Department of Physics , University of Illinois , 1110 W Green Street , Urbana , Illinois 61801 , United States.
International Institute for Carbon Neutral Energy Research (WPI-I2CNER) , Kyushu University , 744 Moto-oka , Nishi-ku, Fukuoka 819-0395 , Japan.
Langmuir. 2018 Mar 6;34(9):2959-2966. doi: 10.1021/acs.langmuir.7b03948. Epub 2018 Feb 26.
Functionalization of semiconductor photoelectrodes is actively pursued as an approach to improve the efficiency of photoelectrochemical reactions by modulating the semiconductor's barrier height, but the selection of molecules for functionalization remains largely empirical. We propose a simple but effective design strategy for the organic functionalization of photocathodes for high-efficiency hydrogen generation based on first-principles density functional theory (DFT) calculations. The surface dipole of the functionalized photocathode determines its barrier height, which can be optimized to enhance charge separation at the semiconductor-electrolyte interface. Focusing on p-Si(111) photocathodes functionalized with different mixed aryl/methyl monolayers, we use DFT to systematically investigate the effect of - the presence and distribution of pi bonds, binding atom (the atom in the functional group that bonds with the Si surface), functional group length, and electrophilic substituent groups - on the surface dipole and charge rearrangement at the functionalized surface. We find that the most important factors affecting the surface dipole are the intrinsic molecular dipole moment of the organic moiety, the presence of electrophilic substituent groups, and the binding atom. Using these findings, a three-step design strategy is proposed for the experimental realization of high-performing functionalized p-Si(111) photocathodes by maximizing the surface dipole.
半导体光电电极的功能化是一种积极的方法，可以通过调节半导体的势垒高度来提高光电化学反应的效率，但功能化分子的选择在很大程度上仍然是经验性的。我们基于第一性原理密度泛函理论（DFT）计算，提出了一种用于高效制氢的光电阴极有机功能化的简单但有效的设计策略。功能化光电阴极的表面偶极决定了其势垒高度，可以通过优化来增强半导体-电解质界面的电荷分离。我们关注用不同混合芳基/甲基单层功能化的 p-Si（111）光电阴极，使用 DFT 系统地研究了 -π键的存在和分布、结合原子（与 Si 表面结合的官能团中的原子）、官能团长度和亲电取代基 - 对功能化表面的表面偶极和电荷重排的影响。我们发现，影响表面偶极的最重要因素是有机部分的固有分子偶极矩、亲电取代基的存在和结合原子。利用这些发现，提出了一个三步设计策略，通过最大化表面偶极来实现高性能功能化 p-Si（111）光电阴极的实验。
