Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, United States.
Department of Chemistry, Rutgers University, Newark, New Jersey 07102, United States.
ACS Appl Mater Interfaces. 2021 May 26;13(20):23532-23546. doi: 10.1021/acsami.1c00735. Epub 2021 May 13.
Ultrathin amorphous silica membranes with embedded organic molecular wires (oligo(-phenylenevinylene), three aryl units) provide chemical separation of incompatible catalytic environments of CO reduction and HO oxidation while maintaining electronic and protonic coupling between them. For an efficient nanoscale artificial photosystem, important performance criteria are high rate and directionality of charge flow. Here, the visible-light-induced charge flow from an anchored Ru bipyridyl light absorber across the silica nanomembrane to CoO water oxidation catalyst is quantitatively evaluated by photocurrent measurements. Charge transfer rates increase linearly with wire density, with 5 nm identified as an optimal target. Accurate measurement of wire and light absorber densities is accomplished by the polarized FT-IRRAS method. Guided by density functional theory (DFT) calculations, four wire derivatives featuring electron-donating (methoxy) and -withdrawing groups (sulfonate, perfluorophenyl) with highest occupied molecular orbital (HOMO) potentials ranging from 1.48 to 0.64 V vs NHE were synthesized and photocurrents evaluated. Charge transfer rates increase sharply with increasing driving force for hole transfer from the excited light absorber to the embedded wire, followed by a decrease as the HOMO potential of the wire moves beyond the CoO valence band level toward more negative values, pointing to an optimal wire HOMO potential around 1.3 V vs NHE. Comparison with photocurrents of samples without nanomembrane indicates that silica layers with optimized wires are able to approach undiminished electron flux at typical solar intensities. Combined with the established high proton conductivity and small-molecule blocking property, the charge transfer measurements demonstrate that oxidation and reduction catalysis can be efficiently integrated on the nanoscale under separation by an ultrathin silica membrane.
具有嵌入式有机分子线（寡聚（苯乙烯基），三个芳基单元）的超薄非晶态二氧化硅膜为 CO 还原和 HO 氧化的不相容催化环境提供了化学分离，同时保持它们之间的电子和质子偶联。对于高效的纳米级人工光合作用系统，重要的性能标准是电荷流动的高速率和方向性。在这里，通过光电流测量定量评估了固定化 Ru 联吡啶光吸收体通过二氧化硅纳米膜到 CoO 水氧化催化剂的可见光诱导电荷流动。电荷转移速率随导线密度线性增加，5nm 被确定为最佳目标。通过偏振 FT-IRRAS 方法准确测量导线和光吸收体的密度。在密度泛函理论（DFT）计算的指导下，合成了具有供电子（甲氧基）和吸电子基团（磺酸盐，全氟苯基）的四个分子线衍生物，最高占据分子轨道（HOMO）势从 1.48V 至 0.64V vs NHE，评估了光电流。电荷转移速率随激发光吸收体到嵌入导线的空穴转移驱动力的增加而急剧增加，随后由于导线的 HOMO 势超过 CoO 价带水平向更负的值移动而减小，表明导线 HOMO 势约为 1.3V vs NHE 时达到最佳。与没有纳米膜的样品的光电流比较表明，具有优化导线的二氧化硅层能够在典型的太阳强度下接近未衰减的电子通量。结合已建立的高质子传导率和小分子阻挡性能，电荷转移测量表明，在超薄二氧化硅膜的分离下，可以有效地在纳米尺度上集成氧化和还原催化。
