The estimation for the barrier of the hydrogen reduction reactionThe reaction at 0.00V relative to normal hydrogen electrode (NHE) is exthothermic electrode is barrierless 1 . At 0.8eV, however, with lower electrode work function (e becomes more stable by 0.8eV), the reaction becomes endothermic. The reaction enthalpy can be estimated by the hypothetic cycle developed by Norskov etc. .

We report results of quantum mechanics (QM) mechanistic studies of Nafion membrane degradation in a polymer electrolyte membrane (PEM) fuel cell. Experiments suggest that Nafion degradation is caused by generation of trace radical species (such as OH(●), H(●)) only when in the presence of H(2), O(2), and Pt. We use density functional theory (DFT) to construct the potential energy surfaces for various plausible reactions involving intermediates that might be formed when Nafion is exposed to H(2) (or H(+)) and O(2) in the presence of the Pt catalyst. We find a barrier of 0.53 eV for OH radical formation from HOOH chemisorbed on Pt(111) and of 0.76 eV from chemisorbed OOH(ad), suggesting that OH might be present during the ORR, particularly when the fuel cell is turned on and off. Based on the QM, we propose two chemical mechanisms for OH radical attack on the Nafion polymer: (1) OH attack on the S-C bond to form H(2)SO(4) plus a carbon radical (barrier: 0.96 eV) followed by decomposition of the carbon radical to form an epoxide (barrier: 1.40 eV). (2) OH attack on H(2) crossover gas to form hydrogen radical (barrier: 0.04 eV), which subsequently attacks a C-F bond to form HF plus carbon radicals (barrier as low as 1.00 eV). This carbon radical can then decompose to form a ketone plus a carbon radical with a barrier of 0.86 eV. The products (HF, OCF(2), SCF(2)) of these proposed mechanisms have all been observed by F NMR in the fuel cell exit gases along with the decrease in pH expected from our mechanism.

We use quantum mechanics, density functional theory at the PBE level, to predict the binding-site preferences and reaction barriers for all intermediates involved in the oxygen reduction reaction (ORR) on the low energy surface of Pt 3 Ni alloy. Here we calculate that the surface layer is Ni depleted (100% Pt) while the second layer is Ni enriched (50% Pt) as shown by experiment. Even though the top layer is pure Pt, we find that the sublayer Ni imposes strong preferences in binding sites for most intermediates, which in turn strongly influences the reaction barriers. This strong preference leads to a strong site dependence of the barriers. Considering water as the solvent, we predict that, at low coverage of O ad and OH ad , the barrier for the rate-determining step is 0.81 eV, whereas, at high coverage, this barrier decreases to 0.43 eV. It can be compared to a barrier of 0.50 eV for pure Pt, explaining the improved ORR rate for the Pt 3 Ni alloy. We report the results both for gas phase and for aqueous phase environments.

An investigation is presented of nickel electrodeposition from acidic solutions in a cylindrical spouted electrochemical reactor. The effects of solution pH, temperature, and applied current on nickel removal/recovery rate, current efficiency, and corrosion rate of deposited nickel on the cathodic particles were explored under galvanostatic operation. Nitrogen sparging was used to decrease the dissolved oxygen concentration in the electrolyte in order to reduce the nickel corrosion rate, thereby increasing the nickel electrowinning rate and current efficiency. A numerical model of electrodeposition, including corrosion and mass transfer in the particulate cathode moving bed, is presented that describes the behavior of the experimental net nickel electrodeposition data quite well.