Activating Inert Perovskite Oxides for CO2 Electroreduction via Slight Cu2+ Doping in B-Sites.

Perovskite oxides are proven as a striking platform for developing high-performance electrocatalysts. Nonetheless, a significant portion of them show CO2 electroreduction (CO2RR) inertness. Here a simple but effective strategy is reported to activate inert perovskite oxides (e.g., SrTiO3) for CO2RR through slight Cu2+ doping in B-sites. For the proof-of-concept catalysts of SrTi1-xCuxO3 (x = 0.025, 0.05, and 0.1), Cu2+ doping (even in trace amount, e.g., x = 0.025) can not only create active, stable CuO6 octahedra, increase electrochemical active surface area, and accelerate charge transfer, but also significantly regulate the electronic structure (e.g., up-shifted band center) to promote activation/adsorption of reaction intermediates. Benefiting from these merits, the stable SrTi1-xCuxO3 catalysts feature great improvements (at least an order of magnitude) in CO2RR activity and selectivity for high-order products (i.e., CH4 and C2+), compared to the SrTiO3 parent. This work provides a new avenue for the conversion of inert perovskite oxides into high-performance electrocatalysts toward CO2RR.

Promoting CO2 Electroreduction Over Nano-Socketed Cu/Perovskite Heterostructures via A-Site-Valence-Controlled Oxygen Vacancies.

Despite the intriguing potential, nano-socketed Cu/perovskite heterostructures for CO2 electroreduction (CO2 RR) are still in their infancy and rational optimization of their CO2 RR properties is lacking. Here, an effective strategy is reported to promote CO2 -to-C2+ conversion over nano-socketed Cu/perovskite heterostructures by A-site-valence-controlled oxygen vacancies. For the proof-of-concept catalysts of Cu/La0.3-x Sr0.6+x TiO3-δ (x from 0 to 0.3), their oxygen vacancy concentrations increase controllably with the decreased A-site valences (or the increased x values). In flow cells, their activity and selectivity for C2+ present positive correlations with the oxygen vacancy concentrations. Among them, the Cu/Sr0.9 TiO3-δ with most oxygen vacancies shows the optimal activity and selectivity for C2+ . And relative to the Cu/La0.3 Sr0.6 TiO3-δ with minimum oxygen vacancies, the Cu/Sr0.9 TiO3-δ exhibits marked improvements (up to 2.4 folds) in activity and selectivity for C2+ . The experiments and theoretical calculations suggest that the optimized performance can be attributed to the merits provided by oxygen vacancies, including the accelerated charge transfer, enhanced adsorption/activation of reaction species, and reduced energy barrier for C─C coupling. Moreover, when explored in a membrane-electrode assembly electrolyzer, the Cu/Sr0.9 TiO3-δ catalyst shows excellent activity, selectivity (43.9%), and stability for C2 H4 at industrial current densities, being the most effective perovskite-based catalyst for CO2 -to-C2 H4 conversion.

Diffusion-Ordered Spectroscopy (DOSY) as a Powerful NMR Method to Investigate Molecular Mobilities and Intermolecular Interactions in Complex Oil Mixtures.

Studying the characteristics and molecular mechanisms of liquid self-diffusion coefficient and viscosity changes is of great significance for, e. g., chemical and petroleum processing. As examples of highly complex liquid,an asphaltene-free high-acid and high-viscosity crude oil and its extracted fractions were studied by comparing their 1 H DOSY diffusion maps. The crude oil exhibited a polydisperse diffusion distribution, including multiple diffusion portions with diffusion coefficients much smaller than that of any single fraction in independent diffusion. The main mechanism that leads to the decreases in the diffusion coefficients of crude oil is attributed to diffusion resistance enhanced by Dynamical Molecular-Interaction Networks (DMINs), rather than by enlargement of the diffusion species caused by molecular aggregation. Constructed through the synergistic interactions of various polar molecules in crude oil, DMINs dynamically bind polar molecules, trap polarizable molecules, and spatially hinder the free motion of non-polar molecules. Overall, this reduces the mobility of all molecular species, as illustrated by the decreased diffusion coefficients. This study demonstrates that DOSY is a powerful NMR method to investigate molecular motion abilities also in complex mixtures. In addition, the insights in the influence of the interaction matrix on the molecular mobility also help to understand the contribution of "structural viscosity" to the viscosity of heavy oil.

