A COMPARISON OF NICKEL BORIDE AND RANEY-NICKEL ELECTRODE ACTIVITY IN THE ELECTROCATALYTIC HYDROGENATION OF PHENANTHRENE

The electrocatalytic activity of nickel boride in the electrocatalytic hydrogenation (ECH) of phenanthrene in ethylene glycol water at 80 de grees C has been compared to that of Raney nickel and fractal nickel. The intrinsic activity of the electrode material (real electrode activ ity) is the same for nickel boride and Raney nickel electrodes and is lower for fractal nickel electrodes. The apparent electrode activity o f nickel boride pressed powder electrodes (Ni2B electrodes) is less th an that of codeposited Raney nickel (RaNi) electrodes and pressed powd er fractal nickel/Raney nickel (Ni/RaNi = 50/50 to 0/100) electrodes. The apparent activity of Ni2B electrodes is improved by adding sodium chloride to the powder and dissolving it after pressing (Ni2B-NaCl ele ctrodes). The Ni2B-NaCl electrodes have the same apparent activity as codeposited RaNi and pressed powder Ni/RaNi (20/80 to 0/100) electrode s. The apparent and real electrode activity of Ni/RaNi electrodes incr eases with the RaNi content up to a 20/80 ratio. The Tafel and alterna ting current (ac) impedance parameters were determined for the hydroge n evolution reaction (HER) in 1 M aqueous sodium hydroxide at 25 degre es C at nickel boride and at codeposited RaNi electrodes. The intrinsi c electrocatalytic activity for HER, expressed by the ratio of the exc hange current density over the roughness factor (I-0/R), is similar fo r Ni2B, Ni2B-NaCl, and codeposited RaNi electrodes. Surface characteri zation of Ni2B and Ni2B-NaCl electrodes was carried out by BET, ac imp edance, scanning electron microscopy, and mercury porosimetry. No dire ct relation between the apparent electrode activity in ECH and the sur face measured by BET and ac impedance was found. The ac impedance meas urements were also carried out in the presence of sodium trans-cinnama te.