High-Rate and Selective C2H6-to-C2H4 Photodehydrogenation Enabled by Partially Oxidized Pdδ+ Species Anchored on ZnO Nanosheets under Mild Conditions.

Photocatalytic C2H6-to-C2H4 conversion is very promising, yet it remains a long-lasting challenge due to the high C-H bond dissociation energy of 420 kJ mol-1. Herein, partially oxidized Pdδ+ species anchored on ZnO nanosheets are designed to weaken the C-H bond by the electron interaction between Pdδ+ species and H atoms, with efforts to achieve high-rate and selective C2H6-to-C2H4 conversion. X-ray photoelectron spectra, Bader charge calculations, and electronic localization function demonstrate the presence of partially oxidized Pdδ+ sites, while quasi-in situ X-ray photoelectron spectra disclose the Pdδ+ sites initially adopt and then donate the photoexcited electrons for C2H6 dehydrogenation. In situ electron paramagnetic resonance spectra, in situ Fourier transform infrared spectra, and trapping agent experiments verify C2H6 initially converts to CH3CH2OH via ·OH radicals, then dehydroxylates to CH3CH2· and finally to C2H4, accompanied by H2 production. Density-functional theory calculations elucidate that loading Pd site can lengthen the C-H bond of C2H6 from 1.10 to 1.12 Å, which favors the C-H bond breakage, affirmed by a lowered energy barrier of 0.04 eV. As a result, the optimized 5.87% Pd-ZnO nanosheets achieve a high C2H4 yield of 16.32 mmol g-1 with a 94.83% selectivity as well as a H2 yield of 14.49 mmol g-1 from C2H6 dehydrogenation in 4 h, outperforming all the previously reported photocatalysts under similar conditions.

Dynamically Reconstructed Triple-Copper-Vacancy Associates Confined in Cu Nanowires Enabling High-Rate and Selective CO2 Electroreduction to C2+ Products.

Electrochemically reconstructed Cu-based catalysts always exhibit enhanced CO2 electroreduction performance; however, it still remains ambiguous whether the reconstructed Cu vacancies have a substantial impact on CO2-to-C2+ reactivity. Herein, Cu vacancies are first constructed through electrochemical reduction of Cu-based nanowires, in which high-angle annular dark-field scanning transmission electron microscopy image manifests the formation of triple-copper-vacancy associates with different concentrations, confirmed by positron annihilation lifetime spectroscopy. In situ attenuated total reflection-surface enhanced infrared absorption spectroscopy discloses the triple-copper-vacancy associates favor *CO adsorption and fast *CO dimerization. Moreover, density-functional-theory calculations unravel the triple-copper-vacancy associates endow the nearby Cu sites with enriched and disparate local charge density, which enhances the *CO adsorption and reduces the CO-CO coupling barrier, affirmed by the decreased *CO dimerization energy barrier by 0.4 eV. As a result, the triple-copper-vacancy associates confined in Cu nanowires achieve a high Faradaic efficiency of over 80% for C2+ products in a wide current density range of 400-800 mA cm-2, outperforming most reported Cu-based electrocatalysts.

Progress and perspective for conversion of plastic wastes into valuable chemicals.

Today, discarded plastics in nature have caused serious "white pollution", however these plastic wastes contain abundant carbon resources that could serve as the feedstock to produce commodities. Because of this, it is requisite to convert these plastic wastes into valuable chemicals. Herein, the state-of-the-art techniques for plastic conversion are divided into two categories, those performed under violent conditions and mild conditions, in which the conversion mechanisms are discussed. The strategies under violent conditions are closer to practical application thanks to their excellent conversion efficiencies, while the strategies under mild conditions are more environmentally friendly, showing enormous development potential in the future. We summarize in detail the pyrolysis, hydropyrolysis, solvolysis and microwave-initiated catalysis for bond cleavage in plastic wastes at temperatures ranging from 448 to 973 K. Also, we overview the photocatalysis, electrocatalysis and biocatalysis for bond cleavage in plastic wastes at near and even normal temperature and pressure. Finally, we present some suggestions and outlooks concerning the improvement of current techniques and in-depth mechanisms of investigation for conversion of plastics into valuable chemicals.

Direct Polyethylene Photoreforming into Exclusive Liquid Fuel over Charge-Asymmetrical Dual Sites under Mild Conditions.

Direct polyethylene photoreforming to high-energy-density C2 fuels under mild conditions is of great significance and still faces a huge challenge, which is partly attributed to the extreme instability of *CH2CH2 adsorbed on the traditional catalysts with single catalytic sites. Herein, charge-asymmetrical dual sites are designed to boost the adsorption of *CH2CH2 for direct polyethylene photoreforming into C2 fuels under normal temperature and pressure. As a prototype, the synthetic Zr-doped CoFe2O4 quantum dots with charge-asymmetrical dual metal sites realize direct polyethylene photoreforming into acetic acid, with 100% selectivity of liquid fuel and the evolution rate of 1.10 mmol g-1 h-1, outperforming those of most previously reported photocatalysts under similar conditions. In situ X-ray photoelectron spectra, density-functional-theory calculations, and control experiments reveal the charge-asymmetrical Zr-Fe dual sites may act as the predominate catalytic sites, which can simultaneously bond with the *CH2CH2 intermediates for the following stepwise oxidation to form C2 products.

Selective CH4 Partial Photooxidation by Positively Charged Metal Clusters Anchored on Carbon Aerogel under Mild Conditions.

