Two-step Electrochemical Method Research Articles

Oxidative MnO2 Template Assisted Electrochemical Fabrication of Graphene/Polypyrrole Supercapacitor Electrodes.

Improving the morphological structure of active materials is a reliable strategy for the fabrication of high-performance supercapacitor electrodes. In this study, we introduce a feasible approach to constructing the graphene/polypyrrole (PPy) composite film implanted onto the current collector through a two-step electrochemical deposition method utilizing MnO2 as an intermediary template. The reduced graphene oxide (rGO) hydrogel film is first hydrothermally grown on a carbon cloth (CC) substrate to obtain a porous rGO@CC electrode on which MnO2 is electrodeposited. Then the as-prepared rGO/MnO2@CC electrode is subjected to the electrochemical polymerization of pyrrole, with MnO2 acting as an oxidizing template to facilitate the oxidative polymerization of pyrrole, ultimately yielding an rGO/PPy composite film on CC. The PPy synthesized via this methodology exhibits a distinctive interconnected structure, resulting in superior electrochemical performance compared with the electrode with PPy directly electrodeposited on rGO@CC. The optimized electrode achieves an impressive specific capacitance of 583.6 F g-1 at 1 A g-1 and retains 83% of its capacitance at 20 A g-1, with a capacitance loss of only 9.5% after 5000 charge-discharge cycles. The corresponding all-solid-state supercapacitor could provide a high energy density of 22.5 Wh kg-1 and a power density of 4.6 kW kg-1, with a capacitance retention of 82.7% after 5000 charge-discharge cycles. Furthermore, the device also demonstrates good flexibility performance upon bending at 90 and 180°. This work presents an innovative method for the preparation of carbon material/conducting polymer electrodes with specific structural characteristics and superior performance.

A two-step electrochemical method for separating Mg(OH)2 and CaCO3: Application to RO reject and polluted groundwater

The process of removing Ca2+ and Mg2+ ions typically results in the co-precipitation of Ca2+ and Mg2+ along with other salt waste. To improve water treatment efficiency towards a zero-waste goal, it is crucial to separate Ca2+ and Mg2+, and recover them in their purified form. This study proposes a two-step electrochemical approach that separately recovers Ca2+ as CaCO3 and Mg2+ as Mg(OH)2. The first step uses an undivided cell with 3D electrodes and controlled flow directions to selectively precipitate CaCO3 on the electrode, keeping the cell removal efficiency. The second step employs a two-compartment cell with a cationic exchange membrane to recover Mg(OH)2. This approach was evaluated on RO reject water with high Ca2+ to Mg2+ ratio and industrial effluent-polluted groundwater with a low ratio. Treatment of domestic RO reject water using undivided cell specifically recovered 64% of CaCO3, although the low conductivity of the RO reject water limited further Mg2+ recovery. Conversely, treating industrial effluent-polluted groundwater with this two-step process successfully recovered 80% of CaCO3 and 94% of Mg(OH)2. SEM, EDAX, and XRD analysis confirmed the quality of the recovered products.

In-situ Zn-Al layered double hydroxide conversion coatings prepared on galvanized steels by a two-step electrochemical method

Zn-Al layered double hydroxide (LDH) pretreatment layer was prepared by a novel two-step electrochemical method on galvanized steel surface from a precursor solution containing Al3+-only. In the first step, anodic currents are applied to Zn deposit to produce Zn2+ in solution near the substrate surface. Cathodic currents are then applied to ensure the cathodic deposition of LDH film. The obtained LDH coatings not only provide excellent adhesion to the metal surface, but also enhance the adhesion between metal substrate and the top epoxy coatings. The “LDH/epoxy” painting system can protect galvanized steel from rusting for at least 150 days.

Phase-Modified Strongly Coupled δ/ε-MnO2 Homojunction Cathode for Kinetics-Enhanced Zinc-Ion Batteries.

