Highly Enhanced Photoelectrochemical Water Oxidation Efficiency Based on Triadic Quantum Dot/Layered Double Hydroxide/BiVO₄ Photoanodes

The water oxidation half-reaction is considered to be a bottleneck for achieving highly efficient solar-driven water splitting due to its multiproton-coupled four-electron process and sluggish kinetics. Herein, a triadic photoanode consisting of dual-sized CdTe quantum dots (QDs), Co-based layered double hydroxide (LDH) nanosheets, and BiVO₄ particles, that is, QD@LDH@BiVO₄, was designed. Two sets of consecutive Type-II band alignments were constructed to improve photogenerated electron–hole separation in the triadic structure. The efficient charge separation resulted in a 2-fold enhancement of the photocurrent of the QD@LDH@BiVO₄ photoanode. A significantly enhanced oxidation efficiency reaching above 90% in the low bias region (i.e., <i>E</i> < 0.8 V vs RHE) could be critical in determining the overall performance of a complete photoelectrochemical cell. The faradaic efficiency for water oxidation was almost 90%. The conduction band energy of QDs is ∼1.0 V more negative than that of LDH, favorable for the electron injection to LDH and enabling a more efficient hole separation. The enhanced photon-to-current conversion efficiency and improved water oxidation efficiency of the triadic structure may result from the non-negligible contribution of hot electrons or holes generated in QDs. Such a band-matching and multidimensional triadic architecture could be a promising strategy for achieving high-efficiency photoanodes by sufficiently utilizing and maximizing the functionalities of QDs

Assembly of Ruthenium-Based Complex into Metal–Organic Framework with Tunable Area-Selected Luminescence and Enhanced Photon-to-Electron Conversion Efficiency

Host–guest photofunctional materials have received much attention recently due to their potential applications in light emitting diodes, polarized emission, and other optoelectronic fields. In this work, we report the encapsulation of a photoactive ruthenium-based complex (4,4′-diphosphonate-2,2′-bipyridine) into the biphenyl-based metal–organic framework (MOF) as a host–guest material toward potential photofunctional applications. The resulting material (denoted as Ru@MOF) presents different two-color blue/red luminescences at the crystal interior and exterior as detected by three-dimensional confocal fluorescence microscopy. Additionally, up-conversion emission and an enhanced photoluminescence lifetime relative to the pristine Ru-based complex can also be observed in this Ru@MOF system. Upon attaching on the rutile TiO₂ nanoarray, the Ru@MOF also exhibits alternated photoelectrochemical properties relative to the pristine complex. Moreover, a density functional theoretical calculation was performed on the Ru@MOF structure to provide understanding of the host–guest interactions. Based on the combination of experimental and theoretical studies on the Ru@MOF system, the aim of this work is to deeply investigate how the host–guest materials can present different photofunctionalities and optoelectronic properties compared with those of the individual components, and to give detailed information on the potential host–guest energy/electronic transfer between the MOF and the complex

Kinetic and Thermodynamic Insights into Advanced Energy Storage Mechanisms of Battery-Type Bimetallic Metal–Organic Frameworks

The engineering of high-performance battery-type electrode materials highly depends on the guidance from the combination of experimental analysis and theoretical simulation. Herein, the joint experimental–theoretical investigation provides a mechanistic explanation for the electrochemical performance enhancement in bimetallic metal–organic frameworks (MOFs). The superior CoNi-MOF in our study exhibits advanced electrochemical energy storage performance, achieving a high specific capacity of 382 C g–1 (1 A g–1), 2.0 and 1.4 times that of Co-MOF and Ni-MOF, respectively. Such a significant enhancement results from the surface-controlled reaction kinetics and the low onset potential contributed by the well-tuned electronic structures of bimetallic MOFs. Our study opens up new perspectives for understanding the advantages of mixed metal sites in MOFs for electrochemical energy storage