Selective partial photooxidation of CH4 into value-added chemicals under mild conditions still remains a huge bottleneck. Herein, we design positively charged metal clusters anchored on a three-dimensional porous carbon aerogel. With 0.75FeCA800-4 as an example, X-ray photoelectron spectra and Raman spectra disclose that the iron sites are positively charged. In situ electron paramagnetic resonance spectra show that the Feδ+ sites could donate electrons to activate CH4 into CH4- by virtue of the excited-state carbon atoms; meanwhile, they could convert H2O2 into •OH radicals under irradiation. In addition, in situ diffuse Fourier-transform infrared spectra suggest the CH3OOH obtained is derived from CH4 oxidation by the hydroxylation of *CH3 and *CH3O intermediates. Consequently, 0.75FeCA800-4 displays a CH3OOH selectivity of near 100% and a CH3OOH evolution rate of 13.2 mmol gFe-1 h-1, higher than those of most previously reported supported catalysts under similar conditions.

Conversion of Waste Plastics into Value-Added Carbonaceous Fuels under Mild Conditions.

Owing to the extremely difficult breakage of the adamant cross-linked structures, converting non-recyclable plastic wastes into valuable fuels usually demands rigorous conditions, wherein the required high temperature and pressure is inevitably energy-wasting and environment-polluting. Given this aspect, herein, the recent achievements in the conversion of plastics into value-added carbonaceous fuels under mild conditions are summarized. In detail, solar-driven conversion of commercial plastics into liquid fuels in alkaline solutions or pure water at ambient temperature and pressure are surveyed; also, enzyme-driven conversion of polyethylene terephthalate into terephthalic acid and ethylene glycol at a mild temperature are emphasized; and low-temperature-driven catalytic conversion of polyethylene into oils and waxes with the help of a light alkane are reviewed. Finally, other potentially used strategies and in situ characterization technologies in plastics degradation under moderate conditions are presented.

Broad-Spectral-Response Photocatalysts for CO2 Reduction.

The poor conversion efficiency of carbon dioxide photoreduction has hindered the practical application at present, and one of the prime reasons for this obstacle is the inefficient solar energy utilization of photocatalysts. Generally speaking, it is contradictory for a photocatalyst to concurrently possess the broad-spectral response and appropriate band-edge positions for coinstantaneous carbon dioxide reduction and water oxidation. In this Outlook, we summarize a series of strategies for realizing visible-light and IR-light-driven carbon dioxide photoreduction under the guarantee of suitable band-edge positions. In detail, we overview the absorbance of visible light enabled by narrow band gaps in photocatalysts, the extended photoabsorption from UV into the visible light range induced by defect levels and dopant energy levels in photocatalysts, and a more negative conduction band and positive valence band acquired by Z-scheme heterojunctions in photocatalysts. Then, we highlight the expansive photoresponse of IR light caused by intermediate bands in semiconductor photocatalysts and partially occupied bands in conductor photocatalysts. Finally, we end this Outlook concerning more design strategies and application fields of broad-spectral-response photocatalysts.

Constructing Co3 O4 Nanowires on Carbon Fiber Film as a Lithiophilic Host for Stable Lithium Metal Anodes.

Lithium metal has been considered as the most promising anode electrode for substantially improving the energy density of next-generation energy storage devices. However, uncontrollable lithium dendrite growth, an unstable solid electrolyte interface (SEI), and infinite volume variation severely shortens its service lifespan and causes safety hazards, thus hindering the practical application of lithium metal electrodes. Here, carbon fiber film (CFF) modified by lithiophilic Co3 O4 nanowires (denoted as Co3 O4 Nws) was proposed as a matrix for prestoring lithium metal through a thermal infusion method. The homogeneous needle-like Co3 O4 nanowires can effectively promote molten lithium to infiltrate into the CFF skeleton. The post-formed Co-Li2 O nanowires produced by the reaction of Co3 O4 Nws and molten lithium can homogeneously distribute lithium ions flux and efficaciously increase the adsorption energy with lithium ions proved by density functional theory (DFT) calculation, boosting a uniform lithium deposition without dendrite growth. Therefore, the obtained composite anode (denoted as CFF/Co-Li2 O@Li) exhibits superior electrochemical performance with high stripping/plating capacities of 3 mAh cm-2 and 5 mAh cm-2 over long-term cycles in symmetrical batteries. Moreover, in comparison with bare lithium anode, superior Coulombic efficiencies coupled with copper collector and full battery behaviors paired with LiFePO4 cathode are achieved when CFF/Co-Li2 O@Li composite anode was employed.

Regulating Lithium Nucleation via CNTs Modifying Carbon Cloth Film for Stable Li Metal Anode.

Li metal is demonstrated as one of the most promising anode materials for high energy density batteries. However, uncontrollable Li dendrite growth and repeated growth of solid electrolyte interface during the charge/discharge process lead to safety issues and capacity decay, preventing its practical application. To address these issues, an effective strategy is to realize uniform Li nucleation. Here, a stable lithium-scaffold composite electrode (CC/CNT@Li) is designed by melting of lithium metal into 3D interconnected lithiophilic carbon nanotube (CNT) on a porous carbon cloth (CC). The 3D interconnected CNTs successfully change the lithiophobic CC into lithiophilic nature, reducing the polarization of the electrode, ensuring homogenous Li nucleation and continuous smooth Li plating. The CNTs on the surface of CC provide adequate Li nucleation sites and reduce the areal current density to avoid Li dendrite growth. The 3D porous structure of CC/CNT offers enough free room for buffering the huge volume change during Li plating/stripping. The CC/CNT@Li composite anode exhibits dendrite-free morphology and superior cycling performances over 500 h with low voltage hysteresis of 18, 23, and 71 mV at the current density of 1, 2, and 5 mA cm-2 , respectively.