Rechargeable Zn-MnO2 batteries using mild water electrolytes have garnered significant interest owing to their impressive theoretical energy density and eco-friendly characteristics. However, MnO2 suffers from huge structural changes during the cycles, resulting in very poor stability at high charge-discharge depths. Briefly, the above problems are caused by slow kinetic processes and the dissolution of Mn atoms in the cycles. In this paper, a 2D homojunction electrode material (δ/ε-MnO2) based on δ-MnO2 and ε-MnO2 has been prepared by a two-step electrochemical deposition method. According to the DFT calculations, the charge transfer and bonding between interfaces result in the generation of electronic states near the Fermi surface, giving δ/ε-MnO2 a more continuous distribution of electron states and better conductivity, which is conducive to the rapid insertion/extraction of Zn2+ and H+. Moreover, the strongly coupled Mn-O-Mn interfacial bond can effectively impede dissolution of Mn atoms and thus maintain the structural integrity of δ/ε-MnO2 during the cycles. Accordingly, the δ/ε-MnO2 cathode exhibits high capacity (383 mAh g-1 at 0.1 A g-1), superior rate performance (150 mAh g-1 at 5 A g-1), and excellent cycling stability over 2000 cycles (91.3% at 3 A g-1). Profoundly, this unique homojunction provides a novel paradigm for reasonable selection of different components.

Activating the redox chemistry of MnO2/Mn2+ in aqueous Zn batteries based on multi-ions doping regulation

Two electron reaction of MnO2/Mn2+ have attracted burgeoning attention, which endows rechargeable aqueous Zn-MnO2 batteries with high energy density besides intrinsic safety, and environmental friendliness. However, it also suffers uncontrolled anode corrosion, sluggish ion diffusion and irreversible structural transformation, leading to poor rate capability and severe fading. Herein, a multi-ions regulated MnO2 (CrNi-MnO2) is designed via a novel two-step electrochemical method under theoretical guidance, contributing to the enhanced electrochemical performance of Zn-MnO2 batteries in terms of dissolution-deposition chemistry. CrNi-MnO2 cathode can significantly improve the conductivity and lower electrostatic interaction, boosting the rate performance and cycling stability. Furthermore, reversible Cr3+/Cr2+ reaction can effectively reduce the accumulation of “dead” MnO2, which can promote the transformation of MnO2/Mn2+ thoroughly in acid-mild electrolyte. Various ex-situ analyses and theory calculations have revealed double-functional role of the doped ions for accelerating MnO2/Mn2+ transformation and Zn2+/H+ co-insertion kinetics. Hence, CrNi-MnO2 cathode exhibits ultra-high capacity, superior rate performance, and excellent cycling stability, providing new insight for developing superb Zn-MnO2 batteries.

Electrochemically synthesized polyanine@Cu-BTC MOF as a bifunctional matrix for aptasensing of tetracycline in aquatic products

The development of new method for the rapid and facile screening of antibiotics residues in food is of great importance in food safety. Herein, a nanocompisite of polyaniline@copper-1,3,5-benzenetricarboxylic acid (PAN@Cu-BTC) with excellent electrochemical activity was directly prepared on the screen-printed electrode surface by a two-step electrochemical synthesis method. Then the tetracycline aptamer (TC-Apt) was assembled onto the electrode surface through the coordination between 5′-PO43- on the aptamer and Cu2+ on the MOF, achieving a novel electrochemical aptasensor for tetracycline (TC). The PAN@Cu-BTC has two functions in the aptasensors, namely the immobilization matrix of the aptamer probe and the internal signal source for target recognition. The electrochemical sensing assays showed that the capture of TC-Apt to the target on the electrode surface could cause the decrease of the electrochemical signal of PAN@Cu-BTC. Based on this, the TC can be analyzed in a wide range from 10 pM to 1 µM, with a low detection limit of 0.32 pM. The recoveries of the aptasensor for the detection of TC from Ctenopharyngodon idella meat were 90.0 %∼102.0 %, indicating that the constructed aptasensor is applicable for the detection of TC residues in fresh aquatic products.

