In the present work the authors show that anodic TiO2 nanotubes (NT) show excellent harvesting properties for Pt single atoms (Pt SAs) from highly dilute Pt solutions. The tube walls of anodic nanotubes, after adequate annealing to anatase, provide ample of suitable trapping sites—that is, surface Ti3+‐Ov (Ov: oxygen vacancy) defects that are highly effective to extract and accumulate Pt in the form of SAs. A saturated (maximized) SA density can be achieved by an overnight immersion of a TiO2 NT layer to a H2PtCl6 solution with a concentration that is as low as 0.01 mm Pt. Such TiO2 NTs with surface trapped Pt SAs provide a maximized high activity for photocatalytic H2 generation (reaching a turnover frequency (TOF) of 1.24 × 106 h−1 at a density of 1.4 × 105 Pt atoms µm−2)—a higher loading with Pt nanoparticles does not further increase the photocatalytic activity. Overall, these findings show that anodic TiO2 nanotubes provide a remarkable substrate for Pt extraction and recovery from very dilute solutions that directly results in a highly efficient photocatalyst, fabricated by a simple immersion technique.

Summary Here, we evaluate three different noble metal co-catalysts (Pd, Pt, and Au) that are present as single atoms (SAs) on the classic benchmark photocatalyst, TiO 2 . To trap the single atoms on the surface, we introduced controlled surface vacancies (Ti 3+ -O v ) on anatase TiO 2 nanosheets by a thermal reduction treatment. After anchoring identical loadings of single atoms of Pd, Pt, and Au, we measure the photocatalytic H 2 generation rate and compare it to the classic nanoparticle co-catalysts on the nanosheets. While nanoparticles yield the well-established the hydrogen evolution reaction activity sequence (Pt > Pd > Au), for the single atom form, Pd radically outperforms Pt and Au. Based on density functional theory (DFT), we ascribe this unusual photocatalytic co-catalyst sequence to the nature of the charge localization on the noble metal SAs embedded in the TiO 2 surface.

In order to induce greater light absorption, nano-patterning is often applied to the metal-oxide buffer layer in inverted bulk-heterojunction(BHJ) solar cells. However, current homogeneity was significantly disturbed at the interface, leading to an efficiency that was not fully optimized. In this work, an additional PC 61 BM layer was inserted between the ZnO ripple and the photoactive layer to enhance the electron extraction. The insertion of additional PC 61 BM layer provided substantial advantages in the operation of inverted BHJ solar cells; specifically, it enhanced current homogeneity and lowered accumulation and trapping of photogenerated charges at the ZnO interface. Inclusion of the additional PC 61 BM layer led to effective quenching of electron-hole recombination by a reduction in the number of accumulated charges at the surface of ZnO ripples. This resulted in a 16% increase in the efficiency of inverted BHJ solar cells to 7.7%, compared to solar cells without the additional PC 61 BM layer.B ulk heterojunction (BHJ) solar cells based on blends of conjugated polymers and soluble fullerene derivatives have generated strong interest in the field of renewable energy because of the potential they offer to lower manufacturing costs for large area, lightweight devices 1-3 . Since the first BHJ solar cell was reported in 1995 4,5 , the power conversion efficiency (PCE) of BHJ solar cells has gradually improved due to the development of new materials and device architectures, recently reaching over 9% in single junction device [6][7][8] .The inverted device architecture in particular has gained considerable attention in the research community because of its better device stability and advantages in processing over the conventional architecture 9-14 . In the inverted structure, since the polarity of charge collection is the opposite of that in the conventional architecture; the selection of an effective electron extraction/transportation buffer layer, which can effectively build-up the symmetry breaking, is the key component for high performance inverted solar cells 15,16 . Such an electron extraction/transportation buffer layer must be highly transparent, electrically conductive, and energetically wellmatched to the lowest unoccupied molecular orbital (LUMO) level of the acceptor.In order to induce greater light absorption in the photoactive layer, nano-patterning is often applied to the metal-oxide buffer layer, which functions as the electron extraction/transportation layer. Not only on metal-oxide buffer layer, plasticizer assistied soft embossing (PASE) structure have been applied on PEDOT5PSS hole extracting layer to improve solar cell performance 17 . For P3HT5PCBM solar cells based on PASE structured PEDOT5PSS layers the averaged overall power efficiency is improved by up to 18%. Many demonstrations of successful PCE enhancement through improved charge extraction and light absorption due to light scattered by the imprinted patterns have been reported to-date [18][19][20][21] . However, in most cases, t...

In the present work we investigate various optical properties (such as light absorption and reflectance) of anodic TiO 2 nanotubes layers directly transferred as self-standing membranes onto quartz substrates. This allows investigation in a transmission geometry which provides significantly more reliable data than measurements on the metallic Ti substrate. Light transmission and reflectance measurements were carried out for layers of thicknesses varying from 1.8 to 50 µm, and the layers were investigated in their amorphous and crystalline form. A series of wavelength-dependent light attenuation coefficients are extrapolated and found to match the photocurrent vs. irradiation wavelength behavior. However, a feature specific to anodic nanotubes is that their intrinsic carbon content causes a sub-bandgap response that is proportional to the carbon contamination content in the TiO 2 nanotubes. Overall the extracted data provide valuable basis and understanding for the design of photo-electrochemical devices based on TiO 2 nanotubes.

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