Asymmetric gradient orbital interaction of hetero-diatomic active sites for promoting C - C coupling.

Diatomic-site catalysts (DACs) garner tremendous attention for selective CO2 photoreduction, especially in the thermodynamical and kinetical mechanism of CO2 to C2+ products. Herein, we first engineer a novel Zn-porphyrin/RuCu-pincer complex DAC (ZnPor-RuCuDAC). The heteronuclear ZnPor-RuCuDAC exhibits the best acetate selectivity (95.1%), while the homoatomic counterparts (ZnPor-Ru2DAC and ZnPor-Cu2DAC) present the best CO selectivity. In-situ spectroscopic measurements reveal that the heteronuclear Ru-Cu sites easily appear C1 intermediate coupling. The in-depth analyses confirm that due to the strong gradient orbital coupling of Ru4d-Cu3d resonance, two formed *CO intermediates of Ru-Cu heteroatom show a significantly weaker electrostatic repulsion for an asymmetric charge distribution, which result from a side-to-side absorption and narrow dihedral angle distortion. Moreover, the strongly overlapped Ru/Cu-d and CO molecular orbitals split into bonding and antibonding orbitals easily, resulting in decreasing energy splitting levels of C1 intermediates. These results collectively augment the collision probability of the two *CO intermediates on heteronuclear DACs. This work first provides a crucial perspective on the symmetry-forbidden coupling mechanism of C1 intermediates on diatomic sites.

Titanium Vacancies in TiO2 Nanofibers Enable Highly Efficient Photodriven Seawater Splitting.

Invited for the cover of this issue are Xiao-Yu Yang and co-workers at Wuhan University of Technology, Heinrich-Heine-Universität Düsseldorf, University of the Witwatersrand, and Ben-Gurion University of the Negev. The image depicts Ti vacancies in TiO2 as powerful drivers of photo- and photo-electrocatalytic seawater splitting for hydrogen production. Read the full text of the article at 10.1002/chem.202101817.

Titanium Vacancies in TiO2 Nanofibers Enable Highly Efficient Photodriven Seawater Splitting.

Photodriven seawater splitting is considered to be one of the most promising techniques for sustainable hydrogen production. However, the high salinity of seawater would deactivate catalysts and consume the photogenerated carriers. Metal vacancies in metal oxide semiconductors are critical to directed electron transfer and high salinity resistance; they are thus desirable but remain a challenge. We demonstrate a facile controllable calcination approach to synthesize TiO2 nanofibers with rich Ti vacancies with excellent photo/electro performances and long-time stability in photodriven seawater splitting, including photocatalysis and photo-electrocatalysis. Experimental measurements and theoretical calculations reveal the formation of titanium vacancies, as well as unidirectional electron trap and superior H+ adsorption ability for efficient charge transfer and resistance to corrosion by seawater. Therefore, atomic-/nanoscale characteristics and mechanism have been proposed to clarify the generation of titanium vacancies and the corresponding interfacial electron transfer.

Discrete Heteropolynuclear Yb/Er Assemblies: Switching on Molecular Upconversion Under Mild Conditions.

The salts {[Ln2 Ln*(Hhmq)3 (OAc)3 (hfac)2 ]+ [Ln*(hfac)3 (OAc)(MeOH)]- } (Hhmq=2-methanolquinolin-8-oxide, hfac=hexafluoroacetylacetonate; Ln, Ln*=Er, Gd, Yb) feature a discrete heteronuclear cation consisting of two types of lanthanide atoms. The quinolinoxy O-atom serves as a µ2 -bridge to two Ln atoms and as a µ3 -bridge to all three atoms, with metal⋅⋅⋅metal distances being around 3.7 Å. For 1 ([Yb2 Er]+ ), near-infrared downshifted luminescence is switched to competitive upconversion luminescence upon irradiation by a 980 nm laser under an extremely low excitation power (0.288 W cm-2 ) through introduction of fluoride ions. The stability of 1 after addition of fluoride was confirmed by powder X-ray diffraction and multistage mass spectrometry, associated with the 1 H NMR of 6 ([La2 Eu]+ ). More importantly, the at least 20-fold enhancement of the quantum yield in non-deuterated solvents at room temperature under low power densities (2 W cm-2 ) is the highest among the few molecular examples reported.

Hierarchically Fractal PtPdCu Sponges and their Directed Mass- and Electron-Transfer Effects.

