Chae Hyun Uk, Ahsan Ragib, Lin Qingfeng, Sarkar Debarghya, Rezaeifar Fatemeh, Cronin Stephen B, Kapadia Rehan
Department of Electrical and Computer Engineering , University of Southern California , Los Angeles , California 90089 , United States.
Nano Lett. 2019 Sep 11;19(9):6227-6234. doi: 10.1021/acs.nanolett.9b02289. Epub 2019 Aug 30.
Using hot electrons to drive electrochemical reactions has drawn considerable interest in driving high-barrier reactions and enabling efficient solar to fuel conversion. However, the conversion efficiency from hot electrons to electrochemical products is typically low due to high hot electron scattering rates. Here, it is shown that the hydrogen evolution reaction (HER) in an acidic solution can be efficiently modulated by hot electrons injected into a thin gold film by an Au-AlO-Si metal-insulator-semiconductor (MIS) junction. Despite the large scattering rates in gold, it is shown that the hot electron driven HER can reach quantum efficiencies as high as ∼85% with a shift in the onset of hydrogen evolution by ∼0.6 V. By simultaneously measuring the currents from the solution, gold, and silicon terminals during the experiments, we find that the HER rate can be decomposed into three components: (i) thermal electron, corresponding to the thermal electron distribution in gold; (ii) hot electron, corresponding to electrons injected from silicon into gold which drive the HER before fully thermalizing; and (iii) silicon direct injection, corresponding to electrons injected from Si into gold that drive the HER before electron-electron scattering occurs. Through a series of control experiments, we eliminate the possibility of the observed HER rate modulation coming from lateral resistivity of the thin gold film, pinholes in the gold, oxidation of the MIS device, and measurement circuit artifacts. Next, we theoretically evaluate the feasibility of hot electron injection modifying the available supply of electrons. Considering electron-electron and electron-phonon scattering, we track how hot electrons injected at different energies interact with the gold-solution interface as they scatter and thermalize. The simulator is first used to reproduce other published experimental pump-probe hot electron measurements, and then simulate the experimental conditions used here. These simulations predict that hot electron injection first increases the supply of electrons to the gold-solution interface at higher energies by several orders of magnitude and causes a peaked electron interaction with the gold-solution interface at the electron injection energy. The first prediction corresponds to the observed hot electron electrochemical current, while the second prediction corresponds to the observed silicon direct injection current. These results indicate that MIS devices offer a versatile platform for hot electron sources that can efficiently drive electrochemical reactions.
利用热电子驱动电化学反应在推动高势垒反应以及实现高效太阳能到燃料的转化方面引起了广泛关注。然而，由于热电子散射速率较高，热电子到电化学产物的转化效率通常较低。在此，研究表明，通过由金 - 氧化铝 - 硅金属 - 绝缘体 - 半导体（MIS）结注入到薄金膜中的热电子，可以有效地调节酸性溶液中的析氢反应（HER）。尽管金中的散射速率很大，但研究表明，热电子驱动的析氢反应能够达到高达约85%的量子效率，析氢起始电位发生约0.6 V的偏移。通过在实验过程中同时测量来自溶液、金和硅电极的电流，我们发现析氢反应速率可以分解为三个分量：（i）热电子，对应于金中的热电子分布；（ii）热电子，对应于从硅注入到金中在完全热化之前驱动析氢反应的电子；（iii）硅直接注入，对应于在电子 - 电子散射发生之前从硅注入到金中驱动析氢反应的电子。通过一系列对照实验，我们排除了观察到的析氢反应速率调制来自薄金膜的横向电阻率、金中的针孔、MIS器件的氧化以及测量电路假象的可能性。接下来，我们从理论上评估热电子注入改变可用电子供应的可行性。考虑电子 - 电子和电子 - 声子散射，我们追踪不同能量注入的热电子在散射和热化过程中如何与金 - 溶液界面相互作用。该模拟器首先用于重现其他已发表的实验泵浦 - 探测热电子测量结果，然后模拟此处使用的实验条件。这些模拟预测，热电子注入首先在更高能量下将电子供应到金 - 溶液界面的数量增加几个数量级，并在电子注入能量处导致与金 - 溶液界面的电子相互作用出现峰值。第一个预测对应于观察到的热电化学电流，而第二个预测对应于观察到的硅直接注入电流。这些结果表明，MIS器件为能够有效驱动电化学反应的热电子源提供了一个通用平台。
