Multiscale Anion-Hybrid in Atomic Ni Sites for High-Rate Water Electrolysis: Insights into the Charge Accumulation Mechanism.

Single-atom catalysts, characterized by transition metal-(N/O)4 units on nanocarbon (M-(N/O)4-C), have emerged as efficient performers in water electrolysis. However, there are few guiding principles for accurately controlling the ligand fields of single atoms to further stimulate the catalyst activities. Herein, using the Ni-(N/O)4-C unit as a model, we develop a further modification of the P anion on the outer shells to modulate the morphology of the ligand. The catalyst thus prepared possesses high activity and excellent long-term durability, surpassing commercial Pt/C, RuO2, and currently reported single-atom catalysts. Notably, mechanistic studies demonstrated that the pseudocapacitive feature of multiscale anion-hybrid nanocarbon is considerable at accumulating enough positive charge [Q], contributing to the high oxygen evolution reaction (OER) order (ß) through the rate formula. DFT calculations also indicate that the catalytic activity is decided by the suitable barrier energy of the intermediates due to charge accumulation. This work reveals the activity origin of single atoms on multihybrid nanocarbon, providing a clear experiential formula for designing the electronic configuration of single-atom catalysts to boost electrocatalytic performance.

Universal Murray's law for optimised fluid transport in synthetic structures.

Materials following Murray's law are of significant interest due to their unique porous structure and optimal mass transfer ability. However, it is challenging to construct such biomimetic hierarchical channels with perfectly cylindrical pores in synthetic systems following the existing theory. Achieving superior mass transport capacity revealed by Murray's law in nanostructured materials has thus far remained out of reach. We propose a Universal Murray's law applicable to a wide range of hierarchical structures, shapes and generalised transfer processes. We experimentally demonstrate optimal flow of various fluids in hierarchically planar and tubular graphene aerogel structures to validate the proposed law. By adjusting the macroscopic pores in such aerogel-based gas sensors, we also show a significantly improved sensor response dynamics. In this work, we provide a solid framework for designing synthetic Murray materials with arbitrarily shaped channels for superior mass transfer capabilities, with future implications in catalysis, sensing and energy applications.

CdS QDs grown on ellipsoidal BiVO4 for efficient photocatalytic degradation of tetracycline.

Designing efficient, inexpensive, and stable photocatalysts to degrade organic pollutants and antibiotics has become an effective way for environmental remediation. In this work, we successfully performed in situ growth of CdS QDs on the surface of elliptical BiVO4 to try to show the advantage of the binary heterojuncted photocatalyst (BVO@CdS) for the photocatalytic degradation of tetracycline (TC). The In situ growth of CdS QDs can provide a large number of reactive sites and also generate a larger contact area with BiVO4. In addition, compared with mechanical composite materials, in situ growth can significantly reduce the energy barrier at the interface between BiVO4 and CdS, providing more channels for the separation and migration of photogenerated charge carriers, and further improving reaction activity. As a result, BVO@CdS-0.05 shows the best degradation efficiency, with a degradation rate of 88% after 30 min under visible light. The TC photodegradation follows a pseudo-second-order reaction with a dynamic constant of 0.472 min-1, which is 6.47 times that of pure BiVO4, 7.24 times that of pure CdS QDs and 2 times that of the mechanical composite. The degradation rate of BVO@CdS-0.05 decreases to 77.8% with a retention rate of 88.5% after four cycles, demonstrating excellent stability. Through liquid chromatography-mass spectrometry (LC-MS) analysis, two possible pathways for TC degradation are proposed. Through free radical capture experiments, electron spin resonance measurements, and photoelectrochemical comprehensive analysis, it is confirmed that BVO@CdS composites have constructed an efficient Z-scheme heterojunction via in situ growth, thereby highly enhancing the separation and transport efficiency of charge carriers.

Hierarchical Hollow TiO2@Bi2WO6 with Light-Driven Excited Bi(3-x)+ Sites for Efficient Photothermal Catalytic CO2 Reduction.