Toward Understanding the Formation Mechanism and OER Catalytic Mechanism of Hydroxides by In Situ and Operando Techniques.

Developing efficient and affordable electrocatalysts for the sluggish oxygen evolution reaction (OER) remains a significant barrier that needs to be overcome for the practical applications of hydrogen production via water electrolysis, transforming CO2 to value-added chemicals, and metal-air batteries. Recently, hydroxides have shown promise as electrocatalysts for OER. In situ or operando techniques are particularly indispensable for monitoring the key intermediates together with understanding the reaction process, which is extremely important for revealing the formation/OER catalytic mechanism of hydroxides and preparing cost-effective electrocatalysts for OER. However, there is a lack of comprehensive discussion on the current status and challenges of studying these mechanisms using in situ or operando techniques, which hinders our ability to identify and address the obstacles present in this field. This review offers an overview of in situ or operando techniques, outlining their capabilities, advantages, and disadvantages. Recent findings related to the formation mechanism and OER catalytic mechanism of hydroxides revealed by in situ or operando techniques are also discussed in detail. Additionally, some current challenges in this field are concluded and appropriate solution strategies are provided.

Multilayered Ceramic Membrane with Ion Conducting Thin Layer Induced by Interface Reaction for Stable Hydrogen Production.

Conventional methods for fabricating multilayered ceramic membranes with ion conducting dense thin layers are often cumbersome, costly, and limited by poor adhesion between layers. Inspired by the architectural structure of the rooted grasses in soil, here, we report an interface-reaction-induced reassembly approach for the direct fabrication of Ce0.9 Gd0.1 O2-δ (CGO) thin layers rooted in the parent multilayered ceramic membranes by only one firing step. The CGO dense layers are very thin, and adhered strongly to the parent support layer, ensuring low ionic transport resistance and structural integrity of the multilayered membranes. When using as an oxygen permeable membrane for upgrading fossil-fuel-derived hydrogen, it shows very long durability in harsh conditions containing H2 O, CH4 , H2 , CO2 and H2 S. Furthermore, our approach is highly scalable and applicable to a wide variety of ion conducting thin layers, including Y0.08 Zr0.92 O2-δ , Ce0.9 Sm0.1 O2-δ and Ce0.9 Pr0.1 O2-δ .

Cation-Radius-Controlled Sn-O Bond Length Boosting CO2 Electroreduction over Sn-Based Perovskite Oxides.

Despite the intriguing potential shown by Sn-based perovskite oxides in CO2 electroreduction (CO2 RR), the rational optimization of their CO2 RR properties is still lacking. Here we report an effective strategy to promote CO2 -to-HCOOH conversion of Sn-based perovskite oxides by A-site-radius-controlled Sn-O bond lengths. For the proof-of-concept examples of Ba1-x Srx SnO3 , as the A-site cation average radii decrease from 1.61 to 1.44 Å, their Sn-O bonds are precisely shortened from 2.06 to 2.02 Å. Our CO2 RR measurements show that the activity and selectivity of these samples for HCOOH production exhibit volcano-type trends with the Sn-O bond lengths. Among these samples, the Ba0.5 Sr0.5 SnO3 features the optimal activity (753.6 mA ⋅ cm-2 ) and selectivity (90.9 %) for HCOOH, better than those of the reported Sn-based oxides. Such optimized CO2 RR properties could be attributed to favorable merits conferred by the precisely controlled Sn-O bond lengths, e.g., the regulated band center, modulated adsorption/activation of intermediates, and reduced energy barrier for *OCHO formation. This work brings a new avenue for rational design of advanced Sn-based perovskite oxides toward CO2 RR.

Bilayer rGO-Based Photothermal Evaporator for Efficient Solar-Driven Water Purification[ ] *.

