Nouraldin Mahmood

Preparation and characterization of low overvoltage transition metal alloy electrocatalysts for hydrogen evolution in alkaline solutions

Abstract Transition metal electrocatalysts for hydrogen evolution were prepared by thermal decomposition of solutions containing nickel or cobalt and molybdenum, tungsten or vanadium on a metallic substrate and curing the oxide coated substrate under an atmosphere of hydrogen at elevated temperatures. The most active and stable hydrogen evolving cathode, based on a nickel and molybdenum combination, exhibited overvoltages of about 60 mV for over 11,000 h of continuous electrolysis in 30 w/o KOH at 500 mA cm −2 and 70°C. The cathode was prepared by high temperature ( ca. 400°C) treatment of a nickel substrate, coated with an aqueous solution containing nickel and molybdenum salts in the atomic ratio 60:40 followed by reduction of the resulting oxides at about 500°C in atmosphere of hydrogen. X-ray diffraction, and thermogravimetric and ESCA measurements, were employed to identify the active component of the nickel-molybdenum system responsible for its electrocatalytic activity. The results indicated that the electrocatalyst is a face centred cubic nickel-molybdenum alloy in which the molybdenum is randomly substituted at the nickel lattice. The electrochemical properties of a number of nickel-molybdenum electrocatalysts (NiMo = 60:40) were determined in the temperature range 20–80°C. Steady state measurements at different temperatures in 30 w/o KOH showed that the electrodes had low apparent activation energies ( ca. 5 kcal mol −1 ) and revealed the presence of two Tafel regions with transfer coefficients of 1.13 and 0.63. The corresponding exchange current densities at 70°C, based on the electrodes geometric areas, were 52 and 150 mA cm −2 respectively. Results of potentiodynamic measurements and preliminary work on hydrogen oxidation are also presented.