Electrochemical properties of lithium air battery (LAB) cells incorporating highly ordered mesoporous carbon replica (CR) support materials were examined in nonaqueous electrolyte solution of 1 mol/l LiTFSA/TEGDME. The CR support was prepared with pore sizes of 10, 40, and 100 nm. The cycle properties of the LAB cells with the CR support was improved by using Pt-Ru electroctalyst. As a result, the LAB cells with Pt-Ru electrocatalyst/CR (pore size: 10 nm) exhibited the highest performance of the first discharge capacity of 1000 mAh/g and capacity retention of about 50% at 10th cycle. Moreover, different growth behavior of the discharge product was observed as a consequence of the pore size of the CR support.
Pt and ceria nanoparticles were deposited into graphene nanosheets (Pt–CeO2-x/GNS) via a polyol-assisted reduction process and examined as catalysts for the electro-oxidation of glycerol in alkaline solutions. The electrochemical activity of the catalyst was evaluated by cyclic voltammogram and chronoamperometry measurements. The products of glycerol oxidation over the catalyst were analyzed by high performance liquid chromatography. It was found that the Pt–CeO2-x/GNS catalyst facilitated the formation of C3 products. The ratio between C3 products and C2 products is 2.6 for the Pt–CeO2-x/GNS, which is much larger than that of 0.8 for the GNS supported Pt nanoparticles (Pt/GNS) at −0.4 V (vs. SCE.). Notably, a glyceraldehyde selectivity of 52% over the Pt–CeO2-x/GNS was obtained at −0.4 V. The enhanced activity and selectivity of Pt–CeO2-x/GNS catalyst relative to the Pt/GNS catalyst is related to the bifunctional and electronic effects.
The reductive desorption of 2-aminoethanethiol (AET) monolayers formed on a polycrystalline gold electrode has been studied using cyclic voltammetry. Three cathodic peaks were observed and they were assigned to reductive desorption from each small domain of Au(111), (100), and (110) over the polycrystalline surface. The kinetics of adsorption were likely under the condition where the kinetic control and the diffusion control were balanced over the concentration range 5–50 μM (M = mol dm−3), whereas it was described by the kinetic control model at 100 μM. The thermodynamics of adsorption was well-described by the Langmuir isotherm. The saturation surface coverage was found to be 5.3 × 10−10 mol cm−2, which suggested that AET adsorbed lying flat on a polycrystalline gold electrode.
The redox behavior of cytochrome c (Cyt c) at a ubiquinone-10 (UQ) incorporated self-assembled monolayer (SAM)-modified electrode was studied by cyclic voltammetry. A well-defined catalytic wave due to the reduction of Cyt c by UQ was observed at around −0.4 V vs. Ag/AgCl (saturated KCl). However, the re-oxidation peak of UQ at around +0.3 V was small, suggesting no significant catalytic ability of UQ for the re-oxidation of Cyt c. These voltammetric behaviors could be well simulated by digital simulation with a simple reaction model in which UQ and Cyt c coexist homogeneously in a reaction layer on the base gold electrode. The parameters obtained by curve fitting of cyclic voltammograms showed that the re-oxidation of Cyt c by UQ is somewhat thermodynamically unfavorable and, importantly, kinetically slow. This slow process is probably originated from spatial separation between the redox species. Such a directional or one-way electron transfer may be occurring in the mitochondrial respiratory chain system to achieve efficient energy production.
We fabricated TiO2-coated porous silica glass tubes containing macropores and evaluated their environmental purification capacity. We used two TiO2 coating methods: outside vapor deposition (OVD), and TiO2 precursor impregnation and calcination onto silica layers. The tubes exhibited air and water purification capabilities. Through a waterborne pathogens removal test, we confirmed that Escherichia coli and Legionella pneumophilia could be eliminated by filtration, even in conditions without UV-C irradiation. Moreover, the tube coated using OVD and irradiated with a UV-C lamp showed the highest Qβ reduction efficiency. The acetaldehyde decomposition properties under high-concentration conditions were outstanding (78% at 700 ppm). From methylene blue decomposition tests, we concluded that the efficiency of TiO2 photocatalytic decomposition was affected by multiple parameters, including the presence of anions and cations, as well as the solution pH.
