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Electrochemical urea oxidation reaction (UOR) is a promising alternative to the oxygen evolution reaction for reducing the overall potential of the hydrogen evolution reaction during water electrolysis. The theoretical potential for the UOR is only 0.37 V versus reversible hydrogen electrode (RHE). However, the kinetics of the six-electron transfer process involved in the UOR are inherently sluggish, resulting in high overpotential during the reaction. This study designed an active catalyst with a lower kinetic barrier in the UOR by fabricating blending CoOOH–Ni(OH)2 nanoclusters through the structural transformation of amorphous Co–Ni hydroxide films. This structural transformation was investigated using high-angle annular dark-field scanning transmission electron microscopy, corresponding energy-dispersive X-ray spectroscopy, and in situ X-ray absorption spectra. The blending CoOOH–Ni(OH)2 nanoclusters exhibited superior electrocatalytic activity in the UOR in an alkaline environment, achieving a low onset potential of 1.24 V (vs. RHE) in 1 M KOH with 0.5 M urea. We employed the CoOOH–Ni(OH)2 nanoclusters as anodic electrocatalysts in a two-cell electrolyzer for asymmetric electrocatalysis. Hydrogen could be produced at a remarkable current density of 10 mA cm−2 at a low applied potential of only 0.45 V. Density functional theory calculations revealed that blending CoOOH–Ni(OH)2 nanoclusters with more oxygen vacancies exhibited a lower Gibbs free energy for the intermediate reaction pathway of NCONH2 → NCONH, compared with the fine structure of CoNiOx (x = 2–3). This study lays down a novel pathway for developing new blending electrocatalysts to be used in electrochemical reactions. [ABSTRACT FROM AUTHOR]

While Ni-rich cathodes have been widely adopted in high-energy lithium-ion batteries, there remains room for improvement regarding their cycle stability and safety. Herein, hexagonal boron nitride (h-BN) is demonstrated, for the first time, to be an effective surface modification additive for Ni-rich cathodes. The h-BN coated Ni-rich cathode, prepared via a rapid low-temperature post-calcination process, shows markedly improved cycle stability and safety with only a trace amount of h-BN being added (1 wt% relative to the cathode oxide). Systematic synchrotron post-mortem and operando X-ray analyses reveal that the improvements could be attributed to the anion-trapping ability of the B atoms in h-BN, which mitigates surface Ni-ion reduction and carbonate accumulation caused by electrolyte corrosion during both cycling and thermal runaway. Furthermore, the high thermal conductivity of h-BN contributes to efficient heat dissipation during the early stages of thermal runaway and therefore delays the onset temperature. This work identifies h-BN as well as the concept of "anion-trapping" as promising strategies for enhancing the cycle life and safety of Ni-rich cathodes and presents an industrially facile method to accomplish such applications. [ABSTRACT FROM AUTHOR]

We have introduced a Friedel–Crafts alkylation strategy of a Ni-salphen complex as derived from 2-hydroxy-5-methoxybenzaldehyde, an isomer of biomass derived vanillin, to construct a Ni-salphen based porous organic polymer (Ni@T-POP). The X-ray absorption spectroscopy (XAS) analysis revealed the existence of Ni–N2O2 core sites in the Ni@T-POP framework, which demonstrates unprecedented catalytic efficiency towards oxidative decontamination of sulfur mustards (HD's) compared to its complex precursor. [ABSTRACT FROM AUTHOR]

We synthesize a Na-doped iridium oxide thin film via a sequential oxidative–reductive reaction in which the Ir3+ precursor undergoes a ligand exchange and oxidation process by sodium hypochlorite and oxygen to form Ir>4+, followed by an immediate reduction step to produce Na-doped iridium oxide. Detailed reaction steps occurring in the wet chemical bath are validated by time-resolved X-ray absorption spectroscopy. Analysis using X-ray photoelectron spectroscopy indicates the composition to be Na0.44IrO1.55(OH)1.55(H2O)0.73. In addition, the Na-doped iridium oxide reveals an amorphous structure with a smooth surface morphology. In electrochemical characterization, the Na-doped iridium oxide exhibits a significantly larger normalized charge storage capacity of 0.32 mC cm−2 nm−1 over that of sputtered iridium oxide (0.08 mC cm−2 nm−1). In a cell viability test, the Na-doped iridium oxide shows a negligible bio-toxicity. In short, the Na-doped iridium oxide demonstrates promising potential as a bio-stimulating electrode for implantable bio-electronics. [ABSTRACT FROM AUTHOR]

