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A self-strengthening coating with silver nanoparticles (Ag NPs) doped chitosan (CHI) and sodium alginate (SA) polyelectrolytes was constructed on the surface of polydopamine (PDA) coated Ti substrate by a layer-by-layer assembly method. The PDA coating exhibited an excellent bond with Ti substrate, and also can uniformly deposit Ag NPs via a mild method without introducing any exogenous reductant. The CHI coating was assembled through a spin-coating method for controlling Ag+ release. The SA was introduced to enhance the anticorrosion performance by forming calcium alginate (CA) in a corrosive medium. The corrosion protection was investigated with electrochemical impedance spectroscopy and polarization curves tests in fluorine-containing artificial saliva. During immersion, the charge-transfer resistance and the protection efficiency (ŋ) presented a continuous increase with the immersion time, demonstrating that this coating possessed a remarkable self-strengthening capability, and the compositions of the outermost film changed from SA to CA with the Ca2+ cations of the corrosive medium as a crosslinker by SEM and EDS analysis. Furthermore, the ŋ remained up to 96.8% after immersion of 30 days, and then the coating also displayed a distinct inhibition zone on S. mutans. These results prove this coating possesses an excellent anticorrosion performance and antibacterial property.

The influence of mercury on the morphology and formation mechanism of gold amalgams in the presence of different reducing agents (ascorbic acid and sodium borohydride) was systematically studied. In the presence of cetyltrimethylammonium bromide (CTAB), chemical reducing agents not only reduced mercury ions in the solution but also replaced the CTAB molecules on the surface of the gold nanorod. The stability of the reducing agents in the colloidal system and the combining capacity of the reducing agent to the gold nanoparticles can affect the alloying process of mercury and gold, thereby forming a rod-shaped or spherical gold amalgam. Once CTAB was removed, a similar transformation process occurs between the gold nanorods and mercury. In addition, without the presence of a stabilizer, mercury that cannot be dispersed undergoes Ostwald ripening growth, which causes the gold amalgam nanoalloys to form a tip-to-tip structure as a result of mercury enrichment because of the weak shielding effects occurring at the tips of the gold nanorods. After the CTAB molecules were substituted with ascorbic acid and alkylthiol molecules, the question of whether the shielding effect weakened or disappeared was also investigated. By investigation, this research found that, in comparison to the blocking effect of CTAB molecules, the binding ability of the reducing agent to gold plays a dominant role in the nanoamalgam formation process.

A series of gold nanoparticles were synthesized by stepwise growth method under the condition of citrate as a reducing agent and stabilizer. The optical properties with the maximum absorption wavelength (λmax) and electrochemical properties of the oxidation potential (Ep) dependence on the particle size were analyzed. The method of calculating the particle size from the UV-visible spectrum and the electrochemical oxidation peak was deduced, following the theoretical prediction trend and consistent with previous observations. Furthermore, we investigated the application performance based on the electrochemical catalytic activity and the aggregation of the spherical gold nanoparticles using L-cysteine as a target. The results indicated that the optical and electrochemical properties of the gold nanoparticles to L-cysteine were closely related to the particle size of gold nanoparticles. With the increased size of the nanoparticles, the full width at half maximum in the UV-visible absorption spectrum increased and the electrochemical oxidation potential was positively shifted.

A gold-ruthenium/zinc oxide nanorod composite was synthesized. The electrochemical catalytic efficiency of the noble metal-semiconductor nanostructure increased by nearly 30% under the irradiation of an external light source. It provides an efficient way of thinking for the design of electrocatalysts with a photoresponse.

The Q-switching performance of graphitic carbon nitride (g-C3 N4) based on saturated absorption is demonstrated in 2 micrometer wavelength region for the first time. The g-C3N4 saturable absorbers, processed by thermal oxidation etching, are employed for passive Q-switching in a Tm:CNNGG laser. With a 5 hours long thermal oxidation etched g-C3N4 saturable absorber, the Q-switched Tm:CNNGG laser generates a shortest pulse duration of 132 ns with a repetition frequency of 16 kHz and a peak power of 98.5 W. The experimental results indicate that g-C3N4 is an excellent saturable absorber for passive Q-switching in 2 micrometer wavelength region.

Pretreatment layers have attracted much attention due to their irreplaceable role in paint system. However, the commonly used pretreatment layers face with one common problem, which the environmental friendliness and excellent properties can not be simultaneous realization. This work reported one facile method to synthesize one stable polyacrylic acid/Ca nanoparticles hybrid hydrosol through the electrostatic interaction between polyacrylic acid and Ca 2+ . Ulteriorly, the fabricated stable hydrosol was utilized as one environmentally friendly pretreatment layer material to fabricate new generation pretreatment layer on cold-roll steel surface through immersion method. The electrochemical and microstructure results indicated that the polyacrylic acid/Ca hybrid hydrosol based pretreatment layer exhibited better anti-corrosion performance and higher root mean square roughness value than polyacrylic acid layer. Meanwhile, neutral salt spray test results reflected that the polyacrylic acid/Ca hybrid pretreatment layer based coating system exhibited better service performance than the no pretreatment or polyacrylic acid layer based coating system. Because of the environmental friendliness, good anti-corrosion performance and higher root mean square roughness value, the polyacrylic acid/Ca nanoparticles hybrid hydrosol based pretreatment layer are expected to act as substitutes for chromate and phosphate conversion layers and will find widespread application in metal surface pretreatment field.

