Synthesis and Characterization of Hydrous Ruthenium Oxide-Carbon Supercapacitors

It is shown that composite Ru oxide-carbon based supercapacitors possess superior energy and power densities as compared to bare carbon. An electroless deposition process was used to synthesize the ruthenium oxide-carbon composites. Ru is dispersed on the carbon matrix as small particles. The effect of electrochemical oxidation and temperature treatment on the material performance has been studied extensively. Increasing the oxidation temperature reduces the proton transport rate and also increases the degree of crystallinity of the deposits. This adversely affects the performance of the composite. Loading a small amount of Ru oxide (9 wt %) on carbon increases the capacitance from 98 to 190 F/g

Theoretical Analysis of Metal Hydride Electrodes: Studies on Equilibrium Potential and Exchange Current Density

A theoretical model for the metal hydride electrode has been developed assuming that hydrogen diffusion in the alloy and charge-transfer at the surface control the discharge process. Theoretical equations for the dependence of equilibrium potential and exchange current density on the surface hydrogen concentration have been derived. These parameters have been used to correlate experimental data with the theoretical electrode discharge model. Analysis of both the experimental and theoretical discharge curves reveals a potential plateau determined by the magnitude of the interactions between the hydrogen in the alloy and the unhydrided metal. Neglecting these hydrogen-metal site interactions results in simulations predicting the electrode potential varying over the entire duration of discharge. The results also indicate that utilization of the electrode is controlled by the rate of hydrogen diffusion in the electrode and by the alloy particle size. Kinetic resistance at the surface is a determining factor of the polarization losses of the electrode. The variation of equilibrium potential and exchange current density with the state of charge has been characterized experimentally. These results are compared with the model predictions, and good agreement is seen

Studies on Electroless Cobalt Coatings for Microencapsulation of Hydrogen Storage Alloys

LaNi4.27Sn0.24 alloy was microencapsulated with cobalt by electroless deposition from an alkaline hypophosphite bath. Discharge curves of the encapsulated alloy indicate an additional contribution to the capacity arising from the cobalt on the surface. Studies on cobalt thin films reveal the presence of adsorbed hydrogen in cobalt. The amount of hydrogen adsorbed was observed to increase with time of cathodic polarization and to reach a maximum. Polarization techniques have been used to characterize the cobalt-plated alloy as a function of state of charge. The equilibrium potential of the microencapsulated electrode at low hydrogen concentration is determined by the potential of the cobalt coating on the surface

Studies on Metal Hydride Electrodes with Different Weights and Binder Contents

LaNi4.27Sn0.24 electrodes were characterized using electrochemical techniques at different alloy weights and binder contents. For a given alloy weight, the polarization resistance (Rp) increases with the state of charge (SOC). This arises due to changes from α to β phase at the alloy surface. The electroactive surface area for the hydrogen adsorption/desorption reaction changes with SOC and this also contributes to the variation of Rp. Since the interfacial area increases with alloy content, the polarization resistance decreases with increase in the alloy weight. An increase in the alloy weight reduces Rp and lowers the total resistance. The electrode utilization decreases by increasing the binder content and the electrode weight. A theoretical model is presented to study the effect of alloy weight and particle size on the electrode performance. The model simulations predict lowering of the utilization with increase in the electrode weight. The effect of particle size on the energy and power density of the electrode was also studied