Alkaline Water Electrolysis Beyond 3 A/cm2 Using Catalyst Coated Diaphragms

Abstract Alkaline water electrolysis using catalyst coated diaphragms (Zirfon UTP 500 and UTP 220) was conducted at current densities from 2 up to 3500 mA/cm2 at varying temperatures (20 – 75°C) in 30 wt.% KOH. The coatings were conducted using two different approaches, which were compared with each other: spray coating and stencil coating. Using platinum group free catalysts, which are either available commercially or easy to synthesize (Raney Ni; FeNi LDH), we reached 3.5 A/cm2 at less than 2.3 or 2.5 V, for Zirfon UTP 220 and 500, respectively. The improvements compared to conventional Ni felt were linked to a reduction in the kinetic overpotential due to better catalytic properties and an increase in active surface area. The internal resistance corrected potential at 1 A/cm2 was as low as 1.75 V (at 75°C), showing that high current operation for industrial alkaline water electrolysers is possible, when ohmic resistances are adequately addressed. The catalyst coated diaphragms were stable under room temperature for at least 60 h, however, showed degradation at 75°C over the course of up to 240 h. The catalyst layers degraded by fracturing followed by delamination to the porous transport layer, where they showed elongated stability.