Silanes and organophosphorus compounds have been widely used in the field of corrosion inhibition. Herein, two corrosion inhibitors containing multiple phosphate groups and different silane groups, namely, 1,3-bis{3-[N-(1-phosphonatediethyl)-isopropyl] aminopropyl}-1,1,3,3-tetramethyldisiloxane (BPIAT) and N,N-di-methylenephosphonate-aminopropyl dimethyl silanol (DMADS), were designed and their corrosion inhibition properties on the iron surface in 0.5 M H2SO4 solution were characterized by polarization curves and electrochemical impedance spectroscopy (EIS) at 25 °C. In order to further analyze the corrosion mechanism thoroughly, three organophosphorus compounds without silane groups, namely, Hexamethylene-diamine tetra(methylene phosphonic acid) (HDTMPA), (ethylenedinitrilo)-tetra methylene phosphonic acid (EDTMP), and diethyl 1-decylphosphonate (DDP), were also investigated. The electrochemical experimental results reveal that five corrosion inhibitors are mixed type inhibitors and the adsorption process obeys Langmuir isotherm, and the corrosion inhibition efficiency of BPIAT and DPSD is significantly higher than that of HDTMPA, EDTMP and DDP. A new corrosion inhibition mechanism was proposed by comparing the corrosion inhibition performance of five corrosion inhibitors. The corrosion inhibitors are absorbed on the iron surface by Fe-O-P covalent bonds and Van Der Waals’ force. Simultaneously, the Si-O-Si structure is conducive to the improvement of the corrosion inhibition efficiency.

Self-strengthening HEDP-Zn films were constructed on the CRS surface and the corrosion protection was afforded by electrochemical impedance spectroscopy (EIS) tests. After immersion in NaCl solution, HEDP-Zn-coated CRS underwent three stages: strengthening, balance and weakening. During immersion, a portion of unstable HEDP-Zn complexes were destroyed, accompanied by the intercalation and departure of Na + , thereby resulting in the changes in microstructure, chemical compositions and thickness of the films. Thus, anticorrosion performance increased due to the increased surface coverage by the complexes and additional binding sites during the first stage but decreased because of the reduced film thickness in the third stage.

In this study, gold amalgam was prepared on a gold nanorods (Au Rs) modified ITO electrode through an electrochemical reduction of mercury ions (Hg2+), and the formation of amalgam was explored under steady and non-steady states. Under static system, Hg2+ was preferentially deposited at the tips of the Au NRs, and diffused along the Au NRs, because of the electrodeposition rate of Hg2+ was higher than the diffusion rate of Hg2+ in the electrolyte. Under disturbed condition, based on the continuous supply of Hg2+, mercury was gradually reduced and swelled into the interior of Au NRs leading to the formation of nanospheres. UV–vis absorption spectroscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) were utilized to demonstrate the reaction processes. This study might be able to provide the experimental basis for the preparation of bimetallic nanoalloys.

Depressed reaction kinetics due to the electrochemical properties of transition metal materials themselves and a discordant coexistence relationship between substrates and these kinds materials rem...

The development of water splitting technology is severely impeded by the limited strategies for preparing efficient photocatalyst with optimal structure. Herein, a facile structure and doping engineering strategy is proposed to obtain the atomic-thin mesoporous graphite carbon nitride (g-C3N4) nanosheets with a large specific surface area of 212.5 m2 g−1, an ultra-large pore volume of 1.55 cm3 g−1, high C and O contents of ∼51.4 and 4.8% via an acid-assisted exfoliation route without any hard templates. The theoretical calculation reveals that the introduction of additional C/O atoms into g-C3N4 matrix would boost the charge transfer rate and charge separation efficiency due to the enhanced electronic polarization effect (Bader Charge) and shortened bond lengths. Additionally, the electronic conductivity is demonstrated to be enhanced due to the formation of delocalized π-bonding both experimentally and theoretically. The synergic contribution of textural and electronic features renders an excellent photoelectrochemical (PEC) performance with 50–60 times larger photocurrent in comparison with the pristine g-C3N4 and high hydrogen evolution rates of 830.1 and 115.5 μmol g−1 h−1 under the solar- and visible-light irradiation, respectively. This in-situ exfoliation approach demonstrates a facile yet efficient method to synthesize highly porous carbon nitride materials with optimal structure and composition for efficient water splitting.

