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Solar-light-driven photosynthesis of hydrogen peroxide (H2O2) from dioxygen (O2) and water (H2O) is a sustainable process. Metal–organic frameworks (MOFs) are promising candidates for the photosynthesis of H2O2 because of their unlimited design flexibility. However, MOF-driven H2O2 production from O2 and H2O remains a challenge because MOF photocatalysts need to exhibit high structural stability in aqueous reaction systems while suppressing H2O2 decomposition. In addition, the efficiency of H2O2 production in pure water has suffered from low O2 solubility in aqueous solution and difficult-to-inhibit side reactions. In the present study, we demonstrate that hydrophobic Zr-based MOF (Zr-MOF) nanosheets modified with perfluoroalkyl carboxylates substantially accelerate the photocatalytic production of H2O2 from O2 and H2O under visible-light (λ > 420 nm) irradiation without any additives. Perfluoroalkyl-functionalization improves the hydrophobicity of the MOF, leading to suppression of H2O2 decomposition on Zr–oxo clusters. The high hydrophobicity enhances the enrichment of O2 on the photocatalyst surface and the selectivity of two-electron oxidation of H2O to generate H2O2, which promotes photocatalytic H2O2 synthesis. The length of the perfluoroalkyl chain plays a critical role in the enhancement of photocatalytic H2O2 production, and optimization of the chain length led to a 7.2-fold increase in activity compared with that of the pristine hydrophilic Zr-MOF. This study provides a noble design strategy for achieving highly selective photocatalytic H2O2 production via O2 reduction and H2O oxidation. [ABSTRACT FROM AUTHOR]

Active, stable Pd species were incorporated within the matrix of fluorite-based high-entropy oxide (HEO) (YZrLaGdHf)xO2 using an entropy-driven strategy based on a liquid-phase reaction. In situ X-ray absorption fine structure analyses and transmission electron microscopy observations at elevated temperatures under H2 confirmed that partially aggregated Pd oxide species in the as-synthesized Pd@(YZrLaGdHf)xO2 were transformed into an entropy-stabilized isolated form at 600 °C. In contrast, Pd species on the (YZrLaGdHf)xO2 surface were readily reduced with the formation of nanoclusters/nanoparticles even in the temperature range of 100 to 200 °C. This Pd@(YZrLaGdHf)xO2 exhibited enhanced activity during the hydrogenation of CO2 to formic acid with a maximum turnover number of 5000 based on the quantity of surface-exposed Pd atoms. This performance was more than eight times higher than that of the Pd/(YZrLaGdHf)xO2 on the basis of supported Pd. An assessment of the kinetics and theoretical investigations suggested that entropy-stabilized isolated Pd species facilitated both H2 dissociation and the attack of dissociated H atoms on C atoms in HCO3– ions. [ABSTRACT FROM AUTHOR]

Localized surface plasmon resonances (LSPR) in near-infrared (NIR) region have been extensively studied for copper chalcogenide nanostructures, not only for the absorption enhancement but also tunable LSPR characteristics with their free carrier concentrations or defects. In the present work, one-step cation exchange method has been used to synthesize Cu2−xS nanowires with x varied between 0 and 1, including Cu2S, Cu7S4 and CuS and so forth. The plasmonic band of Cu2−xS nanowires shifts to a shorter wavelength with the increase in x, as observed in vis-NIR spectra, which is attributed to the increase in density of copper vacancies. The Cu2−xS nanowires have been used as catalysts towards the photocatalytic generation of H2 from ammonia borane (AB). Among samples with different Cu-S compositions, Cu7S4 samples exhibited the highest activity in terms of H2 evolution rate (25.54 mmol/g h). Moreover, a marked enhancement of the H2 evolution rate (157.04 mmol/g h) could be achieved after decorating the Cu2−xS nanowires with Pd nanoparticles to form the hybrid structures. The results of the present investigation may lead to an effective strategy for the design and development of LSPR materials for photocatalytic applications.

Hydrogen spillover, the simultaneous diffusion of protons (H+) and electrons (e−) is considered to be applicable to ubiquitous technologies related to hydrogen but limited to over reducible metal oxides. The present work demonstrates that a non-reducible MgO with heteroatom Al dopants (Al–MgO) allows hydrogen spillover in the same way as reducible metal oxides. Furthermore, a H+ storage capacity of this material owing to hydrogen spillover is more than three times greater than those of various standard metal oxides based on H+ transport channels within its bulk region. Atomic hydrogen diffuses over the non-reducible Al–MgO produces active H+-e− pairs, as also occurs on reducible metal oxides, to enhance the catalytic performance of Ni during CO2 hydrogenation. The H+ and e− diffusion pathways generated by the heteroatom Al doping are disentangled based on systematic characterizations and calculations. This work provides a new strategy for designing functional materials intended to hydrogen spillover for diverse applications in a future hydrogen-based society. Hydrogen spillover is typically associated with reducible metal oxides and considered relevant for various hydrogen-related technologies. Here, the authors demonstrate that a non-reducible MgO doped with heteroatom Al enables hydrogen spillover similarly to reducible metal oxides. [ABSTRACT FROM AUTHOR]