Enhancing hydrogen production in microbial electrolysis cells through development of platinum-free cathode and improvement of reactor design

Microbial electrolysis provides a new approach for hydrogen generation from renewable biomass. At current stage, the most likely limiting factors for successful scale up of this technology are the large internal resistance and high fabrication cost. This dissertation presents an attempt to overcome these limitations by investigating novel microbial electrolysis cell (MEC) architecture and efficient and economic cathode material. A single-chamber membrane-free MEC was designed for the first time, which significantly reduced the internal resistance and high cost associated with membranes. The new MEC achieved a 76% increase in volumetric hydrogen production rate than a two-chamber system. This improvement was also associated with an 18-fold increase in current densities, which indicated its great potential for further enhancement in hydrogen production.;To reduce the high cathode cost associated with platinum catalyst, precious-metal-free cathodes were developed by electrodepositing NiMo and NiW on a carbon fiber weaved cloth material and evaluated in tubular single-chamber MECs. At an applied voltage of 0.6 V, MECs with NiMo cathode accomplished a hydrogen production rate of 2.0 m3/day/m3 at current density of 12 A/m2, which was 33% higher than that of MECs with NiW cathode. Due to better catalytic activity of NiMo catalyst, electrodeposition conditions of NiMo were further optimized to enhance the performance and reduce catalyst loading. And the optimal condition was selected as: a Mo/Ni mass ratio of 6/10 in electrolyte bath, an applied current density of 0.05 A/cm2 and electrodeposition duration of 10 min. Under this optimal condition, the NiMo catalyst had a formula of Ni6MoO3 with a nodular morphology. The NiMo loading was reduced to 1.7 mg/cm2 and the performance of MEC with the developed NiMo cathode was comparable to that with Pt cathode with a similar loading. This result indicates that a much lower cathode fabrication cost can be achieved compared to that using Pt catalyst, and thereby significantly enhancing the economic feasibility of the MEC technology.