In situ AFM studies of SEI formation at a Sn electrode

Early stages of the solid electrolyte interphase (SEI) formation at a tin foil electrode in an ethylene carbonate (EC) based electrolyte were investigated by in situ AFM and cyclic voltammetry (CV) at potentials >0.7 V, i.e., above the potential of Sn–Li alloying. We detected and observed initial steps of the surface film formation at ～2.8 V vs. Li/Li⁺ followed by gradual film morphology changes at potentials 0.7 < U < 2.5 V. The SEI layer undergoes continuous reformation during the following CV cycles between 0.7 and 2.5 V. The surface film on Sn does not effectively prevent the electrolyte reduction and a large fraction of the reaction products dissolve in the electrolyte. The unstable SEI layer on Sn in EC-based electrolytes may compromise the use of tin-based anodes in Li-ion battery systems unless the interfacial chemistry of the electrode and/or electrolyte is modified.     

Fabrication and characterization of large-size electrolyte/anode bilayer structures for low-temperature solid oxide fuel cell stack based on gadolinia-doped ceria electrolyte

Preliminary progress is reported in this communication in building a planar anode-supported low-temperature solid oxide fuel cell (SOFC) stack based on gadolinia-doped ceria (GDC) electrolyte, i.e. fabrication and characterization of a Ø80 planar bilayer structure composed of GDC electrolyte film and Ni–GDC anode substrate. The anode substrates were prepared from mixtures of NiO, GDC, and carbon black by die-pressing. After pre-firing to remove the carbon black, the anode substrates were deposited with a GDC layer using a spray coating technique. The green bilayers of anode substrate and electrolyte film were then co-sintered at 1500 °C for 3 h. Through proper control of the sintering process, bilayer structures with excellent flatness were achieved after co-sintering. Scanning electron microscopy (SEM) observation indicated that the electrolyte film was about 22 μm in thickness, highly dense, crack-free, and well-bonded to the anode substrate. Small disks which were cut out from the Ø80 bilayer structure were electrochemically examined in a single button-cell mode incorporating a (LaSr)(CoFe)O₃–GDC composite cathode. With humidified hydrogen as the fuel and air as the oxidant, the cell demonstrated an open-circuit voltage of 0.884 V and a maximum power density of 562 mW/cm² at 600 °C. The results imply that high-quality anode-supported electrolyte/anode bilayer structures were successfully fabricated. Based on them, planar anode-supported SOFC stacks will be assembled in the future.     

Electrochemical fabrication of novel fluorescent polymeric film: Poly(pyrrole–pyrene)

We describe herein the electrochemical characterization and polymerization of 4-pyren-1-yl-butyric acid 11-pyrrol-1-yl-decyl ester (pyrrole–pyrene) in CH₃CN. The electrochemical oxidation of the pyrrole group at 0.77 V vs Ag/Ag + 10 mM in CH₃CN led to the first example of a fluorescent polypyrrole film. The mechanism of deposition on platinum electrode was studied by voltammetry and chronoamperometry. The optical properties of the polymeric films electrogenerated on ITO electrodes were examined by UV–visible spectroscopy and fluorescence microscopy indicating an increase in fluorescence properties by increased polymer thickness. The electrochemical oxidation of pyrenyl group linked to the polypyrrole backbone was carried out at 1.2 V. This additional polymerization was demonstrated by UV–visible spectroscopy and induced the loss of the fluorescence properties of the resulting polymeric film.     

Ultra-low platinum loading high-performance PEMFCs using buckypaper-supported electrodes

The microstructure of the catalyst layer in proton exchange membrane fuel cells (PEMFCs) greatly influences catalyst (Pt) utilization and cell performance. We demonstrated a functionally graded catalyst layer based on a double-layered carbon nanotube/nanofiber film- (buckypaper) supported Pt composite catalyst to approach an idealized microstructure. The gradient distribution of Pt, electrolyte and porosity along the thickness effectively depresses the transport resistance of proton and gas. A rated power of 0.88 W/cm² at 0.65 V was achieved at 80 °C with a low Pt loading of 0.11 mg/cm² resulting in a relatively high Pt utilization of 0.18g_Pt/kW. The accelerated degradation test of catalyst support showed a good durability of buckypaper support because of the high graphitization degree of carbon nanofibers.     