A high temperature solid oxide electrolysis cell is recognized as a promising technology for CO2 conversion (CO2-SOEC). The development of alternative cathode materials substituting conventional Ni/YSZ is a great challenge for SOECs, on which multi-step elementary reactions (e.g., adsorption of CO2, conversion of reaction intermediates, and desorption of CO) occur in succession. Herein, the Ce decorated La0.43Ca0.37Ti0.94Ni0.06O3−δ perovskite (denoted as LCTNi-Ce) is synthesized and applied as a potential cathode electrocatalyst for a CO2-SOEC. The in situ exsolution strategy and A-site deficiency enable the surface decoration of plenty of Ni nanoparticles (NPs) serving as efficient reactive sites. Furthermore, the Ce decoration leads to increased oxygen vacancy concentration, accelerated oxygen exchange rate and improved CO desorption capacity. The symmetrical half-cell measurement confirmed the boosted electrolysis performance in both CO2/CO and CO2/H2 atmospheres. DRT analysis further evidences the facilitated oxygen ion transportation and gas adsorption/dissociation upon Ce decoration. Compared to a LCTNi cell, the LCTNi-Ce cell exhibits a significantly promoted current density of −0.557 A cm−2 in 50% CO2/50% H2 at 800 °C and 1.3 V, and a reduced Rp value of 0.514 Ω cm−2 under OCV condition. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate the successful construction of two Fe-metalated porous organic polymers having planar (Fe-Tt-POP) and non-planar (Fe-Rb-POP) geometry via the ternary copolymerization strategy for the catalytic oxidative decontamination of different sulfur-based mustard gas simulants (HD). Fe-Tt-POP exhibits superior catalytic performance for the oxidation of thioanisole (TA) in comparison with Fe-Rb-POP. Interestingly, this activity difference can be further explored by in situ operando DRIFTS and DFT computational studies. [ABSTRACT FROM AUTHOR]

There have been several studies on the catalytic activity of the hydrogen evolution reaction (HER) using ultralow loading of Pt catalysts or even Pt single atom catalysts. However, Pt single atom deposited on the surface of the carbon or metal oxide material has some drawbacks, such as high possibility of Pt desorption from the supported material in the electrolyte. Besides, from the reaction mechanism perspective, each Pt atom in this type of catalyst is too far to achieve high HER efficiency via the Tafel reaction pathway. In this work, gold nanodendrites (Au NDs) with high facet surface were chosen as the supported materials for studying the relation between the low loading amount of Pt atoms and the reaction mechanism of the HER activity. The atomic deposition of Pt atoms on the surface of Au NDs can be controlled effectively using a constant-current synthetic method. It was found that the HER electrocatalytic activity of ultralow Pt loading catalyst, with Pt atoms to total surface atoms of Au NDs (O-Pt on Au NDs) of 5.5%, could achieve high efficiency via the Tafel reaction pathway, showing a low overpotential of ∼18 mV at a current density of 10 mA cm−2 and a small Tafel slope of ∼31 mV dec−1, which is close to that of commercial Pt/C with 20 wt% Pt. As confirmed by Inductively Coupled Plasma Mass Spectrometry(ICP-MS), the Pt loading amount of O-Pt on Au NDs was ∼3.8 ± 0.2 μg cm−2 on a physical area of carbon fiber paper. The turnover frequency (TOF) of O-Pt on Au NDs was found to be 40.1 ± 2.5 H2 per s at 50 mV. This work provides a feasible approach to control the atomic deposition of Pt on a specific substrate as an active catalyst for various catalytic applications. [ABSTRACT FROM AUTHOR]