Fractal Pt-based materials with hierarchical structures and high self-similarity have attracted more and more attention due to their bioinspiring maximum optimization of energy utilization and mass transfer. However, their high-efficiency design of the mass- and electron-transfer still remains to be a great challenge. Herein, fractal PtPdCu hollow sponges (denoted as PtPdCu-HS) facilitating both directed mass- and electron-transfer are presented. Such directed transfer effects greatly promote electrocatalytic activity, regarded as 3.9 times the mass activity, 7.3 times the specific activity, higher poison tolerance, and higher stability than commercial Pt/C for the methanol oxidation reaction (MOR). A new "directed mass- and electron-transfer" concept, characteristics, and mechanism are proposed at the micro/nanoscale to clarify the structural design and functional enhancement of fractal electrocatalyst. This work displays new possibilities for designing novel nanomaterials with high activity and superior stability toward electrocatalysis or other practical applications.

Hg2+ Significantly Enhancing the Peroxidase-Like Activity of H2TCPP/ZnS/CoS Nanoperoxidases by Inducing the Formation of Surface-Cation Defects and Application for the Sensitive and Selective Detection of Hg2+ in the Environment.

Exploring excellent peroxidase mimics with enhanced peroxidase-like activity is important to the construction of a fast, low-cost, and convenient colorimetric sensing platform for heavy ions. In this work, 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (H2TCPP) was first used to modify ZnS/CoS and make it show better peroxidase-like activity. The metal-cation vacancies generated by Hg2+ contacting H2TCPP/ZnS/CoS further stimulate the catalytic activity. It is reported that the addition of Hg2+ usually causes a decrease of the peroxidase-like activity of metal sulfides. Oppositely, in our work, Hg2+ can trigger the colorimetric signal amplification because of lots of metal-cation vacancies generated on the surface of the nanocomposites (bimetallic sulfides). The peroxidase-like activity of ZnS/CoS was evaluated by virtue of the chromogenic substrate 3,3,5,5-tetramethylbenzidine (TMB) from colorless to blue in 3 min. The enhanced catalytic activity of H2TCPP/ZnS/CoS was attributed to lots of active sites from the metal-cation defects on the surface of H2TCPP/ZnS/CoS as well as the synergistic effect of porphyrin molecules and ZnS/CoS. The adsorption behavior of H2O2 on the H2TCPP/ZnS/CoS surface with defects was studied by density functional theory calculation. Thus, a colorimetric sensing platform based on Hg2+ trigger signal amplification has been successfully constructed, which can be used to sensitively and selectively determine Hg2+ in environmental samples.

Spatial Heterojunction in Nanostructured TiO2 and Its Cascade Effect for Efficient Photocatalysis.

A highly efficient photoenergy conversion is strongly dependent on the cumulative cascade efficiency of the photogenerated carriers. Spatial heterojunctions are critical to directed charge transfer and, thus, attractive but still a challenge. Here, a spatially ternary titanium-defected TiO2@carbon quantum dots@reduced graphene oxide (denoted as VTi@CQDs@rGO) in one system is shown to demonstrate a cascade effect of charges and significant performances regarding the photocurrent, the apparent quantum yield, and photocatalysis such as H2 production from water splitting and CO2 reduction. A key aspect in the construction is the technologically irrational junction of Ti-vacancies and nanocarbons for the spatially inside-out heterojunction. The new "spatial heterojunctions" concept, characteristics, mechanism, and extension are proposed at an atomic-/nanoscale to clarify the generation of rational heterojunctions as well as the cascade electron transfer.

Construction of Hierarchical Metal-Organic Frameworks by Competitive Coordination Strategy for Highly Efficient CO2 Conversion.

Hierarchical porosity and functionalization help to fully make use of metal-organic frameworks (MOFs) for their diverse applications. Herein, a simple strategy is reported to construct hierarchically porous MOFs through a competitive coordination method using tetrafluoroborate (M(BF4 )x , where M is metal site) as both functional sites and etching agents. The resulting MOFs have in situ formed defect-mesopores and functional sites without sacrificing their structure stability. The formation mechanism of the defect-mesopores is elucidated by a combination of experimental and first-principles calculation method, indicating the general feasibility of this new approach. Compared with the original microporous counterparts, the new hierarchical MOFs exhibit superior adsorption for the bulky dye molecules and catalytic performance for the CO2 conversion attributed to their specific hierarchical pore structures.

Synergetic Transparent Electrode Architecture for Efficient Non-Fullerene Flexible Organic Solar Cells with >12% Efficiency.

