Influence of stack temperature on PEM fuel cell performance

Transcription

1 Influence of stack temperature on PEM fuel cell performance Janusz T. Cieśliński*, Bartosz Dawidowicz*, Sławomir Smoleń** * Gdansk University of Technology, Faculty of Mechanical Engineering, Narutowicza 11/12, Gdansk, Poland jcieslin@pg.gda.pl, bart@mech.pg.gda.pl ** Department of Mechanical Engineering, Hochschule Bremen, J.R. Mayer Institute for Energy Engineering Neustadswall 30, D Brenem, Germany Keywords: fuel cell, PEM, hydrogen, operating temperature 1 Introduction Fuel cells are electrochemical devices where the energy of a chemical reaction is converted directly into electricity by combining hydrogen fuel with oxygen from air. Water and heat are the only by products if hydrogen is used as fuel source [1-3]. Therefore, fuel cells have attracted great attention in recent years as a promising replacement for traditional internal combustion engines due to their high power density and ultra-low emissions [4 6]. Among many kinds of fuel cells, the polymer electrolyte membrane (PEM) fuel cell has received much attention in the last two decades because fuel cells based on proton-exchange membranes have many attractive features, including high power density, rapid start-up, high efficiency, lightweight, compactness, which makes them a promising clean energy technology [6-10]. Thus, PEM fuel cells have been widely recognized as the most promising candidates for future power generating devices in the automotive, distributed power generation and portable electronic applications [6-12]. However, a number of fundamental problems must be overcome to improve their performance and to reduce their cost. The primary aim of the study was to provide steady-state characteristics of the Nexa module (1.2 kw) for different stack temperatures and given load. 2 FUEL CELL MODULE Scheme and view of the tested PEM fuel cell system are shown in Fig. 1 and Fig 2 respectively. The module tested is based on two fuel cell units 1.2 kw each produced by Ballard Power Systems Inc. and called Nexa Fig. 3. Fig. 1. Schematic diagram of the 2x1.2 kw PEM fuel cell system

2 Fig. 2. View of the module 2.1 Nexa fuel cell The Nexa power module produces unregulated DC power for interfacing with external power conditioning equipment. A single fuel cell element produces about 1 volt at an open-circuit and about 0.6 volts at full current output. The Nexa fuel cell stack has a total of 47 fuel cells in series. The geometric area of the single cell is equal to 120 cm 2. The unit is equipped with air compressor and cooling blower. Main specifications of the fuel cell module are summarized in Tab. 1 [13]. Fig. 3. View of the Nexa fuel cell Tab. 1. Technical specifications of the Nexa fuel cell module [13] Performance Fuel Operating environment Emissions Rated net output Heat dissipation Current Voltage Lifetime Gaseous hydrogen Supply pressure Ambient temp. Humidity Pure water (vapor and liquid) CO, CO2, NO x, SO 2 particulate 1200 W 1600 W 46 A DC 26 V DC 1500 hours 99.99%, dry 7 to 17.2 bar 3 to 40 o C 0 to 95% non -condensing Maximum 870 ml/h 0 ppm 2.2 Electronic load unit As it was mentioned above, fuel cells are low voltage generators, so it is necessary to connect them to a converter. The DC DC power electronic converter used in the test bench is a boost chopper. As depicted in Fig. 4, it is composed of an input inductor L, a power semiconductor switch S, and an output capacitor C. State variables of this power electronic system are the input current i FC and the DC link voltage v OUT.

3 Fig. 4. Scheme of the PEMFC system; 1 FC module, 2 filter, 3- IGBT DC DC converter, 4 resistive load [14] 2.3 Microprocessor control unit Microprocessor control unit monitors and controls all electrical and non-electrical parameters of the fuel cells and all auxiliary equipment. The system is based on modular construction. The main microprocessor board is equipped with the main DSP microprocessor and all necessary auxiliary subsystems to perform the main role in the control process. The next parts of the control unit are the expansion boards, which are directly connected to the different parts of the whole system. The separate parts of the system are using the different communication protocols. The expansion boards are used also for collecting the data from all measuring devices. Almost 60 analog and digital signals are coming from the system to the control unit. The main control units also controlling signals to separate units and supervises the process of producing electricity. The last function of the control system is communication with the user. An operator can check and change the parameters on the LCD display but also the external PC computer can be used with the special software for controlling and supervising the whole process. 2.4 Non electrical measurements One of the ideas for designing this system was the ability of measuring all thermal parameters of the operation of fuel cell to maintain the energy balance if the fuel cell. Therefore a set of measuring instruments has been implemented. The system can measure the flow of hydrogen, flow of air for reaction and cooling air and finally the flow of produced water. Then it measures the temperatures in some critical places of the fuel cell, also on air inlets and outlets and process water temperature. It measures the inlet and outlet air humidity. It gives information about oxygen concentration in inlet air for reaction and its outlet after reaction. Finally all electrical parameter are measured including voltages in different parts of the system and currents. All this measurements are giving the clear view of the thermal and electrical behavior of the fuel cell modules. In Fig. 5 the screen from the control computer is shown. Fig. 5. Main screen of the PC software