Preparation of Mo6+, Gd3+-doped TiO2 nanotube arrays and study of their organization and photocatalytic properties

Titanium dioxide nanotube arrays doped with [Formula: see text], [Formula: see text], and [Formula: see text]-[Formula: see text] were prepared by anodic oxidation combined with a two-step electrochemical method. The crystalline structure, surface morphology, light absorption properties, and crystalline transformation process were characterized using XRD, SEM, UV–Vis, DSC, and FT-IR. The results show that [Formula: see text] and [Formula: see text] single doping of TiO2 can promote the transformation of amorphous TiO2 to anatase and inhibit the transformation of anatase phase to rutile, but [Formula: see text]–[Formula: see text] co-doping promotes both phase transformations, and the anatase compositions of the TiO2 heat-treated at 450∘C were all over 91%; The tube diameters of TiO2 nanotubes were all around 60–70 nm; the [Formula: see text] - and [Formula: see text] -doped TiO2 light absorption peaks were all significantly red-shifted, with the most obvious change in the [Formula: see text]–[Formula: see text] co-doping, where the forbidden bandwidth was reduced to 3.01 eV; The degradation rate of pure TiO2 photocatalytic degradation of methylene blue for 8 h was only 41.9%, while the degradation rate of [Formula: see text]–[Formula: see text]co-doped TiO2 was as high as 91.51%; [Formula: see text], [Formula: see text], single doping and co-doping could increase the amount of •OH, •OOH adsorbed on the surface of TiO2, which led to the improvement of catalytic performance.

Design, preparation, and characterization of a novel ZnO/CuO/Al energetic diode with dual functionality: Logic and destruction

Self-destructing chips have promising applications for securing data. This paper proposes a new concept of energetic diodes for the first time, which can be used for self-destructive chips. A simple two-step electrochemical deposition method is used to prepare ZnO/CuO/Al energetic diode, in which N-type ZnO and P-type CuO are constricted to a PN junction. This paper comprehensively discusses the material properties, morphology, semiconductor characteristics, and exploding performances of the energetic diode. Experimental results show that the energetic diode has typical rectification with a turn-on voltage of about 1.78 V and a reverse leakage current of about 3 × 10−4 A. When a constant voltage of 70 V loads to the energetic diode in the forward direction for about 0.14 s or 55 V loads in the reverse direction for about 0.17 s, the loaded power can excite the energetic diode exploding and the current rises to about 100 A. Due to the unique performance of the energetic diode, it has a double function of rectification and explosion. The energetic diode can be used as a logic element in the normal chip to complete the regular operation, and it can release energy to destroy the chip accurately.

Nd-Gd–Platinum doped TiO2 nanotube arrays catalyst for water splitting in Alkaline Medium

The utilization of a highly efficient electrocatalyst for the hydrogen evolution reaction (HER) plays an important role in energy conversion in regard to the development of hydrogen-based clean energy sources. The HER in alkaline media by co-doped lanthanide-platinum TiO2 Nanotube Arrays (TNTA) catalyst electrodes has yet to be studied. Here, we report the robust fabrication of an electrocatalyst and its prominent performance in catalyzing the HER. The catalyst electrode consisted of TiO2 nanotube arrays doped with rare earth metals (neodymium (Nd) and gadolinium (Gd)) and a small loading of Pt metal as double-layer nanotube arrays. This material was obtained by a two-step electrochemical anodization method using a small amount of fluoride salt and a short time of mechanical growth. Additionally, an in situ doping strategy that utilized a hydrothermal treatment for the ternary and quaternary ions of Nd, Gd and Pt was performed, while retaining the anatase phase. The Nd-Gd-TNTA catalyst electrode produced a current density of −47.522 µA cm−2 and exhibited a low activation energy of approximately 2.15 kJ/mol. The Nd-Gd-Pt-TNTA catalyst electrode is the best candidate for supporting the HER and advancing water splitting techniques for high-purity hydrogen production in alkaline media.

