Performance of CO preferential oxidation reactor with noble-metal catalyst coated on ceramic monolith for on-board fuel processing applications

On-board fuel processors are being developed to provide hydrogen-rich gas to the polymer electrolyte fuel cell automotive propulsion systems. Whereas the anode catalyst in the fuel cell has low tolerance for carbon monoxide, 10–100 ppm, reforming of gasoline and other hydrocarbon fuels generally produces 1–2% of CO. Of the many methods of removing CO from the reformer gas, preferential oxidation (PrOx) of CO over noble-metal catalysts is practiced most frequently. In this paper, we present experimental data for CO conversion on a Pt-based catalyst that is active at room temperature and was coated on a ceramic monolith. The data is used to develop an empirical correlation for selectivity for CO oxidation as a function of CO concentration and oxygen stoichiometry at 30,000–80,000/h space velocity. The selectivity correlation is used in a model to analyze the performance of multi-stage, adiabatic PrOx reactors with heat exchange between the stages to cool the reformate to 100 °C. An optimization algorithm is used to determine the operating conditions that can reduce CO concentration to 10 ppm while minimizing parasitic loss of H₂ in the reformate stream. It is found that the 10 ppm constraint limits the maximum inlet CO concentration to 1.05% in a single-stage reactor and to 3.1% in a two-stage reactor. The results clearly show the incremental reduction in parasitic H₂ loss by addition of second and third stages.     

Thermodynamic and economic assessment of a PEMFC-based micro-CCHP system integrated with geothermal-assisted methanol reforming

A micro-combined cooling heating and power (CCHP) system integrated with geothermal-assisted methanol reforming and incorporating a proton exchange membrane fuel cell (PEMFC) stack is presented. The novel CCHP system consists of a geothermal-based methanol steam reforming subsystem, PEMFC, micro gas turbine and lithium bromide (LiBr) absorption chiller. Geothermal energy is used as a heat source to drive methanol steam reforming to produce hydrogen. The unreacted methanol and hydrogen are efficiently utilized via the gas turbine and PEMFC to generate electricity, respectively. For thermodynamic and economic analysis, the effects of the thermodynamic parameters (geothermal temperature and molar ratio of water to methanol) and economic factors (such as methanol price, hydrogen price and service life) on the proposed system performance are investigated. The results indicate that the ExUF (exergy utilization factor the exergy utilization factor), TPES (trigeneration primary energy saving) and energy efficiency of the novel system can be reached at 8.8%, 47.24% and 66.3%, respectively; the levelized cost of energy is 0.0422 $/kWh, and the annual total cost saving ratio can be reached at 20.9%, compared with the conventional system. The novel system achieves thermodynamic and economic potential, and provides an alternative and promising way for efficiently utilizing abundant geothermal energy and methanol resources.     

Experimental analysis of performance degradation of 3-cell PEMFC stack under dynamic load cycle

A vehicular fuel cell is dynamically operated at the demand of the driver, so that the durability of the fuel cell quickly deteriorates. This study analyzes the durability of a 3-cell short stack under normal vehicle operation. An acceleration test is scheduled with operation temperatures of 55 °C and 70 °C at 50% relative humidity for 300 h. The dynamic load cycle (DLC) conditions are a repetition of the New European Driving Cycle (NEDC), which can allow a short stack to run on the vehicle operating load. At 100-hour intervals, recovery procedures are conducted to understand the order of performance retrieval. Significant stack degradation is observed at 75 °C operation for 300 h. Results show that the recovery protocol can return the performance of the fuel cell at a low and a middle current density regime, but it is hard to recover the performance at a very high current density regime. Performance recovery is very effective for lower temperature operation (55 °C), but the recovery procedures only returned about 4% of the performance at 300 h and 75 °C.     

Experimental study on improving the dynamic characteristics of open-cathode PEMFC stack with dead-end anode by condensation and circulation of hydrogen

Water management is one of the most important issues for proton exchange membrane fuel cell stack. Liquid water accumulates in the stack may impede the transport of the reaction gas, resulting in unstable output performance and poor durability. In this study, Condensation mode and Condensation Circulation mode are proposed to reduce the accumulation of liquid water in the anode compartment, thus reducing the risk of flooding. Comparative research among the traditional dead-end anode (DEA) mode and presented modes are carried out on a ten-cell open-cathode PEMFC stack. The comparisons show that the proposed strategies can effectively alleviate the voltage decay caused by flooding and improve output stability. And the Condensation Circulation mode is more effective than the Condensation mode.     

