Water-Soluble Polyaniline–Polyacrylic Acid Composites as Efficient Corrosion Inhibitors for 316SS

Water-soluble polyaniline–poly­(acrylic acid) (PANI–PAA) composites with excellent processability and electroactivity were prepared by a one-step in situ polymerization. PAA as a matrix not only improves the solubility of PANI in water but also prevents the formation of macroscopic PANI clusters. The corrosion-inhibition performance of 316 stainless steel (316SS) was evaluated in 0.5 M HCl by electrochemical measurements in the presence of PANI–PAA composites. The results show that PANI–PAA acts as a mixed-type inhibitor, and its inhibition efficiency (<i>IE</i>_(R)) increases with inhibitor concentration. The adsorption of the inhibitor on 316SS surface obeys a Langmuir adsorption isotherm. The PANI–PAA composite with an optimized concentration of 200 ppm shows marked increase in <i>IE</i>_(R), i.e., 91.68%. The enhanced efficiency is attributed to an insulating interfacial layer formed by the adsorption of PANI–PAA, which obstructs the corrosion reaction at the interface

Silver Nanoparticle-Induced Growth of Nanowire-Covered Porous MnO₂ Spheres with Superior Supercapacitance

We report a facile, low-cost, ultrasound-assisted synthesis of nanowire-covered porous MnO₂ spheres with superior supercapacitance at high charging rates with long-term durability. The use of catalytic silver nanoparticles is crucial to the growth mechanism in the initial stage, and the resulting silver oxides later grow the nanowires in such a way that they always terminate the wires, thus automatically covering the structures and increasing conductivity. The optimal Ag₂O–MnO₂ structures have a specific capacitance of 536.4 F/g at 5 mV/s. At a high scan rate of 100 mV/s, only 200 F/g remain for the reported carbon nanotube/MnO₂ material with an excellent capacitance at low scan rate (1230 F/g, 1 mV/s), while the Ag₂O–MnO₂ reported here still has 417.2 F/g. The material reaches a stable region of 91.3% capacitance retention over 10000 charge/discharge cycles at 5 A/g

Silver Doping Mediated Route to Bimetallically Doped Carbon Spheres with Controllable Nanoparticle Distributions

We report a facile and efficient approach to prepare bimetallically doped Ag−M−carbon composites. Only if Ag nanoparticles (NPs) are embedded first into the submicrometer carbon spheres (CSs) can the second metal M (Pd, Pt, and Au) also be introduced into their interior. Especially at not too high concentrations of M-precursor ions (CM-ion), the locations and number density of the resulting NPs mirror those of the Ag NPs in/on the CSs. Therefore, the controllability of the Ag predoping allows control over the location dependent distribution of the NPs in the resulting bimetallic composites. The size and shape of the resulting NPs in the composites are largely controlled by the concentration CM-ion. The different shapes include solid core−shell and hollow NPs, as well as hedgehog-like hollow structures and dendritic aggregates. The nucleation and growth mechanisms, which differ between the different metals M, are discussed to explain the morphologies and the location dependence of the NPs in/on the CSs

Hierarchically MnO₂–Nanosheet Covered Submicrometer-FeCo₂O₄‑Tube Forest as Binder-Free Electrodes for High Energy Density All-Solid-State Supercapacitors

The current problem of the still relatively low energy densities of supercapacitors can be effectively addressed by designing electrodes hierarchically on micro- and nanoscale. Herein, we report the synthesis of hierarchically porous, nanosheet covered submicrometer tube forests on Ni foam. Chemical deposition and thermal treatment result in homogeneous forests of 750 nm diameter FeCo₂O₄ tubes, which after hydrothermal reaction in KMnO₄ are wrapped in MnO₂-nanosheet-built porous covers. The covers’ thickness can be adjusted from 200 to 800 nm by KMnO₄ concentration. An optimal thickness (380 nm) with a MnO₂ content of 42 wt % doubles the specific capacitance (3.30 F cm^–2 at 1.0 mA cm^–2) of the bare FeCo₂O₄-tube forests. A symmetric solid-state supercapacitor made from these binder-free electrodes achieves 2.52 F cm^–2 at 2 mA cm^–2, much higher than reported for capacitors based on similar core–shell nanowire arrays. The large capacitance and high cell voltage of 1.7 V allow high energy and power densities (93.6 Wh kg^–1, 10.1 kW kg^–1). The device also exhibits superior rate capability (71% capacitance at 20 mA cm^–2) and remarkable cycling stability with 94% capacitance retention being stable after 1500 cycles

