Strain-modulated Ru-O Covalency in Ru-Sn Oxide Enabling Efficient and Stable Water Oxidation in Acidic Solution.

RuO2 is one of the benchmark electrocatalysts used as the anode material in proton exchange membrane water electrolyser. However, its long-term stability is compromised due to the participation of lattice oxygen and metal dissolution during oxygen evolution reaction (OER). In this work, weakened covalency of Ru-O bond was tailored by introducing tensile strain to RuO6 octahedrons in a binary Ru-Sn oxide matrix, prohibiting the participation of lattice oxygen and the dissolution of Ru, thereby significantly improving the long-term stability. Moreover, the tensile strain also optimized the adsorption energy of intermediates and boosted the OER activity. Remarkably, the RuSnOx electrocatalyst exhibited excellent OER activity in 0.1 M HClO4 and required merely 184 mV overpotential at a current density of 10 mA cm-2 . Moreover, it delivered a current density of 10 mA cm-2 for at least 150 h with negligible potential increase. This work exemplifies an effective strategy for engineering Ru-based catalysts with extraordinary performance toward water splitting.

Constructing Fe-N4 Sites through Anion Exchange-mediated Transformation of Fe Coordination Environments in Hierarchical Carbon Support for Efficient Oxygen Reduction.

Metal single atoms (SAs) anchored in carbon support via coordinating with N atoms are efficient active sites to oxygen reduction reaction (ORR). However, rational design of single atom catalysts with highly exposed active sites is challenging and urgently desirable. Herein, an anion exchange strategy is presented to fabricate Fe-N4 moieties anchored in hierarchical carbon nanoplates composed of hollow carbon spheres (Fe-SA/N-HCS). With the coordinating O atoms are substituted by N atoms, Fe SAs with Fe-O4 configuration are transformed into the ones with Fe-N4 configuration during the thermal activation process. Insights into the evolution of central atoms demonstrate that the SAs with specific coordination environment can be obtained by modulating in situ anion exchange process. The strategy produces a large quantity of electrochemical accessible site and high utilization rate of Fe-N4 . Fe-SA/N-HCS shows excellent ORR electrocatalytic performance with half-wave potential of 0.91 V (vs. RHE) in 0.1 M KOH, and outstanding performance when used in rechargeable aqueous and flexible Zn-air batteries. The evolution pathway for SAs demonstrated in this work offers a novel strategy to design SACs with various coordination environment and enhanced electrocatalytic activity.

Hydrogen Spillover-Bridged Volmer/Tafel Processes Enabling Ampere-Level Current Density Alkaline Hydrogen Evolution Reaction under Low Overpotential.

Water-alkaline electrolysis holds a great promise for industry-scale hydrogen production but is hindered by the lack of enabling hydrogen evolution reaction electrocatalysts to operate at ampere-level current densities under low overpotentials. Here, we report the use of hydrogen spillover-bridged water dissociation/hydrogen formation processes occurring at the synergistically hybridized Ni3S2/Cr2S3 sites to incapacitate the inhibition effect of high-current-density-induced high hydrogen coverage at the water dissociation site and concurrently promote Volmer/Tafel processes. The mechanistic insights critically important to enable ampere-level current density operation are depicted from the experimental and theoretical studies. The Volmer process is drastically boosted by the strong H2O adsorption at Cr5c sites of Cr2S3, the efficient H2O* dissociation via a heterolytic cleavage process (Cr5c-H2O* + S3c(#) → Cr5c-OH* + S3c-H#) on the Cr5c/S3c sites in Cr2S3, and the rapid desorption of OH* from Cr5c sites of Cr2S3 via a new water-assisted desorption mechanism (Cr5c-OH* + H2O(aq) → Cr5c-H2O* + OH-(aq)), while the efficient Tafel process is achieved through hydrogen spillover to rapidly transfer H# from the synergistically located H-rich site (Cr2S3) to the H-deficient site (Ni3S2) with excellent hydrogen formation activity. As a result, the hybridized Ni3S2/Cr2S3 electrocatalyst can readily achieve a current density of 3.5 A cm-2 under an overpotential of 251 ± 3 mV in 1.0 M KOH electrolyte. The concept exemplified in this work provides a useful means to address the shortfalls of ampere-level current-density-tolerant Hydrogen evolution reaction (HER) electrocatalysts.

