Abstract
Decreasing the Pt loading and surface area of the cathode was found to accelerate the hydrogen evolution reaction in microbial electrolysis cells (MEC) at low substrate concentrations. The experimental wire cathode used in this study had a reduced Pt loading of 20 µg Pt/cm2 and only 14% of the surface area of the control disk-type cathode. With the wire cathodes, peak current densities of 33.1 ± 2.3 A/m2 to 30.4 ± 0.5 A/m2 were obtained at substrate concentrations of 0.4 g/L and 1.0 g/L, respectively, which were 5.4 to 6.2 times higher than those obtained with the disk electrode (5.1–5.7 A/m2). The higher cathode overpotentials and higher current densities obtained with the wire electrode compared to those observed with the disk electrode were advantageous for hydrogen recovery, energy recovery efficiencies, and the hydrogen volume produced (8.5 ± 1.2 mL at 0.4 g/L to 23.0 ± 2.2 mL at 1.0 g/L with the wire electrode; 6.8 ± 0.4 mL at 0.4 g/L to 21.8 ± 2.2 mL at 1.0 g/L with the disk electrode). Therefore, the wire electrode, which used only 0.6% of the Pt catalyst amount in typical disk-type electrodes (0.5 mg Pt/cm2), was effective at various substrate concentrations. The results of this study are very promising because the capital cost of the MEC reactors can be greatly reduced if the wire-type electrodes with ultralow Pt loading are utilized in field applications.
Highlights
The microbial electrolysis cell (MEC) is a novel technology that converts organic matter into waste and wastewater into hydrogen gas [1,2]
This apparent inconsistency is due to the reduced area of the wire electrodes, as a result of which they showed significantly higher current densities when calculated based on the cathode size
Ultralow Pt catalyst loading (20 μg Pt/cm2) produced higher volumes of hydrogen gas, in addition to showing better coulombic efficiency, cathodic hydrogen recovery, and energy efficiency compared to a disk electrode (0.5 mg Pt/cm2, surface area 7 cm2)
Summary
The microbial electrolysis cell (MEC) is a novel technology that converts organic matter into waste and wastewater into hydrogen gas [1,2]. The current is passed to the cathode, where hydrogen gas is generated under the influence of external power. While separators such as ion exchange membranes (anion exchange membrane (AEM) and cation exchange membrane (CEM)), bipolar membranes, and porous membranes are typically used between the cathode and anode in typical two-chamber MECs, membrane-less single-chamber MECs exhibit superior hydrogen production rates and yields in comparison, owing to low internal resistance [5]. Single-chamber MECs are very challenging to control because the hydrogen generated at the cathode may follow various reaction pathways and convert into low-value products, becoming detrimental to the overall MEC performance [6,7]. The presence of a separator between the electrodes becomes inevitable and could cause potential losses, which need to be minimized [8]
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