Effect of Supporting Electrolyte on Capacitance and Impedance Properties of Electrodeposited PEDOT/ERGO Electrodes for Supercapacitor

In this study, the ability of Poly (3,4-ethylenedioxythiophene)/electrochemically reduced graphene oxide (PEDOT/ERGO) electrodes for supercapacitors to store electrical energy is studied. PEDOT/ERGO electrodes are produced using a simple two-step electrochemical method that involves electrochemically reduction of graphene oxide, and then PEDOT is electrochemically deposited onto the ERGO in different electrolyte solutions. Electrochemical techniques such as cyclic voltammetry (CV), galvanostatic charge discharge (GCD), and electrochemical impedance spectroscopy (EIS) are utilized to investigate the electrochemical characteristics of PEDOT/ERGO electrodes produced in different electrolyte systems including 0.1 M lithium perchloride/acetonitrile (LiClO4/ACN), tetraethylammoniumtetrafluoroborate/acetonitrile (Et4NBF4/ACN), and tetrabutylammonium hexaflorophosphate/acetonitrile (Bu4NPF6/ACN). The electrolyte type has a significant impact on electrochemical results. PEDOT/ERGO manufactured in LiClO4/ACN demonstrates a high specific capacitance (Csp) and low charge transfer resistance (Rct). According to results, the Csp value is decreased in the following order; 26.48 mFcm-2 for LiClO4, 20.58 mFcm-2 for Et4NBF4, 8.96 mFcm-2 for Bu4NPF6.

A Novel Two-Step Electrochemical Deposition Method for Sn-Pd Electrocatalyst Synthesis for a Potential Application in Direct Ethanol Fuel Cells

Sn-Pd electrocatalysts with a constant atomic ratio of 60 at.% Sn-40 at.% Pd suitable for potential application in direct ethanol fuel cells were synthesized using a novel two-step electrodeposition method. First, Sn was electrodeposited in various forms of dendrites, from spear-like and needle-like to individual fern-like dendrites to a network of intertwined fern-like dendrites, by varying the cathodic potential and then performing electrodeposition of Pd at a constant current density in the second step. A morphological and elemental analysis of Sn and Sn-Pd electrocatalysts was performed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques, while the size of Sn dendrites was analyzed using the particle size distribution (PSD) method. Cyclic voltammetry (CV) and chronoamperometry were applied in order to study the catalytic behavior of Sn-Pd electrocatalysts in the ethanol oxidation reaction (EOR), while CO stripping was used to estimate the antipoisoning capability of the electrocatalysts. The Sn surface morphology of the sub-layer was highly correlated with the electrocatalytic activity of the examined Sn-Pd electrocatalysts. The high activity it presented towards the EOR showed the suitability of the Sn-Pd electrocatalyst constructed from individual fern-like Sn dendrites as a sub-layer. Compared to Pd alone, this Sn-Pd catalyst showed more than 3 times higher activity and improved EOR kinetics. This enhancement in the catalytic activity of the Sn-Pd electrocatalysts is attributed to both the morphological characteristics of Sn as a sub-layer and the bifunctional effect.

Cobalt sulfide nanosheets decorated on polypyrrole nanowires for improved charge storage in supercapacitors

