SPECTROSCOPIC STUDY ON PLATE-TYPE AND SPONGE-TYPE RANEY-NICKEL ELECTRODES FOR FUEL-CELLS

Sponge-type Raney nickel catalysts were used as anodes in liquid fuel cells utilizing methanol or hydrazine, Raney nickel electrodes were pr epared from substrates of spongy nickel plates coated with aluminium b y use of a plasma flame gun. Electrode performance in both methanol an d hydrazine fuel cells was improved with increases in both the alloyin g and the electrolyte temperature. Good polarization characteristics r esulted from an increase in activated nickel grains, which were observ ed by SEM, and from an increase in BET surface area of the electrode, The broad peaks observed in X-ray diffraction of Raney nickel implied crystal distortion, which should be related to an increase in surface area. Surface chemical specification and distribution of aluminium and nickel in the plate-type Raney nickel catalyst based on XPS, shows th at the catalyst surface is covered with Ni2O3 and/or Ni(OH)(2) within 200 Angstrom of the surface, while Al2O3 and/or Al(OH)(3) are distribu ted evenly in the vertical direction over about 1200 Angstrom. The XAN ES spectrum from the Ni K-edge of the Raney nickel did not change much from that of nickel metal. The EXAFS function, however, diminished mo re quickly, and from this, the coordination number of nickel in Raney nickel catalysts was estimated to be 6, compared with 12 for ordinary nickel. This indicates that the other six nickel atoms shift from the original sites. EXAFS studies as well as XRD, indicate that the crysta l structure of the activated nickel contains a great number of crystal defects. EPR measurements indicate the g-values of the active Raney n ickel catalyst and the catalyst when deactivated by electrochemical re moval of hydrogen to be 2.07 and 2.22 respectively. The change of g-va lue is attributed not to the lattice defects but to the adsorption of hydrogen.