The exact understanding for each promotional role of cation and anion vacancies in bifunctional water splitting activity will assist in the development of an efficient activation strategy of inert catalysts. Herein, systematic first-principles computations demonstrate that the synergy of anion-oxygen and cation-manganese vacancies (V O and V Mn ) in manganese dioxide (MnO 2 ) nanosheets results in abnormal local lattice distortion and electronic modulation. Such alterations enrich the accessible active centers, increase conductivity, enhance the water dissociation step, and favor intermediate adsorption-desorption, consequently promoting HER and OER kinetics. As proof of concept, robust electrocatalysts, MnO 2 ultrathin nanosheets doped with dual vacancies (DV-MnO 2 ) are obtained via a maturely chemical strategy. Detailed characterizations confirm the cation vacancies-V Mn contribute to enhanced conductivity and anion vacancies-V O enrich the active centers with optimized local electronic configurations, consistent with the simulative predictions. As expected, DV-MnO 2 exhibits exceptional bifunctionality with the strong assistance of synergetic dual vacancies which act as abundant "hot spots" for active multiple intermediates. Leading to a lower cell voltage (1.55 V) in alkali electrolyte is required to reach 10 mA cm −2 for the overall water splitting system. These atomic-level insights on synergetic DV can favor the development of activating strategy from inert electrocatalysts.

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because solar energy is freely available and hydrogen fuel is clean with high gravimetric energy density. For practical applications, it is very important to develop a low-cost water-splitting photocatalyst with an ≈10% solar-to-hydrogen energy conversion. [4] Nearly half of the energy in the sunlight that reaches Earth's surface comes from visible light photons (400-700 nm); therefore, it is important to develop a visible light active photocatalyst for efficient solar-to-fuel conversion. [5] Most of the research on photocatalysts has focused on wide bandgap semiconductors, such as TiO 2 , [6][7][8] SrTiO 3 , [9,10] and carbon nitride (CN). [11][12][13] Some of these photocatalysts have achieved very good operation stabilities that surpass 1000 h, along with more than 50% maximum external quantum efficiency for watersplitting reactions. [14][15][16] However, the wide and difficult-to-tune bandgaps of such photocatalysts restrict light absorption to only the ultraviolet (UV) region and thus fundamentally limit the practical applications for solar light harvesting to fuel. [16,17] Therefore, novel photocatalyst semiconductor materials with narrower bandgaps that can absorb a greater proportion of solar spectrum are needed to achieve the maximum theoretical solar energy conversion efficiency for practical applications.The ligand-to-metal charge transfer (LMCT) facilitated activation of TiO 2 has noteworthy potential for solar energy harvesting. However, the fast back electron transfer from TiO 2 to an oxidized sensitizer is a key limiting factor causing low photocatalyst efficiency. Herein, a new catalyst design to both increase LMCT efficiency and minimize the back electron transfer is presented. A phase-selective modification of mixed-phase TiO 2 (anatase: rutile interface) with poly-salophen organic polymer is developed. The salophen and salen family organic monomers are selectively bound and polymerized on the anatase phase but not the rutile phase, which results in the formation of a three-phase system. Such a three-phase system converts an unfavorable polymer TiO 2 core-shell structure to an intimately mixed blend morphology, consisting of interfaced crystalline rutile TiO 2 and an amorphous polymer-covered anatase-phase TiO 2 . The developed mixed-blend morphology poly-S@P25 can produce H 2 of 37 410 µmol h -1 g -1 of polymer, which is ≈3.4 times higher than core-shell poly-S@anatase TiO 2 . This approach overcomes the drawback of the traditional core-shell structured system for efficient electron harvesting from the LMCT process.

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Commercial rutile TiO2 particles (200–300 nm) were modified by the temperature-regulated chemical vapor deposition (tr-CVD) of Fe-oxide and subsequent annealing at various temperatures (300~750 °C). As a result of the modification, the photocatalytic activity of the TiO2 regarding acetaldehyde removal under visible light was enhanced, and the enhancement effects were dependent on the annealing temperature. Specifically, the enhancement effects of the modification were most pronounced when Fe-TiO2 was annealed at 375 °C, whereas the effects were significantly reduced by annealing at higher temperatures (525 and 750 °C). The analytical results with various techniques, including two surface-sensitive methods (XPS (X-ray photoelectron spectroscopy) and TOF-SIMS (time of fight-secondary ion mass spectrometry)), revealed that the stronger metal support interaction between TiO2 and the loaded Fe-oxide at high temperature (>375 °C) resulted in the decreased charge separation efficiency and photocatalytic activity of the Fe-TiO2 under light irradiation. The production scale for the Fe-TiO2 photocatalysts can be easily increased (from 200 g to 8 kg per the unit process) by upsizing the reactor volume. The mass-produced samples exhibited similar activity to the samples produced at small scale, and they were photocatalytically active after being spread on a cement block (stainless steel plate) using a surface hardening agent (paint), showing the high applicability in real applications.

Titanium oxide (TiO2) nanostructures, the most widely used photocatalysts, are known to suffer from poisoning of the active sites during photocatalytic decomposition of volatile organic compounds. Partially oxidized organic compounds with low volatility stick to the catalyst surface, limiting the practical application for air purification. In this work, we studied the UV-driven photocatalytic activity of bare TiO2 toward toluene decomposition under various conditions and found that surface deactivation is pronounced either under dry conditions or humid conditions with a very high toluene concentration (~442 ppm). In contrast, when the humidity was relatively high (~34 %RH) and toluene concentration was low (~66 ppm), such deactivation was not significant. We then modified TiO2 surfaces by deposition of polydimethylsiloxane and subsequent annealing, which yielded a more hydrophilic surface. We provide experimental evidence that our hydrophilic TiO2 does not show deactivation under the conditions that induce significant deactivation with bare TiO2. Conversion of toluene into dimethylacetamide was observed on the hydrophilic TiO2 and did not result in poisoning of active sites. Our hydrophilic TiO2 shows high potential for application in air purification for extended time, which is not possible using bare TiO2 due to the significant poisoning of active sites.

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