Interfacial evaporation has emerged as a promising approach to produce freshwater. However, an urgent concern is that, due to the illegal discharge of industrial wastewater, most water bodies are polluted by trace volatile organic compounds (VOCs), which are easily volatilized and enriched in the collected water during the interfacial evaporation process. Herein, a bilayer photothermal evaporator was reasonably designed for contaminated water purification. The bottom hydrophilic rGO-sodium alginate (SA) sheets purposefully disintegrate water transport channels, thus quickly removing VOCs through physical adsorption. The rGO-SA-TiO2 upper layer sufficiently absorbs incident light and therefore persistently generates reactive oxidizing species to degrade upward VOCs. Notably, the oriented microchannels inside the evaporator allow sustained light reflections to improve the utilization of solar energy. The evaporation rate can reach 1.63 kg m-2  h-1 with a considerably high VOC removal efficiency of up to 96 %. Such an integrated bilayer evaporator provides an effective strategy to obtain clean water via solar distillation.

Enhanced solar-driven evaporation process via f-MWCNTs/PVDF photothermal membrane for forward osmosis draw solution recovery.

Product water recovery and draw solution (DS) reuse is the most energy-intensive stage in forward osmosis (FO) technology. Sucrose solution is the most suitable DS for FO application in food and beverages. However, sucrose DS recovery by conventional pressure-driven or thermal-driven concentration techniques consumes high energy. Herein, we developed a spontaneous and sustainable solar-driven evaporation process based on a photothermal membrane for the concentration and recovery of sucrose solution. The photothermal membrane composed of multi-walled carbon nanotubes (f-MWCNTs) phtotothermal layer on a hydrophilic polyvinylidene fluoride (PVDF) substrate. The f-MWCNTs photothermal layer with rough surface and interconnected network structures not only improves the light harvesting and light-to-heat conversion performance, but also facilitates the transport of water molecules. The hydrophilic PVDF substrate can promote the rapid transport of water for adequate water supply to photothermal layer. As a result, the optimized f-MWCNTs/PVDF photothermal membrane exhibits an excellent light absorption of 95%, and a high surface temperature of 74 °C at 1 kW m-2. Besides, it realizes an evaporation rate of 1.17 kg m-2h-1for 5% (w/v) of sucrose solution, which is about 5 times higher than that of the natural evaporation. The designed photothermal evaporation process is capable of concentrating sucrose solution efficiently from 5% to 75% (w/v), which has great potential in FO process and juice concentration.

Hydrogen Purification through a Highly Stable Dual-Phase Oxygen-Permeable Membrane.

Using oxygen permeable membranes (OPMs) to upgrade low-purity hydrogen is a promising concept for high-purity H2 production. At high temperatures, water dissociates into hydrogen and oxygen. The oxygen permeates through OPM and oxidizes hydrogen in a waste stream on the other side of the membrane. Pure hydrogen can be obtained on the water-splitting side after condensation. However, the existing Co- and Fe-based OPMs are chemically instable as a result of the over-reduction of Co and Fe ions under reducing atmospheres. Herein, a dual-phase membrane Ce0.9 Pr0.1 O2-δ -Pr0.1 Sr0.9 Mg0.1 Ti0.9 O3-δ (CPO-PSM-Ti) with excellent chemical stability and mixed oxygen ionic-electronic conductivity under reducing atmospheres was developed for H2 purification. An acceptable H2 production rate of 0.52 mL min-1 cm-2 is achieved at 940 °C. No obvious degradation during 180 h of operation indicates the robust stability of CPO-PSM-Ti membrane. The proven mixed conductivity and excellent stability of CPO-PSM-Ti give prospective advantages over existing OPMs for upgrading low-purity hydrogen.

Multifunctional Nickel Sulfide Nanosheet Arrays for Solar-Intensified Oxygen Evolution Reaction.