Nanostructured cobalt sulfide-based electrode materials for supercapacitors (SCs) still suffer from easy aggregation, sluggish reaction kinetics, and poor structural stability. To resolve these issues, we adopt a two-step electrochemical deposition method to fabricate CoS nanosheets decorated on polypyrrole (PPy) nanowires that grow directly on Ni foam. The PPy nanowires serve as supports for growing CoS nanosheets, which not only make the CoS nanosheets well dispersed but also reduce their size and thickness. In addition, the intensive interaction between CoS and PPy endows the nanoarchitecture with high mechanical strength. Therefore, the constructed [email protected] nanocomposites feature abundant electroactive sites, high charge transport and transfer efficiencies, a short ion diffusion distance, and good structural stability. As a result, the optimized [email protected] nanocomposites as SC electrodes demonstrate specific capacities of 860C g−1 at 1 A g−1 and 595C g−1 at 20 A g−1, as well as a 92% initial capacity retention after 5000 cycles at 10 A g−1. Furthermore, a fabricated asymmetric supercapacitor (ASC) device with [email protected] nanocomposites as the positive electrode realizes a specific energy of 51.1 Wh kg−1 at 800 W kg−1, suggesting a promising potential for their practical application in SCs. This work may provide a feasible strategy for fabricating other metal sulfide/conducting polymer nanocomposites with enhanced charge storage capabilities as SC electrodes.

Highly Sensitive Electrochemical Detection of Paraquat in Environmental Water Samples Using a Vertically Ordered Mesoporous Silica Film and a Nanocarbon Composite.

Herein, we demonstrate a sensitive and rapid electrochemical method for the detection of paraquat (PQ) using a glassy carbon electrode (GCE) modified with vertically ordered mesoporous silica films (VMSF) and a nanocarbon composite. The three-dimensional graphene-carbon nanotube (3DG-CNT) nanocarbon composite has a 3D network structure, a large electroactive area and oxygen-containing groups, promoting electron transfer between PQ and the underlying electrode and providing a suitable microenvironment for the stable growth of VMSF. This VMSF/3DG-CNT nanocomposite film could be prepared on the GCE’s surface by a two-step electrochemical method with good controllability and convenience. Owing to the synergistic effect of the electrocatalytic ability of 3DG-CNT and the electrostatically enriched capacity of VMSF, the proposed VMSF/3DG-CNT/GCE has superior analytical sensitivity compared with the bare GCE. Furthermore, VMSF has excellent anti-fouling ability that makes the fabricated sensor exhibit satisfactory performance for direct analysis of PQ in environmental water samples.

Two-step electrochemical synthesis of “ant-nest” like Co-O, pyrrolic N co-modified graphite felt for high-efficient H2O2 production

Heteroatom modified catalyst applying for the two-electron oxygen reduction reaction has the potential application for efficient on-site production of H2O2. At present, state of the art catalyst synthesis is often energy-intensive and tends to destroy the original structure of heteroatoms. Based on the above considerations, Co-O, pyrrolic N structures co-modified graphite felt catalyst (Co-PDA-GF) is successfully synthesized by a simple two-step electrochemical method. Interestingly, the introduction of Co2+ during the dopamine (DA) polymerization process changes the surface morphology of GF from a “thin-film” like to an “ant-nest” like. The cumulative H2O2 concentration achieves 421 mg L−1 in 6 h test time, which is 16 times higher than that of R-GF, and the Methylene blue (MB) in-situ removal rate reaches 97.2% within 3 h. The enhanced H2O2 yield of Co-PDA-GF catalyst is attributed to the increased oxygen-containing functional groups (-COOH, -C-O-C) and defect structures, and most importantly, Co-O and pyrrolic N synergistic modulation effects on local electronic modulation. This work provides new insights on DA polymerization morphology control and designing of high-efficient 2e− ORR catalyst with a low-energy method.

Decorating cobalt selenide nanoparticles on polypyrrole nanowires as nanocomposite electrodes for hybrid supercapacitors