Converting CO2 into valuable chemicals via sustainable energy sources is indispensable for human development. Photothermal catalysis combines the high selectivity of photocatalysis and the high yield of thermal catalysis, which is promising for CO2 reduction. However, the present photothermal catalysts suffer from low activity due to their poor light absorption ability and fast recombination of photogenerated electrons and holes. Here, a TiO2@Bi2WO6 heterojunction photocatalyst featuring a hierarchical hollow structure was prepared by an in situ growth method. The visible light absorption and photothermal effect of the TiO2@Bi2WO6 photocatalyst is promoted by a hierarchical hollow structure, while the recombination phenomenon is significantly mitigated due to the construction of the heterojunction interface and the existence of excited Bi(3-x)+ sites. Such a catalyst exhibits excellent photothermal performance with a CO yield of 43.7 µmol h-1 g-1, which is 15 and 4.7 times higher than that of pure Bi2WO6 and that of physically mixed TiO2/Bi2WO6, respectively. An in situ study shows that the pathway for the transformation of CO2 into CO over our TiO2@Bi2WO6 proceeds via two important intermediates, including COO- and COOH-. Our work provides a new idea of excited states for the design and synthesis of highly efficient photothermal catalysts for CO2 conversion.

Engineering surface framework TiO6 single sites for unprecedented deep oxidative desulfurization.

Catalytic oxidative desulfurization (ODS) using titanium silicate catalysts has emerged as an efficient technique for the complete removal of organosulfur compounds from automotive fuels. However, the precise control of highly accessible and stable-framework Ti active sites remains highly challenging. Here we reveal for the first time by using density functional theory calculations that framework hexa-coordinated Ti (TiO6) species of mesoporous titanium silicates are the most active sites for ODS and lead to a lower-energy pathway of ODS. A novel method to achieve highly accessible and homogeneously distributed framework TiO6 active single sites at the mesoporous surface has been developed. Such surface framework TiO6 species exhibit an exceptional ODS performance. A removal of 920 ppm of benzothiophene is achieved at 60°C in 60 min, which is 1.67 times that of the best catalyst reported so far. For bulky molecules such as 4,6-dimethyldibenzothiophene (DMDBT), it takes only 3 min to remove 500 ppm of DMDBT at 60°C with our catalyst, which is five times faster than that with the current best catalyst. Such a catalyst can be easily upscaled and could be used for concrete industrial application in the ODS of bulky organosulfur compounds with minimized energy consumption and high reaction efficiency.

Synergistic Protecting-Etching Synthesis of Carbon Nanoboxes@Silicon for High-Capacity Lithium-Ion Battery.

Silicon (Si) is considered as the most likely choice for the high-capacity lithium-ion batteries owing to its ultrahigh theoretical capacity (4200 mA h g-1) being over 10 times than that of traditional graphite anode materials (372 mA h g-1). However, its widespread application is limited by problems such as a large volume expansion and low electrical conductivity. Herein, we design a hollow nitrogen-doped carbon-coated silicon (Si@Co-HNC) composite in a water-based system via a synergistic protecting-etching strategy of tannic acid. The prepared Si@Co-HNC composite can effectively mitigate the volume change of silicon and improve the electrical conductivity. Moreover, the abundant voids inside the carbon layer and the porous carbon layer accelerate the transport of electrons and lithium ions, resulting in excellent electrochemical performance. The reversible discharge capacity of 1205 mA h g-1 can be retained after 120 cycles at a current density of 0.5 A g-1. In particular, the discharge capacity can be maintained at 1066 mA h g-1 after 300 cycles at a high current density of 1 A g-1. This study provides a new strategy for the design of Si-based anode materials with excellent electrical conductivity and structural stability.

Synergistic effect of K and Zn on Fe-based catalysts for efficient CO2 hydrogenation.

