David Emmerson Brown

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.

The Genesis and Development of the Commercial BP Doubly Promoted Catalyst for Ammonia Synthesis

In the 1970s BP started developing a new catalyst for ammonia synthesis which in final form comprises ruthenium, two promoters and a graphitised carbon support. This became the first new catalyst for ammonia synthesis to be commercialised since Fritz Haber’s promoted iron catalyst. The catalyst is commercialised in the KBR Advanced Ammonia Process (KAAP). We describe the development of the catalyst, starting in the 1960s with studies to elucidate the mechanism of selective hydrogenation catalysts using nickel single crystals and LEED. These identified a phenomenon dubbed surface reorientation, in which an adsorbate such as sulphur causes the structure of the surface monolayer of a metal to change e.g. from fcc [111] to [100]. These ideas led to discovery of an active platinum/alkali metal/carbon catalyst for the dehydrocyclisation of hexane. That catalyst was not commercial, but it led in turn to the identification of highly active ruthenium/alkali metal/carbon catalysts for ammonia synthesis. The best new catalyst is about 20 times more active than a commercial Haber catalyst. The special carbon support is mesoporous and graphitic. Scale up of catalyst production and testing are described briefly, as are some process considerations.Graphical Abstract