# Selected Aspects of Designing Modular PEMFC Stacks as Power Sources for Unmanned Aerial Vehicles
## 2 Experimental Parts
### Method of Measurement and Measuring Equipment Used  
The U-I and P-I curves for the 2000-W power source (I) were measured using electrochemical stations (CLB-2000, BioLogic, Claix, France, 2 kW) equipped with electronic load. In the case of power source (II) with 500-W modular PEMFC stacks, a programmable electronic load (Dynaloal XBL 50-150-800, TDI Power, Hackettstown, NJ, USA) was used along with an electrochemical interface (FC350 Fuel Cell Interface, Gamry, Warminster, PA, USA). Variations in current (I) and voltage (U) during operation of the humidification implemented by the SCU system were measured using the oscilloscopic method (DS1062 CA digital oscilloscope, Rigol, Suzhou, China). During the operation of both investigated PEMFC stacks, total consumption of hydrogen was measured using a digital electronic mass flow meter (EL-Flow, Bronkhorst High-Tech, Ruurlo, The Netherlands). The hydrogen pressure supplied to the stacks was monitored by an electronic pressure regulator (EL-PRESS, Bronkhorst High-Tech, Ruurlo, The Netherlands). The resulting values were saved on the computer for further analysis. Measurements of the electrical parameters of 1000-W PEMFC modules (1) and (2) used for the construction of power source (I) were  
Figure 2: (a) A 0.5-kW PEMFC stack consisting of three fuel cell modules (1–3) connected in parallel with a potential connection to an electrochemical battery. The photos of (b) the 3-modular PEMFC stack and (c) copper-coated glass/epoxy laminate separation plates. conducted using electrochemical impedance spectroscopy (EIS). The main component of the station was an electronic load (Dynaload XBL 50-150-800), which enabled strictly controlled current loading and determination of impedance spectra via EIS using fuel cell stack test cards (Gamry, Warminster, PA, USA). The electronic load was controlled from a PC, which simultaneously collected measurement data. Measurements were carried out at four fixed DC values (1, 10, 16, and 25 A) over which a small variable sinusoidal load was applied. The impedance of the 1-kW PEMFC module was determined for a frequency within the range 10 kHz-0.1 Hz. The recorded voltage was used to determine the impedance spectra. The commercial software ZPlot (Scribner, New York, NY, USA) was used to fit an equation describing the assumed equivalent electrical circuit (EEC) to the measured data. The hydrogen necessary to operate the fuel cell was supplied from the gas installation as well as from two composite bottles (2 \(\times\) 6.8 dm\({}^{3}\), supplier Horizon, Fuel Cell Technologies, Singapore) and pressure was reduced to 0.5 bar. The amount of compressed hydrogen storage in the two composite cylinders of the 2-kW PEMFC stack or in the 1 dm\({}^{3}\) ultra-light cylinder for the 500-W PEMFC stack was monitored by AST2000H2 hydrogen pressure sensors (American Sensor Technologies, Inc., Budd Lake, NJ, USA). The temperature of the PEMFC stack during operation was monitored by Pt1000 resistance temperature sensors located inside modules (1) and (2). Signals from temperature measurement, on the basis of which the operation of the cooling fans was monitored, were sent to the PEMFC controller. During the electric measurements, the energy consumption of the auxiliary devices was analyzed and the measurements monitored. Using a Power Log 65 logger, the parameters (voltage, current, and power) of the fan system cooling the stack were recorded. The temperature distribution was also measured by a thermal imaging camera (Thermo Tracer NEC H2640) (Figure 3). Thermal images were recorded, following the determination of the stack temperature under a load of 800 W, on an uncovered side surface of the two-module PEMFC stack. Single-module 2-kW PEMFC stacks, such as a BCH Energy 2000 (Jiangsu Ice-City Hydrogen Energy Technology Co., Ltd., Danyang, China) and a Horizon 2000 PEMFC stack from H-series, were chosen as reference devices in order to compare their performance with the newly-built two-module PEMFC stacks (2M).