Electrochemical water splitting for hydrogen production is currently hindered by the sluggish kinetic of anodic oxygen evolution reaction (OER). By integrating photothermal materials into electrocatalytic network and thus allowing solar energy to work as additional driving force, the OER is expected to be boosted. However, the rational design of such electrochemical system still remains a challenge due to the spatial inconsistency between photothermal component and electrocatalytic component. Herein, it is reported that multifunctional nickel sulfide (Ni3 S2 ) nanosheet arrays show both photothermal and electrocatalytic properties for solar-intensified electrocatalytic system, which well eliminates the spatial inconsistency between the aforementioned two types of functional components by using one bifunctional material. The deliberate design of nanoarray architecture formed by the interconnected Ni3 S2 nanosheets endows larger surface area and higher surface roughness, thus enhancing light absorption by suppressing diffuse reflection and facilitating electron transfer in electrocatalytic reactions. Therefore, the OER activity is significantly improved. Under light illumination, the current density of Ni3 S2 nanosheets could reach 492.2 mA cm-2 at 1.55 V, about 2.5-fold that in dark conditions, with a Tafel slope of as low as 60 dec-1 . The solar-intensified electrochemical system based on multifunctional material presents prospective potential in electrochemical water splitting for efficient hydrogen production.

Elevated caproic acid production from one-stage anaerobic fermentation of organic waste and its selective recovery by electro-membrane process.

A constructed microbial consortia-based strategy to enhance caproic acid production from one-stage mixed-fermentation of glucose was developed, which incubated with acidogens (Clostridium sensu stricto 1, 11 dominated) and chain elongators (including Clostridium sensu stricto 12, Sporanaerobacter, and Caproiciproducens) acclimated from anaerobic sludge. Significant product upgrading toward caproic acid (8.31 g‧L-1) and improved substrate degradation was achieved, which can be greatly attributed to the lactic acid platform. Whereas, a small amount of caproic acid was observed in the control incubating with acidogens, with an average concentration of 2.09 g‧L-1. The strategy accelerated the shape and cooperation of the specific microbial community dominated by Clostridium sensu stricto and Caproiciproducens, which thereby contributed to caproic acid production via the fatty acid biosynthesis pathway. Moreover, the tailored electrodialysis with bipolar membrane enabled progressive up-concentration and acidification, allowing selective separation of caproic acid as an immiscible product with a purity of 82.58 % from the mixture.

Frustrated Lewis pair catalyst realizes efficient green diesel production.

Hydrotreating renewable oils over sulfided metal catalysts is commercially applied to produce green diesel, but it requires a continuous sulfur replenishment to maintain catalyst activity, which inevitably results in sulfur contamination and increases production costs. We report a robust P-doped NiAl-oxide catalyst with frustrated Lewis pairs (i.e., P atom bonded with the O atom acts as an electron donor, while the spatially separated Ni atom acts as an electron acceptor) that allows efficient green diesel production without sulfur replenishment. The catalyst runs more than 500 h at a weight hourly space velocity (WHSV) of 28.3 h-1 without deactivation (methyl laurate as a model compound), and is able to completely convert a real feedstock of soybean oil to diesel-range hydrocarbons with selectivity >90% during 500 h of operation. This work is expected to open up a new avenue for designing non-sulfur catalysts that can make the green diesel production greener.

Superexchange-stabilized long-distance Cu sites in rock-salt-ordered double perovskite oxides for CO2 electromethanation.

Cu-oxide-based catalysts are promising for CO2 electroreduction (CO2RR) to CH4, but suffer from inevitable reduction (to metallic Cu) and uncontrollable structural collapse. Here we report Cu-based rock-salt-ordered double perovskite oxides with superexchange-stabilized long-distance Cu sites for efficient and stable CO2-to-CH4 conversion. For the proof-of-concept catalyst of Sr2CuWO6, its corner-linked CuO6 and WO6 octahedral motifs alternate in all three crystallographic dimensions, creating sufficiently long Cu-Cu distances (at least 5.4 Å) and introducing marked superexchange interaction mainly manifested by O-anion-mediated electron transfer (from Cu to W sites). In CO2RR, the Sr2CuWO6 exhibits significant improvements (up to 14.1 folds) in activity and selectivity for CH4, together with well boosted stability, relative to a physical-mixture counterpart of CuO/WO3. Moreover, the Sr2CuWO6 is the most effective Cu-based-perovskite catalyst for CO2 methanation, achieving a remarkable selectivity of 73.1% at 400 mA cm-2 for CH4. Our experiments and theoretical calculations highlight the long Cu-Cu distances promoting *CO hydrogenation and the superexchange interaction stabilizing Cu sites as responsible for the superb performance.

