Abstract In this work, we have successfully developed a series of ordered Fe‐ and N‐doped carbon (Fe‐N‐C) catalysts for alkaline anion‐exchange membrane fuel cells (AEMFCs) using ordered SiO 2 nanospheres as a scaffold template. Compared to the previous work, the SiO 2 nanosphere templates used in this work are more well‐ordered and size‐controlled, which increases the surface area of the Fe‐N‐C framework material. We observed that the 30 nm@Fe‐N‐C sample exhibits orderly arranged mesopores, interconnected conductive networks, and large surface area (1192 m 2 g −1 ). Moreover, the 30 nm@Fe‐N‐C sample shows significantly enhanced oxygen reduction reaction (ORR) activity compared to commercial Pt/C. A more‐positive half‐wave potential of 0.84 V (vs. reversible hydrogen electrode, RHE) and remarkably stable limiting current of ≈6.1 mA cm −2 is demonstrated by a three‐electrode configuration rotating disk electrode (RDE) system in 0.1 m KOH solution. An AEMFC based on the 30 nm@Fe‐N‐C sample showed a maximum power density of 100 mW m −2 at a high current density of 230 mA cm −2 . In addition, we found the AEMFC based on 30 nm@Fe‐N‐C catalyst could steadily operate for more than 60 h with only 4.65 % performance degradation under constant voltage conditions (0.6 V). More interestingly, this catalyst shows an excellent tolerance for CO as well as remarkably long‐term stability with more than 89.9 % retention of its initial activity after 41.6 min operation, which is obviously superior to the commercial Pt/C catalyst (59 % initial activity retention).
The metal bipolar plates (BPs) have replaced the graphite BPs in vehicle-used proton exchange membrane fuel cell (PEMFC) stack because of their high volume power density. To investigate the durability of metal BP stack, this paper performed a durability test of 2000 hours on a 10-cell metal BP fuel cell stack. The degradations of the average voltage and individual cell voltage in fuel cell stack were analyzed. To investigate the degradation mechanism, the stack was disassembled and the morphologies and compositions of no. 1, no. 5, and no. 10 cells after 2000 hours were characterized by SEM, TEM, and ASS. The results indicated that at 800 mA/cm2, the voltage decay rate is 42.303 μV/hour and the voltage decay percentage of the stack is 14.34% after 2000 hours according to the linearly fitting result. According to the US Department of Energy (DOE) definition of fuel cell stack life, only the voltage decay rate of OCV and the tenth cell is lower than the maximum voltage degradation rates of 10 000 hours. The decreases of homogeneity of stack were the main reason for its performance degradation. Especially for the tenth cell, its performance has almost no drop. The main failure reason of this metal BP stack is structural design rather than metal corrosion. The losses of Pt catalyst and C supporting are the main reason of performance degradation.
Pt-doped proton exchange membranes (PEMs) can effectively reduce oxygen permeation and thus enhance the durability of PEM, which have been widely employed in fuel cell. However, until now, no study related to the oxygen permeation capability of Pt-doped PEM during actual operation has been reported. In this article, the oxygen permeation of Pt-doped PEM under fuel cell operation is analyzed by the embedded microelectrode method. The test results show that the anode/cathode pressure difference is the main influencing factor for the oxygen permeation of the PEM: the oxygen permeation behavior of the Pt-free PEM exists and gradually decreases with an increase in the anode/cathode pressure difference, and the oxygen permeation behavior of the PEM disappears when the pressure difference exceeds 60 kPa. Due to the presence of Pt nanoparticles, the Pt-doped PEM exhibits negligible oxygen permeation in the anode/cathode pressure difference from −100 kPa to 100 kPa and demonstrates excellent oxygen consumption ability.
A series of different α-Fe2O3 nanoparticles composites containing different amounts of graphene coatings have been successfully prepared using a simple electrostatic self-assembly (ESA) method. The structure and electrochemical properties of these α-Fe2O3@graphene composites have been investigated. The α-Fe2O3 nanoparticles composite containing 40 wt% graphene coating exhibits the highest specific capacity (385 mAh g−1) under 1000 mA g−1, resulting in superior cycle stability with no downward trend after 500 cycles. These results demonstrate that graphene coatings can be used to enhance the electrochemical properties and morphological stability of α-Fe2O3 nanoparticles as anodic materials for high performance lithium-ion batteries (LIBs). The low-energy self-assembly method employed in the paper has good potential for the broad-scale preparation of other graphene-modified materials because of its simplicity and the relatively low temperature conditions.
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