Demcotech Engineering, P.O. Box 9624, Edenglen, South Africa; Electrochemistry for Energy and Environment Group, Research Focus Area: Chemical Resource Beneficiation (CRB), North-West University, Private Bag X6001, Potchefstroom, South Africa
Gillespie, M.I., Demcotech Engineering, P.O. Box 9624, Edenglen, South Africa; Van Der Merwe, F., Electrochemistry for Energy and Environment Group, Research Focus Area: Chemical Resource Beneficiation (CRB), North-West University, Private Bag X6001, Potchefstroom, South Africa; Kriek, R.J., Electrochemistry for Energy and Environment Group, Research Focus Area: Chemical Resource Beneficiation (CRB), North-West University, Private Bag X6001, Potchefstroom, South Africa
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, RuO<inf>2</inf>/IrO<inf>2</inf>/TiO<inf>2</inf> 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. © 2015 Elsevier B.V. All rights reserved.