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Purpose The purpose of this paper is to investigate the influence of the potential of hydrogen (pH) and dissolved oxygen in artificial seawater on the passivation behavior of 316L stainless steel. Design/methodology/approach The corrosion behavior was studied by using electrochemical measurements such as electrochemical impedance spectroscopy and polarization curve. The passive films were characterized with X-ray photoelectron spectroscopy. Findings The polarization resistance of the passive film decreases as the pH value drops ascribed to the formation of much more point defects. The donor carrier concentration (ND) in the passive film formed in the deaerated condition is lower than that in aerated conditions. Nevertheless, this phenomenon is the opposite when the pH value is 1 due to the significant decrease of Fe oxides/hydroxides coupled with the stable content of Cr oxides/hydroxides species. In addition, the compositional variation of the passive film also leads to the changes of its semiconductor properties from N-type to bipolar type. Originality/value This paper shows the variation of polarization resistance, corrosion potential, passive film composition and semiconductor properties with the pH value and dissolved oxygen. The results can serve as references to the further study on crevice corrosion of 316L in seawater.

It has been of interest in seeking electrocatalysts that could exercise equally high-efficient and durable hydrogen evolution upon nonselective electrolytes in both acidic and alkaline environments. Herein, we report a facile strategy to fabricate cobalt tungsten phosphides (CoxW2−xP2/C) hollow polyhedrons with tunable composition based on metal-organic frameworks (MOFs) template method. By the deliberate control of W doping, the synthesized catalyst with the composition of Co0.9W1.1P2/C is found to be able to achieve a current density of 10 mA·cm−2 at overpotentials of 35 and 54 mV in acidic and alkaline media, respectively. This combined electrochemical property stands atop the state-of-the-art electrocatalyst counterparts. To unveil the peculiar behavior of the structure, density functional theory (DFT) calculation was implemented and reveals that the surface W-doping facilitates the optimization of hydrogen absorption free energy (ΔGH*) as well as the thermodynamic and kinetics barriers for water dissociation, which is coupled with the hollow structure of Co-W phosphides, leading to the prominent HER catalytic performance. Ministry of Education (MOE) This work was supported by the National Science Foundation for Young Scientists of China (No. 51901018), China Postdoctoral Science Foundation (No. 2019M660456), the National Natural Science Foundation of China (Nos. 51771027 and 21676216), Young Elite Scientists Sponsorship Program by China Association for Science and Technology (YESS, 2019QNRC001), the Fundamental Research Funds for the Central Universities (No. FRF-MP-19-001), National Key Research and Development Program of China (No. 2017YFB0702100) and Singapore MOE AcRF Tier 1 grant M4011528.

Many noble metals are efficient catalysts for oxygen reduction reaction (ORR), including silver (Ag). Among all these noble metals, Ag is the most affordable because of its relative abundance. Surface energy has been proven to play a crucial role in the catalytic process, and straining is an effective operation to raise the surface energy over electrocatalysts. In this work, sonication was utilized to induce strain in Ag nanowires (NWs) through lattice deformation. A 0.18 J/m2 improvement of the surface energy around the stacking faults area has been calculated via density functional theory. The diffusion-limiting current density was evaluated and increases by >20% (from -4.98 to -6.00 mA/cm2) after sonication straining. Meanwhile, the onset potential remains almost constant (i.e., 0.95 V vs RHE). The results show that induction of strain has a strong impact on the diffusion-limiting current density and significantly improves the ORR catalytic performance of Ag NWs.

Understanding the limitations of electrocatalytic activity and developing advanced catalysts with enhanced activity are of exceptional importance for future hydrogen energy applications. Due to the complexity of electrolytic hydrogen evolution in alkaline media, there are limited non-noble metal catalysts to afford large scale applications. Tungsten-based catalysts exhibit favorable stability but relatively low activity owing to their strong H* adsorption characteristics. In this work, cobalt hydroxides/cubic phase WN nanoparticles with strengthened interfaces and adjustable nitrogen vacancies anchored on multi-walled carbon nanotubes (Co(OH)2/c-WN1−x/CNTs) are exploited as highly efficient alkaline hydrogen evolution electrocatalysts, which exhibit remarkable activity with an overpotential of 78 mV at 10 mA cm−2 and a low Tafel slope of 43 mV dec−1 in 1 M KOH media. Density-functional theory calculations revealed that the interfacial combinations of Co(OH)2/c-WN1−x were tuned to facilitate the kinetics of hydrogen evolution, where Co(OH)2 promoted the adsorption of water molecules and the H–OH dissociation, and cubic phase WN with nitrogen vacancies (c-WN1−x) accelerated hydrogen generation by optimizing the hydrogen adsorption free energy.

The catalysis of Au thin film could be improved by fabrication of array structures in large area. In this work, nanoimprint lithography has been developed to fabricate flexible Au micro-array (MA) electrodes with ∼ 100% coverage. Advanced electron microscopy characterisations have directly visualised the atomic-scale three-dimensional (3D) nanostructures with a maximum depth of 6 atomic layers. In-situ observation unveils the crystal growth in the form of twinning. High double layer capacitance brings about large number of active sites on the Au thin film and has a logarithmic relationship with mesh grade. Electrochemistry testing shows that the Au MAs perform much better ethanol oxidation reaction than the planar sample; MAs with higher mesh grade have a greater active site utilisation ratio (ASUR), which is important to build electrochemical double layer for efficient charge transfer. Further improvement on ASUR is expected for greater electrocatalytic performance and potential application in direct ethanol fuel cell.[Figure not available: see fulltext.]. Ministry of Education (MOE) This research was supported by the MOE AcRF Tier 1 grant M4011528. The XRD and FEG-TEM characterisations were performed at Facility for Analysis, Characterisation, Testing and Simulation (FACTS) Lab; the FEG-SEM/FIB characterisations were carried out at Microelectronics Reliability and Characterisation (MRC) Lab.

