Lifetime Of Proton Exchange Membrane Fuel Cell Research Articles

Study on Air-cooled Self-humidifying PEMFC Control Method Based on Segmented Predict Negative Feedback Control

In order to obtain the optimal output performance of the air-cooled self-humidifying proton exchange membrane fuel cell (PEMFC), the operating temperature, the air flow, purge interval and some other parameters must be controlled strictly. As a key factor, the operating temperature mainly determines the optimal output performance of the fuel cell. However, some intrinsic issues such as long adjusting time, over-shoot still exist inevitably for the traditional PID temperature-controlled method in circumstances of the load variation. Consequently, output performance of PEMFC decreases because the operating temperature of the fuel cell fails to reach, and the corresponding lifetime of PEMFC is also reduced. In this study, a segmented predict negative feedback control method, based on the advance proportional control one, is proposed and verified by experiments to overcome the shortcomings of PID temperature control. The results demonstrate that the optimal output performance of PEMFC can be realized by utilizing the proposed method for temperature control due to its excellent properties, simple controlling and small over-shoot.

Electrocatalysis of Oxygen Reduction with in-Situ formed Pt Nano-Rafts on Molybdenum Carbide Support

Proton exchange membrane fuel cell (PEMFC), is a technology that has the potential to economically replace combustion engines for transport with high efficiency, and clean (only water emission) energy. The US department of energy (DOE) identifies two remaining major hurdles to the deployment of this alternative: cost and durability of the cathode.1Reducing the amount of platinum, still the only material with the needed catalytic activity for oxygen reduction reaction on the cathode, and the most expensive component, will help overcome the first problem and the creation of a new, ‘non-carbon’, more oxidation-resistant catalyst support material could overcome the second.At present, carbon is the preferred support, because it exhibits the primary features required: abundant, high surface area, good electrical conductivity, and low cost. However, the use of carbon is clearly problematic. It is well known that the conditions in PEMFCs are oxidizing, especially in the cathode.2-4 These conditions are detrimental to the carbon and the catalysts which interact with it and shorten the lifetime of PEMFCs.5 , 6For this reasons, electronically conductive ceramic supports are being pursued as alternative supports for PEMFCs.A novel catalytic synthesis of Pt/Mo2C, from a physical mixture of solid precursors, led to the production of unique platinum structures: Nano-rafts, containing less than six atoms of Pt on a molybdenum carbide support (Figure 1). No evidence of nano-crystalline Pt is evident in this XRD trace as one would typically see on Pt/C catalysts (ca. 20–30 Å sized Pt nano clusters - Figure 2). XRD traces only show a cubic phase Mo2C (a=4.225Å) with an average crystallite size on the order of 22-23Å as determined by full profile fitting methods. Electrochemical half-cell tests (Figure 3) of oxygen reduction demonstrate nano raft structures allow for more efficient utilization of platinum, with higher half wave potential than i) traditional, commercial carbon supported catalysts and ii). Mo2C supports loaded with Pt using incipient wetness. X-ray photoelectron spectroscopy indicate the Pt nano-rafts have unique chemistry, specifically there is evidence of uniquely strong charge transfer to the support. Density functional theory calculations also suggested a strong charge transfer from platinum to Mo2C should be expected commensurate with enhanced durability when compared to commercial Pt/C catalysts. We will present these data along with other results and discuss the impact that the Nano-raft structure has on support durability in half-cell AST measurements. References A. Rabis, P. Rodriguez, and T. Schmidt, J. ACS Catalysis 2 (2012) 864.T. Barth, G. Lunde, Z. physic. Chem 121 (1926) 78.E. V. Clougherty, K. H. Lothrop, J.A. Kafalas, Nature (London) 191 (1961) 1194.E. Rudy, S. Windisch, A.J. Stosick, J.R. Hoffman, Trans. Metall. Soc. AIME 239 (1967) 1247.G.A., Journal of the Electrochemical Society 125 (1978) 1719.J. P. Meyers, R.M. Darling, Journal of the Electrochemical Society 153 (2006) A1432. Acknowledgments The research was funded by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technology and Fuel Cell Technology Programs.