• PPy@Co 0.85 Se nanocomposites are fabricated by a two-step electrochemical method. • Dispersed Co 0.85 Se nanoparticles are decorated on PPy nanowires growing on Ni foam. • PPy@Co 0.85 Se electrodes demonstrate improved rate capacities and cyclic stability. • The improved charge storage property arises from structural merits of nanocomposites. Cobalt selenide electrode materials for hybrid supercapacitors (HSCs) still suffer from the unsatisfactory rate performance and cyclic stability thanks to their limited electrical conductivity and poor structural stability. To address these issues, we here report on the construction of polypyrrole (PPy)@Co 0.85 Se nanocomposites that grow on Ni foam by a two-step electrochemical synthesis method. In such nanocomposites, well dispersed Co 0.85 Se nanoparticles are decorated on conductive PPy nanowires, which are featured by enhanced electrical conductivity, rich electroactive sites, easy adsorption/desorption and diffusion of electrolyte ions, and good mechanical stability. As a result, the obtained PPy@Co 0.85 Se nanocomposites give a maximum specific capacity of 827 C g −1 at 1 A/g, a capacity retention of 67 % at 20 A/g, and an initial capacity retention of 93 % after 5000 cycles at 10 A/g. Furthermore, a two-electrode HSC device is assembled with PPy@Co 0.85 Se as the positive electrode, which demonstrates an energy density of 51.9 Wh kg −1 at a power density of 812 W kg −1 as well as an initial capacity retention of 96 % after 5000 cycles at 5 A/g. These results showcase a great potential for future application of the synthesized PPy@Co 0.85 Se nanocomposites in HSCs, and our work may provide an efficient strategy for engineering other metal selenide-based electrode materials for HSCs.

Tuning structural properties, morphology and magnetic characteristics of nanostructured Ni-Co-Fe/ITO ternary alloys by galvanostatic pretreatment process.

In this research, the structural properties, surface morphology, and magnetic characteristics of nanostructured ternary ferromagnetic alloys grown by a cost-effective and effortless two-step electrochemical deposition method on indium tin oxide (ITO) substrates with and without a galvanostatic pretreatment process (GPP) were examined. The GPP was applied at various pretreatment current densities (PCDs) such as -10, -20, and - 30 mA/cm2 . The effect of the PCD on the Ni, Co, and Fe contents is found to be insignificant and all resultant Ni-Co-Fe thin films show an abnormal co-deposition. The films have nano-sized crystallites ranging from 17.3 to 19.6nm and showed a face-centered cubic structure with the [111] preferential growth. Compared to the non-GPP applied Ni-Co-Fe film, growing the ternary Ni-Co-Fe film on ITO at the PCD of -30 mA/cm2 causes an improvement in the crystal quality and a reduction in the particle size from 150 ± 50 to 70 ± 20 nm. A decrement in the surface roughness and coercivity was also achieved by applying the GPP at the PCD of -30 mA/cm2 , but the opposite is true for the GPP performed at the PCD of -10mA/cm2 . The GPP has an effect on the magnetic Squareness Ratio (SQR), but the influence of the PCD on the SQR parameter is negligible. The obtained findings reveal that the properties of the Ni-Co-Fe/ITO ternary alloys can be tuned through the GPP applied in various PCDs. HIGHLIGHTS: • The effect of the PCD on the Ni, Co, and Fe contents is found to be insignificant. • The films have nano-sized crystallites and showed a face-centered cubic structure with the [111] preferential growth. • The analysis reveals that the GPP changes the crystal quality, Hc parameter, surface roughness, and particle size of the films. • The GPP has an effect on the magnetic squareness ratio (SQR), but the influence of the PCD on the SQR parameter is negligible. • The films had nano-sized crystallites ranging from 17.3 to 19.6nm. • The films were ferromagnetic, and the Hc and SQR parameters of the films ranged from 30.2 to 42.7Oe and from 8.8% to 19.6%.

Synthesis of phosphonated graphene oxide by electrochemical exfoliation to enhance the performance and durability of high-temperature proton exchange membrane fuel cells

The doping of functionalized graphene oxide (GO) in the membranes becomes a promising method for improving the performance of high-temperature proton exchange membrane fuel cells (HT-PEMFC). Phosphonated graphene oxide (PGO) with a P/O ratio of 8.5% was quickly synthesised by one-step electrochemical exfoliation based on a three-dimensiaonal (3D) printed reactor and natural graphite flakes. Compared with the GO prepared by the two-step electrochemical exfoliation method, the PGO synthesized by the one-step electrochemical exfoliation can better improve the performance of the membrane-electrode-assembly (MEA) based on the polybenzimidazole (PBI) membrane in the HT-PEMFC. The doping of 1.5 wt% GO synthesised by electrochemical exfoliation with the 2-step method or reactor method in PBI increased the peak power density by 17.4% or 35.4% compared to MEA based on pure PBI membrane at 150 °C, respectively. In addition, the doping of PGO in PBI improves its durability under accelerated stress test (AST).