We firstly report remarkable stability and performance of non-precious catalyst, nitrogen doped graphene (NG) towards oxygen reduction reaction (ORR) in a protic ionic liquid (N,N-diethylmethylammonium trifluoromethanesulfonate(dema-TfO)) at intermediate temperatures. Our electrochemical results indicate that an elevated operating temperature has an enhancing effect on ORR activity of NG in dema-TfO. In addition, even after 2000 cycles of potential sweep in the potential range from 1.0 V to 1.5 V vs. RHE at 120°C in dema-TfO, NG keeps the same ORR onset potential with 14% decrease in oxygen reduction current, showing the excellent stability of NG. Whereas commercially available Pt/C (Pt 37.5% in weight) shows 13% negative ORR onset potential shift along with 56% loss of oxygen reduction current during the stability test. TEM and EDS observations taken after durability test were also in agreement with the higher durability of NG over Pt/C at 120°C in dema-TfO. Raman and XPS results taken after the durability test also substantiated the structural stability of NG in dema-TfO at intermediate temperatures. The greater durability and comparable electrochemical activity of NG with Pt/C can unfold the possibilities of non-precious catalyst for intermediate temperature PEFCs.
d-Fructose dehydrogenase (FDH) contains a flavin adenine dinucleotide (FAD) in subunit I and three heme c moieties (1c, 2c, and 3c from the N-terminus) as the electron transfer relaying sites. The electron transfer in direct electron transfer-type bioelectrocatalysis of FDH is proposed to proceed in sequence from FAD, through heme 3c, to heme 2c without going through heme 1c. In order to improve the performance of the bioelectrocatalysis, we constructed a variant (M450QΔ1cFDH) in which 143 amino acid residues involving heme 1c were removed and M450 as the sixth axial ligand of heme 2c was replaced with glutamine to negatively shift the formal potential of heme 2c. The M450QΔ1cFDH variant was adsorbed on a planar gold electrode. The variant-adsorbed electrode produced a clear sigmoidal steady-state catalytic wave of fructose oxidation in cyclic voltammetry. The limiting current density was 1.4 times larger than that of the recombinant (native) FDH. The half-wave potential of the wave shifted by 0.2 V to the negative direction. M450QΔ1cFDH adsorbed rather homogeneously in orientations suitable for DET-type bioelectrocatalysis.
An instantly usable screen-printed Ag/AgCl electrode with long-term stability was fabricated for use as a cost-effective disposable reference electrode. A new silica gel–poly(vinylidene difluoride) ink was prepared to form the hydrophilic liquid junction and electrolyte layer of a planar-type reference electrode and the temporal evolution of its open-circuit potential in different electrolyte solutions was subsequently compared to that of a commercial reference electrode. The potential stabilized within 3 min and remained constant over 20 days. The impedance of the liquid junction was ∼2500 Ω, which is close to the value observed for a commercial reference electrode. These results implied that the as-fabricated reference electrode was well-suited for practical measurements.
The rhombohedral structure Li2NaV2(PO4)3/C composites were successfully synthesized by a sodium citrate induced sol-gel method. The Li2NaV2(PO4)3/C consists of microplates roughly 80–90 nm in thin. The carbon content in the LNVP/C is approximately 8.29 wt%. As cathode materials for lithium-ion batteries, a cathodic peak at 3.67 V and an anodic peak at 3.82 V can be seen in CV curves, corresponding to the redox couple of V4+/V3+. In addition, the electrode can deliver an initial discharge capacity of 111.4 mAh g−1 at 1 C and about 96.4% of the initial capacity is maintained after 150 cycles. LNVP/C also exhibits high coulomb efficiency and good rate performance.