Although monoclinic WO3 is widely studied as a prototypical photoanode material for solar water splitting, limited success, hitherto, in fabricating WO3 photoanodes that simultaneously demonstrate high efficiency and reproducibility has been realized. The difficulty in controlling both the efficiency and reproducibility is derived from the ever-changing structures/compositions and chemical environments of the precursors, such as peroxytungstic acid and freshly prepared tungstic acid, which render the fabrication processes of the WO3 photoanodes particularly uncontrollable. Herein, a highly reproducible sol-gel process was developed to establish efficient and translucent WO3 photoanodes using a chemically stable ammonium metatungstate precursor. Under standard simulated sunlight of air mass 1.5 G, 100 mW cm−2, the WO3 photoanode delivered photocurrent densities of ca. 2.05 and 2.25 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (RHE), when tested in 1 mol L−1 H2SO4 and CH3SO3H, respectively. Hence, the WO3 photoanodes fabricated herein are one of the WO3 photoanodes with the highest performance ever reported. The reproducibility of the fabrication scheme was evaluated by testing 50 randomly selected WO3 samples in 1 mol L−1 H2SO4, which yielded an average photocurrent density of 1.8 mA cm−2 at 1.23 VRHE with a small standard deviation. Additionally, the effectiveness of the ammonium metatungstate precursor solution was maintained for at least 3 weeks, when compared with the associated upper-limit values of peroxytungstic and tungstic acid based precursors after 3 d. This study presents a key step to the future development of WO3 photoanodes for efficient solar water splitting.

Multimetal high-entropy alloys (HEAs) have been recognized as potential catalysts that can possibly replace the conventional metal oxides and noble metals for use in energy conversion and water splitting such as oxygen evolution reactions (OERs). However, their higher catalysis is restrained by the difficulty in the synthesis of HEAs with desirable morphologies and deformed crystal lattice structures. In this work, an advanced approach was developed to fabricate the smallest possible HEA (i.e., MnFeCoNiCu) with deformed nanoparticles supported on the carbon cloth (CC) surface. The nanoparticles were characterized to be single face-centered cubic (FCC) crystals with highly deformed lattices, giving rise to various defects (such as twins, dislocations and stacking faults). The high surface tension caused by these defects leads to a substantial reduction in the overpotential down to 263 mV for the production of 10 mA cm−2 with a very low Tafel slope of 43 mV dec−1 and a rather small charge transfer resistance of 0.644 Ω in 1.0 M KOH, which is exceptionally lower than that of RuO2 and the state-of-the-art HEAs and competitive in comparison to most metal oxides. This work proves that the lattice deformation manipulates the displacement of atoms over the nanoparticle surface that facilitates their catalytic activities that are higher than those of the state-of-the-art counterparts reported in the literature. It also provides an insight into the performance improvement of other nanostructures in energy applications.

Three new 3d−4f heterometallic coordination polymers(CPs), namely, [Pr2(CuL)2(nipt)3(H2O)]·2H2O (Cu2Pr2, 1), [Eu2(CuL)2(nipt)3(H2O)]·2H2O(Cu2Eu2, 2) and [Tb2(CuL)4(nipt)3]·8.3H2O(Cu4Tb2, 3)(CuL, H2L=2,3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-dien; nipt2-=5-nitroisophthalate) were obtained by a solvothermal method and structurally characterized by single-crystal X-ray diffraction analyses, elemental analyses, Fourier transform infrared spectra and ultraviolet visible absorption spectra. In Cu2Pr2 and Cu2Eu2, μ3-bridged and μ5-bridged nipt2- ligands alternately linked three Ln3+ and five metal ions(three Ln3+ and two Cu2+ ions) to generate a 2D heterometallic framework with 3,3,4,5-connected (3.4.5)(32.42.5.63.72)(42.63.8)(42.6) topology. In Cu4Tb2, μ2-bridged and μ4-bridged nipt2- ligands alternately connected two Tb3+ and four metal ions(two Tb3+ and two Cu2+ ions) by carboxylating into a corrugated heterometallic 2D layer with 3-connected (63) topology. The magnetic properties of Cu2Pr2 and Cu2Eu2 were also discussed, the results show that both CPs have a weak antimagnetic interaction. Moreover, the near-infrared luminescence properties of Cu2Pr2 and Cu2Eu2 were also studied.

A pure nanostructured Ni coating was directly prepared by continuous cathode plasma electrolytic deposition (CPED) on aluminium alloy 6061. The microstructures and compositions of the as-deposited coatings were studied by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD), followed by hardness and adhesion evaluations. Due to the plasma micro-arc and rapid quench, the Ni coatings prepared by CPED exhibit typically molten morphologies with nanocrystalline structures, which are capable of increasing the hardness values of the coatings. In addition, the adhesion abilities of the as-prepared coatings could be enhanced by metallurgical bonding between the coatings and the substrate. Moreover, the continuous CPED method is a high-efficiency approach to fabricate coatings with large areas.

Herein, we report a hybrid electrocatalyst consisting of Ru clusters trapped in NiCo-layered double hydroxide (NiCo-LDH) as the basis for an efficient hydrogen evolution reaction (HER) in alkaline media. Benefiting from the fast water dissociation kinetics on NiCo-LDH and favorable H recombination on Ru, the resultant Ru-NiCo-LDH shows an extremely low HER overpotential of 28 mV at a current density of 10 mA cm−2 with a small Tafel slope of 42 mV dec−1. This superior catalytic activity can be ascribed to its high charge transfer ability and to the synergistic effect of the highly dispersed Ru and the NiCo-LDH. Moreover, we also found that the oxidized Ru incorporated in NiCo-LDH was entirely reduced to Ru0 under hydrogen-evolution conditions, which suggests that Ru0 is the true catalytically active phase responsible for the outstanding HER performance. Keywords: Ruthenium, NiCo-layered double hydroxide, Hydrogen evolution reaction, Water dissociation

The hollow mesoporous Co(PO3)2@carbon nanocomposite (H–Co(PO3)2@C) was synthesized using ZIF-67 as the template by a facile one-step thermal decomposition reaction. As an anode for lithium ion batt...

Transition metal oxides CuO-ZnO nano-flowers have been simultaneously synthesized by the low voltage liquid plasma discharge method using brass cathode. The effects of discharge statue (normal and abnormal glow discharge) on the nanostructures were investigated. It was found that a lower discharge voltage 52 V in the normal glow discharge period is beneficial to produce homogeneous nano-flower structures while a higher voltage tend to result in inhomogeneous products including larger particles. The obtained products were characterized by SEM, XRD, high-resolution TEM, Raman and XPS. Moreover, the nano-flowers exhibit a favorable electrocatalytic activity of glucose oxidation. This research was funded by the Chinese Natural Science Foundation (Grant number: 21504025 and 51305230).

