Processing of R-nickel catalysts for alkaline fuel cell applications

Platinum and other platinum group metals either as single or in combinations, has been preferred for use as catalyst for the hydrogen oxidation reaction (HOR) in alkaline fuel cell. However, also Raney nickel catalyst has been the target of interest. The performance of R-nickel electrodes in HOR has been tried to enhance by using Copper. However, the copper, especially if anode is overloaded, is not stable but dissolves in the electrolyte. 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. Experimental details Mechanical alloying of R-nickel mixtures was carried out in a planetary-type ball mill Fritsch Pulverisette 5 in an argon atmosphere. The nickel was a commercially available R-nickel powder. The carbon was Black Pearls 2000 from Cabot Corporation. The nickel to carbon ratio was set to 10:1 in all experiments. The activity of the prepared R-nickel catalysts in HOR was measured in an electrochemical half cell configuration. For testing flat electrodes of 10 cm2 of active area were prepared. The gas diffusion layer consisted of 60 wt-% PTFE in acetylene black and nickel mesh as current collector. The active layer contained the same diffusion material with 30 mg/cm2 of prepared nickel powder. The electrodes were pressed and heat treated at 340 oC. The polarization curves, referred to Hg/HgO electrode, were measured in 6 M KOH at 333 K in 100% hydrogen. Results and discussion The electrode with ball milled R-nickel with carbon showed a smaller polarisation (voltage drop) compared to the electrode with R-nickel catalyst without ball milling when current was connected through the electrode. Increasing the current to 400 mA/cm2 also increased the polarisation. With the electrode that had no been milled with carbon the polarisation increased sharply at after current density 250 mA/cm2 and no polarisation was recorded at 400 mA/cm2. This is probably due to inefficient conductivity in the catalyst layer. The electrode with the ball milled R-nickel had a polarisation of 53 mV at 400 mA/cm2. The ball milling of R-nickel catalyst with carbon decreased the polarisation and increased the performance of the R-nickel catalyst. Addition of a small amount (1 %) of platinum to the R-nickel catalyst further decreased the polarisation.