The combination of n-type TiO2 and p-type BiOCl photooxidizing water and photoreducing the formed O2 back to water, respectively, in acidic solution enabled a sustainable photofuel cell utilizing natural light.

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CO2 photoconversion is a promising method to reduce atmospheric CO2 concentrations and mitigate energy problems simultaneously. Among the various efficient and stable semiconductor photocatalysts used for this purpose, layered double hydroxides (LDHs) have attracted attention as catalysts for CO2 photoconversion into CO and/or methanol. In this study, various LDHs of the formula [MII3GaIII(OH)8]2A⋅m H2O (MII=ZnII, CuII; A2−=CO32−, [Cu(OH)4]2−) were synthesized and used for CO2 photoconversion at a reaction pressure of 0.40 MPa in the presence of H2 to result in the exclusive production of methanol. Furthermore, the pretreatment of carbonate‐type LDHs at 423 K boosted the reaction rates by a factor of 7.5–20. Interestingly, [Zn3Ga(OH)8]2CO3⋅m H2O was the only LDH that produced methane primarily by an eight‐electron reduction (rather than the production of methanol by a six‐electron reduction) at a total formation rate of 2.7 μmol h−1 gcat−1 after it was preheated at 423 K and protected by an Ar atmosphere. Conversely, the methanol photogeneration rates of tetrahydroxycuprate‐type LDHs were suppressed to less than 0.1 μmol h−1 gcat−1 at 0.40 MPa. In summary, the contribution of the interlayer reaction space created by the partial removal of water molecules and/or carbonate ions of LDHs was suggested.

-We reported a new PhotoFuel Cell (PFC) comprising two photocatalysts for use of acidic water as a recyclable medium. Nitrogen and oxygen flow was required in the photoanode and photocathode, respectively. In this study, we developed a gas-circulating PFC that needs no gas supply from outside. In the gas-circulating PFC, the reverse reaction of water oxidation at the anode was prevented by the gas flow of photogenerated O 2 from the anode to the cathode inside the PFC. The gas-circulating PFC accommodated an organic solvent layer over the aqueous electrolyte for the anode, and also a vent hole in the upper part of the Proton-Conducting Polymer (PCP) film. O 2 transferred from the anode electrolyte to the organic solvent due to the solubility difference between the HCl solution and organic solvent. O 2 transfer from the gas phase in the anode to that in the cathode was achieved by the vent hole in the PCP film due to the pressure difference due to the progress of the reaction. By the addition of a hexane layer to the anode of the PFC, it was demonstrated to achieve a photocurrent value of 69.7 lA per 1.3 cm 2 of photocatalysts. However, in the stability tests for more than 7 h, the small amount of remaining O 2 in the electrolyte (2.85 lmol L À1 ) exhibited serious effects on the PFC performance. The I SC , V OC and P Max values of the gas-circulating PFC were 29.2 lA, 1.18 V and 6.10 lW, that were 40%, 74% and 44%, respectively, of those for a N 2 and O 2 flow-type PFC. Apparently, photocurrents were dramatically suppressed by the reverse reaction at the photoanode in the extended tests for the gas-circulating PFC.

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Excellent CO2 conversion: The cover image demonstrates a photocatalytic reactor with a thin film of layered double hydroxide (LDH) inside it. The reaction gas pressure was 0.40 MPa and CO2 reduction was tested using H2 and an LDH photocatalyst comprising zinc, gallium, and/or copper. In view of the application, H2 is sustainably formed from water. This study enables a carbon‐neutral cycle to convert CO2 into fuels (methanol and/or methane) avoiding the net increase in atmospheric CO2 concentrations associated with fossil‐derived alternatives. If the LDH catalysts were used after the exposure to air, the CO2 was photoconverted into methanol. In contrast, if the catalysts were preheated at 423 K and protected in argon gas, methane (using LDH comprising Zn and Ga) and methanol (using LDH comprising Zn, Cu, and Ga) were produced up to the formation rate of 2.7 μmol h−1 gcat−1. More details are found in the Full Paper by Masaya Miyano and colleagues at Chiba University on page 892 in Issue 2, 2017 (DOI: 10.1002/ente.201600578).