The application of Pt-based catalysts in propane dehydrogenation (PDH) is restricted by low propylene selectivity, metal sintering and carbon deposition. It has been reported that the performance of catalysts is strongly related to the electronic and geometric properties of the Pt particles and the acidity of the support. Herein, we report that a niobium-modified alumina supported platinum catalyst exhibits high propylene selectivity and superior stability. A high conversion of 28.8% and a high propylene selectivity above 96% are achieved over the Pt/Nb1Al2-O catalyst for propane dehydrogenation at 600 °C after 8 h in a fixed bed reactor. Consecutive dehydrogenation–regeneration operations showed that the stability of Pt/Nb1Al2-O was much higher than that of Pt/Al2O3. NH3-TPD revealed that the strong acidity is decreased, while the medium acidity is increased after introducing niobium into Al2O3, which may be attributed to the formation of new acid sites, probably Lewis acid sites from niobium oxide species. CO-adsorbed FTIR spectroscopy, CO chemisorption, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) results revealed the enhancement of electron density and the decrease of dispersion of Pt particles after the introduction of Nb, which is beneficial for inhibiting the by-reactions (carbon formation and C–C bond cleavage). [ABSTRACT FROM AUTHOR]

Rechargeable aqueous zinc-ion batteries (ZIBs) are emerging as an alternative to lithium-ion batteries in large-scale energy storage applications due to their safety and environmental friendliness. However, their application is hindered by the lack of suitable cathode materials that provide high capacity and long cycling stability. In this work, we have designed Cu–MnO nanospheres with abundant manganese/oxygen defects as a cathode material via calcination and reduction of manganese dioxide (MnO2) in an Ar/H2 atmosphere. Investigation of the electrochemical mechanism showed that the spinel-type Cu–MnO electrode started to transform into layered-type Cu–MnO2·nH2O nanoflowers upon initial charging, and thus, the subsequent Zn2+ intercalation and H+ conversion reactions took place in the Cu–MnO2·nH2O material. The underlying phase transformation of the Cu–MnO nanospheres and energy storage mechanism of the Cu–MnO2·nH2O nanoflowers were systematically investigated using a broad range of characterization techniques. Manganese vacancy was also observed in Cu–MnO2·nH2O, which interestingly triggered the lattice oxygen redox reaction. As a result, when employed as a cathode material in zinc-ion batteries, Cu–MnO2·nH2O delivered a high specific capacity of 320 mA h g−1 and long-term cycling stability with a capacity retention of over 70% after 1000 cycles. This work not only provides insight into the design of transition-metal-modified manganese monoxide cathodes but also broadens the horizon for understanding the electrochemical properties and energy-storage mechanism of low-valance manganese-based cathode materials in rechargeable zinc-ion batteries. [ABSTRACT FROM AUTHOR]