Scalable Spray Drying Production of Amorphous V2 O5 -EGO 2D Heterostructured Xerogels for High-Rate and High-Capacity Aqueous Zinc Ion Batteries.

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising in stationary grid energy storage due to their advantages in safety and cost-effectiveness, and the search for competent cathode materials is one core task in the development of ZIBs. Herein, the authors design a 2D heterostructure combining amorphous vanadium pentoxide and electrochemically produced graphene oxide (EGO) using a fast and scalable spray drying technique. The unique 2D heterostructured xerogel is achieved by controlling the concentration of EGO in the precursor solution. Driven by the improved electrochemical kinetics, the resultant xerogel can deliver an excellent rate capability (334 mAh g-1 at 5 A g-1 ) as well as a high specific capacity (462 mAh g-1 at 0.2 A g-1 ) as the cathode material in ZIB. It is also shown that the coin cell constructed based on spray-dried xerogel can output steady, high energy densities over a broad power density window. This work provides a scalable and cost-effective approach for making high performance electrode materials from cheap sources through existing industrialized materials processing.

Effects of compositional engineering and surface passivation on the properties of halide perovskites: a theoretical understanding.

Halide perovskite solar cells have demonstrated high power conversion efficiency. Compositional engineering and surface passivation technologies have been drawing great attention to enhance their energy conversion efficiency and moisture resistance. In this study, the density functional theory method was employed to understand the effects of compositional engineering at the A site of perovskites and the 3-butenoic acid-based passivation layer on the structural, electronic and optical properties of halide perovskites. Our results suggest that the electronic and optical properties of CsPbI3 can be tuned by the mixing of caesium and FA cations. Moreover, the calculation of adsorption energies on mixed-cation Cs1-xFAxPbI3(001) surfaces reveals that the much stronger adsorption strength of 3-butenoic acid facilitates blocking of the interaction of surfaces with water molecules. Meanwhile, the calculated results indicate that adopting such an organic molecule as a passivation layer does not compromise their excellent electronic and optical properties. Our theoretical understanding of the A cation engineering and organic molecule-based surface passivation will be beneficial to the improvement of the overall performance of perovskite solar cells.

A Yolk-Shell Structured Silicon Anode with Superior Conductivity and High Tap Density for Full Lithium-Ion Batteries.

The poor cycling stability resulting from the large volume expansion caused by lithiation is a critical issue for Si-based anodes. Herein, we report for the first time of a new yolk-shell structured high tap density composite made of a carbon-coated rigid SiO2 outer shell to confine multiple Si NPs (yolks) and carbon nanotubes (CNTs) with embedded Fe2 O3 nanoparticles (NPs). The high tap density achieved and superior conductivity can be attributed to the efficiently utilised inner void containing multiple Si yolks, Fe2 O3 NPs, and CNTs Li+ storage materials, and the bridged spaces between the inner Si yolks and outer shell through a conductive CNTs "highway". Half cells can achieve a high area capacity of 3.6 mAh cm-2 and 95 % reversible capacity retention after 450 cycles. The full cell constructed using a Li-rich Li2 V2 O5 cathode can achieve a high reversible capacity of 260 mAh g-1 after 300 cycles.

Ultrathin Nitrogen-Doped Holey Carbon@Graphene Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions in Alkaline and Acidic Media.

Efficient nonprecious-metal oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts are key for the commercial viability of fuel cells, metal-air batteries, and water-splitting systems. Thus, high-performance ORR and OER electrocatalysts in acidic electrolytes are needed to support high-efficiency proton exchange membrane (PEM)-based systems. Herein, we report a new approach to design and prepare an ultrathin N-doped holey carbon layer (HCL) on a graphene sheet that exhibits outstanding bifunctional ORR/OER activities in both alkaline and acidic media. The edge sites of HCL are utilized to achieve selective doping of highly active pyridinic-N. The sandwiched graphene sheet provides mechanical support, stabilizes HCL structure and promotes charge transfer. The synergetic effect of the catalyst structure overcomes the drawbacks of holey graphene approaches. The resulting ORR and OER performances are equal to or better than the top-ranked electrocatalysts.

Engineered Hematite Mesoporous Single Crystals Drive Drastic Enhancement in Solar Water Splitting.

