An electrolysis-cell design for simultaneous electrochemical reduction of CnormalO2 and normalH2O to make syngas (CO+normalH2) at room temperature (25°C) was developed, based on a technology very close to that of proton-exchange-membrane fuel cells (PEMFC), i.e., based on the use of gas-diffusion electrodes so as to achieve high current densities. While a configuration involving a proton-exchange membrane (Nafion) as electrolyte was shown to be unfavorable for CnormalO2 reduction, a modified configuration based on the insertion of a pH-buffer layer (aqueous KHCnormalO3 ) between the silver-based cathode catalyst layer and the Nafion membrane allows for a great enhancement of the cathode selectivity for CnormalO2 reduction to CO [ca. 30mA∕cm2 at a potential of −1.7to−1.75V vs SCE (saturated-calomel reference electrode)]. A CO∕normalH2 ratio of 1∕2 , suitable for methanol synthesis, is obtained at a potential of ca. −2V vs SCE and a total current density of ca. 80mA∕cm2 . An issue that has been identified is the change in product selectivity upon long-term electrolysis. Results obtained with two other cell designs are also presented and compared.

The electrochemical behavior of a promising hydrogen/bromine redox flow battery is investigated for grid-scale energy-storage application with some of the best redox-flow-battery performance results to date, including a peak power of 1.4 W/cm 2 and a 91% voltaic efficiency at 0.4 W/cm 2 constant-power operation. The kinetics of bromine on various materials is discussed, with both rotating-disk-electrode and cell studies demonstrating that a carbon porous electrode for the bromine reaction can conduct platinumcomparable performance as long as sufficient surface area is realized. The effect of flow-cell designs and operating temperature is examined, and ohmic and mass-transfer losses are decreased by utilizing a flow-through electrode design and increasing cell temperature. Charge/discharge and discharge-rate tests also reveal that this system has highly reversible behavior and good rate capability. The environmental concerns and limited resources of fossil fuels have stimulated research for renewable energy sources such as wind and solar energy. Globally, there is 94 GW of electricity-generating wind power as of 2007, and it is estimated to reach 474 GW by 2020. 1The electricity from solar photovoltaics is growing at 40% per year worldwide, and the United States has targeted 100 GW of solar power by 2020.1 However, the electricity from these and other renewable resources is not constant and reliable due to their sensitive response to local weather conditions. To level out the variable generation of energy, large-scale electrical-energy storage (EES) is required. For the energy storage and load leveling, redox-flow batteries (RFB) have been considered as promising candidates due to their independently controllable power and energy, rapid response time, and high energy efficiency. Extensive research has been performed on RFB systems, including iron-chromium, all-vanadium, sodium-polysulfide, etc. 2-5However, due to the challenging issues such as low cell performance, power density, durability, and high electrolyte cost, their wide-spread adoption has not been realized. For example, the all-vanadium system, which is considered one of the closest to commercialization, utilizes a relatively expensive reactant and achieves power densities that are on the order of 0.2 to 0.7 W/cm 2 with relatively low efficiency. A hydrogen/bromine system is proposed as the reactants are earth-abundant and inexpensive and, as will be shown, high performance with high efficiency is obtainable.Yeo and Chin first investigated the hydrogen/bromine flow battery and reported excellent electric-to-electric efficiency, introducing it as a promising RFB system for energy-storage applications.6 The operating principle of the H 2 /Br 2 RFB can be described with a typical cell structure as in Figure 1. During discharge, a solution of Br 2 in HBr (aq) is fed into the cathode compartment where bromine reacts with protons supplied from the anode side and is reduced to bromide, generating the theoretical electric potential of 1.098 V at 25• C. The redu...

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Li[Ni1/3Co1/3Mn1/3]normalO2 -based laminates of approximately the same loading and of varying levels of poly(vinylidene fluoride) (PVDF) binder and acetylene black (ratio held constant) were fabricated and calendered to different porosities, with the objective to investigate performance on a volume basis. The electronic conductivity of the laminates depends strongly on the inactive material content but not significantly on porosity. Electrochemical impedance spectroscopy studies found that charge-transfer resistance with calendering varied greatly with inactive material content. When the electrode contains low levels of inactive material (2% PVDF and 1.6% carbon), calendering significantly reduced the bulk resistance of the electrode. With high levels of inactive material (8% PVDF and 6.4% carbon), charge-transfer resistance increased with increased calendering. Above a certain level, depending on the overall composition, the inactive material reduces ionic transport to the active material surface. For a plug-in hybrid electric vehicle required to go 40 miles at an average rate of 20 miles/h with a 38 kW 10 s power-pulse capability, the cell chemistry studied is energy-limited. Therefore, based on the results of this study, the cathode should be compressed to 10% porosity with a minimal amount of inactive material.

Experimental data for CnormalO2 (and normalH2O ) reduction to CO (and H2 ) on flat gold and silver electrodes in KHCnormalO3 and NaClnormalO4 aqueous electrolytes and at room temperature are analyzed using a steady-state mathematical model. Rate constants and charge transfer coefficients for CnormalO2 and normalH2O reduction reactions are derived from the experimental data, assuming that the rate-determining steps for CnormalO2 and normalH2O reduction reactions are the formation of CnormalO2⋅− and H⋅ radicals adsorbed at the electrode surface on both metal electrodes, respectively. It is found that CnormalO2 reduction to CO is positively shifted by ∼370mV on gold as compared to silver, while hydrogen evolution is positively shifted by only ∼110mV . This explains why higher CO current efficiencies are obtained on gold ( ∼90% for gold as compared to only ∼68% for silver in potassium bicarbonate). The current fade for CO evolution at low electrode potential is related to the current increase for hydrogen evolution, which yields a high pH increase and CnormalO2 concentration decrease at the electrode surface. Finally, an analysis of data for various CnormalO2 partial pressures in equilibrium with the electrolyte is performed, in which the effect of acid–base reactions coupled with the CO evolution reaction is accounted for.