ZnO nanoparticles deposited on WO3 nanosheet arrays (NSAs) were prepared by hydrothermal process and impregnation method followed by thermal treatment for photocatalytic degradation of nonbiodegradable azo dyes methylene blue (MB) under solar light irradiation. The uniform WO3 NSAs grew on the 316L stainless steel substrate and ZnO nanoparticles immobilized on the surface of WO3 NSAs. The morphology and structure of WO3/ZnO NSAs can be well tailored by adjusting the preparative factors (e.g., hydrothermal time and the concentration of precursor solution). The detailed characterizations of the WO3/ZnO NSAs such as morphology, crystal structure and light absorption were examined. The X-ray diffraction and X-ray photoelectron spectroscopy results showed that the as-prepared samples were two-phase photocatalysts including WO3 NSAs and ZnO nanoparticles. The UV-Vis diffuse reflectance spectroscopy results indicated that the introdution of ZnO altered the optical properties of the photocatalysts. After ZnO loading at the optimum amount, the WO3/ZnO heterojunction with good stability displayed superior photocatalytic activities compared with WO3 NSAs in the degradation of MB. The enhanced photocatalytic performance should be attributed to favorable band structures, strong light-absorption ability and fast separation of photogenerated electron-hole pairs. Particularly, the 30-WZ nanocomposite exhibited the highest photocurrent density of about 1.275 mA/cm2 at 0.8 V versus Ag/AgCl under solar light illumination. In addition, the photogenerated reactive species were identified through free radicals trapping experiments, which revealed that the photodegradation of MB over WO3/ZnO NSAs was dominated by hydroxyl radical rather than the hole and superoxide radical. The mechanism for photocatalytic degradation reaction over the WO3/ZnO heterojunction was also investigated.

Pu-erh tea is produced from the leaves of large-leaf tea species (Camellia sinensis var. assamica) in the Yunnan province of China and divided into ripened pu-erh tea (RIPT, with pile-fermentation) and raw pu-erh tea (RAPT) according to processing methods. RIPT extract showed more potent anti-diabetic effects on two-hour postprandial blood glucose (2h-PBG) and fasting blood glucose (FBG) than RAPT extract. UHPLC-Q-TOF/MS and UHPLC-PDA analyses found that 17 newly formed components and the increased components after fermentation, such as quinic acid, gallic acid, caffeine, puerin I and so on, might be the main contributors to the enhanced activities of RIPT. In addition, the probiotic role of RIPT to some beneficial gut bacteria, such as lactobacillus, Prevotellaceae NK3B31 group, Alloprevotella and Prevotella, was observed in our study. These results might provide a clue to anti-diabetic mechanism and active components of pu-erh tea, and use as a functional beverage worth to be further studied.

Low-cost and earth-abundant nickel chalcogenides with versatilities in electrocatalysis, conversion and storage of energy are hindered in practical application due to the low electrical conductivity and small specific surface area. In the present work, we report a simple preparation of 2D nanocomposites of NiSx (5 nm) uniformly embedded in several layered graphite (NiSx@graphite) through the sulfidation of nickel naphtalenedicarboxylic acid framework nanosheets (∼9 nm). The obtained NiSx@graphite nanosheet composites are used for oxygen evolution reaction (OER) catalysis. Electrochemical studies reveal that their OER activities under strongly alkaline conditions are ranked in the order of Ni9S8@graphite > NiS@graphite > NiS2@graphite. The outstanding OER performance offered by Ni9S8@graphite owes to the synergistic effects of large specific surface area and the special structure between nickel sulfide and graphite layer, and the intrinsic large TOFs and the optimal adsorption energy of Ni9S8. Furthermore, Ni9S8@graphite as an anode material used for lithium ion batteries (LIBs) also shows a high specific capacity with competitive rate performance. Such excellent performance and low price render nickel chalcogenides a promising candidate for the future OER catalyst and LIBs application. Ministry of Education (MOE) This work was financially supported by the China Scholarship Council (201706280166), the National Natural Science Foundation of China (grant numbers 51472198, 51772237, 51777152), Singapore MOE Tier 1 (grant number M4011959), the Fundamental Research Funds for the Central Universities (grant number XJJ2016020), the Scientific Research Foundation for the Returned Overseas Chinese Scholars.

Ni2P has been intensively investigated for hydrogen evolution reaction (HER) in recent years since the HER activity of Ni2P (001) is theoretically superior to Pt. Most of these works have focused on acid system as Ni2P is unstable in alkaline media. However, alkaline water splitting is more practical for industry due to the lack of suitable acidic oxygen evolution catalyst. Thus, providing an efficient alkaline HER catalyst by enhancing the stability and activity of Ni2P is needed. Herein, we have grown mesoporous (FexNi1-x)2P nanosheets on Ni foam (NF) as HER catalyst with activities being related to Fe/Ni ratio. FeNiP/NF with Fe/Ni ratio of 5/5 and high-density exposure of (001) surface shows much better stability and HER activity in alkaline than Ni2P. Our experimental results reveal that the homogeneous lattice substitution of Fe modified the electronic structure of Ni2P, enhanced the intrinsic activity and the number of active sites. Density functional theory calculation reveals that the Fe incorporation improves the HER activity of the highly exposed FeNiP (001) surface by reducing the energy barriers of HER reactants (H and H2O) adsorption compared with Ni2P. This work provides an effective pathway for the future development of HER catalyst in alkaline conditions by introducing hetero-atom into the host lattice.

A versatile and straightforward room-temperature strategy is demonstrated to synthesize boundary defect-rich ultrathin transition metal hydroxide nanosheet networks by in situ etching of a cobalt metal–organic framework (Co-MOF, ZIF-L-Co). The resultant defect-rich ultrathin Co(OH)2 (D-U-Co(OH)2) nanoarray is one of the most active monometal-based oxygen evolution catalysts to date. Its activity is 3–4 times higher than that of the commercial RuO2 and superior to that of the reported exfoliated bimetallic catalysts. Co-MOF can also be grown on various substrates, and the chemical composition of the defect-rich 2D materials is tunable by changing the metal ions in the etchants. Owing to these merits of the unique synthesis route, our work provides an opportunity for synthesizing advanced nanomaterials that are difficult to get access to by conventional methods.