Excessive emission of CO2 into the atmosphere has severely impacted the global ecological environment. Converting CO2 into valuable chemicals and fuels is of great significance for sustainable development. However, low activity and undesirable selectivity often result from the inherent inertness of CO2. Herein, K- or/and Zn-modified Fe-based catalysts were prepared by an incipient-wetness impregnation method for CO2 hydrogenation via a cascade reaction. The results indicate that K species exist as K2O while Zn species exist as ZnFe2O4. In the CO2 hydrogenation pathway, K2O facilitates the adsorption of CO2 and restrains the adsorption of H2, accelerating the transformation of CO2 into C2-C4 olefins rather than paraffins while Zn species promote the dispersion of Fe species, leading to improved activity. Synergistically, a K- and Zn-modified Fe-based catalyst (2Zn-10K-Fe/Al) shows excellent catalytic CO2 hydrogenation activity, achieving a CO2 conversion of 77% which is 1.8 times that (42%) of the unmodified Fe-based catalyst (Fe/Al). Our catalyst also shows a significantly promoted selectivity to C2-C4 olefins of 17% in comparison with the Fe/Al catalyst (0%). It is envisioned that such a binary effect of elements might contribute to the low-cost and industrial production of Fe-based catalysts for selective CO2 conversion.

Solvent-Free Synthesis of Hollow Carbon Nanostructures for Efficient Sodium Storage.

The structural characteristics of hollow carbon nanostructures (HCNs) result in intriguing physicochemical properties and various applications, especially for electrochemical energy storage applications. However, the currently solvent-based template methods to prepare HCNs are still far from meeting the facile, environment-friendly, and scalable demand. Herein, we explored a general and facile solvent-free block copolymer self-assembly approach to prepare various hollow hard carbon nanostructures, including hollow carbon nanofibers, hollow carbon Janus nanotadpoles, hollow carbon spheres, etc. It was found that the obtained HCNs possess abundant active sites, fast pathways for electrons/ions transport, and superior electronic conducting connectivity, which are promising for efficient electrochemical energy storage. Typically, the resultant hollow carbon nanofibers with a thick-walled tube deliver a high reversible capacity (431 mAh g-1) and excellent rate performance (259 mAh g-1 at 800 mA g-1) for sodium ion storage. This intelligent solvent-free block copolymer self-assembly method would inspire the design of hollow hard carbon-based nanostructures for advanced applications in various energy conversion and storage.

Aqueous batteries: from laboratory to market.

This perspective discusses the fundamental benefits and drawbacks of aqueous batteries and the challenges of the development of such battery technology from laboratory scale to industrial applications.

Intraparticle ripening to create hierarchically porous Ti-MOF single crystals for deep oxidative desulfurization.

The catalytic oxidative desulfurization (ODS) technique is able to remove sulfur compounds from fuels, conducive to achieving deep desulfurization for the good of the ecological environment. Ti-based metal-organic frameworks (Ti-MOFs) possessing good affinity to organic reactants and considerable numbers of Ti active sites are promising catalysts for ODS. However, current Ti-MOFs suffer from severe diffusion limitations caused by the size mismatch between sole micropores and bulky sulfur compounds, leading to poor ODS performance. Here, a facile method of intraparticle ripening without any additive is developed to obtain hierarchically meso-microporous Ti-MIL-125 single crystals (Meso-Ti-MIL-125) for the first time. Such Meso-Ti-MIL-125 shows a BET surface area of 1401 m2 g-1 and a mesoporous volume that is 1.7 times as high as that of the conventional Ti-MIL-125. Our novel Meso-Ti-MIL-125 exhibits excellent catalytic performance in the ODS of a series of bulky thiophenic sulfur compounds, completely removing benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (DMDBT) from model fuels, which is, respectively, 2.4 times, 1.5 times, and 6.7 times higher than the removal achieved with conventional Ti-MIL-125. Such a facile synthetic strategy is envisioned to be applied in many kinds of crystalline materials, such as zeolites, for industrial production.

H2 -free Semi-hydrogenation of Butadiene by the Atomic Sieving Effect of Pd Membrane with Tree-like Pd Dendrites Array.

