5.1.2. Smallest-Scale MEC

An MEC system with a single power source unit was designed. They used transparent glass serum vials with graphite plates functioning as anodes, which they found to be effective. It was soaked overnight, rinsed thrice in Milli-Q water, and further polished by sandpaper. Following the introduction of the unbent piece of wire through a hole drilled at the top center of the graphite plate, the bent end of the wire was inserted into a second hole and folded to form a tight connection between the wire and the plate. At 0.6 V of applied voltage, MECs having NiMo cathodes exhibited 33% better performance than NiW cathodes by accomplishing a hydrogen production rate (HPR) of 2.0 <sup>m</sup>3·day−1·m<sup>−</sup><sup>3</sup> at a current density of 270 <sup>A</sup>·m<sup>−</sup>3; however, this was slightly lower than MECs with a Pt catalyst which could accomplish 2.3 <sup>m</sup>3·day−1·m<sup>−</sup><sup>3</sup> [65].

5.1.3. A Cathode-on-Top Single-Chamber MEC

The reactor was made up of two parts: a top cover and the main chamber, both of which were constructed of glass and had a capacity of 0.4 L, as described in Figure 5 [62]. The substrate and electrolyte were pumped in via the bottom intake, and the produced gas was collected from the cathode with the use of a gasbag. HPR increased from 0.03 <sup>L</sup>·L−1·day−<sup>1</sup> to 1.58 <sup>L</sup>·L−1·day−<sup>1</sup> in a 24 h batch test when the applied voltage was expanded from 0.2 V to 1.0 V, and total hydrogen recoveries rose from 26.03% to 87.73% when the applied voltage was increased from 0.2 V to 1.0 V. The greatest total energy recovery was 86.78% at an applied voltage of 0.6 V [67].

**Figure 5.** A cathode-on-top type of microbial dual-chambered reactor.