In order to reduce the thickness of recast layer and improve the surface quality of film cooling holes, a novel high speed self-adjusting electrical discharge machining (EDM)/ electrochemical machining (ECM) approach was developed by applying two independent flushing systems that were able to switch automatically in the machining process. The new flushing systems used different work-liquids and online dynamically changing discharge parameters. With the change in gap distance and the depth of the hole drilled, the dominant machining mechanism is graduated changed from EDM to electrochemical discharge machining (ECDM) and ECM. The formation mechanism of the recast layer on nickel alloy was investigated by comparing the surface characters of the bulk material and those of the recast layer using transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS). The results from comparison experiments, in which different discharge parameters and sustaining time were applied, show that this new flushing systems would ensure much better flushing continuity of the working fluid and improve the discharge gap status. In addition, low voltage and current would benefit the ECM process and the removal of recast layer.

In this work, defect-engineered carbon nanotube networks are grown in situ on a 316L stainless steel substrate using chemical vapor deposition and an annealing treatment. The defective carbon nanotube networks can be applied directly as electrodes for the simultaneous determination of ascorbic acid and uric acid using cyclic voltammetry and differential pulse voltammetry. Carbon nanotube networks annealed at 500 °C enable simultaneous determination of ascorbic acid and uric acid with linear responses from 100 to 3000 μM and from 10 to 150 μM, respectively. The excellent electrocatalytic activity of the defective carbon nanotube networks is attributed to the engineered defects and the large number of exposed edge planes. Keywords: Carbon nanotube networks, 316L stainless steel, Electrochemical electrodes, Ascorbic acid, Uric acid

Theoretically, the accomplishment of phase transformation requires sufficient energy to overcome the barriers of structure rearrangements. The transition of an amorphous structure to a crystalline structure is implemented traditionally by heating at high temperatures. However, phase transformation under ambient condition without involving external energy has not been reported. Here, we demonstrate that the phase transformation of GeO2 glass to nanocrystals can be triggered at ambient conditions when subjected to aqueous environments. In this case, continuous chemical reactions between amorphous GeO2 and water are responsible for the amorphous-to-crystalline transition. The dynamic evolution process is monitored by using in situ liquid-cell transmission electron microscopy, clearly revealing this phase transformation. It is the hydrolysis of amorphous GeO2 that leads to the formation of clusters with a size of ∼0.4 nm, followed by the development of dense liquid clusters, which subsequently aggregate to fa...

VS4 anode materials with controllable morphologies from hierarchical microflower, octopus-like structure, seagrass-like structure to urchin-like structure have been successfully synthesized by a facile solvothermal synthesis approach using different alcohols as solvents. Their structures and electrochemical properties with various morphologies are systematically investigated, and the structure–property relationship is established. Experimental results reveal that Li+ ion storage behavior in VS4 significantly depends on physical features such as the morphology, crystallite size, and specific surface area. According to this study, electrochemical performance degrades on the order of urchin-like VS4 > octopus-like VS4 > seagrass-like VS4 > flower-like VS4. Among them, urchin-like VS4 demonstrates the best electrochemical performance benefiting from its peculiar structure which possesses large surface area that accommodates the volume change to a certain extent, and single-crystal thorns that provide fast ele...

As an n-type semiconductor with an excellent physicochemical properties, iron oxide (Fe2O3) has been extensively used in the fields of environmental pollution control and solar energy conversion. However, the high recombination rate of the photoinduced electron-hole pairs and poor charge mobility for Fe2O3 nanomaterial generally result in low photocatalytic efficiency. Herein, an uniform CdS nanorods grown directly on one-dimensional α-Fe2O3 nanotube arrays (NTAs) are successfully synthesized by a facile hydrothermal method and the constructed heterojunction can be a kind of efficient and recyclable photocatalysts. Successful deposition of CdS nanorods onto the α-Fe2O3 NTAs is verified by field emission scanning electron microscopy(FESEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDS). UV–Vis diffuse reflectance spectroscopy indicates that α-Fe2O3/CdS NTAs possess the intense visible light absorption and also display a red-shift of the band-edge compared with the pure α-Fe2O3 NTAs. The as-obtained α-Fe2O3/CdS NTAs display excellent photocatalytic activity for decomposition of methylene blue (MB), methyl orange (MO), and phenol under visible light illumination. Among all the tested photocatalysts, the film synthesized for 3h with good stability exhibits the best photocatalytic properties and produces the highest photocurrent of 1.43 mA/cm2 at 0.8 V vs. Ag/AgCl electrode, owing to its well formed heterojunction structure, effective electron-hole pair separation and direct electron transfer pathway along the CdS nanorods and α-Fe2O3 NTAs. Besides, the photogenerated holes (h+) and superoxide radicals (O2 −) play dominant roles in the photocatalytic process. On the basis of the photocatalytic results and energy band diagram, the photocatalytic process mechanism is proposed. Considering the easy preparation and excellent performance, α-Fe2O3/CdS NTAs could be a promising and competitive visible-light-driven photocatalyst in the field of environment remediation.

In this study, hierarchical copper nano-dendrites (CuNDs) are fabricated via the electrodeposition method. The electrochemical behaviors of the as-obtained hierarchical CuNDs in 0.1 M NaOH aqueous solution are subsequently studied. The CuNDs experience a non-equilibrium oxidation process when subjected to cyclic voltammetry (CV) measurements. The first oxidation peak O1 in CV is attributed to the formation of an epitaxial Cu2O layer over the surface of the hierarchical CuNDs. However, the second oxidation peak O2 in CV appears unusually broad across a wide potential range. In this region, the reaction process starts with the nucleation and growth of Cu(OH)2 nanoneedles, followed by the oxidation of Cu2O. Upon the increase of potential, Cu2O is gradually transformed to CuO and Cu(OH)2, forming a dual-layer structure with high productivity of Cu(OH)2 nanoneedles.

