Performance evaluation of a membraneless divergent electrode-flow-through (DEFT) alkaline electrolyser based on optimisation of electrolytic flow and electrode gap

Abstract

A membraneless divergent electrode-flow-through (DEFT) alkaline electrolysis design and operating principle is investigated, which allows for the ohmic drop contribution and performance threshold limitations of a conventional membrane barrier to be overcome. Employing mesh electrodes of 30 mm diameter, operation of the electrolyser at an electrolytic flow velocity of 0.075–0.1 m s−1, resulted in an optimal electrode gap of ∼2.5 mm, while operating at greater velocities (>0.1–0.2 m s−1) allows for the employment of a smaller optimal gap of ∼0.8 mm. At an electrode gap of 2.5 mm and current densities of 3500 mA cm−2, hydrogen purity of 99.83% has been recorded. With pure nickel electrodes current densities of 101.19 mA cm−2 (at 1.80 VDC) and 326.33 mA cm−2 (at 2 VDC) have been achieved, while the use of superior catalysts, namely, RuO2/IrO2/TiO2 and Pt for the anode and cathode respectively, resulted in the current densities to increase to 219.99 mA cm−2 (at 1.8 VDC) and 474.40 mA cm−2 (at 2 VDC) at an electrode gap of 2.5 mm and a minimum flow velocity of 0.075 m s−1. The test rig is capable of generating hydrogen at a rate of 63.6 L/hr at normal temperature and pressure (NTP). The production rate follows current density linearly at high overpotentials