4 Current [A] Voltage [V] Voltage [V] 3rd International Conference, Low Temperature and Waste Heat Use in Energy Supply Systems 3 Results Fig. 6 illustrates the polarization curves of a fuel cell at several operating temperatures with the range of 30 o C to 65 o C. These curves indicate that fuel cell performance was improved with operating temperature increase. The improvement in the fuel cell stack performance with operating temperature increase, in terms of the measured voltage, can be explained by the increase in the gas diffusivity and membrane conductivity at higher temperatures. The gas diffusivity is improved with fuel cell temperature increase, therefore, the fuel cell stack performance is improved at higher temperatures. As a result the kinetics reaction is improved [15] 'C 35 'C 45 'C 55 'C 60 'C 65 'C Current [A] Fig. 6. Effect of the operation temperature on the polarization curves Fig. 7 displays voltage and current output as a function of stack power. Operating temperature of fuel cell was changed from 30 o C to 65 o C. Current output increases almost linearly with stack power reading ca. 38 A for power output 1015 W. Simultaneously, recorded voltage drops from 38 V to 27 V for maximum power output and the power Voltage Current 35 'C 45 'C 55 'C 60 'C 65 'C Power [W] Fig. 7. Effect of operating temperature on the performance of fuel cell

5 Power [W] 3rd International Conference, Low Temperature and Waste Heat Use in Energy Supply Systems Fig. 8. shows effect of operating temperature on the power of fuel cell. Electrical power decreases slightly with increase stack temperature from 1015 W for 30 o C to 1004 W for 65 o C Temperature [ o C] Fig. 8. Effect of operating stack temperature on the power of fuel cell 4 Conclusions In this work, the effect of the operation temperatures on the performance of a 1.2 kw PEM fuel cell has been studied. The polarization curves of the fuel cell showed that the fuel cell performance was improved with increase stack temperature. The power of fuel cell was decreasing with increasing stack temperature. 5 References [1] D. Oliver, J. Murphy, G. Duncan Hitchens, D.J. Manko, J. Power Sources 47 (1994) [2] S.J.C. Cleghorn, X. Ren, T.E. Springer,M.S.Wilson, C. Zawodzinski, T.A. Zawodzinski, S. Gottesfeld, Int. J. Hydrogen Energy 22 (1997) [3] Prater FK.B., J. Power Sources 61 (1996) [4] Xiaochen Yu, Biao Zhou, Andrzej Sobiesiak. J. Power Sources, 147 (2005) 184 [5] Bauen, D. Hart, J. Power Sources, 86 (2000) 482 [6] Moisés Bautista Rodríguez, M.G. Araceli Rosas Paleta, J. Antonio Rivera Marquez, A. Belén Tapia Pachuca, J. Roberto García de la Vega. Int. J. Electrochem. Sci., 4 (2009) 1754 [7] Moisés Bautista Rodriguez, Araceli Rosas Paleta, J. Antonio Rivera Marquez, A. Belén Tapia Pachuca, J. Roberto García de la Vega. Int. J. Electrochem, Sci., 4 (2009) 1754 [8] Rongzhong Jiang, Deryn Chu. J. Power Sources, 92 (2001) 193 [9] Moisés Bautisata Rodriguez, Araceli Rosas Paleta, Andrés Rodríguez Castellanos, J. Antonio Rivera Márquez, Omar Solorza Feria, J. Antonio Guevara Garcia, J. Ignacio Castillo Velásquez. Int. J. Electrochem. Sci., 2 (2007) 820 [10] A.Bilodeau, K. Agbossou. J. Power Sources, 162 (2006) 757. [11] P. Costamagana, S. Srinivasan, J. Power Sources, 102 (2001) 242 [12] P.Costamagana, S. Srinivasan, J. Power Sources, 102 (2001) 253 [13] NexaTM Power Module User s Manual, Ballard Power Systems, June 2003 [14] Kaczmarczyk T.: Electronic load unit for PEMFC. MSc Thesis, GUT, Gdańsk 2008 [15] J. Zhang, Y. Tang, C. Song, X. Cheng, J. Zhang, H. Wnag. Electrochimica Acta, 52 (2007) 5095