Enhanced the synergistic degradation effect between active hydroxyl and reactive oxygen species for indoor formaldehyde based on platinum atoms modified MnOOH/MnO2 catalyst

Maintaining high activity during prolonged catalysis is always the pursuit in catalytic degradation of organic pollutants. For indoor formaldehyde (HCHO) degradation, the accumulation of intermediates is the major factor limiting the conversion of HCHO to final product CO2 (HCHO-to-CO2 conversion) and long-lasting catalysis. Herein, a three-dimensional radialized nanostructure catalyst self-assembled by MnOOH/MnO2 nanosheets anchored with Pt single atoms (PtSA-MnOOH/MnO2 with a trace platinum loading amount of 0.09%) is developed by thermally assisted two-step electrochemical method, which achieves enhanced CO2 production in catalytic HCHO degradation at the room temperature by the collaborative action of active hydroxyl (OH*) and active oxygen species (O2*). By boosting intermediates’ decomposing, the catalyst implements real-time HCHO-to-CO2 conversion (∼85.7%) and long-term continuous HCHO removal (∼98%) during 100 h in a 15 ppm HCHO atmosphere at 25 °C under a weight hourly space velocity of 30000 mL/gcat∙h. Density functional theory calculation shows that the formation energy of O2* from O2 over PtSA-MnOOH/MnO2 is nearly half lower than that over Pt-MnO2 catalyst. And decomposing accumulated intermediates gives the credit to OH* species sustainably generated by the combined action of MnOOH and O2*. The synergistic action between PtSA and MnOOH contributes to the continuous production of O2* and OH* for enhancing CO2 production in indoor catalytic formaldehyde degradation.

Performance and Durability of HT-PEMFC Enhanced By One-Step Electrochemical Exfoliated Phosphonated Graphene Oxide