Natural gas to fuels and chemicals: improved methane aromatization in an oxygen-permeable membrane reactor.

Adding value with membranes: Improved methane aromatization was achieved by using an oxygen-permeable membrane. The resulting membrane reactor shows a superior methane conversion and a higher resistance towards catalyst deactivation.

Synthesis and characterization of porous reduced graphene oxide based geopolymeric membrane with titanium dioxide coating for forward osmosis application.

Forward Osmosis (FO) is a promising separation technology with a wide range of applications in water and wastewater treatment. FO membrane is the core of the forward osmosis process. Recently, the organic membrane has been widely used for forward osmosis applications even though inorganic membrane has excellent mechanical properties, decent chemical resistance, high durability, high porosity, and good hydrophilicity. Nevertheless, the utilization of inorganic membrane is hindered by the heat-intensive steps involved in its fabrication and the use of expensive source material. Geopolymerization provides a cost-effective technique for the preparation of inorganic membranes because of its sintering-free steps and utilization of fly ash as source material. Herein, we present a sintering-free, environmentally friendly, and cost-effective synthesis of geopolymeric membrane for application in forward osmosis. Fly ash was mixed with alkaline activator solution and porous reduced graphene oxide (PRGO) to prepare geopolymer slurry. The hydrogen peroxide and egg albumen were used as foaming agent and surfactant, while the membrane surface was coated with titanium dioxide to enhance the hydrophilicity of the membrane surface. The PRGO content improved the mechanical properties of the geopolymeric membrane. The average maximum flux recorded was 21 L/m2 h with geopolymer substrate having a pore size of 1.8 µm and hydrophilic coated layer pore size of 0.25 µm. The varying concentrations of PRGO control the substrate's mechanical properties and pore size, as well as provide new insights for future studies. These preliminary results show that low-cost geopolymer material is a promising candidate for FO membrane fabrication.

Developing a class of dual atom materials for multifunctional catalytic reactions.

Dual atom catalysts, bridging single atom and metal/alloy nanoparticle catalysts, offer more opportunities to enhance the kinetics and multifunctional performance of oxygen reduction/evolution and hydrogen evolution reactions. However, the rational design of efficient multifunctional dual atom catalysts remains a blind area and is challenging. In this study, we achieved controllable regulation from Co nanoparticles to CoN4 single atoms to Co2N5 dual atoms using an atomization and sintering strategy via an N-stripping and thermal-migrating process. More importantly, this strategy could be extended to the fabrication of 22 distinct dual atom catalysts. In particular, the Co2N5 dual atom with tailored spin states could achieve ideally balanced adsorption/desorption of intermediates, thus realizing superior multifunctional activity. In addition, it endows Zn-air batteries with long-term stability for 800 h, allows water splitting to continuously operate for 1000 h, and can enable solar-powered water splitting systems with uninterrupted large-scale hydrogen production throughout day and night. This universal and scalable strategy provides opportunities for the controlled design of efficient multifunctional dual atom catalysts in energy conversion technologies.

Spin state modulation on dual Fe center by adjacent Ni sites enabling the boosted activities and ultra-long stability in Zn-air batteries.

Breakthrough in developing cost-effective Fe-based catalysts with superior oxygen reduction reaction (ORR) activities and ultra-long-term stability for application in Zn-air batteries (ZABs) remain a priority but still full of challenges. Herein, the neighboring NiN4 single-metal-atom and Fe2N5 dual-metal-atoms on the N-doped hollow carbon sphere (Fe/Ni-NHCS) were deliberately constructed as the efficient and robust ORR catalyst for ZABs. Both theory calculations and magnetic measurements demonstrate that the introduction of NiN4 provides a significant role on optimizing the electron spin state of Fe2N5 sites and reducing the energy barrier for the adsorption and conversion of the oxygen-containing intermediates, enabling the Fe/Ni-NHCS with excellent ORR performance and ultralow byproduct HO2- yield (0.5%). Impressively, the ZABs driven by Fe/Ni-NHCS exhibit unprecedented long-term rechargeable stability over 1200 h. This work paves a new venue to manipulate the spin state of active sites for simultaneously achieving superior catalytic activities and ultra-long-term stability in energy conversion technologies.