H2 -free semi-hydrogenation at room temperature shows great advantage for replacing the thermocatalytic process in industry owing to the high energy and resource saving, however, remains great challenges. Herein, a tree-like Pd dendrites array decorated Pd membrane was constructed as the core device in an electrochemistry assisted gas-fed membrane reactor for butadiene semi-hydrogenation. It reveals that hydrogen atomic sieving effect of this Pd-based membrane under electrochemical condition was the key for semi-hydrogenation. The configuration study of Pd nanostructured membrane demonstrates that the penetration of hydrogen atoms through Pd membrane from electrochemical side to chemical side is affected by the consumption of hydrogen atom in semi-hydrogenation step. Such atomic sieving property of nanostructured Pd membrane with 5.1 times increase in catalytic active surface area brings above 14 times higher in butadiene conversion than that of bare Pd foil, with ≈90 % of butenes selectivity at butadiene conversion ≈98 % over 300 h of H2 -free reaction under 15 mA cm-2 .

Tunable CO2-to-syngas conversion via strong electronic coupling in S-scheme ZnGa2O4/g-C3N4 photocatalysts.

The conversion of CO2 into syngas, a mixture of CO and H2, via photocatalytic reduction, is a promising approach towards achieving a sustainable carbon economy. However, the evolution of highly adjustable syngas, particularly without the use of sacrifice reagents or additional cocatalysts, remains a significant challenge. In this study, a step-scheme (S-scheme) 0D ZnGa2O4 nanodots (∼7 nm) rooted g-C3N4 nanosheets (denoted as ZnGa2O4/C3N4) heterojunction photocatalyst was synthesized vis a facial in-situ growth strategy for efficient CO2-to-syngas conversion. Both experimental and theoretical studies have demonstrated that the polymeric nature of g-C3N4 and highly distributed ZnGa2O4 nanodots synergistically contribute to a strong interaction between metal oxide and C3N4 support. Furthermore, the desirable S-scheme heterojunction in ZnGa2O4/C3N4 efficiently promotes charge separation, enabling strong photoredox ability. As a result, the S-scheme ZnGa2O4/C3N4 exhibited remarkable activity and selectivity in photochemical conversion of CO2 into syngas, with a syngas production rate of up to 103.3 µ mol g-1 h-1, even in the absence of sacrificial agents and cocatalyst. Impressively, the CO/H2 ratio of syngas can be tunable within a wide range from 1:4 to 2:1. This work exemplifies the effectiveness of a meticulously designed S-scheme heterojunction photocatalyst for CO2-to-syngas conversion with adjustable composition, thus paving the way for new possibilities in sustainable energy conversion and utilization.

Manipulating multi-spectral slow photons in bilayer inverse opal TiO2@BiVO4 composites for highly enhanced visible light photocatalysis.

Manipulation of light has been proved to be a promising strategy to increase light harvesting in solar-to-chemical energy conversion, especially in photocatalysis. Inverse opal (IO) photonic structures are highly promising for light manipulation as their periodic dielectric structures enable them to slow down light and localize it within the structure, thereby improving light harvesting and photocatalytic efficiency. However, slow photons are confined to narrow wavelength ranges and hence limit the amount of energy that can be captured through light manipulation. To address this challenge, we synthesized bilayer IO TiO2@BiVO4 structures that manifested two distinct stop band gap (SBG) peaks, arising from different pore sizes in each layer, with slow photons available at either edge of each SBG. In addition, we achieved precise control over the frequencies of these multi-spectral slow photons through pore size and incidence angle variations, that enabled us to tune their wavelengths to the electronic absorption of the photocatalyst for optimal light utilization in aqueous phase visible light photocatalysis. This first proof of concept involving multi-spectral slow photon utilization enabled us to achieve up to 8.5 times and 2.2 times higher photocatalytic efficiencies than the corresponding non-structured and monolayer IO photocatalysts respectively. Through this work, we have successfully and significantly improved light harvesting efficiency in slow photon-assisted photocatalysis, the principles of which can be extended to other light harvesting applications.

Electrochemistry-assisted selective butadiene hydrogenation with water.