Aqueous rechargeable zinc-based batteries are attractive as promising candidates for practical electric vehicles. However, such batteries still suffer from the poor cycling stability and potential safety issue due to the dendrite formation. Herein, we design three-dimensional (3D) graphene foams co-doped with sulfur and nitrogen via an in-situ reduction of graphene oxide and subsequent thermal annealing process. Performed as both cathodic and anodic matrixes, the unique features of 3D porous graphene framework with N, S co-doping not only enable the reversible plating/striping process of zinc, but also facilitate the redox reactions of iodine species. Thus, the rationally designed aqueous rechargeable zinc-iodine system can integrate the redox reactions of zinc and iodine redox couple at the interface of graphene foam and electrolytes along with reversible ion shuttles (e.g., Zn2+, I−/I3−) for efficient energy storage. More importantly, the 3D porous architecture with N, S co-doping can enhance the battery Coulombic efficiency by shortening the potential gap of charging/discharging process and suppress the formation of zinc dendrites by improve the reaction kinetics of reversible redox reactions.

Polyacrylic acid (PAA)–metal complex-based hybrid films with favorable anticorrosion performance were constructed directly on iron substrates. Thus, a high affinity of PAA for oxidized iron surface and its strong complexation ability to metal ions were fully used. The self-assembled PAA layer was first prepared on iron substrates by self-assembled PAA polymer in alcohol–water mixed solution. Despite a relatively poor anticorrosion performance, the as-prepared self-assembled PAA layer could be used as a functional bottom layer to fabricate PAA–metal complex films because PAA can strongly complex metal ions. Here, organic PAA films were further functionalized by directly immersing PAA film-coated iron specimens in aqueous solutions containing Ce3+ or Zn2+ or both metal ions to allow the complexation reaction between PAA and metal ions to proceed spontaneously. The obtained PAA–M (M = Ce, Zn here) hybrid films could more strongly suppress the corrosion of iron substrates in NaCl corrosive solution than organic self-assembled PAA films. PAA–Zn films exhibited the strongest corrosion protection ability, as exemplified by the appearance of only one time constant related to resistance and capacitance of hybrid films in the impedance spectra. In the mixed solution of Ce3+ and Zn2+ ions, the presence of Ce3+ could significantly promote the combination of Zn2+ with PAA polymers. However, as-fabricated PAA–Ce–Zn hybrid films showed impedance behavior quite differently from that of PAA–Zn films. This study is helpful in designing and fabricating environmentally friendly organic–inorganic hybrid conversion coatings with excellent anticorrosion performance.

A flexible electrode based on polypyrrole-supported free-standing molybdenum oxide-molybdenum disulfide/polypyrrole nanostructure (MoO3–MoS2/PPy) was synthesized. The petal-like MoO3–MoS2 sheets grown on PPy were prepared step by step through simple electrodeposition and hydrothermal methods. The corresponding surface morphological and structural characterizations were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that the prepared petal MoO3–MoS2 hybrid nanomaterials were uniformly distributed on the PPy skeleton and exhibited a three-dimensional porous network structure. The flexible electrode was used for non-enzymatic detection of hydrogen peroxide (H2O2), and the developed MoO3–MoS2/PPy nanomaterials exhibited high electrochemical sensing performance in the range of 0.3–150 μM, with the detection limit of 0.18 μM (S/N = 3). The excellent detection properties enabled the MoO3–MoS2/PPy flexible electrode to detect H2O2 released by living cells. The resulting MoO3–MoS2/PPy flexible electrode also has the advantages of customizable shape and adjustability, which provides a potential platform for constructing clinically diagnosed in vivo portable instruments and real-time environmental monitoring.

Potassium-ion batteries (KIBs) have emerged as attractive alternatives to dominative lithium-ion batteries for grid-level electricity storage due to lower potential of K+/K redox couple in non-aqueous electrolyte and abundant potassium resource. The current intercalation cathodes used in KIBs provide limited active sites in their frameworks while conversion chemistry offers the feasibility for much improved potassium-ion storage capability. We for the first time demonstrate a rechargeable potassium-iodine (K-I2) battery enabled by a two-electron K-I2 conversion reaction. With the help of in-situ Raman and ex-situ X-ray photoelectron spectroscopy, we confirm that the highly reversible conversion among I2, KI3 and KI involves solid-liquid-solid phase transitions and the formation of soluble KI3 intermediate enables the fast reaction kinetics. The K-I2 battery delivers a reversible capacity of 156 mA h/g and a small capacity decay of 0.058% per cycle over 500 cycles.

The aim of this work is to develop an eco-friendly pH-responsive intelligent coating with long-term corrosion protection by a convenient method. Herein, an eco-friendly and long-term pH-responsive intelligent anti-corrosion coating (BTA-CaCO3@TA coating) is fabricated through the addition of a hydrophilic pH-responsive release material (BTA-CaCO3@TA microspheres) into a waterborne epoxy resin coating. The electrochemical impedance spectroscopy results indicated that BTA-CaCO3@TA microspheres could endow the coating with long-term corrosion protection. The |Z|f=0.01Hz values of the BTA-CaCO3@TA coating after 130 days of immersion were still higher than those of the pure waterborne epoxy resin coating at the beginning of immersion. The excellent long-term protection performance was related to the good dispersibility of BTA-CaCO3@TA microspheres in the waterborne coatings, the TA conversion film and the BTA inhibitor protection film, which formed on the steel surface in situ. This synergistic strategy demonstrated its future application for protecting metals from corrosion.