시동/정지 반복에 의한 데드엔드형 고분자전해질 연료전지의 성능 감소

고분자전해질연료전지(PEMFC)는 시동/정지과정에서 성능과 수명이 감소한다. 본 연구에서는 캐소드가스로 산소를 사용하는 데드엔드 형 PEMFC의 시동/정지 과정의 영향을 분극곡선, 임피던스(EIS), SEM과 TEM을 사용해 연구하였다. 시동/정지 과정에서 PEMFC 성능감소를 막기 위해서는 더미 로드를 사용해야 함을 보였다. 시동/정지 반복과정 중 50% 상대습도(RH)에서 캐소드 카본지지체의 부식에 의한 열화가 100% RH보다 심했다. 데드엔드 형 PEMFC의 정지과정에서 PEMFC에 물을 공급해줌으로써 50% RH에서 열화속도를 감소시켰다. During start up and shut down of a proton exchange membrane fuel cells (PEMFC), the performance and lifetime of PEMFC were reduced. In this study, effect of startup and shutdown were investigated in dead-end type PEMFC using oxygen as a cathode gas with polarization curve, impedance spectroscopy (EIS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Dummy load which eliminates residual hydrogen and oxygen during startup and shutdown operation should be applied to mitigated the degradation of PEMFC performance. At 50% relative humidity (RH) under the repetitive on/off cycling, the cell performance decayed faster than at 100% RH because of corrosion of the cathode carbon support. Water suppling into cell reduced the degradation rate of dead-end type PEMFC during start up and shut down cycling at 50% RH.

Effect of driving cycle on the performance of PEM fuel cell and microstructure of membrane electrode assembly

Driving cycle effect on proton exchange membrane fuel cell (PEMFC) performance and microstructure of membrane electrode assembly (MEA) is simulated to predict the lifetime of PEMFC. The single cell performance after different simulated cycles (100, 150 and 200 cycles) was evaluated by I– V curves. Electro-chemical impedance spectroscopy (EIS) was used to characterize the electro-chemical properties of fuel cell and the active surface area was characterized by cyclic voltammetry (CV). It was found that after 100, 150 and 200 cycles the electro-chemical surface area (ESA) for electro-chemical reaction decreased about 13.6%, 15.4% and 38.9%, respectively, and the performance of PEMFC declined about 0.1 V at 500 mA cm −2 after 200 driving cycles. Impedance analysis and equivalent circuit showed that ohmic and charge transfer resistance respectively increased from 2.06 to 2.13, 2.215, 2.435 Ω cm 2 and from 0.7 to 0.905, 1.26, 1.915 Ω cm 2 after three kinds of driving cycles, and they all increased with increasing driving cycles, which may be one reason for the decline of PEMFC performance. Besides, scanning electron microscopy (SEM) result revealed that the thickness of catalyst layer after cycle test was weakening much more than the fresh one.

Modeling and Investigation of Design Factors and Their Impact on Carbon Corrosion of PEMFC Electrodes

Models of carbon corrosion induced by oxygen and hydrogen coexistence on the negative electrode are presented. In proton exchange membrane fuel cells (PEMFCs), this phenomenon occurs under several situations, such as start-up, shutdown, and hydrogen starvation. In the absence of hydrogen, the source of protons on the negative electrode is the oxygen reduction reaction. The solution potential decreases and induces an overpotential, , large enough to cause carbon corrosion on the positive electrode even at low temperatures. The carbon corrosion current is large enough to influence the lifetime of PEMFCs not only in the case of high oxygen partial pressure, such as observed during start-up, but also in the case of low partial pressures such as a result of the permeation of oxygen through the membrane. The influence of key parameters for carbon corrosion is investigated. It is clear that the oxygen reduction activity on the negative electrode, the thickness of the membrane, and the cell potential can affect the carbon corrosion on the positive electrode significantly.