Unique CO-tolerance of Pt–WOx materials

Well-defined tungsten-oxide-supported platinum nanoparticles (Pt/WO_x) were elaborated by impregnation-reduction of a platinum salt onto commercial monoclinic WO₃. Field-emission gun scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM) revealed that the Pt particles are well-distributed on the oxide support, present a narrow particle size distribution centered on ca. 2–3 nm and a low degree of agglomeration. Carbon black was added to ensure electronic percolation in the electrodes during the electrochemical measurements. CO_ads electrooxidation currents were monitored at potentials as low as 0.1 V vs. RHE on Pt/WO_x, demonstrating high CO-tolerance compared to carbon-supported Pt or PtRu catalysts.     

Highly active Co-doped LaMnO3 perovskite oxide and N-doped carbon nanotube hybrid bi-functional catalyst for rechargeable zinc–air batteries

Herein, non-precious cobalt doped lanthanum manganese perovskite oxide nanoparticles are used as a growth substrate for nitrogen-doped carbon nanotubes to form efficient and durable hybrid bi-functional catalyst (LMCO/NCNT). LMCO/NCNT demonstrates significantly enhanced onset and half-wave oxygen reduction reaction (ORR) potentials (− 0.11 and − 0.24 V vs. SCE, respectively), and oxygen evolution reaction (OER) current density (27 mA cm^− 2 at 0.9 V vs. SCE). Likewise, practical rechargeable zinc–air battery testing using atmospheric air reveals superior discharge voltages obtained with LMCO/NCNT, particularly at current densities higher than 30 mA cm^− 2, and significantly lower charge voltages at all current densities tested, compared to state-of-art commercial platinum on carbon catalyst. In addition, very stable charge and discharge voltages of 2.2 and 1.0 V, respectively, are obtained over 60 cycles. The excellent performance and durability of the hybrid catalyst are attributed to very uniformly distributed LMCO nanoparticles on the surface of NCNT resulting in enhanced surface area and material utilization.     

CO tolerant Pt/WC methanol electro-oxidation catalyst

Platinum supported on WC (Pt/WC) catalyst (20 wt.% Pt) was synthesized as a new methanol electro-oxidation catalyst. Particle size of 7.5 nm was obtained from X-ray diffraction results and a uniform distribution of particles was observed by transmission electron microscopy. In cyclic voltammetry (CV) measurement, the reduction peak potential of PtO increased from 0.72 V in commercial Pt/C to 0.76 V in Pt/WC. By combining the CV and CO stripping results, spill-over of H⁺ from Pt to WC was observed. Electrochemically active surface area calculated from the desorption area of H⁺ were 11.2 and 5.74 m²/g catalyst for Pt/WC and Pt/C, while those obtained from the desorption area of CO were 4.42 and 6.40 m²/g catalyst, respectively. CO electro-oxidation peak potential greatly decreased from 0.80 V in Pt/C to 0.68 V in Pt/WC. The reaction of WC with water to produce WC–OH could lower to CO electro-oxidation peak potential. Specific activity for methanol electro-oxidation increased from 144 mA/m² in Pt/C to 188 mA/m² in Pt/WC.     

Stability of carbon-supported palladium nanoparticles in alkaline media: A case study of graphitized and more amorphous supports

The stability and degradation mechanism of graphitized (Graphene nanosheets) and more amorphous (Vulcan XC-72R) carbon-supported palladium nanoparticles was investigated. Coupling identical-location transmission electron microscopy (ILTEM) and electrochemistry enabled to correlate the distribution of the Pd nanoparticles under accelerated stress test (up to 1000 cycles between 0.1 and 1.23 V vs. RHE, in a 0.1 M NaOH solution at 25 °C) with changes in electrochemical accessible surface area (ECSA). The carbon-supported Pd nanoparticles undergo similar rates of degradation in terms of electrochemical surface areas on both supports. However, their mechanisms of degradation differ: on amorphous carbon, the primary mode of degradation is Pd nanoparticles detachment (and minor agglomeration), whereas on graphitized supports it is more likely their coalescence and dissolution/redeposition. “Bulk” carbon-corrosion is negligible in both cases, as proven by ex situ Raman spectroscopy. So, using a graphitized carbon support (Graphene nanosheets) versus a more amorphous one (Vulcan XC-72R) does not enable to significantly depreciate the Pd/C catalyst degradation in alkaline media.     