Binder is one of the key materials which affect the electrochemical performance of the Li-ion batteries. As a promising binder, carboxylmethyl cellulose (CMC) is a derivative of cellulose, in which the hydroxyl (3 per unit) is replaced by the carboxymethyl group. It attaches more and more attention. However, few studies have been carried out on CMC with the degree of substitution (DS). In this study, CMC with different DS was synthesized by a specially designed method. The raw materials and products were characterized with FT-IR, 1H-NMR, 13C-NMR and XRD. A series of CMC with different DS were prepared as silicon-based binder of anode of lithium-ion batteries. Electrical tests, including galvanostatic charge-discharge, cyclic voltammetry, AC impedance and rate capability were performed to evaluate the silicon-based anode. Results showed that the discharging specific capacity of silicon-based anode using CMC of DS = 0.55 in the first and 50th cycle were 2917.0 mAh/g and 1607.6 mAh/g, and the electrochemical performance was superior to those using CMC with lower (0.23 and 0.43) or higher (0.72 and 0.86) DS. The current study confirms that DS of CMC has strongly affected battery performance parameters such as deliverable capacity, power, cycle-life and storage performance etc. The working mechanism is also investigated on why the CMC with the best DS is compatible with the silicon-based anode.
An electrochemical sensor based on a three-dimensional (3D) graphene/carbon nanotube (G/CNT) hybrid was developed for the sensitive detection of olaquindox (OLA). 3D G/CNT hybrid through covalent C-C bonding was fabricated by one-step synthesis using catalytic chemical vapor deposition. To construct the base of the sensor, a novel composite was fabricated by a functionalized 3D G/CNT with poly-(dimethy diallyl ammonium chloride) and Nafion via simple grind and ultrasonication dispersion methods. The electrochemical determination of OLA exhibited an oxidation peak at −0.685 V with a higher current response. Due to the effective surface area and active sites, a good linear relationship was observed between the OLA concentration and peak current over the range of 1.5 × 10−6–2.7 × 10−3 mg mL−1 with a detection limit of 6.12 × 10−8 mg mL−1 (3σ). The proposed electrochemical sensor was used to detect OLA in swine samples at a recovery ranging from 97.78% to 104.25%, which exhibits a broader prospect to supervise animal products and a high potential for food security applications.
A novel method of Ni recovery from the acid leaching solution of electroplating sludge through preparing Ni-Fe alloy with high Fe2+ content (i.e., 0.5 g/L) is proposed in this paper, and the corresponding electrodeposition process was studied using conventional electrochemical techniques and scanning electron microscopy. The obtained results showed that adding saccharin Na at concentrations from 0 to 14 g/L to the deposition bath increased the cathodic polarization potential of Ni-Fe co-deposition, with sensible grain refinement and disappearance of surface cracks observed after the addition of 14 g/L saccharin Na. Two different mathematical models of metal nucleation were tested, and the different morphologies of the deposits formed with and without saccharin Na suggested disparate nucleation mechanisms. The Ni-Fe deposition potential shifted positively in the presence of thiourea, and it should not be added together with saccharin Na during the nucleation stage for the grain refinement of the deposits. The iron contents in the deposits decreased with the increase of thiourea concentration ascribed to the thiourea complex which adsorbed on the cathodic surface preventing Fe2+electrodeposition from the electrolytes.
This paper reports the occurrence of electrochemical oscillations (EOs) in Cu electro-oxidation of phosphoric acid solution, and systematically investigated the effect of potential, electrolyte composition and concentration, temperature, stirring rate, and scanning speed on EOs. The mechanism of EOs occurred as a result of deposition and dissolution effects of CuH2PO4 through electro-oxidation of the Cu anode. The experimental result for amplitude and frequency can be explained by this simplified qualitative analysis, and further verified the previously speculated EO mechanism. This study provides insights into the relevance of micro-chemical mechanisms for the macroscopic non-equilibrium phenomenon and presents novel concepts for highly efficient electrodissolution in metallurgy.
Mechanical attrition (MA) is applied to assist the electroplating Ni-P coating on a magnesium alloy substrate. The influence of MA on the microstructure and electrochemical performance of the coating was studied with SEM, XRD, electrochemical impedance spectroscopy (EIS) and polarization curves. The results show that under MA, the Ni-P electroplating becomes compact and free of cracks and pores, leading to significant improvement in the coating corrosion resistance. MA promote transformation the coating from amorphous state to crystalline one and produce an obvious transition layer at the coating-substrate interface, which is beneficial to enhancing the coating adhesion strength and other mechanical properties.