Herein, the electrodeposited-film electrode CFeCoNiP was fabricated to serve as a bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Kinetic Tafel slope analysis suggests that the HER follows the Volmer–Tafel mechanism (29 mV dec−1), indicating that the recombination of the two adsorbed hydrogen atoms is the rate-determining step. The FeCoNi-based thick film (thickness: 168.3 μm) shows a metallic state favorable for electron transfer; on the other hand, in the case of the FeCoNi-based thin film (thickness: 389.2 nm), the in operando XAS investigation reveals that Fe3+-assisted water dissociation promotes the formation of Co2+–μ-H–Ni3+ (catalyst-Had) species, which subsequently undergoes reductive elimination to furnish H2 gas via the HER process. During the OER, the CoNi–oxide matrix acts as a chemical and electroconductive host to build/stabilize the key intermediate [Fe4+＝O/Fe3+–O˙] motifs; this subsequently triggers the catalytic O–O bond formation (30 mV dec−1) through the radical–radical coupling of the adjacent [Fe4+＝O/Fe3+–O˙] motifs or/and OH− attack on the Fe4+-induced electrophilic oxygen center, leading to the release of O2. The mechanistic experiments provide advanced insights into the catalytic kinetics/intermediates and demonstrate that the electronically cooperative interplay among Fe/Co/Ni leads to enhanced alkaline water electrolysis. The CFeCoNiP catalyst exhibits an excellent HER activity (specific activity js = 0.227 mA cm−2) with a low charge transfer resistance (3.9 Ω) and an overpotential of 37 mV, achieving the current density of 10 mA cm2; moreover, it shows good OER activity (js = 1.798 mA cm−2) with low charge transfer resistance (2.1 Ω) and an overpotential of 250 mV, approaching a current density of 10 mA cm−2 in a 1 M NaOH aqueous solution. The CFeCoNiP/NF (electrodeposited on Ni foam) electrode-pair device achieved the current densities of 100 and 500 mA cm−2 at the voltages of 1.65 and 1.86 V, respectively, under alkaline conditions. [ABSTRACT FROM AUTHOR]

The mechanistic investigation of copper-catalysed transformations has been an important and fundamental task. Herein, we report via XAS and EPR spectroscopy that the sodium bis(trimethylsilyl)amide could reduce Cu(II) to a Cu(I) species serving as an electron donor. XAS spectroscopy demonstrates that the newly formed Cu(I) species is the Cu[N(TMS)2]2Na ate complex, in which the nitrogen atoms coordinate with copper linearly. [ABSTRACT FROM AUTHOR]

Atomically dispersed metal catalysts have demonstrated superb electrocatalytic activity because of optimal atom efficiency. However, a rational design of low-cost, high-performance single atom catalysts remains a great challenge due to the elusive chemical reactions of the formation of metal active sites. In this work, biomass hydrogel is prepared as a template for mass production of three-dimensional carbon aerogel-supported single metal atom catalysts. By tailoring the structure of the hydrogel templates, the obtained carbon aerogels exhibit an increase of microporous defects which capture and stabilize isolated metal atoms and minimize aggregation during pyrolysis. Extended X-ray absorption fine structure, Mössbauer spectroscopy, and nitrogen adsorption–desorption isotherm measurements indicate that single metal centers of FeN4 are formed and embedded within the hierarchical porous carbon frameworks. The obtained composites exhibit outstanding catalytic activity towards oxygen reduction in alkaline media, with a high onset potential of +1.05 V and half-wave potential of +0.88 V, as well as excellent durability. Remarkably, when the carbon aerogels are used as the cathode catalyst in an aluminum–air battery, the battery achieves an ultrahigh open-circuit voltage of 1.81 V, large power density of 181.1 mW cm−2 and stable discharge voltage of 1.70 V at 20 mA cm−2, markedly better than those with commercial Pt/C as the cathode catalyst. [ABSTRACT FROM AUTHOR]

Transformation of lignin into high value-added phenolics is of great significance but extremely challenging. Herein, we report a single-step process for the preparation of phenolics from both 2-methoxy-4-propylphenol (one of the major products derived from lignin) and lignin oil (lignin-derived monomers) over Au-based catalysts. In this process, the desired Ar–OH substituents can be maintained and phenolics can be obtained with high yields. The performance of the Au/Nb2O5 catalyst is compared with those of Au/TiO2, Au/Al2O3 and Au/ZrO2 and it is shown that Au/Nb2O5 has high activity, excellent stability and remarkable selectivity to phenolics, with the yields of phenolics reaching 84.2% for 2-methoxy-4-propylphenol and 66.7 wt% for lignin oil. The detailed studies reveal that the hydrodeoxygenation of 2-methoxy-4-propylphenol undergoes two-steps, i.e., hydrolysis to propylcatechol catalyzed by the acid sites of supports, and the hydrogenolysis of propylcatechol to propylphenol realized by the synergistic effect between Au and the supports. It is found that the high hydrodeoxygenation activity of Au/Nb2O5 depends on both the electron-rich Au nanoparticles and the Nb2O5 support with the efficient cleavage of the Caromatic–O linkage. This study provides a new catalytic system towards highly efficient and selective conversion of lignin oils to valuable phenolics. [ABSTRACT FROM AUTHOR]