Flexible organic solar cells (OSCs) are considered one key component in wearable, intelligent electronics due to the unique capacity for highly flexible renewable energy sources. However, it is urgently required to enhance their efficiency, as it is far inferior to that of their conventional, glass-based counterparts. To boost the performance of flexible OSCs on plastic substrates, we here present a synergetic transparent electrode structure, which combines electrically conductive silver nanowires, a sol-gel-derived ZnO planarization layer, and imprinted light-trapping nanostructures. This synergetic composite electrode exhibits good properties in terms of optical transparency, electrical conductivity, mechanical flexibility, and low-temperature processability. As a result, the single-junction non-fullerene-based flexible OSCs achieve a power conversion efficiency exceeding 12% due to the synergetic interplay between broadband light trapping and suppressed charge recombination loss. Moreover, these flexible OSCs are repeatedly bendable in both inward and outward bending directions, retaining over 60% of the initial efficiency after 1000 cycles of the bending test at a 3.0 mm radius. These results convey a clear depiction of the practicality of flexible OSCs in a variety of high-performance flexible applications.

Homojunction of Oxygen and Titanium Vacancies and its Interfacial n-p Effect.

The homojunction of oxygen/metal vacancies and its interfacial n-p effect on the physiochemical properties are rarely reported. Interfacial n-p homojunctions of TiO2 are fabricated by directly decorating interfacial p-type titanium-defected TiO2 around n-type oxygen-defected TiO2 nanocrystals in amorphous-anatase homogeneous nanostructures. Experimental measurements and theoretical calculations on the cell lattice parameters show that the homojunction of oxygen and titanium vacancies changes the charge density of TiO2 ; a strong EPR signal caused by oxygen vacancies and an unreported strong titanium vacancies signal of 2D 1 H TQ-SQ MAS NMR are present. Amorphous-anatase TiO2 shows significant performance regarding the photogeneration current, photocatalysis, and energy storage, owing to interfacial n-type to p-type conductivity with high charge mobility and less structural confinement of amorphous clusters. A new "homojunction of oxygen and titanium vacancies" concept, characteristics, and mechanism are proposed at an atomic-/nanoscale to clarify the generation of oxygen vacancies and titanium vacancies as well as the interface electron transfer.

Polymer Solar Cells with 90% External Quantum Efficiency Featuring an Ideal Light- and Charge-Manipulation Layer.

Rapid progress in the power conversion efficiency (PCE) of polymer solar cells (PSEs) is beneficial from the factors that match the irradiated solar spectrum, maximize incident light absorption, and reduce photogenerated charge recombination. To optimize the device efficiency, a nanopatterned ZnO:Al2 O3 composite film is presented as an efficient light- and charge-manipulation layer (LCML). The Al2 O3 shells on the ZnO nanoparticles offer the passivation effect that allows optimal electron collection by suppressing charge-recombination loss. Both the increased refractive index and the patterned deterministic aperiodic nanostructure in the ZnO:Al2 O3 LCML cause broadband light harvesting. Highly efficient single-junction PSCs for different binary blends are obtained with a peak external quantum efficiency of up to 90%, showing certified PCEs of 9.69% and 13.03% for a fullerene blend of PTB7:PC71 BM and a nonfullerene blend, FTAZ:IDIC, respectively. Because of the substantial increase in efficiency, this method unlocks the full potential of the ZnO:Al2 O3 LCML toward future photovoltaic applications.

Assembly of a Highly Stable Luminescent Zn5 Cluster and Application to Bio-Imaging.

The assembly sequence of the coordination cluster [Zn5 (H2 L(n) )6 ](NO3 )4 ]⋅8 H2 O⋅2 CH3 OH (Zn5 , H3 L(n) =(1,2-bis(benzo[d]imidazol-2-yl)-ethenol) involves in situ dehydration of 1,2-bis(benzo[d]imidazol-2-yl)-1,2-ethanediol (H4 L) through the formation of the [Zn(H3 L)2 ](+) monomer, dimerization to [Zn2 (H3 L)2 ](+) , dehydration of the ligand to [Zn2 (H2 L(n) )2 ](+) , and the final formation of the pentanuclear cluster. The cluster has the following special characteristics: 1) high stability in both refluxing 37 % HCl and 27 % NH3 , 2) low cytotoxicity, and 3) pH-sensitive fluorescence in the visible-to-near-infrared (Vis/NIR) region in the solid state and in solution. We have applied it as a fluorescent probe both in vivo and in vitro. Its H-bonding ability is the key to its affinity and selectivity for imaging lysosomes in HeLa cells and tumors in male BALB/C mice. It provides a new type of sensitive and biocompatible fluorescent probe for detecting small tumors (13.5 mm(3) ).