Molybdenum sulfide nanosheets on nitrogen-doped carbon nanowires (MoS2/CN NWs) were utilized to construct an electrochemical biosensor for hydrogen peroxide (H2O2). Polypyrrole nanowires (PPy NWs) were synthesized using a surfactant-assisted method, and few layers of MoS2 nanosheet grew on PPy NWs by a hydrothermal approach. After a sintering process, the prepared MoS2/CN nanohybrid was supposed to enhance the electrochemical catalytic performance for H2O2 resulting from the synergistic effect between the high stability of CN NWs and abundant active sites of MoS2 nanosheets. The CN NWs served as the framework for the few-layered MoS2 to form a core-shell structure which could increase the stability and electrochemical conductivity of MoS2 nanocomposite. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) were used to characterize the crystallinity of MoS2 and the nitrogen-doped carbon nanowires. The electrochemical responses showed that the MoS2/CN NWs modified electrode has a good catalytic performance toward H2O2 determination with a wide linear range from 2 to 500 μM, and a low detection limit of 0.73 μM (S/N = 3). Moreover, the fabricated electrochemical biosensor performed monitoring of H2O2 released from A549 living cells, indicating that the MoS2/CN NWs offered a simple and convenient pathway in the fields of electrochemical sensing.

A coordination-induced film-forming method was developed to construct 2-hydroxyphosphonoacetic acid (HPAA)-Zn2+ complex conversion layer (HPAA-Zn2+ layer for short) on cold-rolled steel (CRS) substrate. Moreover, the incorporation of Mo component into the HPAA-Zn2+ layer can significantly improve the uniformity and anticorrosion properties. The results showed that Mo-incorporated HPAA-Zn2+ layer displayed the best anticorrosion performance when the molar ratio of HPAA/Zn2+ was 1:1, the film-forming time was 10 min, and the concentration of molybdate was 0.1 wt%. In addition, energy dispersive spectroscopic (EDS) and X-ray photoelectron spectroscopic (XPS) results demonstrated that the Mo-incorporated HPAA-Zn2+ layer was mainly composed of ZnO and HPAA-Zn2+ complex and also confirmed that Mo-O-P bonds occurred between molybdate anion and HPAA molecule.

Seeing that amino trimethylene phosphonic acid (ATMP) possesses very strong complexation ability to metal ions and the phosphonic acid group has good affinity for the oxidized iron surface, herein a simple and rapid film-forming method (one-step assembly method) was developed to construct the ATMP-Zn complex conversion layers (ATMP-Zn layers for short) on the cold-rolled steel (CRS) substrate. Zinc ions were found to participate in the formation process of ATMP-based composite film, which made the Zn-containing ATMP film significantly different in appearance, thickness, microstructure and film-forming mechanisms from the Zn-free ATMP film. There was mainly iron (ш) phosphonate in the Zn-free ATMP film, whereas there were Zn2+-ATMP complex and a certain amount of ZnO in the ATMP-Zn composite film. In addition, electrochemical test results clearly indicate that corrosion resistance of ATMP-Zn composite film was greatly enhanced due to the presence of Zn component. Moreover, the corrosion resistance performance could be controlled by adjusting film-forming time, pH and ATMP concentration in the film-forming solutions. The present study provides a new method for the design and fabrication of high-quality environmentally-friendly conversion layers.

Amorphous phytic acid nanoparticles were prepared via a condensation reaction of phytic acid with aminopropyltriethoxysilane. X-ray photoelectron spectroscopy and fourier transform infrared characterizations demonstrated that there were abundant phosphate groups on the surface of as-prepared phytic acid nanoparticles. The advanced composite phytic acid nanoparticles doped silane sol-gel coating was fabricated on the cold-rolled steel substrates using sol-gel technique and introducing phytic acid nanoparticles into the coating. The results of electrochemical tests showed that the doping of phytic acid nanoparticles greatly improved the anti-corrosion and durable performances of the silane coatings. The simple strategy which utilized the “active” nanoparticles to improve the corrosion mitigation and durable performances of coating is expected to find wide application in the anti-corrosion coating industry.

In this work, a novel CoO/CoFe2O4 bi-component nanorod coated with S-doped carbon nanospheres shell (CO/CFO@SC Nr) composites have been synthesized through one in-situ polymerization and subsequent annealing treatment. The S-doped carbon shell, special structure and synergistic effect between CoO and CoFe2O4 significantly enhance the electrochemical performance of the CoO/CoFe2O4 anode material. CO/CFO@SC Nr composites present an impressive capacity of 511.3 mAh g−1 after 700 cycles when tested at a high current density of 2000 mA g−1. In addition, this is the first time that polythiophene is used as sulfur and carbon source to synthesis transition metal oxide (TMO) @S-doped carbon core-shell composites. This work illuminates a new preparation way for fabrication other TMO@S-doped carbon core-shell materials for lithium-ion batteries and other energy storage devices.

