The Study On The Dynamic Response Performance Of PEMFC With RuO₂·xH₂O

It is generally accepted that polymer electrolyte membrane PEM fuel cells are considered to be the most promising for both stationary and mobile applications due to their significant advantages such as high efficiency and the absence of noxious emissions. However, operations of fuel cell in the application of these systems are dynamic, and the transient behavior happens when the loading changes (e.g. for starting vehicle or recovery energy during deceleration).Transient operations may result in the oxidant starvation due to gas response rate lagging the loading rate, which will affect the durability and reliability of fuel cells further.The commercial success of PEM fuel cells depends on cell performance durability and cost competitiveness with other energy conversion and power generation devices. Understanding the dynamic responses of fuel cells to changes in external load and operating parameters is important to be able to understand fuel cell performances and design optimizations.Carbon nanotubes (CNTs), among many other applications, are of great interest also for electrochemical use because of their suitable characteristics. Electrode materials should exhibit high conducting properties, high mesoporosity to enable easy electrolyte circulation and access of ions to interface for exchange of charges. Carbon nanotubes, perfectly fulfil these requirements.RuO2 is supercapacitor material, which owns higher power capacity and easier preparation technology. In this paper, two methods : impregnation-sol-gel method and electrochemical deposition method were used to prepare RuO2 ? xH2O. And the first time, RuO2 ? xH2O/CNTs and Pt/C catalyst are used to improved the capacitance of the dynamic response of PEM fuel cell .In this study, RuO₂·xH₂O was loaded on CNTs by impregnation-sol-gel method to prepare a composite capacitor with both double-layer capacitance and Faraday pseudocapacitance. This composite capacitor has high energy and power density. The prepared composite capacitor RuO₂·xH₂O/CNTs was sprayed onto the surface of the Pt/C electrode to form the cathode. The single cells with and without RuO₂·xH₂O/CNTs at the cathode were both tested. Dynamic response performance, cyclic voltammetry, electrochemical impedance spectra and polarization curve tests were carried out for these two cells. Results show that the addition of RuO₂·xH₂O/CNTs significantly increases the dynamic response performance, which is very helpful to improve the reliability of the PEM fuel cell.The dynamic response performance of PEM fuel cell was improved by spraying RuO₂·xH₂O/CNTs composite material on the Pt/C electrode of the cathode. The CV tests of CNTs with and without RuO₂·xH₂O illustrate that the capacitance of CNTs is obviously increased when RuO₂·xH₂O is added. TEM of RuO₂·xH₂O/CNTs shows that the average diameter of the RuO₂·xH₂O particles prepared by sol-gel method is 3 nm and the particles are well dispersed. Electrochemical impedance spectra tests of single fuel cells display that when RuO₂·xH₂O/CNTs is added at the cathode Rct descends, indicating the electrochemical reaction is easier to occur. Compared with Pt/C electrode, the dynamic response performance of the RuO₂·xH₂O/CNTs and Pt/C composite electrode is much better, which reveals that the rapid charge-discharge functions of RuO₂·xH₂O/CNTs can effectively improve the dynamic response performance as well as the fuel cell life and reliability.In addition, electrochemical deposition was used to deposit hydrated ruthenium oxide on the surface of Pt/C electrode. SEM of RuO₂·xH₂O/Pt/C shows that RuO₂·xH₂O are well dispersed and no reunion phenomenon. And electrochemical tests concluds that: Specific capacitance of electrode is obviously increased when RuO₂·xH₂O is added and Rct descends. Results show that the addition of RuO₂·xH₂O significantly increases the dynamic response performance, which is very helpful to improve the reliability of the PEM fuel cell.