Li3VO4 (LVO) anode materials with controllable morphologies ranging from spherical-assemblies, single-crystal nanorods, and flower shapes to bulk-shapes were fabricated via a solvothermal approach using different alcohols (i.e., ethanol, methanol, propanol, and butanol). XRD, SEM, BET, Raman and FTIR and galvanostatic charge/discharge measurements were carried out to correlate their structure/morphology with their electrochemical characteristics. The experimental results reveal that both structure and morphology play important roles in the Li+ ion storage of LVO, which degrades in the sequential order from nanorods, to spheres, to flowers and finally to bulk. The LVO nanorods are hierarchical and have a small particle size, high specific surface area, and high crystallinity; thus, they exhibit the largest Li+ ion diffusion coefficient and best electrochemical performance among the four electrodes. Moreover, coating carbon on the single-crystal LVO nanorods further enhances their Li+ ion storage ability. Consequently, the carbon-coated LVO nanorods deliver a high reversible capacity of 440 mA h g−1 at 0.1 A g−1 with good cycling stability and demonstrate great practical application. In addition, the results promote a better fundamental understanding of the Li+ ion storage behavior in LVO and provide insight into the optimal design of LVO and other vanadium-based electrode materials. MOE (Min. of Education, S’pore) Accepted version

The use of Ni-based oxides/hydroxides in the oxygen evolution reaction has been extensively reported and fluoride precursors have frequently been used in their synthesis. However, there have been no studies of the effect of fluoride in Ni-based oxides/hydroxides on the hydrogen evolution reaction (HER) as these materials are generally considered inactive for HER. Recently the HER activities of Ni-based oxides/hydroxides have been improved by doping with anions (P, S, and Se). However, these compounds are chemically unstable during HER and can be converted into the corresponding oxides/hydroxides. In this paper we discovered an interesting phenomenon: the NiFe hydroxide can be turned into an active HER material by incorporating fluoride into it. In 1M KOH, a significant shift of ~91mV was observed in the HER overpotential at −10mA/cm2 due to the enhanced charge transfer ability triggered by fluoride. This discovery provides a new approach to turning normally inactive materials, whose catalytic activity is hindered by low intrinsic conductivity, into electrocatalysts, and will lead to the discovery of new catalysts. Keywords: Ni-based hydroxide, Hydrogen evolution, Fluoride incorporation, Charge transfer, Electrocatalysis

To enhance the energy density of solid-state supercapacitors, a novel solid-state cell, made of redox-active poly(vinyl alcohol) (PVA) hydrogel electrolytes and functionalized carbon nanotube-coated cellulose paper electrodes, was investigated in this work. Briefly, acidic PVA–[BMIM]Cl–lactic acid–LiBr and neutral PVA–[BMIM]Cl–sodium acetate–LiBr hydrogel polymer electrolytes are used as catholyte and anolyte, respectively. The acidic condition of the catholyte contributes to suppression of the undesired irreversible reaction of Br– and extension of the oxygen evolution reaction potential to a higher value than that of the redox potential of Br–/Br3– reaction. The observed Br–/Br3– redox activity at the cathode contributes to enhance the cathode capacitance. The neutral condition of the anolyte helps extend the operating voltage window of the supercapacitor by introducing hydrogen evolution reaction overpotential to the anode. The electrosorption of nascent H on the negative electrode also increases the a...

In the present paper, the corrosion fatigue crack initiation and initial propagation mechanism of E690 steel in simulated seawater were studied by stress-controlled fatigue tests and a series of subsequent characterizations on the fracture surface, microstructure and secondary cracks. Results show that the corrosion fatigue crack initiation and initial propagation mechanism evolves with elevated peak stress level in simulated seawater. When peak stress is far below the proof stress, cracks preferentially initiate at the parent austenite grain boundaries (PAGBs) with 68.4% probability and at the ferrite lath boundaries (FLBs) with 31.6% probability. Meanwhile, the cracks also preferentially propagate along the PAGBs and FLBs. Upon the peak stress close to or above the proof stress, cracks turn to initiate from the emerging corrosion pits and propagate without zigzag detour but by splitting the ferrite laths which transversely block its propagation way.

Preparing well-defined single-layer two-dimensional (2D) holey conjugated polymers (HCP) is very challenging. Here, we report a bottom-up method to produce free-standing single-layer nitrogen-rich graphene-like holey conjugated polymers (NG-HCP) nanosheets through solution-process. The as-prepared 2D NG-HCP sheet possesses a thickness of 1.0 ± 0.2 nm and consists of graphene-like subunits as well as homogeneous hexagonal micropores (ca. 11.65 A). The synergistic effect of high porosity, heteroatomic doping and good dispersity of NG-HCP nanosheets make them suitable as excellent anode materials for Li-ion batteries (LIBs), leading to an extremely high reversible capacity of 1320 mAh g−1 (at 20 mA g−1), a good rate performance, and an excellent cycle life with an approximate 100% Coulombic efficiency for more than 600 cycles. Our findings would open new opportunities to develop state-of-the-art free-standing 2D-HCP materials for low-cost and high performance energy storage as well as optoelectronic devices.

Benefitting from high abundance and low cost, sodium-ion batteries (NIBs) have been considered as promising energy storage device in large-scale application. However, low cycling stability and poor rate performance originated from the large size and heavy weight of the sodium ions hinder its application. In this work, a green ball dianthus-like sodium titanate (Na 2 Ti 6 O 13 ) with a tunnel structure and large interlayer space has been synthesized via hydrothermal method and its formation mechanism has been investigated. As NIBs anode materials, Na 2 Ti 6 O 13 exhibits excellent rate performance and superior cyclability. A high reversible capacity over 100 mA h g −1 is delivered at 1000 mA g −1 after 300 cycles. Even after 200 cycles at 500 mA g −1 and 200 cycles at 1000 mA g −1 , the electrode can afford a capacity of 66 mA h g −1 at 2000 mA g −1 without apparent decay after 200 cycles. This outstanding performance can attribute to the unique nano-structure and large interlayer space of Na 2 Ti 6 O 13 with a green ball dianthus-like morphology.