The design of a flexible electrode based on carbon cloth (CC) which can solve the problem of the weak coupling effect and binding force between the substrate and active materials has stimulated intensive research on configuring supercapacitors with these materials to achieve high energy and power densities. In this paper, a N,P-doped carbon (NPC) layer as an intermediate layer is sandwiched between the active materials and carbon cloth, which can not only enable the stable and homogeneous growth of active materials on the carbon fiber but also maintain the long cycle life of the flexible electrode in supercapacitors owing to its rich structural defects, excellent hydrophilic characteristics and mechanism of heteroatom doping. Such a sandwiched flexible electrode consisting of bimetallic sulfide (BS), an N,P-doped carbon layer and carbon cloth (denoted as CC–NPC–BS) is assembled as a positive electrode in a solid-state asymmetric supercapacitor (ASC) device, which delivers a high energy density of 56.7 W h kg−1 at a power density of 1.5 kW kg−1 and has outstanding long cycling stability with 85% capacitance retention after 15 000 cycles.

A nickel-cobalt-sulfide nanosheet (Ni-Co-S NS)/polypyrrole nanowire (PPy NW) core/shell-structured composites on nickel foam (NF) was synthesized by facile electrodeposition processes for electrochemical non-enzymatic glucose sensor. PPy NWs grew on the NF substrate by a potentiostatic deposition method, and then the PPy NWs were further served as skeletons for electrodeposition Ni-Co-S nanosheets. The ternary Ni-Co-S NSs as the shell and PPy NWs as the core on the flexible NF constructed the 3D micro/nano structure. The as-prepared Ni-Co-S/PPy/NF electrode was characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometer (EDS). The electrochemical sensor was used for the detection of glucose by chronoamperometry. The introduction of the interconnected Ni-Co-S NSs can provide accessible pathways for electrolyte and have high sensitivity to glucose. Compared with the NF and PPy/NF electrodes, the Ni-Co-S/PPy/NF micro/nanohybrid electrode exhibited higher catalytic activity towards electro-oxidation of glucose. The developed Ni-Co-S/PPy/NF electrode showed two linear electrochemical responses to glucose in the range from 2 μM to 140 μM with a correlation coefficient of R2 = 0.937 and 0.14 mM to 2 mM with a correlation coefficient R2 = 0.978, and the detection limit is 0.82 μM. Furthermore, the prepared biosensor demonstrated high selectivity to glucose in the presence of uric acid, ascorbic acid and D-fructose.

For the wearable and flexible applications, solid-state supercapacitors have been attracted significant attention owing to their unique features. Herein, we demonstrated the fabrication of a high-energy solid-state hybrid supercapacitor by using cobalt hexacyanoferrate nanoparticles and molybdenum oxide thin films grown on the flexible carbon fiber cloth. The flexible hybrid supercapacitor using a neutral gel electrolyte can be operated in a stable potential window of 2.0 V and delivers a maximal energy density of 67.8 Wh kg−1 at the power density of 1003 W kg−1, outstanding reliability without capacitance degradation under various twisting rates, and remarkable cycling stability retaining 74% of initial capacitance after 10000 cycles.

Many fundamental researches about the effect of some basic properties of a pre-treatment layer, such as anti-corrosive performance, surface roughness and chemical composition on the overall performance of paint systems were investigated. Three kinds of pre-treatment layers: bare polyacrylic acid (PAA) layer, Mo based layer and Mo doped PAA layer were deposited on cold-rolled steel surfaces through immersing the steel samples in the corresponding solution. The electrochemical measurements results indicated that after been treated in PAA solution, the steels became vulnerable to corrosion and the Mo based layer and Mo doped PAA layer could improve the corrosion resistance of steel to a certain degree. The values of root-mean-square roughness of the bare steel, bare PAA layer, Mo based layer and Mo doped PAA layer were 15.0 nm, 11.3 nm, 13.0 nm and 59.1 nm, respectively. The corresponding values of arithmetic average roughness of the samples were 16.9 nm, 10.5 nm, 9.1 nm and 41.0 nm, respectively. The spectroscopy results indicated that the surface of the bare PAA and Mo doped PAA layer covered steels contained abundant COOH groups and the composition of Mo based layer covered steel surface was mainly oxides. According to the impact test and neutral salt spray test results, the corrosion mitigation performance, microstructure and chemical composition of the pre-treatment layer could all affect the overall performance of the paint system. All the results indicated that the anti-corrosive performance was not the only index, the microstructure and chemical composition also needed to be considered in the development of a new generation pre-treatment layer.

