Egwu Eric Kalu

Electroreduction of Nitrate and Nitrite Ion on a Platinum‐Group‐Metal Catalyst‐Modified Carbon Fiber Electrode Chronoamperometry and Mechanism Studies

The mechanisms of nitrate and nitrite ion electroreduction on a carbon fiber electrode modified with platinum group metal catalyst are studied. Chronoamperometry studies reveal that two different mechanisms exist in two cathodic regions. A plot of log i vs. E reveals the presence of adsorption pseudocapacitance and is supported by impedance measurement at the electrode/solution interface. In the −600 to −800 mV (Ag/AgCl) potential region, the Tafel slope for nitrate ion reduction varies between ca. 221 and 236 mV/dec, while in the −925 to −1000 mV (Ag/AgCl) region, the slope was ca. 80 to 85 mV/dec. For nitrite ion reduction, the Tafel slope was ca. 232 to 250 mV/dec in the −500 to −700 mV (Ag/AgCl) potential region, and between −925 and −1000 mV (Ag/AgCl), the slope was between 80 and 86 mV/dec. The adsorption of nitrogen dioxide on the electrode surface was determined to be the rate‐limiting step in both potential regions. The present results indicate that although the first step of nitrate reduction in neutral solution takes a similar path as nitrate/nitrite ion reduction in alkaline solution, the rest of the mechanistic pathways are different in alkaline or acidic solution.

Continuous-flow biodiesel production using slit-channel reactors.

Slit-channel reactors are reactors whose active surface areas are orders of magnitude higher than those of micro-reactors but have low fabrication costs relative to micro-reactors. We successfully produced biodiesel with different degrees of conversion using homogeneous catalyst in the slit-channel reactor. The reactor performance shows that percent conversion of soybean oil to biodiesel increases with channel depth, as expected, due to more efficient mixing. Shallow slit-channels require short average residence times for complete product conversion. Present results show that the slit-channel reactor provides an improved performance over traditional batch reactors using homogeneous sodium alkoxide catalyst. It is aimed to couple the reactors with solid catalysts in converting soybean oil to biodiesel and implementation method is suggested. The cost advantages resulting from the ease of fabrication of slit-channel reactors over micro-reactors and how these factors relate to the oil conversion efficiency to biodiesel are briefly noted and discussed.

Evaluation of Oxygen Transport Parameters in H 2 SO 4 ‐ CH 3 OH Mixtures Using Electrochemical Methods

The effects of the addition of methanol on the diffusion coefficient and solubility of oxygen in different solutions of 0.5 M H 2 SO 4 and 1.0 M CH 3 OH were studied for a wide range of methanol to sulfuric acid concentration ratios using platinum and gold microelectrodes. The studies were performed at room temperature and atmospheric pressure using cyclic voltammetry and potential step techniques. Solutions with a given methanol to sulfuric acid ratio were prepared, and the limiting currents vs. time were measured for the different electrodes. By using a planar geometry approximation to the microelectrodes, the values of diffusion coefficient and solubility were determined for the different solutions. The transport parameters and reduction potentials of oxygen were affected by the concentration of methanol in 0.5 M H 2 SO 4 . Although the transport parameters measured by the gold and platinum electrodes were in qualitative agreement, their actual values were found to be different. The dissolved oxygen concentration in 0.5 M H 2 SO 4 solution was determined to be 1.22 X 10 -6 mol/cm 3 with the platinum electrode and 1.16 X 10 -6 mol/cm 3 with the gold electrode, while the O 2 diffusion coefficient was determined to be 1.04 X 10 -5 cm 2 /s for platinum and 1.34 X 10 -5 cm 2 /s for gold. The reasons for the observed differences in the transport parameters determined with the two electrodes are discussed.

Binder-free Co–Mn composite oxide for Li–air battery electrode

Binder-free Co–Mn composite oxide was successfully deposited at low temperature on a woven substrate through a combination of electroless and electrolytic steps. The principle of the approach was illustrated with cobalt metal and a successful thin film metal oxide formation was supported by CV, XRD and XPS data. The viability of the binder-free Co–Mn oxide electrode was tested as a Li–air battery electrocatalyst and yielded an initial specific capacity of up to 2000 mA h g−1 and survived multiple charge–discharge–recharge cycles. The oxidation time in the electrolytic oxidation-step was found to affect the battery discharge period. In comparison to the conventional polymeric binder methods, the present binder-free method is potentially adaptable to a roll–roll continuous processing approach.

Decoration of carbon nanotubes with iron–cobalt (FeCo) alloy using polymer-stabilization and electroless deposition techniques for thermotherapy applications

FeCo nanoparticles were successfully plated onto the surface of CNTs via a one-step catalyzation method for electroless deposition. The FeCo plated CNTs were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis and vibrating sample magnetometry (VSM). FeCo deposition and plating uniformity were also characterized. The results show the approach as a feasible means of decorating CNTs with metal nanoparticles without the use of Sn sensitization solution. The CNT–FeCo composite easily heated to the desired temperature range of 43–46 °C required to inhibit thermotolerance development in cancer thermotherapy. Using the elemental mappings of the deposited nanoparticles, a quantitative distribution index is defined and it is used to quantitatively characterize the influence of catalyst on the deposit uniformity on the CNTs. Pd distribution appears to control the plating uniformity and hence has significant influence on the magnetic properties of the deposit.