Mesoporous single crystals (MSCs) rendering highly accessible surface area and long-range electron conductivity are extremely significant in many fields, including catalyst, solar fuel, and electrical energy storage technologies. Hematite semiconductor, whose performance has been crucially limited by its pristine poor charge separation efficiency in solar water splitting, should benefit from this strategy. Despite successful synthesis of many metal oxide MSCs, the fabrication of hematite MSCs remains to be a great challenge due to its quite slow hydrolysis rate in water. Herein, for the first time, we have developed a synthetic strategy to prepare hematite MSCs and systematically investigated their growth mechanism. The electrode fabricated with these crystals is able to achieve a photocurrent density of 0.61 mA/cm(2) at 1.23 V vs RHE under AM 1.5G simulated sunlight, which is 20 times higher than that of electrodes made of solid single crystals. The enhancement is ascribed to the superior light absorption and enhanced charges separation. Our results demonstrate the advantage of incorporation of nanopores into the large-sized hematite single crystals and provide a valuable insight for the development of high performance photoelectrodes in PEC application.

Strongly Coupled CoCr2 O4 /Carbon Nanosheets as High Performance Electrocatalysts for Oxygen Evolution Reaction.

A strongly coupled CoCr2 O4 /carbon nanosheet composite is concurrently grown via a facile one-step molten-salt calcination approach. The strong coupling between carbon and CoCr2 O4 has improved the electrical conductivity and preserved the active sites in catalysts. These results may pave the way to improve the performance of spinel oxides as electrocatalysts for oxygen evolution reactions.

Improved conductivity of NdFeO3 through partial substitution of Nd by Ca: a theoretical study.

NdFeO3 is an important candidate material for gas sensors and intermediate-temperature solid oxide fuel cells (IT-SOFC). However, its low conductivity prohibits its applications. In this study, we report that the doping of Ca by partially replacing Nd can effectively increase its conductivity. Through the electronic structure analysis of Nd(1-x)Ca(x)FeO3 (x = 0.00, 0.25, 0.50, 0.75 or 1.00) based on the first-principles density functional theory calculations, it is found that the hole states introduced by Ca substitution appear just above the Fermi level, which implies a high mobility of electrons/holes along the Fe-O-Fe bonding network. Specifically, it becomes easier to form O vacancies after Ca doping. Since the diffusion of O anions occurs through a vacancy hopping mechanism, the ion conductivity is also improved. These findings help us to gain an in-depth understanding of the colossally increased conductivity of Ca doped NdFeO3 and turn the electronic conduction for its practical application in gas sensors and IT-SOFC.

Hydrothermal transformation of dried grass into graphitic carbon-based high performance electrocatalyst for oxygen reduction reaction.

In this work, we present a low cost and environmentally benign hydrothermal method using dried grass as the sole starting material without any synthetic chemicals to directly produce high quality nitrogen-doped carbon nanodot/nanosheet aggregates (N-CNAs), achieving a high yield of 25.2%. The fabricated N-CNAs possess an N/C atomic ratio of 3.41%, consist of three typed of doped N at a ratio of 2.6 (pyridinic):1.7 (pyrrolic):1 (graphitic). The experimental results reveal that for oxygen reduction reaction (ORR), the performance of N-CNAs, in terms of electrocatalytic activity, stability and resistance to crossover effects, is better or comparable to the commercial Pt/C electrocatalyst. The theoretical studies further indicate that the doped pyridinic-N plays a key role for N-CNAs' excellent four-electron ORR electrocatalytic activity.

Fluorine-doped porous single-crystal rutile TiO2 nanorods for enhancing photoelectrochemical water splitting.

Fluorine-doped hierarchical porous single-crystal rutile TiO(2) nanorods have been synthesized through a silica template method, in which F(-) ions acts as both n-type dopants and capping agents to make the isotropic growth of the nanorods. The combination of high crystallinity, abundant surface reactive sites, large porosity, and improved electronic conductivity leads to an excellent photoelectrochemical activity. The photoanode made of F-doped porous single crystals displays a remarkably enhanced solar-to-hydrogen conversion efficiency (≈0.35 % at -0.33 V vs. Ag/AgCl) under 100 mW cm(-2) of AM=1.5 solar simulator illumination that is ten times of the pristine solid TiO(2) single crystals.

Thermal Shock Synthesis for Loading Sub-2 nm Ru Nanoclusters on Titanium Nitride as a Remarkable Electrocatalyst toward Hydrogen Evolution Reaction.