Evolution of the oxide films formed on the surface of 316 stainless steel needles during the electrochemical polarization in 0.1 M NaOH solution is investigated by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). During the polarization process, the films can grow from ~ 4 nm to dozens of nanometers and are composed of crystalline structures incorporated with amorphous phases. Additionally, Cr (III) species that are formed at low potentials will transform into Cr (VI) species in secondary passive region. Fe element is present as Fe3O4-like spinel oxides while no Fe2O3 is found in the films. The Fe/Cr ratio increases with the increase of applied potential.

A specific investigation has been carried out of the electronic structures, Ni oxidation properties, and electrochemical activities of (FexNi1−x)2P for oxygen evolution reaction (OER) in alkaline and neutral media, respectively. The optimized hierarchical Fe-Ni phosphide electrode shows exceptional OER performances under both alkaline and neutral conditions, even much superior to RuO2 catalyst. It only needs extremely low overpotentials of 156 mV and 255 mV to catalyze 10 and 500 mA/cm2 OER current densities in 1 M KOH. Furthermore, a current density of 10 mA/cm2 was achieved at a small overpotential of 396 mV in 0.1 M phosphate buffer.

In this work, orthorhombic Li3VO4 with the controllable morphology has been synthesized by tuning the solvent composition (volume ratios of ethanol to deionized water) in a solvothermal approach. The resulting Li3VO4 samples with various morphologies (coral-shaped particle, self-assembled hierarchical microsphere, cube-like particle, sheet-like structure) show then different electrochemical performances when employed as anodes for Li-ion battery applications. The Li3VO4 with self-assembled hierarchical microsphere morphology (volume ratio of ethanol to deionized water at 15:15) exhibits the best electrochemical performance. The subsequent carbon coating process on microsphere samples is claimed to significantly improve both the capacities at both low (350–430 mAh g−1 at 100 mA g−1) and high current (180–350 mAh g−1 at 2 A g−1) conditions, and their excellent cycling stability. MOE (Min. of Education, S’pore) Accepted version

Vacancy engineering, that is, self-doping of vacancy in semiconductors, has become a commonly used strategy to tune the photocatalytic performances. However, there still lacks fundamental understanding of the role of the vacancies in semiconductor materials. Herein, the g-C3N4 nanosheets with tunable nitrogen vacancies are prepared as the photocatalysts for H2 evolution and CO2 reduction to CO. On the basis of both experimental investigation and DFT calculations, nitrogen vacancies in g-C3N4 induce the formation of midgap states under the conduction band edge. The position of midgap states becomes deeper with the increasing of nitrogen vacancies. The g-C3N4 nanosheets with the optimized density of nitrogen vacancies display about 18 times and 4 times enhancement for H2 evolution and of CO2 reduction to CO, respectively, as compared to the bulk g-C3N4. This is attributed to the synergistic effects of several factors including (1) nitrogen vacancies cause the excitation of electrons to midgap states below t...

One key challenge facing room temperature Na-ion batteries lies in identifying earth-abundant, environmentally friendly and safe materials that can provide efficient Na+ storage sites in Na-ion batteries. Herein, we report such a material, polyoxometalate Na2H8[MnV13O38] (NMV), with entirely different composition and structure from those cathode compounds reported before. Ex-situ XPS and FTIR analyses reveal that NMV cathode behaves like an “electron/Na-ion sponge”, with 11 electrons/Na+ acceptability per mole, which has a decisive contribution to the high capacity. The extraordinary structural features, evidenced by X-ray crystallographic analysis, of Na2H8[MnV13O38] with a flexible 2D lamellar network and 1D open channels provide diverse Na ion migration pathways, yielding good rate capability. First-principle calculations demonstrate that a super-reduced state, [MnV13O38]20−, is formed with slightly expanded size (ca. 7.5%) upon Na+ insertion compared to the original [MnV13O38]9–. This “ion sponge” fea...

The growth of WO3/Fe2O3 nanosheet arrays on iron foil was fabricated by a facile and efficient hydrothermal treatment. The morphology and optical property of as-prepared WO3/Fe2O3 nanocomposites were characterized by using field-emission scanning electron microscopy, energy-dispersive X-ray spectrometry, transmission electron microscopy, X-ray diffraction and UV–Vis diffuse reflectance spectra. The photocatalytic activity of the as-synthesized WO3/Fe2O3 nanocomposite was evaluated by the degradation of methylene blue (MB) in aqueous solution under visible-light (λ > 420 nm) irradiation. It was observed that the sample obtained with a hydrothermal reaction time for 2 h exhibited the best photocatalytic performance. The kinetics of the MB degradation was found to comply with the Langmuir–Hinshelwood model. The photocatalytic efficiencies of WO3/Fe2O3NSAs correlated with the effective separation of photogenerated electron–hole pairs. Hence, the WO3/Fe2O3NSAs are excellent candidate for visible-light-driven photocatalysts.

Tin(IV) oxide has been intensively employed in optoelectronic devices due to its excellent electrical and optical properties. But the high recombination rates of the photogenerated electron-hole pairs of SnO2 nanomaterials often results in low photocatalytic efficiency. Herein, we proposed a facile route to prepare a novel Fe2O3/SnO2 heterojunction structure. The nanobelt arrays grown on iron foil naturally form a Schottky-type contact and provide a direct pathway for the photogenerated excitons. Hence, the Fe2O3/SnO2 nanobelt arrays exhibit much improved photocatalytic performance with the degradation rate constant on the Fe2O3/SnO2 film of approximately 12 times to that of α-Fe2O3 nanobelt arrays.

NiFe-layered double hydroxide (LDH) is thought of as a promising bifunctional water-splitting catalyst, owing to its excellent performances for alkaline oxygen evolution reactions (OERs). However, it shows extremely poor activity toward hydrogen evolution reactions (HERs) due to the weak hydrogen adsorption. We demonstrated that the integration of Rh species and NiFe-LDH can dramatically improve its HER kinetics without sacrificing the OER performance. The Rh species were initially integrated into NiFe-LDH as oxidized dopants and metallic clusters (< 1 nm). In 1 M KOH electrolyte, an overpotential of 58 mV is needed to catalyze 10 mA cm-2 HER current density. Furthermore, this catalyst only requires 1.46 V to drive an electrolyzer at 10 mA cm-2. A strong interaction between metallic Rh clusters and NiFe hydroxide during the HER process is revealed. The theoretical calculation shows the Rh ions replace Fe ions as the major active sites that are responsible for OERs.

