RANEY-NICKEL ACTIVATED H-2-CATHODES .1. MODELING THE CURRENT VOLTAGE BEHAVIOR OF FLAT RANEY-NICKEL COATED MICROPOROUS ELECTRODES

The current voltage behaviour of hydrogen evolving electrodes covered with a closed, smooth layer of Raney-nickel has been treated theoretically. Since the pores of Raney-nickel typically are from 1 to 10 nm wide, they are able, according to the Young-Laplace equation, to keep evolved hydrogen in solution up to concentrations of the order of 0.1 mol dm-3 which correspond to very high effective pressures of the order of 100 MPa. High concentrations of dissolved hydrogen cause substantial concentration-polarisation in the pores even at pore depths of several tenths of micrometres. The consequence is a limited effective pore length and catalyst utilization, respectively. This results in current voltage curves with steadily increasing Tafel slopes, which reach a limiting value of l40 mV dec-1 (alpha = 0.5) at 90-degrees-C at current densities well above 1000 mA cm-2.