When the capacitor was connected to
When the capacitor was connected to the Al/phosphate cell via a switch capacitor regulator circuit and was charged from 1.4V to 1.8V, the charging times were 0.51±0.02s and 0.34±0.03s for the single cell and the 2-cell configuration, respectively (Fig. 5). The charge/discharge cycle was observed approximately 2times/s with 1.96Hz frequency using a single fuel cell connected to the switch capacitor regulator circuit and approximately 3 times/s with 2.94Hz using two-cell fuel cell. These times were less than the times required when charging and discharging potentials were 1.66V and −0.037V, respectively. The difference between the charging and discharging potentials resulted in the reduction of the charge/discharge frequency. As illustrated in Fig. 6, the cell performance (charge/discharge cycles) significantly increased with increasing phosphate buffer solution concentration. A dynamic linear range of 10mM to 800mM phosphate was achieved.
Base on the observed charge and discharge potentials, the average power density generated in a single charge/discharge cycle was calculated  to be 13.0μWcm using a single cell configuration and this stored energy was used to operate a red LED intermittently with a charge/discharge cycle of 0.51±0.02s (1.96Hz). For the 2-cell configuration, the average power density generated in a single charge/discharge cycle was 20.1μWcm and the total energy stored by the capacitor was approximately 5.42μJcm in each cycle, which was sufficient to power the LED intermittently (every 0.34±0.03s) as long as there is more Al sites available for pitting corrosion. For higher charging and discharging frequency, a smaller capacitor may be utilized. The performance of the fuel cell configuration was enhanced by using two Al/phosphate Celecoxib connected in series to a capacitor via a switched capacitor regulator in order to obtained sufficient power and drive signal to operate a small electronic device. The utilization of the switched capacitor regulator circuit and the 1μF capacitor results in the generation of higher voltage and sufficient power to operate an electronic device by charging the capacitor using the electricity generated from the 2-cell configuration. Therefore, the combination of the Al/phosphate cell, capacitor, and the switched capacitor regulator circuit resulted in the amplification of the cell voltage along with current to levels which were adequate enough to provide the drive strength required for small electronic devices without design changes to the Al/phosphate cell.
Conclusion In this investigation, we constructed an energy generation system using Al/phosphate cell in combination with a capacitor to deliver sufficient power to drive a small electronic device via a switched capacitor regulator circuit. The capacitor is used to store the energy generated by the cell and this stored energy is then discharge from the capacitor to power a LED. The charge/discharge frequency of the capacitor was used to calculate the power of the Al/phosphate cell. The power was enhanced by using 2-cell configuration and by varying the charge and discharge potentials. The time needed to charge the capacitor from 1.4 to 1.8V was 0.51±0.02s using a single fuel cell configuration and 0.34±0.03s using a 2-cell configuration. We demonstrate that two Al/phosphate cells connected in series can generate an open circuit voltage (Voc) up to 1.66V and power density of 20.1μWcm to intermittently power a LED via a switched capacitor regulator circuit. The results demonstrate that the switched capacitor regulator circuit can be used to enhance energy generation when electrochemical cells are used in combination with a capacitor to automatically power small electronic devices.
Conflict of interest
Acknowledgment This work was supported by the National Science Foundation (Award ECCS-#1349603).
Introduction Microbial fuel cells (MFCs) are electrochemical devices that generate electricity via the metabolic activity of microorganisms, when breaking down a wide range of organic matter, including waste and wastewater. With the depleting fossil fuels and necessity of seeking alternative and sustainable technologies, the MFC technology has justifiably received increased attention from the scientific community. MFC applications primarily include electricity generation, wastewater treatment, hydrogen production and bio-sensing [13,19,23,24,29]. Further developments may include pollution treatment, resource recovery and powering of other remote equipment such as portable IT systems, environmental monitoring tools and medical support apparatus [15,17,18,25,31,42].