Alpha-Nickel Hydroxide Coating of Metallic Nickel for Enhanced Alkaline Hydrogen Evolution.

In this work, alkaline hydrogen evolution reaction (HER) processes of three typical nickel-based electrocatalysts [i. e., Ni, α-Ni(OH)2 , and ß-Ni(OH)2 ] were investigated to probe critical factors that determine the activity and durability. The HER activity trend was observed as Ni≫α-Ni(OH)2 >ß-Ni(OH)2 , likely attributed to a synergy between metallic Ni and Ni(OH)2 components on the Ni surface and fast water dissociation kinetics on the α-Ni(OH)2 surface. With the HER proceeding, the metallic Ni surface, however, gradually became α-Ni(OH)2 , and α-Ni(OH)2 surface ultimately transformed into ß-phase, leading to a dramatic activity decrease of Ni electrodes. Therefore, Ni electrodes were coated with α-Ni(OH)2 nanosheets to slow down the nickel hydroxylation and optimize the surface ratio of Ni(OH)2 to metallic Ni. This simple coating procedure enhanced both activity and durability of Ni electrocatalysts.

Highly selective butyric acid production by coupled acidogenesis and ion substitution electrodialysis.

Selective production of carboxylic acids (CAs) from mixed culture fermentation remains a difficult task in organic waste valorization. Herein, we developed a facile and sustainable carbon loop strategy to regulate the fermentation micro-environment and steer acidogenesis towards selective butyric acid production. This new ion substitution electrodialysis-anaerobic membrane bioreactor (ISED-AnMBR) integrated system demonstrated a high butyric acid production at 11.19 g/L with a mass fraction of 76.05%. In comparison, only 1.04 g/L with a mass fraction of 30.56% was observed in the uncoupled control reactor. The carbon recovery reached a maximum of 96.09% with the assistance of ISED. Inorganic carbon assimilation was believed to be an important contributor, which was verified by 13C isotopic tracing. Microbial community structure shows the dominance of Clostridia (80.16%) in the unique micro-environment (e.g., pH 4.80-5.50) controlled by ISED, which is believed beneficial to the growth of such fermentative bacteria with main products of butyric acid and acetic acid. In addition, the emergence of chain elongators such as Clostridium sensu stricto 12 was observed to have a great influence on butyric acid production. This work provides a new approach to generate tailored longer chain carboxylic acids from organic waste with high titer thus contributing to a circular economy.

Coupling solar-driven interfacial evaporation with forward osmosis for continuous water treatment.

Forward osmosis (FO) driven by osmotic pressure difference has great potential in water treatment. However, it remains a challenge to maintain a steady water flux at continuous operation. Herein, a FO and photothermal evaporation (PE) coupling system (FO-PE) based on high-performance polyamide FO membrane and photothermal polypyrrole nano-sponge (PPy/sponge) is developed for continuous FO separation with a steady water flux. The PE unit with a photothermal PPy/sponge floating on the surface of draw solution (DS) can continuously in situ concentrate DS by solar-driven interfacial water evaporation, which effectively offsets the dilution effect due to the injected water from FO unit. A good balance between the permeated water in FO and the evaporated water in PE can be established by coordinately regulating the initial concentration of DS and light intensity. As a consequence, the polyamide FO membrane exhibits a steady water flux of 11.7 L m-2 h-1 over time under FO coupling PE condition, effectively alleviating the decline in water flux under FO alone. Additionally, it shows a low reverse salt flux of 3 g m-2 h-1. The FO-PE coupling system utilizing clean and renewable solar energy to achieve a continuous FO separation is significantly meaningful for practical applications.