Processing of Raney-Nickel Catalysts for Alkaline Fuel Cell Applications

Abstract

Platinum and other platinum group metals, either as singles or in combinations, have been preferred for use in low temperature fuel cells, mainly alkaline fuel cells (AFCs), polymer membrane electrolyte fuel cells (PEMs), and direct methanol fuel cells (DMFCs), for hydrogen oxidation reaction (HOR). However, also the Raney-nickel catalyst, which is among the most active non-noble metals for the HOR, has been the target of interest, especially in AFCs. However, electrodes with nonsupport Raney-nickel catalysts have been reported to suffer from insufficient conductivity. So, in this work, in order to enhance the electrical conductivity in the catalyst layer and to increase the catalytic activity, the Raney-nickel catalysts were alloyed with carbon in a planetary-type ball mill. In some samples platinum was added chemically to still enhance the catalytic properties. The activity of the processed materials was tested in the anode reaction of the alkaline fuel cell by measuring the half-cell polarization curves. It was found that the effective mixing of Raney-nickel powder and carbon in the ball mill was beneficial compared with poorer mixing in the knife mill. However, in order to achieve the same current densities at the same polarization level as the commercial Pt catalyst (2mg∕cm2), much higher Raney-nickel contents (73mg∕cm2) were needed. Good contact between Raney-nickel and conductive material (carbon) in the catalyst layer of the alkaline fuel cell electrode can improve the performance of the Raney-nickel catalyst in the hydrogen oxidation reaction. The polarization was lowered especially at the higher current densities (>250mA∕cm2).