Ultrathin Amorphous Silica Membrane Enhances Proton Transfer across Solid‐to‐Solid Interfaces of Stacked Metal Oxide Nanolayers while Blocking Oxygen

Abstract

A large jump of proton transfer rates across solid‐to‐solid interfaces by inserting an ultrathin amorphous silica layer into stacked metal oxide nanolayers is discovered using electrochemical impedance spectroscopy and Fourier‐transform infrared reflection absorption spectroscopy (FT‐IRRAS). The triple stacked nanolayers of Co3O4, SiO2, and TiO2 prepared by atomic layer deposition (ALD) enable a proton flux of 2400 ± 60 s−1 nm−2 (pH 4, room temperature), while a single TiO2 (5 nm) layer exhibits a threefold lower flux of 830 s−1 nm−2. Based on FT‐IRRAS measurements, this remarkable enhancement is proposed to originate from the sandwiched silica layer forming interfacial SiOTi and SiOCo linkages to TiO2 and Co3O4 nanolayers, respectively, with the O bridges providing fast H+ hopping pathways across the solid‐to‐solid interfaces. Together with the complete O2 impermeability of a 2 nm ALD‐grown SiO2 layer, the high flux for proton transport across multi‐stack metal oxide layers opens up the integration of incompatible catalytic environments to form functional nanoscale assemblies such as artificial photosystems for CO2 reduction by H2O.

Structure and Orientation of Molecular Wires Embedded in Ultrathin Silica Membrane for Artificial Photosynthesis Elucidated by Polarized FT-IRRAS

“…2, and infrared evidence for the complete removal of residual organic Si precursor ligands shown in Figure 2(a) of a previous publication. 8 Figure 7 (2) and (3)) as described in detail in a previous report 8 and reproduced for convenience as Figure S3 in this paper. The 21 transverse (TO) SiOSi mode gives rise to shoulders in the 1150-1050 cm -1 region, 8 but is strongly overlapped here by SiOCo stretch modes of the Si(-O-Co) 3 anchor moiety of the wire with maximum at 1139 cm -1 and shoulders at 1107 and 1050 cm -1 (Figure 7(a), trace (1)).…”

“…8 Figure 7 (2) and (3)) as described in detail in a previous report 8 and reproduced for convenience as Figure S3 in this paper. The 21 transverse (TO) SiOSi mode gives rise to shoulders in the 1150-1050 cm -1 region, 8 but is strongly overlapped here by SiOCo stretch modes of the Si(-O-Co) 3 anchor moiety of the wire with maximum at 1139 cm -1 and shoulders at 1107 and 1050 cm -1 (Figure 7(a), trace (1)). Comparison of the intensity of the 1235 cm -1 silica band for 20 cycle and 40 cycle layers shows that the silica absorbance grows linearly with numbers of ALD cycles, providing a convenient measure of the relative amounts of silica deposited.…”

“…7 Proton conductivity across the 2 nm silica membrane was quantified by electrochemical impedance spectroscopy and found to exceed the flux needed under maximum solar intensity by three orders of magnitude, and cyclic voltammetry confirmed that the silica nanolayer completely blocks O 2 from crossing the membrane. 8 While visible light driven electrochemical and transient optical monitoring of charge transport demonstrates that a substantial fraction of embedded wire molecules span the silica nanolayer so as to function as charge conduits, [3][4][5][6] experimental information on the orientation of anchored wires is lacking. Here, we report an infrared spectroscopic study of wire molecules anchored on planar Co 3 O 4 and embedded in ultrathin silica layers by polarized Fourier transform-infrared reflection-absorption spectroscopy (FT-IRRAS) and non-polarized grazing angle attenuated total reflection Fourier transform-infrared spectroscopy (GATR FT-IR).…”

Controlling and Optimizing Photoinduced Charge Transfer across Ultrathin Silica Separation Membrane with Embedded Molecular Wires for Artificial Photosynthesis

“…Hence, the flow of protons generated by H 2 O oxidation on the Co 3 O 4 surface through the oxide nanowall to the sites of CO 2 reduction on the opposite side does not pose efficiency limitations under artificial photosynthesis conditions. 18 While motivated by the specific Co 3 O 4 -SiO 2 core-shell nanotube system described above, maximizing controlled charge transfer through embedded molecular wires for driving a catalyst on the opposite side of an ultrathin silica separation membrane may open up the efficient coupling of incompatible redox catalysis environments of systems of various designs. The task requires optimization of the coupling and energetic alignment of light absorber, wire, and catalyst.…”

High Surface Area VOx/TiO2/SBA-15 Model Catalysts for Ammonia SCR Prepared by Atomic Layer Deposition

“…Compared to these conventional synthesis techniques, atomic layer deposition (ALD) enables accurate control at the atomic scale without damaging the structure of the original matrix [9,[14][15][16]. Although ALD has been widely applied to metal-oxide deposition, such as SiO 2 [17][18][19], TiO 2 [20][21][22][23][24], and VO x [9,[25][26][27][28][29], there are only very few studies on the deposition of vanadia and titania on mesoporous SBA-15 [30], and its application to NH 3 -SCR [29].…”