The high-temperature proton exchange membrane fuel cell (HT-PEMFC) conducts protons through the hydrogen bond network established by the polymer and phosphoric acid (PA), which reduces the dependence on humidity and allows its operating temperature to be higher than 100°C [1]. A higher operating temperature is conducive to improve catalyst activity, reducing carbon dioxide adsorption on the catalyst thus reducing the requirement for hydrogen purity, and convenient water management [2]. As the most widely commercialized HT-PEMFC proton exchange membrane material, the performance and durability of Polybenzimidazole (PBI) still need to be improved. In particular, it has insufficient proton conductivity, insufficient mechanical properties, and phosphoric acid leaching issues under high acid doping level [3] [4] [5].The doping of functionalized graphene oxide in the PBI membrane can build additional proton transfer channels, promote proton hopping and act as a trap for PA to reduce its leaching by virtue of abundant functional groups of functionalized GO [6] [7] [8]. Among the groups that can be used for functionalization, the phosphoric acid group has become one of the most promising due to its strong hydrogen bonding and water retention ability [9] [10] [11]. Phosphonated graphene oxide (PGO) is usually synthesized by further phosphonation of GO obtained by chemical exfoliation [6] [7]. Chemical exfoliation methods usually require the long-term action of strong acids and strong oxidants [12]. The safety and environmental issues caused by those methods can not be underestimated. And the two-step synthesis method of PGO has a long reaction period.This work achieved the rapid, safe, and large-yield production of electrochemically exfoliated PGO by using a 3D printed reactor, ammonium dihydrogen phosphate as the electrolyte and natural graphite flakes as the raw material. The two-step electrochemical exfoliation method of producing GIC with concentrated sulfuric acid as the first electrolyte is also used to synthesize electrochemical exfoliated (E)GO. 1.5wt% EGO or PGO was doped in the PBI membrane to explore the effect of different GO on the performance and durability of the PBI- membrane-based HT-PEMFC. Compared with pure PBI, the doping of EGO and PGO increases the peak power density of HT-PEMFC by 17.4% and 35.4%, respectively.[1] Y.-L. Ma, J.S. Wainright, M.H. Litt, R.F. Savinell, Journal of The Electrochemical Society 2004, 151, A8.[2] H. Su, S. Pasupathi, B. Bladergroen, V. Linkov, B.G. Pollet, International Journal of Hydrogen Energy 2013, 38, 11370.[3] S. Galbiati, A. Baricci, A. Casalegno, R. Marchesi, International Journal of Hydrogen Energy 2013, 38, 6469.[4] S.H. Eberhardt, F. Marone, M. Stampanoni, F.N. Büchi, T.J. Schmidt, Journal of Synchrotron Radiation 2014, 21, 1319.[5] Q. He, X. Yang, W. Chen, S. Mukerjee, B. Koel, S. Chen, Physical Chemistry Chemical Physics 2010, 12, 12544.[6] J. Yang, C. Liu, L. Gao, J. Wang, Y. Xu, R. He, RSC Advances 2015, 5, 101049.[7] C. Xu, Y. Cao, R. Kumar, X. Wu, X. Wang, K. Scott, Journal of Materials Chemistry 2011, 21, 11359.[8] Y. Cai, Z. Yue, S.X.-J. of A.P. Science, undefined 2017, Wiley Online Library 2017, 134, 44986.[9] E. Abouzari-Lotf, H. Ghassemi, A. Shockravi, T. Zawodzinski, D. Schiraldi, Polymer 2011, 52, 4709.[10] E. Abouzari-Lotf, M. Zakeri, M.M. Nasef, M. Miyake, P. Mozarmnia, N.A. Bazilah, N.F. Emelin, A. Ahmad, Journal of Power Sources 2019, 412, 238.[11] S. Some, I. Shackery, S.J. Kim, S.C. Jun, Chemistry - A European Journal 2015, 21, 15480.[12] C. Xu, Y. Cao, R. Kumar, X. Wu, X. Wang, K. Scott, Journal of Materials Chemistry 2011, 21, 11359.

Enhanced electrochemical performance of the cobalt chloride carbonate hydroxide hydrate via micromorphology and phase transformation

Micromorphology and conductivity are two vital factors for the practical capacitance of the electrode materials for supercapacitors. In this work, a novel two-step electrochemical activation method involving a cyclic voltammetry (CV) treatment within 0–0.7 V followed by a CV treatment within −1.2–0 V is explored to induce the micromorphology and phase transformation of the cobalt chloride carbonate hydroxide hydrate (CCCH) nanoneedle arrays. The first-step activation transforms the CCCH to Co(OH)2 and then the reversible transformation between Co(OH)2 and CoOOH generates plenty of pores in the sample, thereby increasing the specific capacitance from 0.54 to 1.74 F cm−2 at the current density of 10 mA cm−2. The second-step activation inducing the reversible transformation between Co(OH)2 and Co not only endows the final sample with a nanosheets-assembled fasciculate structure but also decreases the internal resistance via generating Co0 in the final sample (CCCH-P75N50). Consequently, the CCCH-P75N50 shows a high specific capacitance of 3.83 F cm−2 at the current density of 10 mA cm−2. Besides, the aqueous asymmetric supercapacitor assembled with CCCH-P75N50 and commercial conductive carbon cloth (CC) delivers a high energy density of 2.75 mWh cm−3 at a power density of 37.5 mW cm−3. This work provides a novel, facile and promising method to optimize the micromorphology and conductivity of Co-based electrodes.