Fabrication of metallic nanoparticles by electrochemical discharges

A method for the fabrication of metallic nanoparticles in large quantities by electrochemical discharges is presented. In an aqueous electrolyte, large current density (∼1 A/mm² at ∼20 V) leads to the formation of a ‘gas film’ around the electrode through which discharges occur. When metal ions are additionally present in the electrolyte and when the applied potential is cathodic, metal nanoparticles (typically 10–150 nm) are produced. The nanoparticles are formed in the solution and the gas film prevents them from depositing on the electrode. To control the size of the particles a method based on ‘rotating electrode’ is developed. Rotating the cathode rotates the fluid around it, which provides centrifugal force to the particles to move away from the electrode where they cannot grow. This method has been successfully used for fabrication of nanoparticles from several metal salts.     

Use of a carbon nanocage as a catalyst support in polymer electrolyte membrane fuel cells

The corrosion-resistance of a carbon nanocage used as a catalyst support in a polymer electrolyte membrane fuel cell was investigated by measuring CO₂ generation using on-line mass spectrometry at a constant potential of 1.4 V for 30 min. Polarization curves of membrane electrode assemblies containing Pt/carbon nanocage were obtained and used to evaluate performance degradation. The carbon nanocage was found to possess significant resistance to electrochemical corrosion, exhibiting low performance degradation of only about 2.3% after the corrosion test. This high corrosion resistance is attributed both to the strong hydrophobic nature of the surface and the graphitic structure of the carbon nanocage.     

FeAgMo2O8 — A novel oxygen evolution catalyst material for alkaline metal–air batteries

This paper reports about FeAgMo₂O₈ — a novel oxygen evolution catalyst material for secondary (rechargeable) metal–air batteries. Bifunctional air electrodes were made using FeAgMo₂O₈ as a charging catalyst for oxygen evolution reaction (OER) and silverized carbon black (Ag/C) was employed as a discharging catalyst for oxygen reduction reaction (ORR). Corresponding air electrodes were investigated using 10 M KOH as an electrolyte. At current densities between 20 and 50 mA per cm² we observed discharging and charging voltages of 1.20 to 1.15 V and 1.96 to 2.05 V, respectively.     

High oxygen-reduction activity of silk-derived activated carbon

Activated carbon prepared from silk fibroin, which is free of metal elements, showed a high catalytic activity for the oxygen-reduction reaction (ORR). The activated carbon had a very high onset potential of E_onset = 0.83 V (vs. RHE) in oxygen-saturated 0.5 M H₂SO₄ at 60 °C. The ORR on the activated carbon proceeded by a four-electron process in the high-electrode-potential region; this gradually decreased to a 3.5-electron reaction below about 0.6 V (vs. RHE). Only about 1% of nitrogen atoms (mostly quaternary) remained in the activated carbon by heat-treatment at up to 1200 °C are responsible for the high catalytic activity. The open circuit voltage of a polymer electrolyte fuel cell using the activated carbon as the cathode and a platinum/carbon black anode under pure oxygen and hydrogen gases, respectively, both at one atmosphere, was 0.96 V at 27 °C.     

Anodization of Au thin film on Al in oxalic acid

An Au thin film, which was sputter-deposited on an Al substrate, was potentiostatically anodized in oxalic acid. The Au film was first anodized and a spongelike nanoporous film grew down to the interface between Au and Al. Then, the Al was anodized and a very thin and fine nanoporous alumina film was formed underneath the nanoporous Au. Under the same anodization conditions, the current density for Al was ~ 40 μA cm^− 2, less than 1% of that for Au (~ 30 mA cm^− 2). The growth rates of the nanoporous films were ~ 0.7 nm/min for Al and 26 nm/min for Au, indicating that the growth rate of nanoporous alumina was less than 3% of that of nanoporous Au. Al is suitable as the substrate for preparing nanoporous Au films because the electrochemical reactions of both the electrolyte and the substrate are significantly suppressed when the nanopores penetrate Au and the electrolyte reaches the substrate.     

N-Phenylmaleimide as a new polymerizable additive for overcharge protection of lithium-ion batteries

Electrochemical properties and overcharge behavior of N-phenylmaleimide (NPM) as a new polymerizable electrolyte additive for overcharge protection of lithium-ion batteries are studied by cyclic voltammetry, charge–discharge performance, electrochemical impedance spectroscopy and scanning electron microscopy (SEM). The results show that NPM can electrochemically polymerize at the overcharge potential of 3.8–4.2 V (vs. Li/Li⁺) and form a thin polymer film on the surface of the cathode, thus preventing voltage runaway. On the other hand, the use of NPM as an overcharge protection electrolyte additive does not influence the normal performance of lithium-ion batteries.     

