Johnson Samantha I, Blakemore James D, Brunschwig Bruce S, Lewis Nathan S, Gray Harry B, Goddard William A, Persson Petter
Materials Research Center, California Institute of Technology, Pasadena, CA 91125, USA.
Phys Chem Chem Phys. 2021 Apr 28;23(16):9921-9929. doi: 10.1039/d1cp00545f.
The attachment of the 2,2'-bipyridine (bpy) moieties to the surface of planar silicon(111) (photo)electrodes was investigated using ab initio simulations performed on a new cluster model for methyl-terminated silicon. Density functional theory (B3LYP) with implicit solvation techniques indicated that adventitious chlorine atoms, when present in the organic linker backbone, led to instability at very negative potentials of the surface-modified electrode. In prior experimental work, chlorine atoms were present as a trace surface impurity due to required surface processing chemistry, and thus could plausibly result in the observed surface instability of the linker. Free energy calculations for the Cl-atom release process with model silyl-linker constructs revealed a modest barrier (14.9 kcal mol-1) that decreased as the electrode potential became more negative. A small library of new bpy-derived structures has additionally been explored computationally to identify strategies that could minimize chlorine-induced linker instability. Structures with fluorine substituents are predicted to be more stable than their chlorine analogues, whereas fully non-halogenated structures are predicted to exhibit the highest stability. The behavior of a hydrogen-evolving molecular catalyst CpRh(bpy) (Cp = pentamethylcyclopentadienyl) immobilized on a silicon(111) cluster was explored theoretically to evaluate differences between the homogeneous and surface-attached behavior of this species in a tautomerization reaction observed under reductive conditions for catalytic H2 evolution. The calculated free energy difference between the tautomers is small, hence the results suggest that use of reductively stable linkers can enable robust attachment of catalysts while maintaining chemical behavior on the electrode similar to that exhibited in homogeneous solution.
利用对甲基封端硅的新簇模型进行的从头算模拟，研究了2,2'-联吡啶（bpy）部分与平面硅（111）（光）电极表面的附着情况。采用隐式溶剂化技术的密度泛函理论（B3LYP）表明，当有机连接体主链中存在外来氯原子时，会导致表面改性电极在非常负的电位下不稳定。在先前的实验工作中，由于所需的表面处理化学过程，氯原子作为痕量表面杂质存在，因此可能导致观察到的连接体表面不稳定性。用模型硅烷基连接体构建体对Cl原子释放过程进行的自由能计算表明，存在一个适度的势垒（14.9 kcal mol-1），该势垒随着电极电位变得更负而降低。此外，还通过计算探索了一个新的bpy衍生结构的小文库，以确定可以最小化氯诱导的连接体不稳定性的策略。预测具有氟取代基的结构比其氯类似物更稳定，而完全无卤化的结构预计表现出最高的稳定性。从理论上探索了固定在硅（111）簇上的析氢分子催化剂CpRh（bpy）（Cp = 五甲基环戊二烯基）的行为，以评估该物种在催化析氢的还原条件下观察到的互变异构反应中的均相和表面附着行为之间的差异。互变异构体之间计算出的自由能差很小，因此结果表明，使用还原稳定的连接体可以实现催化剂的牢固附着，同时在电极上保持与均相溶液中相似的化学行为。