Alkene feedstocks are used to produce polymers with a market expected to reach 128.4 million metric tons by 2027. Butadiene is one of the impurities poisoning alkene polymerization catalysts and is usually removed by thermocatalytic selective hydrogenation. Excessive use of H2, poor alkene selectivity and high operating temperature (e.g. up to 350 °C) remain the most significant drawbacks of the thermocatalytic process, calling for innovative alternatives. Here we report a room-temperature (25~30 °C) electrochemistry-assisted selective hydrogenation process in a gas-fed fixed bed reactor, using water as the hydrogen source. Using a palladium membrane as the catalyst, this process offers a robust catalytic performance for selective butadiene hydrogenation, with alkene selectivity staying around 92% at a butadiene conversion above 97% for over 360 h of time on stream. The overall energy consumption of this process is 0.003 Wh/mLbutadiene, which is thousands of times lower than that of the thermocatalytic route. This study proposes an alternative electrochemical technology for industrial hydrogenation without the need for elevated temperature and hydrogen gas.

N-Doping Coupled with Co-Vacancies Activating Sulfur Atoms and Narrowing Bandgap for CoS Toward Synergistically Accelerating Hydrogen Evolution.

The combination of hetero-elemental doping and vacancy engineering will be developed as one of the most efficient strategies to design excellent electrocatalysts for hydrogen evolution reaction (HER). Herein, a novel strategy for N-doping coupled with Co-vacancies is demonstrated to precisely activate inert S atoms adjacent to Co-vacancies and significantly improve charge transfer for CoS toward accelerating HER. In this strategy, N-doping favors the presence of Co-vacancies, due to greatly decreasing their formation energy. The as-developed strategy realizes the upshift of S 3p orbitals followed by more overlapping between S 3py and H 1s orbitals, which results in the favorable hydrogen atom adsorption free energy change (ΔGH ) to activate inert S atoms as newborn catalytical sites. Besides, this strategy synergistically decreases the bandgap of CoS, thereby achieving satisfactory electrical conductivity and low charge-transfer resistance for the as-obtained electrocatalysts. With an excellent HER activity of -89.0 mV at 10.0 mA cm-2 in alkaline environments, this work provides a new approach to unlocking inert sites and significantly improving charge transfer toward cobalt-based materials for highly efficient HER.

Chelation-Assisted formation of carbon nanotubes interconnected Yolk-Shell Silicon/Carbon anodes for High-Performance Lithium-ion batteries.

As a viable replacement to commercial graphite anodes, silicon (Si) anodes have gained much attention from academics because of their considerable theoretical specific capacity and appropriate reaction voltage. Nevertheless, some limitations still exist in developing silicon anodes, including significant volume expansion and poor electrical conductivity. Herein, the carbon nanotubes (CNTs) interconnected yolk-shell silicon/carbon anodes (YS-Si@CoNC) were prepared via the chelation competition induced polymerization (CCIP) approach. The YS-Si@CoNC anode, designed in this study, demonstrates improved performance. At the current density of 0.5 A g-1 and 1 A g-1, a capacity of 1001 mAh g-1 and 956.5 mAh g-1 can be achieved after 150 cycles and after 300 cycles, respectively. In particular, at the current density of 5 A g-1, the reversible specific capacity of 688 mAh g-1 is realized. The exceptional outcomes are mainly attributed to the internal voids that adequately alleviate the volumetric expansion and the CNTs and carbon shells that provide an efficient conducting matrix to fasten the diffusion of electrons and lithium-ions. Our research presents a convenient way of designing Si/C anode materials with a yolk-shell structure to guarantee impressive electrical conductivity and robust structural integrity for high-performance LIBs.

Ammonium Ion Batteries: Material, Electrochemistry and Strategy.

Ammonium-ion batteries (AIBs) have recently attracted increasing attention in the field of aqueous batteries owing to their high safety and fast diffusion kinetics. The NH4 + storage mechanism is quite different from that of spherical metal ions (e.g. Li+ , Na+ , K+ , Mg2+ , and Zn2+ ) because of the formation of hydrogen bonds between NH4 + and host materials. Although many materials have been proposed as electrode materials for AIBs, their performances hardly meet the requirement of future electrochemical energy storage devices. It is thus urgent to design and exploit advanced materials for AIBs. This review highlights the state-of-the-art research on AIBs. The insights into the basic configuration, operating mechanism and recent progress of electrode materials and corresponding electrolytes for AIBs have been comprehensively outlined. The electrode materials are classified and compared according to different NH4 + storage behaviour in the structure. The challenges, design strategies and perspectives are also discussed for the future development of AIBs.