A novel anode material of antimony nitride for rechargeable lithium batteries

Antimony nitride thin film has been successfully fabricated by magnetron sputtering method and its electrochemistry with lithium was investigated for the first time. The reversible discharge capacity of Sb₃N/Li cells cycled between 0.3 V and 3.0 V was found above 600 mAh/g. By using transmission electron microscopy and selected area electron diffraction measurements, the conversion reaction of Sb₃N into Li₃Sb and Li₃N was revealed during the lithium electrochemical reaction of Sb₃N thin film electrode. The high reversible capacity and the good cycleability made Sb₃N one of promising anode materials for future rechargeable lithium batteries.     

Asymmetric electrochemical capacitor microdevice designed with vanadium nitride and nickel oxide thin film electrodes

Vanadium nitride thin film has been coupled with electrodeposited nickel oxide in order to design an electrochemical capacitor microdevice. VN has been used as negative electrode while NiO was used as the positive one in 1 M KOH electrolyte. VN exhibits a pseudo-capacitive behavior while NiO shows a faradaic behavior. This asymmetric microdevice has been operated between 0.5 and up to 1.8 V in aqueous based electrolyte (1 M KOH). Long term cycling ability (10,000 charge/discharge cycles) has been demonstrated with interesting energy (1.0 μW h cm^− 2) and power (40 mW cm^− 2) densities.     

Polyacrylamide-lithium chloride polymer electrolyte and its applications in electrochemical capacitors

A neutral polymer electrolyte containing lithium chloride (LiCl) and polyacrylamide (PAM) was developed. The LiCl-PAM electrolyte film had an amorphous structure and an ionic conductivity > 10 mS cm^− 1. The addition of LiCl to the polyacrylamide did not alter the chemical bonding of PAM. Symmetric double layer capacitors (EDLC) were constructed using CNT-graphite electrodes. The solid EDLC retained approximately 85% of the capacitance achieved with a baseline cell in a LiCl aqueous solution. The solid EDLC devices demonstrated a wide voltage window (1.5 V), good cycle life (> 10,000 cycles), and excellent rate capability (up to 5 V s^− 1).     

Lithium antimonite: A new class of anode material for lithium-ion battery

LiSbO₃ has been synthesized by chemical mixing followed by thermal treatment at 800 °C. Field emission scanning electron microscopy revealed bar shaped multifaceted grains, 0.5–4 μm long and 0.5–1 μm wide, that cluster together as soft agglomeration. 2032 type coin cell vs Li/Li⁺ shows a flat charge–discharge plateau together with low Li intercalation/de-intercalation potential (0.2/0.5 V). A high discharge capacity of 580 mA h g^?1 has been obtained in the 1st cycle with 100% Coulombic efficiency. About 96% of the Coulombic efficiency is retained up to the 12th cycle, but at the 15th cycle, the Coulombic efficiency drops down to 88%. AC impedance spectroscopy shows an increase in electrolyte resistance (R_s) from 4.43 Ohm after the initial cycle to 12.4 Ohm after the 15th cycle indicating a probable dissolution of Sb into the electrolyte causing the capacity fading observed.     

A Li3V2(PO4)3/C thin film with high rate capability as a cathode material for lithium-ion batteries

A monoclinic lithium vanadium phosphate (Li₃V₂(PO₄)₃) and carbon composite thin film (LVP/C) is prepared via electrostatic spray deposition. The film is studied with X-ray diffraction, scanning and transmission electron microscopy and galvanostatic cell cycling. The LVP/C film is composed of carbon-coated Li₃V₂(PO₄)₃ nanoparticles (50 nm) that are well distributed in a carbon matrix. In the voltage range of 3.0–4.3 V, it exhibits a reversible capacity of 118 mA h g^?1 and good capacity retention at the current rate of 1 C, while delivers 80 mA h g^?1 at 24 C. These results suggest a practical strategy to develop new cathode materials for high power lithium-ion batteries.     

A novel single electrode supported direct methanol fuel cell

In this paper a single electrode supported direct methanol fuel cell (DMFC) is fabricated and tested. The novel architecture combines the elimination of the polymer electrolyte membrane (PEM) and the integration of the anode and cathode into one component. The thin film fabrication involves a sequential deposition of an anode catalyst layer, a cellulose acetate electronic insulating layer and a cathode catalyst layer onto a single carbon fibre paper substrate. The single electrode supported DMFC has a total thickness of 3.88 × 10^?2 cm and showed a 104% improvement in volumetric specific power density over a two electrode DMFC configuration under passive conditions at ambient temperature and pressure (1 atm, 25 °C).