Exploring highly efficient and durable bifunctional electrocatalysts from earth-abundant low-cost transition metals is central to obtaining clean hydrogen energy through large-scale electrolytic water splitting. Porous nickel–cobalt nitride nanosheets on macroporous Ni foam (NF) are synthesized through facile electrodeposition followed by a one-step annealing process in a NH3 atmosphere. The transformation from a metal hydroxide into a metal nitride could efficiently enhance the electrocatalytic performance for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Interestingly, the incorporation of nickel further boosts the catalytic activity of cobalt nitride. When used as bifunctional electrocatalysts, the obtained nickel–cobalt nitride electrocatalyst shows good stability and superior catalytic performance toward both HER and OER with low overpotentials of 0.29 and 0.18 V, respectively, to achieve a current density of 10 mA cm−2. The good electrocatalytic performance was also evidenced by the fabrication of an electrolyzer for overall water splitting, which exhibits a high gas generation rate for hydrogen and oxygen with excellent stability during prolonged alkaline water electrolysis. The present work provides an efficient approach to prepare a 3 D interconnected porous nickel–cobalt nitride network with exposed inner active sites for overall water splitting.

Phytic acid conversion coating and Zn2 + doped phytic acid conversion coating were fabricated on Q235 steels by immersing the steel samples in corresponding coating bath for 600 s. The changes of coating formation process and adsorption action of phytic acid on steel surface due to addition of Zn2 + in coating bath were investigated. Scanning electron microscopy images exhibited that phytic acid conversion coating was porous network structure consisting of needle-like crystals, but Zn2 + doped phytic acid conversion coating was one uniform layer except some fine cracks. Energy dispersive spectroscopic, X-ray diffraction and X-ray photoelectron spectroscopic characterizations demonstrated that the roles of Zn2 + during the coating formation process could conclude to two sides: (i) Zn2 + could promote the adsorption reaction of phytic acid to form one thicker phytic acid conversion coating on steel surface; (ii) a part of Zn2 + could form ZnO and aggregation of the complex of phytic acid, Zn and Fe and doped to the formed conversion coatings. And the electrochemical measurements results showed that the corrosion protection efficiency of Zn2 + doped phytic acid conversion coating was higher than that of phytic acid conversion coating.

This paper describes stable and highly dispersed aqueous colloids of polyaniline (PANI) nanofibers that were prepared by a chemical method and used to modify a glassy carbon electrode (GCE). The materials combines the good electrical conductivity and network structure of PANI nanofibers with the complexing capacity of mercaptosuccinic acid. The modified GCEs exhibit high sensitivity to Cd(II) and Pb(II) ions, with detection limits of 50 ng·L−1 and 200 ng·L−1, respectively. The modified GCE was applied to the simultaneous determination of the cancer biomarkers carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) by using particles of metal-organic frameworks (MOFs) prepared from Pb(II) or Cd(II) and 2-aminoterephthalic acid. The particles are used as electrochemical labels for secondary anti-CEA and secondary anti-AFP antibody in a sandwich assay. The two ions in the MOFs labels on the secondary antibody can be detected best at voltages of −0.63 and −0.88 V (vs Ag/AgCl), respectively. The assay has a linear response in the 0.3 pg·mL−1 to 3 ng·mL−1 concentration range of both CEA and AFP, and the respective detection limits are 0.03 pg·mL−1 and 0.1 pg·mL−1. In our preception, this assay has a wide scope in that it may be applied to a variety of sandwich types of immunoassays.

A hierarchical porous CoO/Cu2O nanoarray assembled on three-dimensional Cu foam was successfully fabricated by a facile solution-phase cation exchange technique. The morphology and crystalline structure of the target composite were optimized by investigating the sintering conditions. The unique bimetallic oxides demonstrate a secondary porous structure on primary nanoarrays, which facilitated the electrolyte permeation and decreased the ionic transport distance. Owing to the conductive Cu framework and synergistic biactive components, the as-prepared composite displayed superior electrochemical performance with high capacity and rate capability. Moreover, it showed stable cycling performance and a capacity of 832 mAh g−1 even after 50 discharge/charge cycles. The ionic transfer kinetics were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The cycled electrodes were also carefully examined to explain the origin of the enhanced performance. With a superb electrochemical performance and facile fabrication route, the freestanding CoO/Cu2O composites have a promising future as next-generation anodes for lithium–ion batteries.

In polymer nanocomposites, particle-polymer interactions influence the properties of the matrix polymer next to the particle surface, providing different physicochemical properties than in the bulk matrix. This region is often referred to as the interphase, but detailed characterization of its properties remains a challenge. Here we employ two atomic force microscopy (AFM) force methods, differing by a factor of about 15 in probing rate, to directly measure the surface nanomechanical properties of the transition region between filler particle and matrix over a controlled temperature range. The nanocomposite consists of poly(ethyl methacrylate) (PEMA) and poly(isobutyl methacrylate) (PiBMA) with a high concentration of hydrophobized silica nanoparticles. Both AFM methods demonstrate that the interphase region around a 40-nm-sized particle located on the surface of the nanocomposite could extend to 55-70nm, and the interphase exhibits a gradient distribution in surface nanomechanical properties. However, the slower probing rate provides somewhat lower numerical values for the surface stiffness. The analysis of the local glass transition temperature (T