Solar-to-thermal energy conversion is one of the most efficient ways to harvest solar energy. In this study, a novel phase change composite with porous carbon monolith derived from natural wood is fabricated to harvest solar irradiation and store it as thermal energy. Organic phase change material n-octadecane is physically adsorbed inside the porous structure of the carbonized wood, and a thin graphite coating encapsulates the exterior of the wood structure to further prevent n-octadecane leakage. The carbonized wood scaffold and the graphite coating not only stabilize the form of the n-octadecane during phase change, but also enhance its thermal conductivity by 143% while retaining 87% of its latent heat. Under 1-sun irradiation, the composite achieves an apparent 97% solar-to-thermal conversion efficiency.

Atomic vacancy has been demonstrated to generate new energy states in the bandgap whereby providing more active sites in many electrocatalytic processes. In this work, a novel process is developed to yield both Co and O vacancies in the synthetical Co3O4 nanosheets when subjected to a laser beam. The method, capable of creating both Co and O vacancies and embarking upon the prediction of the number of vacancies generated, is more reliable/controllable over other methods. The coupling of two types of vacancies eases the occurrence of Co3O4 oxidation reaction at a very low overpotential, which then facilities the OER at an overpotential of 290 mV with a small Tafel slope of 76 mV dec−1, much better than the pristine Co3O4 and the benchmark RuO2. DFT calculations suggest that the induced multi- vacancies create trap state in the bandgap of Co3O4 promoting the adsorption capability and advancing the water splitting.

Herein, we demonstrate a facile method to prepare hollow-structured oxygen-vacancy-rich Fe2O3/MnO2 nanorods. Our results show that oxygen vacancies are induced by nanoscale ion intermixing between Fe and Mn ions during the annealing process. Owing to their unique core–shell hollow nanostructure and the presence of oxygen vacancies, the Fe2O3/MnO2 nanorods show excellent electrochemical performances as an anode material for lithium ion batteries and a reversible capacity higher than 700 mA h g−1 after 2000 cycles.

In the present study, we report a synthetic strategy for the direct fabrication of hybrid vertical graphene/lithium titanate–CNTs arrays via atomic layer deposition in combination with chemical vapor deposition. A novel array architecture was formed where active lithium titanate (Li4Ti5O12, LTO) was uniformly sandwiched by a vertical graphene backbone and an interconnected CNTs shell. The hybrid omnibearing conductive network was identified to be an extremely stable porous structure and demonstrated superior ultra-high rate capability (146 mA h g−1 at 50C and 131 mA h g−1 at 100C) with a capacity of 136 mA h g−1 at 20C after 10 000 cycles when used as an electrode in lithium ion batteries. This special electrode construction strategy is expected to provide a new route for the manufacture of electrochemical energy storage with ultra-high rate capability and ultra-stability.

Herein we converted Fe–Ni hydroxide nanosheets into an Fe–Ni phosphide nanoparticle-stack array on Ni foam by low-temperature phosphorization treatment for promoting the specific surface area of Fe–Ni phosphide and further improving its oxygen evolution reaction (OER) activities. The alkaline electro-activated Fe–Ni–P nanoparticle-stack array exhibits exceptional OER activities in both alkaline and neutral media.

Herein, we have developed an effective strategy to immobilize spinel cobalt oxide (Co3O4) particles of nanometer and subnanometer sizes on carbon sphere support via impregnation and deposition-precipitation methods. With carbon spheres support, very small Co3O4 nanoparticles of around 1–2 nm are uniformly distributed on the surface. Based on XPS analysis, the surface cobalt species are found coordinated with hydroxyl groups from carbon spheres. Among the various catalysts investigated, the Co/C-300 nanocatalyst with 1–2 nm cobalt oxide clusters exhibits the highest activity with over 99% of methyl orange degraded in less than 10 min of reaction. The higher activity of Co/C-300 nanocatalyst was attributed to small size of Co3O4 nanoparticles with more surface sites exposed for dye degradation reaction. The Co/C-300 nanocatalyst is reasonably stable and could be recycled for at least four runs without losing activity substantially.

In order to improve the sluggish kinetics of the redox reactions occurring at the battery-type electrodes of hybrid supercapacitors, a Venus flytrap-like hierarchical NiCoMn–O@NiMoO4@C nanosheet arrays electrode material are developed based on three aspects of considerations: 1. The developed NiCoMn-based trimetallic (NiCoMn–O) oxides has better electrical conductivity than any of its bimetallic or monometallic counterparts and the self-decorated nanoneedles on its surface can create more electroactive sites for electrolyte to access. 2 NiMoO4 layer is one of the important redox active materials in this composite since its high electrochemical activity in alkaline solution. 3. Carbon protection shell cannot only enhance the rate capability by shorting the electron transport pathway of the composite but also improve its cycling stability via buffering the volume change during the charge/discharge processes. Consequently, the obtained NiCoMn–O@NiMoO4@C electrode can provide a maximum specific capacitance of 2189.5 F/g (at 0.25 A/g) and 81.6% of its initial specific capacitance can be maintained after 1500 cycles GCD tests (at 6 A/g). The prepared NiCoMn–O@NiMoO4@C//AC hybrid supercapacitor exhibits the maximum energy density of 59.9 Wh/kg (at 0.25 A/g) and its specific capacitance can maintain 88.3% of its initial value after 3000 cycles GCD tests (at 6 A/g).

The rational design and exploration of highly efficient, low-cost, and robust electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical for development of rechargeable metal-air batteries. Herein, we report a novel approach for the synthesis of bifunctional electrocatalysts, where Fe0.5Co0.5 and Fe0.5Co0.4Ni0.1 alloys are encapsulated in the nitrogen-doped carbon nanotubes-grafted porous polyhedron-derived hybrid fibers (FeCo/FeCoNi@NCNTs-HF). Benefiting from its hierarchically porous structure and strong synergetic coupling among FeCo, FeCoNi alloys, and N-doped carbon species. The obtained electrocatalyst exhibits a positive half-wave potential of 0.850 V for ORR and a low potential of 1.608 V to achieve a current density of 10 mA cm−2 for OER, as well as superior stability in alkaline media. As a demonstration, FeCo/FeCoNi@NCNTs-HF is employed as the electrocatalysts in the air cathode of a Zn-air battery, which shows superior discharge and charge performance, large power density, high specific capacity, and outstanding cycling stability of 240 h (360 cycles). More impressively, excellent cyclabilitiy with a lifetime of 670 h (1005 cycles) is also achieved by the Zn-air battery with FeCo/FeCoNi@NCNTs-HF as the self-supported air electrode. This work will open a novel avenue to develop advanced bifunctional electrocatalysts for the next generation of metal-air batteries. Agency for Science, Technology and Research (A*STAR) Nanyang Technological University This work was supported by the Agency for Science, Technology and Research and Nanyang Technological University, Singapore for providing funding and PhD scholarships.