Quantitative structural parameters of pyrochlore Nd2Ru2O7, with temperature dependence, have been derived upon fitting XRD and EXAFS data. An anomalous expansion of the lattice parameter and the Ru–O bond length indicates a structural instability at low temperatures; in particular, an increase in the non-thermal term of the mean square fluctuation in the bond length is the evidence for a static disorder of Ru atoms. This static disorder is closely correlated with a decrease in the average Ru–O–Ru bond angle with decreasing temperature, favoring the short-range ferromagnetic coupling in the material. This ferromagnetic coupling formed thus triggered the spin frustration at low temperature when the contradictory constraints of antiferromagnetic interaction act upon the same Ru site in the corner-sharing tetrahedrons of pyrochlore Nd2Ru2O7. This study demonstrates that the spin frustration arising from the competition of ferromagnetic/antiferromagnetic interactions in pyrochlore Nd2Ru2O7 will cause structural instability especially on the atomic scale, which provides a new point of view to help understand its particular magnetic state. [ABSTRACT FROM AUTHOR]

Gasochromic VO2 thin films were fabricated by the sol–gel spin-coating technique. The results of X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectroscopy reveal that the origin of gasochromic coloration in VO2 is strongly related to the modulation of its structure and the electron–electron correlation. Upon gasochromic coloration, not only does the valence state change with the incorporation of hydrogen, but also the film undergoes the modification of the local atomic structure. The structural distortion varies the strength of hybridization of the O 2p–V 3d states and the bond distance of V–O and V–O varies. In the hydric process, the local atomic structure of VO2 changes from that of an un-symmetric to that of a symmetric V–O framework. The incorporated hydrogen adds electrons into the V 3d t2g orbital, enhancing the electron–electron correlation by reducing the V–V distance. This work presents a new physical insight in which the modulation of the electron–electron correlation is exploited to control the bleached and colored states, giving rise to the gasochromic phenomenon. The strong correlation among atomic spatial rearrangement, electronic structures, and transmittance supports a cooperative mechanism of the VO2 gasochromic transition. These results reveal a clear correlation between the dynamics of the lattice structure and the electronic properties and suggest a possible pathway to gasochromism and elucidation of its mechanism. [ABSTRACT FROM AUTHOR]