Cobalt oxide nanosheets (Co3O4 NSs)/polypyrrole nanowire (PPy NW) core-shell nano-heterostructures based on nickel foam (NF) were fabricated for electrochemical non-enzymatic glucose determination. The Co3O4/PPy nanostructures grew directly on nickel foam substrate by electrochemical deposition processes. The PPy NW core and the Co3O4 NS shell constructed the hierarchical nanocomposites to form a three dimensional micro−nanostructure in the micropores of NF. The as-prepared Co3O4/PPy/NF heterostructures were characterized by using scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The introduction of the Co3O4 NSs can provide a high surface area and lead to high sensitivity to glucose. Chronoamperometry was used to evaluate the sensitivity of the sensor toward glucose. Compared with NF, PPy/NF, and Co(OH)2/PPy/NF electrodes, the Co3O4/PPy/NF electrode exhibited higher electrocatalytic activity for the oxidation of glucose, and the proposed glucose sensor showed linear electrochemical responses to glucose with a low detection limit of 0.74 μM (S/N=3). In addition, the prepared biosensor revealed good selectivity in the presence of electro-active species such as d-fructose, uric acid, ascorbic acid and hydrogen peroxide, and provided an excellent platform for the determination of glucose in human urine samples.

An electrochemical aptasensor for the lipopolysaccharide (LPS) detection was constructed by using copper-based metal-organic framework (Cu-MOF) as a label and the LPS aptamer of specific single-stranded DNA as a probe. The carboxyl-functionalized polypyrrole nanowires (PPy NWs) were synthesized by electrochemical polymerization method, and the amino-terminated aptamer covalently coupling with the carboxyl group of the PPy NWs was immobilized onto the modified electrode. The aptamer can specifically combine with the target LPS molecules, and Cu-MOF was labeled by adsorption based on specific interactions of LPS carbohydrate portions with anionic groups. The fabrication processes of the aptasensor were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Differential pulse voltammetry (DPV) was used to measure electrochemical performance of the aptasensor, and the electrochemical signal can be directly measured by the electrochemical redox reaction of Cu(II)/Cu(I) existed in the Cu-MOF. The electrochemical aptasensor exhibited a high sensitivity toward LPS ranging from 1.0 pg/mL to 1.0 ng/mL with a detection limit of 0.29 pg/mL. Moreover, the developed sensor was found to have good selectivity, stability and regeneration properties, and the sensor also successfully detected LPS in real tap water samples.

Improving surface selectivity and maximizing electrode surface area are critical needs for the electroreduction of nitrate. Herein, preferential (100) oriented Pt nanoflowers with an extended surface area were prepared by potentiostatic deposition on carbon cloth (Pt NFs/CC), and then Cu atoms were adsorbed on the Pt NFs (Cu/Pt NFs/CC) for application of nitrate electroreduction. The results reveal that Cu/Pt NFs/CC with 8.7% Cu coverage exhibits a high selectivity for nitrate electroreduction to N2 following two steps: Nitrate firstly converts into nitrite on Cu sites adsorbed on Pt NFs, then nitrite subsequently selective reduction and ammonia oxidation to N2 occur on the large exposed (100) terraces in Pt NFs. In addition, electrocatalytic activity and selectivity of nitrate reduction strongly rely on the Cu surface coverage on Pt NFs, the lower activity of nitrate reduction is displayed with increase of Cu coverage. Accordingly, the selective reduction of nitrate to N2 is feasible at such nanostructured Pt nanoflowers modified with Cu.

Because traditional chromating and phosphating processes are harmful to the environment and human health, an eco-friendly tannic acid (TA)-based conversion film technology is established by adopting a new self-assembly strategy of TA/metal complexes on iron surfaces in aqueous solutions. In this study, TA and TA/Zn films were conveniently fabricated by anchoring a certain amount of TA molecules on the iron surface through the coordination interaction between phenolic hydroxyls and metal ions. In contrast, the introduction of Zn ions in the film-forming process cannot only complex with more TA molecules to form a thicker conversion film but also accelerate the film-forming process and transform into ZnO, which can further inhibit iron corrosion. This combination leads to the excellent corrosion protection of TA/Zn film-modified iron (the corrosion protection efficiency is up to 92.39%). Moreover, impact tests show that the TA/Zn film can enhance the adhesion between the iron substrate and outer coating.

A polyelectrolytes coating with self-healing and self-strengthening dual-function was fabricated on the titanium sheet for anticorrosion studies in fluorine-containing artificial saliva. The coating contains a polydopamine bottom film and 2-hydroxypropyltrimethyl ammonium chloride chitosan and sodium alginate multilayers. The incorporated polydopamine bottom film was modified to assure the adhesion of the polyelectrolytes coating on the titanium sheet. Based on the scratch assay, there are two stages for the scratched coating immersed in fluorine-containing artificial saliva: healing and strengthening. Results exhibited that the coating possesses a remarkable self-healing property in the early-stage immersion due to the swollen polyelectrolytes migrating to the scratched region and the calcium cations of the corrosive medium as an ionic crosslinker intercalated in the swollen polyelectrolytes forming calcium alginate and filling the micro-scale scratch. During the later-stage immersion, the self-healing coating showed excellent self-strengthening performance originating from the formation of the more and more compact film with calcium cations intercalated. This research provides an effective strategy to prolong the service life and improve corrosion performance for the implants in the human body environments.