Heterogeneous catalysts embracing metal entities on suitable supports are profound in catalyzing various chemical reactions, and substantial synthetic endeavors in metal-support interaction modulation are made to enhance catalytic performance. Here, it is reported the loading of sub-2 nm Ru nanocrystals (NCs) on titanium nitride support (HTS-Ru-NCs/TiN) via a special Ru-Ti interaction using the high-temperature shock (HTS) method. Direct dechlorination of the adsorbed RuCl3, ultrafast nucleation process, and short coalescence duration at ultrahigh temperatures contribute to the immobilization of Ru NCs on TiN support via producing the Ru-Ti interfacial perimeter. HTS-Ru-NCs/TiN shows remarkable activity toward hydrogen evolution reaction (HER) in alkaline solution, yielding ultralow overpotentials of 16.3 and 86.6 mV to achieve 10 and 100 mA cm-2, respectively. The alkaline and anion exchange membrane water electrolyzers assembled using HTS-Ru-NCs/TiN yield 1.0 A cm-2 at 1.65 and 1.67 V, respectively, which validate its applicability in the hydrogen production industry. Theoretical simulations reveal the favorable formation of Ru─O and Ti─H bonds at the interfacial perimeters between Ru NCs and TiN, which accelerates the prerequisite water dissociation kinetics for enhanced HER activity. This exemplified work motivates the design of specific interfacial perimeters via the HTS strategy to improve the performance of diverse catalysis.

Cross-linked g-C3 N4 /rGO nanocomposites with tunable band structure and enhanced visible light photocatalytic activity.

Cross-linked rather than non-covalently bonded graphitic carbon nitride (g-C3 N4 )/reduced graphene oxide (rGO) nanocomposites with tunable band structures have been successfully fabricated by thermal treatment of a mixture of cyanamide and graphene oxide with different weight ratios. The experimental results indicate that compared to pure g-C3 N4 , the fabricated CN/rGO nanocomposites show narrowed bandgaps with an increased in the rGO ratio. Furthermore, the band structure of the CN/rGO nanocomposites can be readily tuned by simply controlling the weight ratio of the rGO. It is found that an appropriate rGO ratio in nanocomposite leads to a noticeable positively shifted valence band edge potential, meaning an increased oxidation power. The tunable band structure of the CN/rGO nanocomposites can be ascribed to the formation of C-O-C covalent bonding between the rGO and g-C3 N4 layers, which is experimentally confirmed by Fourier transform infrared (FT-IR) and X-ray photoelectron (XPS) data. The resulting nanocomposites are evaluated as photocatalysts by photocatalytic degradation of rhodamine B (RhB) and 4-nitrophenol under visible light irradiation (λ > 400 nm). The results demonstrate that the photocatalytic activities of the CN/rGO nanocomposites are strongly influenced by rGO ratio. With a rGO ratio of 2.5%, the CN/rGO-2.5% nanocomposite exhibits the highest photocatalytic efficiency, which is almost 3.0 and 2.7 times that of pure g-C3 N4 toward photocatalytic degradation of RhB and 4-nitrophenol, respectively. This improved photocatalytic activity could be attributed to the improved visible light utilization, oxidation power, and electron transport property, due to the significantly narrowed bandgap, positively shifted valence band-edge potential, and enhanced electronic conductivity.

Vapor-phase hydrothermal growth of novel segmentally configured nanotubular crystal structure.

A new form of nanotubular crystal structure is directly grown by a vapor-phase hydrothermal method via an epitaxial orientated crystal growth mechanism. The as-prepared nanotubes possess a unique multi-tunnel core-shell layered nanotubular structure with droplet shaped polygonal periphery and segmental crystal configuration. They are dimension-tunable and demonstrate superior ion exchange properties in terms of exchange rate and ion accommodating capacity.

Stabilization and Performance Enhancement Strategies for Halide Perovskite Photocatalysts.

Solar-energy-powered photocatalytic fuel production and chemical synthesis are widely recognized as viable technological solutions for a sustainable energy future. However, the requirement of high-performance photocatalysts is a major bottleneck. Halide perovskites, a category of diversified semiconductor materials with suitable energy-band-enabled high-light-utilization efficiencies, exceptionally long charge-carrier-diffusion-length-facilitated charge transport, and readily tailorable compositional, structural, and morphological properties, have emerged as a new class of photocatalysts for efficient hydrogen evolution, CO2 reduction, and various organic synthesis reactions. Despite the noticeable progress, the development of high-performance halide perovskite photocatalysts (HPPs) is still hindered by several key challenges: the strong ionic nature and high hydrolysis tendency induce instability and an unsatisfactory activity due to the need for a coactive component to realize redox processes. Herein, the recently developed advanced strategies to enhance the stability and photocatalytic activity of HPPs are comprehensively reviewed. The widely applicable stability enhancement strategies are first articulated, and the activity improvement strategies for fuel production and chemical synthesis are then explored. Finally, the challenges and future perspectives associated with the application of HPPs in efficient production of fuels and value-added chemicals are presented, indicating the irreplaceable role of the HPPs in the field of photocatalysis.