Anion exchange membrane fuel cells are a potentially cost-effective energy conversion technology, however, the electrocatalyst for the anodic hydrogen oxidation reaction (HOR) suffers from sluggish kinetics under alkaline conditions. Herein, we report that Ru-based nanosheets with amorphous-crystalline heterointerfaces of Ru and Ti-doped RuO 2 (a/c-Ru/Ti-RuO 2 ) can serve as a highly efficient HOR catalyst with a mass activity of 4.16 A mg Ru -1 , which is 19.8-fold higher than that of commercial Pt/C. Detailed characterization studies show that abundant amorphous-crystalline heterointerfaces of a/c-Ru/Ti-RuO 2 nanosheets provide oxygen vacancies and unsaturated coordination bonds for balancing adsorption of hydrogen and hydroxyl species on Ru active sites to elevate HOR activity. Moreover, Ti doping can facilitate CO oxidation, leading to enhanced strength to CO poisoning. This work provides a strategy for enhancing alkaline HOR performance over Ru-based catalysts with heteroatom and heterointerface dual-engineering, which will attract immediate interest in chemistry, materials science and beyond., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A novel bis-benzimidazole organic siloxane precursor (BBM-Si) was prepared, and was combined with tetraethylorthosilicate (TEOS) as a mixed Si source. Then, bridged periodic mesoporous organosilica (BBM-PMO) spherical nanoparticles were synthesized by co-condensation using cetyltrimethylammonium bromide (CTAB) as structure directing agent. The optical properties showed that BBM qualifies as an "aggregation induced emission enhanced" (AIEE) molecule, exhibiting characteristics of excited-state intramolecular proton transfer (ESIPT), such as a large Stokes shift and dual fluorescence emission. For the BBM-PMO materials, the silica skeleton provides a rigid environment that limits molecular rotation, resulting in improved fluorescence emission. In particular, the BBM-PMOs exhibited dual emission of the enol and keto forms, achieving a ratiometric response to Cu 2+ with high sensitivity and selectivity in a broad pH range. Additionally, the limit of detection was as low as 7.15 × 10 -9 M in aqueous solution. The X-ray absorption near-edge spectroscopy (XANES) showed the coordination structure through the interaction between copper ions and N atoms of benzimidazole in the BBM-PMO coordinated to Cu 2+ . These results demonstrate that BBM-PMO hybrid materials have potential applications in the fields of bio-imaging and environmental monitoring., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Quantitative structural parameters of pyrochlore Nd2Ru2O7, with temperature dependence, have been derived upon fitting XRD and EXAFS data. An anomalous expansion of the lattice parameter and the Ru-O bond length indicates a structural instability at low temperatures; in particular, an increase in the non-thermal term of the mean square fluctuation in the bond length is the evidence for a static disorder of Ru atoms. This static disorder is closely correlated with a decrease in the average Ru-O-Ru bond angle with decreasing temperature, favoring the short-range ferromagnetic coupling in the material. This ferromagnetic coupling formed thus triggered the spin frustration at low temperature when the contradictory constraints of antiferromagnetic interaction act upon the same Ru site in the corner-sharing tetrahedrons of pyrochlore Nd2Ru2O7. This study demonstrates that the spin frustration arising from the competition of ferromagnetic/antiferromagnetic interactions in pyrochlore Nd2Ru2O7 will cause structural instability especially on the atomic scale, which provides a new point of view to help understand its particular magnetic state.

Gasochromic VO2 thin films were fabricated by the sol-gel spin-coating technique. The results of X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectroscopy reveal that the origin of gasochromic coloration in VO2 is strongly related to the modulation of its structure and the electron-electron correlation. Upon gasochromic coloration, not only does the valence state change with the incorporation of hydrogen, but also the film undergoes the modification of the local atomic structure. The structural distortion varies the strength of hybridization of the O 2p-V 3d states and the bond distance of V-O and V-O varies. In the hydric process, the local atomic structure of VO2 changes from that of an un-symmetric to that of a symmetric V-O framework. The incorporated hydrogen adds electrons into the V 3d t2g orbital, enhancing the electron-electron correlation by reducing the V-V distance. This work presents a new physical insight in which the modulation of the electron-electron correlation is exploited to control the bleached and colored states, giving rise to the gasochromic phenomenon. The strong correlation among atomic spatial rearrangement, electronic structures, and transmittance supports a cooperative mechanism of the VO2 gasochromic transition. These results reveal a clear correlation between the dynamics of the lattice structure and the electronic properties and suggest a possible pathway to gasochromism and elucidation of its mechanism.

The structural properties of (Bi0.5Na0.5)Ti1-xZrxO3 (where 0 ≤ x ≤ 0.7) have been investigated using powder diffraction and X-ray absorption spectroscopy. Diffraction measurements on (Bi0.5Na0.5)TiO3 confirm that both monoclinic Cc and rhombohedral R3c phases are present at room temperature. Doping small amounts of Zr into the B site of (Bi0.5Na0.5)TiO3 initially stabilizes the rhombohedral phase before the orthorhombic Pnma phase begins to form at x = 0.5. Analysis of the Ti K-edge and Zr L3-edge XANES spectra show that the crystallographic phase change has very little effect on the local structure of Ti(4+)/Zr(4+) cations, suggesting that there is little change in the cation off-center displacement within the BO6 octahedra with each successive phase change.