Hierarchically Porous MnO₂ Microspheres Doped with Homogeneously Distributed Fe₃O₄ Nanoparticles for Supercapacitors

Hierarchically porous yet densely packed MnO₂ microspheres doped with Fe₃O₄ nanoparticles are synthesized via a one-step and low-cost ultrasound assisted method. The scalable synthesis is based on Fe²⁺ and ultrasound assisted nucleation and growth at a constant temperature in a range of 25–70 °C. Single-crystalline Fe₃O₄ particles of 3–5 nm in diameter are homogeneously distributed throughout the spheres and none are on the surface. A systematic optimization of reaction parameters results in isolated, porous, and uniform Fe₃O₄–MnO₂ composite spheres. The spheres’ average diameter is dependent on the temperature, and thus is controllable in a range of 0.7–1.28 μm. The involved growth mechanism is discussed. The specific capacitance is optimized at an Fe/Mn atomic ratio of <i>r</i> = 0.075 to be 448 F/g at a scan rate of 5 mV/s, which is nearly 1.5 times that of the extremely high reported value for MnO₂ nanostructures (309 F/g). Especially, such a structure allows significantly improved stability at high charging rates. The composite has a capacitance of 367.4 F/g at a high scan rate of 100 mV/s, which is 82% of that at 5 mV/s. Also, it has an excellent cycling performance with a capacitance retention of 76% after 5000 charge/discharge cycles at 5 A/g

Sub-3-nm High-Entropy Metal Sulfide Nanoparticles with Synergistic Effects as Promising Electrocatalysts for Enhanced Oxygen Evolution Reaction

Both high-entropy materials and metal–organic frameworks (MOFs) can be used as efficient catalysts for oxygen evolution, but it remains a challenge to combine their advantages to further improve the oxygen evolution reaction (OER). Herein, MOFs are served as precursors to prepare the high-entropy metal sulfide (HEMS) (MnFeCoNiCu)S2 nanoparticles based on the maximized configurational entropy theory, exhibiting ultra-efficient OER performance. The strong synergistic effect among Mn, Fe, Co, Ni, and Cu builds a stable electronic structure and provides a favorable local coordination environment, which enhance the catalytic performance greatly. In addition, the appropriate doping of sulfur source contributes to modulate the electronic structure, which promotes the formation of single-phase HEMS nanoparticles with the dimeter of sub-3 nm. The (MnFeCoNiCu)S2 nanoparticles display the best OER performance (a low overpotential of 221 mV at 10 mA cm–2 in 1 M KOH solution) and good stability (remains to be 97.6% after 12 h by chronoamperometry). This work provides a potential application for high-entropy materials based on MOF precursors as OER catalysts

Achieving Rich Mixed-Valence Polysulfide/Carbon Nanotube Films toward Ultrahigh Volume Energy Density and Largely Deformable Pseudocapacitors