In this work, Co3O4 nanosheets were fabricated on indium tin oxide (ITO) substrates by developing a simple electrochemical deposition and annealing method. The as-prepared Co3O4 nanosheets were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), attenuated total reflection infrared (ATR-IR) spectroscopy and Raman spectroscopy. The Co3O4 nanosheets modified ITO electrode was used for the electrochemical analysis of various trace lead ions by differential pulse anodic stripping voltammetry. The electrode was found to be highly selective to Pb(II) in the range of 1–100 μg L−1, and exhibited a sensitive current response with a limit of detection (LOD) of 0.52 μg L−1. Furthermore, the developed electrochemical Pb(II) sensor exhibited a high stability and reproducibility with a simple regeneration process.

A simple and practical method was developed to prepare a series of phytic acid (PA)–metal complex coatings on iron substrate by directly immersing the iron samples in the mixed solutions containing PA and metal ions. The key technologies of fabricating PA–metal complex coatings include: (i) anchoring of PA molecules onto the iron surface via complexation with Fe2+ ions dissolved from the iron substrate, and (ii) layer-by-layer deposition of PA–metal complexes on the PA/Fe2+ bottom layer through the bridging effect of additive metal ions. The present method was applicable to the film-forming process of a variety of metal ions, such as Zn2+, Ca2+, Co2+ and Ni2+, and the as-prepared PA–metal complex coatings were defined as PA–M conversion coatings (M = Zn2+, Ca2+, Co2+ and Ni2+ herein). Due to the strong coordination ability, PA molecules may be self-assembled on the iron surface, forming a layer of organic thin film (here defined as PA film), without the help of additive metal ions. However, the comparison between PA film and PA–M coatings shows that PA–M coatings were much thicker (over 15 μm) and denser and also possessed much stronger anti-corrosion performance compared to the PA film. The present study provides a new path for the fabrication of environmentally-friendly PA-based chemical conversion coatings and further broadens the application range of PA in metal surface pretreatment.

The Fe-doping of hierarchical Co hydroxide nanosheet arrays (CoyFe1−y(OH)x NSAs) integrated on a three-dimensional electrode is shown to contribute to both increasing the available surface area and number of active sites. Ultrathin secondary nanosheets with different Co to Fe ratios that are subsequently grown on these primary nanoarrays are found to exhibit high oxygen evolution reaction (OER) activity. The optimal composition of CoyFe1−y(OH)x NSAs turns out to be Co0.7Fe0.3(OH)x NSAs, which allows for an OER onset overpotential as low as 220 mV and a small Tafel slope at 62.4 mV dec−1, while also providing excellent long-term durability (>100 h) and a high turnover frequency (TOF) of 0.172 s−1 at an overpotential of 380 mV. The specific activity of Fe-doped Co0.7Fe0.3(OH)x NSAs at an overpotential of 350 mV (0.37 mA cmBET−2) is also twice as high as that of undoped Co(OH)2 NSAs.

With the rapid development of rechargeable zinc ion (Zn-ion) batteries, it is essential to understand and modulate the energy storage process of the active component to maximize the battery performance. In this research, manganese oxide (MnO2) wrapped zinc hexacyanoferrate (ZnHCF) nanocubes (ZnHCF@MnO2) were prepared using an in situ co-precipitation method. The resulting composite with a unique structure was able to modulate the Zn-ion storage because of the incorporation of capacitive and intercalative properties of both components together with the redox reactions, benefiting from the synergistic effects. Thus, the encapsulation of ZnHCF nanocubes with MnO2 nanosheets gives a high discharge capability for Zn-ion storage with an operation voltage as high as ∼1.7 V. Impressively, the flexible quasi-solid-state Zn-ion battery was assembled using a neutral polymer gel electrolyte, and this resulted in a battery which had potential applications for specific wearable electronics.

Burgeoning interest in flexible and wearable electronics sparks the rapid development of flexible fiber-shape supercapacitors (SCs). Herein, three-dimensional porous reduced graphene oxide (RGO) aerogel is deposited on flexible Ni wire via a simple aqueous reduction method. RGO aerogel exhibits good capacitive performance, thanks to its unique porous structure and good electrical conductivity. In order to fabricate an asymmetric SC, nickel hydroxide nanosheets are controllably deposited on the RGO sheets as the positive electrode while the RGO aerogel coated Ni wire is used as negative one. The obtained flexible fiber SCs exhibit good performance with high power/energy densities (10.3 kW kg–1/3430 mW cm–3, 24.5 Wh kg–1/0.83 mWh cm–3) and good cycling stability (83% retention, even after 6000 cycles). The solid-state nature combined with good flexibility makes the fiber SCs attractive for energy storage applications in portable and wearable electronics. The interfacial deposition of reduced graphene oxide ...