state spectroscopic measurements indicate that the accelerated recombination caused by electron accumulation limits the H-2 generation efficiency. The addition of a reversible electron acceptor and mediator, methyl viologen (MV2+), accelerates the extraction of electrons from the (CNx)-C-NCN and increases the H-2 production efficiency under one sun irradiation by more than 30%. These results demonstrate quantitatively that while long-lived electrons are essential to drive photoinduced H-2 generation in many photocatalysts, excessive electron accumulation may result in accelerated recombination losses and lower performance, and thus highlight the importance of efficient electron and hole extraction in enabling efficient water splitting photocatalysts.