Research on VS4 is lagging due to the difficulty in its tailored synthesis. Herein, unique architecture design of one-dimensional VS4 nanowires anchored on reduced graphene oxide is demonstrated via a facile solvothermal synthesis. Different amounts of reduced graphene oxide with VS4 are synthesized and compared regarding their rate capability and cycling stability. Among them, VS4 nanowires@15 wt% reduced graphene oxide present the best electrochemical performance. The superior performance is attributed to the optimal amount of reduced graphene oxide and one-dimensional VS4 nanowires based on (i) the large surface area that could accommodate volume changes, (ii) enhanced accessibility of the electrolyte, and (iii) improvement in electrical conductivity. In addition, kinetic parameters derived from electrochemical impedance spectroscopy spectra and sweep rate dependent cyclic voltammetry curves such as charge transfer resistances and Li+ ion apparent diffusion coefficients both support this claim. The diffusion coefficient is calculated to be 1.694 × 10-12 cm2 s-1 for VS4 nanowires/15 wt% reduced graphene oxide, highest among all samples. Ministry of Education (MOE) This research was supported by Tier 1 (AcRF grant MOE Singapore M4011528), Tier 2 (AcRF grant MOE Singapore M4020159), Tier 2 (MOE2015-T2-1-148), Chinese Natural Science Foundation (Grant No. 51271031), and Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 51802091).

Multifunctional electrocatalysts based on earth-abundant elements are key for the development of Integrated Energy Systems (IES) such as electrolytic water splitting powered by metal-air batteries. Herein, hierarchical CuCoNC nanowire arrays are constructed on copper foam, enriching multiple active species on the catalytic scaffolds that lead to remarkable trifunctional activities of OER with η10 = 245 mV, HER with η10 = 59 mV and ORR comparable to Pt/C. While for overall water splitting a cell voltage of only 1.78 V is required to achieve a high current density of 500 mA cm−2, for Zn-air batteries (ZABs) a highly stabilized round-trip efficiency of >58% is achieved for over 360 h under 10 mA cm−2. Ultimately, a highly efficient IES of ZAB-powered water splitting employing a single catalyst is demonstrated with a hydrogen evolution rate of 69 μL s−1, showcasing a smart material design in simultaneously achieving multi-functionality and maximizing the energy efficiency.

The atmospheric microplasma in the gas-liquid phase technique serves as a new potential efficient and green catalyst preparation technique to fabricate nanomaterials. Due to the presence of diverse reactive species, this technique can promote rapid complex reactions in solutions, which are typically sluggish in traditional chemical processes. Here, atmospheric microplasma induced liquid chemistry (AMILC) is applied to fabricate three-dimensional (3D) binary Pt3Co nanoflowers. Nano-architectures of Pt3Co bimetals (2D nanosheets and 3D nanoflowers) can be formed by tuning the initial cobalt molar concentration in the solution. 3D nanoflowers show a 'nano-bouquet' like nanostructure with Co-oxide forming leaves and Pt3Co forming waxberries. 3D nanoflowers show promising electrocatalytic behavior towards ethanol and glucose sensing in alkaline condition. Additionally, AMILC takes less synthesis duration (∼10 min) without hazardous chemicals for Pt3Co bimetal nanostructure preparation compared to conventional chemical approaches (>2 h), indicating that AMILC is a potential candidate with better energy efficiency, lower carbon footprint and green plasma chemistry process for 3D nanostructure material synthesis in catalyst applications.

In this paper, Co3Se4 nanoparticles embedded in nitrogen-doped porous carbon polyhedra are synthesized via a facile one-step thermal selenization, using zeolitic imidazolate framework-67 (ZIF-67) as the template. The electrochemical properties of the fabricated nanocomposite are evaluated for use as anodes for lithium ion batteries and found to exhibit a specific capacity (950 mAh g-1 at 0.2 C) and excellent cyclic stability (899 mAh g-1 at 1 C after 1000 cycles). Both are much higher than those of the state-of-the-art Co-Se based nanocomposites. This extraordinary lithium storage is attributed to the synergetic effect between the Co3Se4 nanocrystals and nitrogen-doped porous carbon framework, and is believed to offer a potential candidate anode material for next-generation lithium ion batteries.

Ni-Fe layered double hydroxides (LDHs) thin film was in situ synthesized and intercalated with carbonate (Ni-Fe−CO32− LDHs) on the surface of carbon steels through wet/dry cycle immersion methods. The effect of different treatments on the Ni-Fe LDHs thin film morphology were systemically investigated. Ni-Fe-MoO42− LDHs/epoxy composite coating was prepared via anion-exchange method using Ni-Fe LDHs loaded with MoO42− (Ni-Fe-MoO42− LDHs) as a conversion film. X-ray diffraction (XRD) proved that the d -spacing of Ni-Fe LDHs value increased from 7.4 A to 8.0 A. Electrochemical impedance spectroscopy (EIS) results show that the presence of Ni-Fe-MoO42− LDHs can efficiently improve the corrosion resistance of Q235 substrate. The corrosion resistance of Ni-Fe-MoO42− LDHs/epoxy composite coating was evaluated by EIS, scanning electrochemical microscopy (SECM) and neutral salt spray tests. The results demonstrate that the presence of Ni-Fe-MoO42− LDHs thin film significantly improves the corrosion resistance of epoxy topcoat, and the composite coating exhibit a long-time and active protection for carbon steels. In addition, the presence of Ni-Fe LDHs thin film can significantly improve the adhesion of the epoxy coating.