Portable Conductometric Sensing Probe for Real-Time Monitoring Ammonia Profile in Coastal Waters.

An ability to real-time and continuously monitor ammonium/ammonia profiles of coastal waters over a prolonged period in a simple and maintenance-free fashion would enable economic conducting large-scale assessments, providing the needed scientific insights to better control and mitigate the impact of eutrophication on coastal ecosystems. However, this is a challenging task due to the lack of capable sensors. Here, we demonstrate the use of a membrane-based conductometric ammonia sensing probe (CASP) for real-time monitoring of ammonia levels in coastal waters. A boric acid/glycerol receiving phase is investigated and innovatively utilized to overcome the high salinity of coastal water-induced analytical errors. A calibration-free approach is used to eliminate the need for ongoing calibration, while the issues concerning practical applications, such as salinity variation, ammonia intake capability, and biofouling, are systematically investigated. The field deployment at an estuary confluence water site over a half-moon cycle period confirms that CASP is capable of continuously monitoring the ammonia profile of coastal waters in real-time with high resolution and accuracy to unveil the dynamic ammonia concentration changes over a prolonged period.

Vapor-phase hydrothermal transformation of HTiOF3 intermediates into {001} faceted anatase single-crystalline nanosheets.

For the first time, a facile, one-pot hydrofluoric acid vapor-phase hydrothermal (HF-VPH) method is demonstrated to directly grow single-crystalline anatase TiO(2) nanosheets with 98.2% of exposed {001} faceted surfaces on the Ti substrate via a distinctive two-stage formation mechanism. The first stage produces a new intermediate crystal (orthorhombic HTiOF(3) ) that is transformed into anatase TiO(2) nanosheets during the second stage. The findings reveal that the HF-VPH reaction environment is unique and differs remarkably from that of liquid-phase hydrothermal processes. The uniqueness of the HF-VPH conditions can be readily used to effectively control the nanostructure growth.

Nanocrystal Cu2O-loaded TiO2 nanotube array films as high-performance visible-light bactericidal photocatalyst.

In this work, we report the use of a non-toxic nanocrystal Cu(2)O-loaded TiO(2) nanotube array (Cu(2)O/TNTs) film as high-performance visible-light bactericidal photocatalyst. The samples were characterized by field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible diffusion reflection spectroscopy. This Cu(2)O/TNTs film photocatalyst is capable of complete inactivation of Escherichia coli in 5 × 10(7) colony-forming units/mL within a record short disinfection time of 20 min under visible-light irradiation. The average bactericidal percentage of the Cu(2)O/TNTs for E. coli under visible-light irradiation are 20 times and 6.6 times higher than those of TNTs under the same conditions and Cu(2)O/TNTs without light, respectively. This superior bactericidal performance is mainly attributed to the high ability to produce OH radicals by both photogenerated electron and hole of the prepared photocatalyst under visible light. The Cu(2)O/TNTs film photocatalyst makes it applicable to broad fields including drinking water disinfection.

Interpolation between W Dopant and Co Vacancy in CoOOH for Enhanced Oxygen Evolution Catalysis.

Electronic structure engineering via integrating two defect structures with opposite modulation effects holds the key to fully unlocking the power of a catalyst. Herein, an interpolation principle is proposed to activate CoOOH via W doping and Co vacancies for the oxygen evolution reaction. Density functional theory suggests opposite roles for the W dopant and the Co vacancy but a synergy between them in tuning the electronic states of the Co site, leading to near-ideal intermediate energetics and dramatically lowered catalytic overpotential. Experimental studies confirm the modulation of the electronic structure and validate the greatly enhanced catalytic activity with a small overpotential of 298.5 mV to drive 50 mA cm-2 . The discovery of the interpolation between dopants and vacancies opens up a new methodology to design efficient catalysts for various electrochemical reactions.