In this work, new insights into dependence of electrochemical performance enhancement on transition metals’ rich mixed valence and their atomic ratio as well as redox active polysulfides are proposed. Especially, the influence of atomic ratio is further demonstrated by both experiments and density functional theoretical calculation where increasing Co/S leads to the enlargement of both interatom distance and hole diameter in a MnxCoySz cell. We rationally designed and prepared novel flexible electrodes of a rich mixed-valence polysulfide MnxCoySz/carbon nanotube film (CNTF) through acid activation of a dense CNTF into a hydrogel-like conductive matrix, growth of the MnxCoy(CO3)0.5OH precursor on each CNT, and controlled sulfidation. Nanostructure control allows us to obtain fast electron/ion transfer and increased availability of active sites/interfaces. The optimal MnCo9S10/CNTF shows a specific capacitance reaching 450 F cm–3 at 10 mA cm–2, much higher than reported values for CNT-based electrodes. Also, it exhibits remarkable cycling stability with only 1.6% capacity loss after 10 000 cycles at a high current density of 80 mA cm–2. An all-solid-state asymmetric supercapacitor (ASC) applying MnCo9S10/CNTF delivers an exceptionally high volumetric energy density of 67 mW h cm–3 (at 10 W cm–3). Particularly, integrated electric sources with adjustable output voltages can be obtained by connecting several ASCs in series, and there are no structural failure and capacity loss during repeated large-angle twisting and vigorous hammering. This work provides a general route to energy storage devices with ultrahigh volumetric energy density and outstanding reliability for wearable electronics

Achieving Rich Mixed-Valence Polysulfide/Carbon Nanotube Films toward Ultrahigh Volume Energy Density and Largely Deformable Pseudocapacitors

In this work, new insights into dependence of electrochemical performance enhancement on transition metals’ rich mixed valence and their atomic ratio as well as redox active polysulfides are proposed. Especially, the influence of atomic ratio is further demonstrated by both experiments and density functional theoretical calculation where increasing Co/S leads to the enlargement of both interatom distance and hole diameter in a MnxCoySz cell. We rationally designed and prepared novel flexible electrodes of a rich mixed-valence polysulfide MnxCoySz/carbon nanotube film (CNTF) through acid activation of a dense CNTF into a hydrogel-like conductive matrix, growth of the MnxCoy(CO3)0.5OH precursor on each CNT, and controlled sulfidation. Nanostructure control allows us to obtain fast electron/ion transfer and increased availability of active sites/interfaces. The optimal MnCo9S10/CNTF shows a specific capacitance reaching 450 F cm–3 at 10 mA cm–2, much higher than reported values for CNT-based electrodes. Also, it exhibits remarkable cycling stability with only 1.6% capacity loss after 10 000 cycles at a high current density of 80 mA cm–2. An all-solid-state asymmetric supercapacitor (ASC) applying MnCo9S10/CNTF delivers an exceptionally high volumetric energy density of 67 mW h cm–3 (at 10 W cm–3). Particularly, integrated electric sources with adjustable output voltages can be obtained by connecting several ASCs in series, and there are no structural failure and capacity loss during repeated large-angle twisting and vigorous hammering. This work provides a general route to energy storage devices with ultrahigh volumetric energy density and outstanding reliability for wearable electronics

Amorphous Bimetallic Metal–Organic Frameworks with an Optimized D‑Band Center Enable Accelerating Oxygen Evolution Reaction

Development of oxygen evolution reaction (OER) electrocatalysts with low cost and high performance is the key procedure in industrial electrolysis of water to produce hydrogen. Unfortunately, current reports heavily rely on empirical investigation and overlook the relationship between types of elements and the degree of amorphous, which hinders the design of amorphous metal–organic frameworks (MOFs) with high catalytic activity. Here, we prepared a series of bimetallic Fe-M-MOFs to explore the types of elements/degree of amorphous/catalytic property relationship. The amorphous FeNi-MOF containing crystalline nanostructures has the best OER performance and splendid stability. Additionally, density functional theory (DFT) demonstrates that benefiting from the strong coupling between Fe and Ni atoms, the d-band center of the active sites in FeNi-MOF (−0.92 eV) moves down compared to Fe-MOF (−1.24 eV), optimizing the *OOH intermediate toward rapid OER kinetics. This work provides a brand new approach to design efficient amorphous MOF electrocatalysts from the perspective of types of elements/degree of amorphous and regulation of the d-band center