“Model-based” design of thermal management system of a fuel cell “air-independent” propulsion system for underwater shipboard

The thermal management of the fuel cell stack is critical for high-performance long-term operation. A fuel cell system of underwater vessel has a liquid-to-liquid cooling circuits which is composed of two liquid cooling pumps, two three-way valves, and a shell and tube heat exchanger. The liquid-to-liquid cooling technique makes it easier to reject the reaction heat into the surrounding but it is required refined cooling structure and control algorithm. In this study, a model-based design is applied to evaluate the control algorithm. A fuel cell system simulation model is developed and polarization curves and transient response are validated. A proportional integral controller and control strategy is developed and a nominal state feedback controller is also developed. Those control algorithms are evaluated via the dynamic response under step increases of load, and the control performance of the nominal state feedback controller is compared with the conventional controller (PI). The results show that the presented the nominal state feedback control of performs better than the PI control method with less wear and less control effort on the two circuit cooling modules. The proposed the nominal state feedback control can increase the system energy by 23.9%.     

PEMFC电化学建模及其PID控制

针对目前质子膜燃料电池(PEMFC)模型难以适用控制系统的设计,因此提出了电化学方法建立PEMFC数学模型,并在此基础上采用PID控制其输出电压。首先分析PEMFC内部运行机理;然后假定外部负载电流干扰的情况下,PEMFC电堆工作温度稳定在80℃,在M atlab/simu link环境下建立系统仿真模型,模拟输出电压动态变化过程;并采用PID算法控制电堆阴阳极入口气体压力,使PEMFC系统的输出电压达到预定值。仿真结果表明该模型能够较好的反映出系统的动态特性,且PID算法用于PEMFC发电系统的控制是可行的。     

质子交换膜燃料电池热管理研究

论述了质子交换膜燃料电池热管理的重要性以及对电池性能的影响,指出了质子交换膜燃料电池热管理的设计要求,分析比较了目前燃料电池几种常用的冷却方式,介绍了燃料电池涉及电池温度的CFD模型以及温度控制仿真模型。     

质子交换膜燃料电池新型抗CO阳极结构

质子交换膜燃料电池(PEMFC)广泛采用重整气为燃料,其存在的主要问题是重整气中含有一定浓度的CO(5×10-5～10-2),CO在Pt表面具有强烈的吸附作用,使电催化剂"中毒".通过对提高质子交换膜燃料电池抗CO问题进行研究,在阳极扩散层流场侧担载催化剂(Pt、PtRu)的方法对电极进行修饰,在注入较少量氧化剂(体积百分比为2%的空气)的条件下使电池抗CO性能显著增强,且可以避免电极局部温度过高及可能带来的安全性问题.     

微乳法制备燃料电池铂黑催化剂

采用微乳法在正庚烷/Triton X-100/正己醇/水体系合成了一系列Pt黑催化剂,首先通过绘制体系的部分拟三元相图确定微乳单相区及合适的表面活性剂与助表面活性剂体积比,进一步考察了表面活性剂浓度对制备铂黑催化剂粒径及催化性能的影响,同时还讨论了分离、洗涤和干燥等操作过程对颗粒分散性的影响.利用透射电镜(TEM)、X射线衍射(XRD)、循环伏安法(CV)、动电位线性扫描(LSV)等手段对催化剂进行表征,结果表明该微乳体系下制得的催化剂平均粒径可控制在2～4 nm,采用无水乙醇取代水来改善干燥环境能够成功解决铂黑的团聚问题,得到的铂黑颗粒分散性能好,电化学活性与商业品相当.     

表面改性不锈钢双极板的性能研究

双极板是质子交换膜燃料电池的重要的多功能组件.不锈钢材料由于具有良好的耐腐蚀性能成为金属双极板理想的选择.但其表面高电阻的钝化膜会降低电池性能.测定了经过镀铬后再离子氮化的304不锈钢在模拟PEMFC环境下的电化学性能,测量了氮化层与碳纸之间的接触电阻.结果表明,该表面改性方法使304不锈钢在模拟PEMFC阴极和阳极情况下的钝化电流密度降低,均低于双极板设计标准16 μA/cm2;改性后的304不锈钢的接触电阻值降低,电性能得到了提高.