The vigorous development of efficient platinum group metal-free catalysts is considerably important to facilitate the universal application of proton exchange membrane fuel cells. Although nitrogen-coordinated atomic iron intercalated in carbon matrix (Fe-N-C) catalysts exhibit promising catalytic activity, the performance in fuel cells, especially the short lifetime, remains an obstacle. Herein, a highly-active Fe-N-C catalyst with a power density of >1 w cm-2 and prolonged discharge stability with a current density of 357 mA cm-2 after 40 h of constant voltage discharge at 0.7 V in H2 -O2 fuel cells using a controllable and efficient N-C coating strategy is developed. It is clarified that a thicker N-C coating may be more favorable to enhance the stability of Fe-N-C catalysts at the expense of their catalytic activity. The stability enhancement mechanism of the N-C coating strategy is proven to be the synergistic effect of reduced carbon corrosion and iron loss. It is believed that these findings can contribute to the development of Fe-N-C catalysts with high activity and long lifetimes.
Hydrogen has the potential to be one of the solutions that can address environmental pollution and greenhouse emissions from traditional fossil fuels. However, high costs hinder its large-scale commercialization, particularly for enabling devices such as proton exchange membrane fuel cells (PEMFCs). The precious metal Pt is indispensable in boosting the oxygen reduction reaction (ORR) in cathode electrocatalysts from the most crucial component, i.e., the membrane electrode assembly (MEA). MEAs account for a considerable amount of the entire cost of PEMFCs. To address these bottlenecks, researchers either increase Pt utilization efficiency or produce MEAs with enhanced performance but less Pt. Only a few reviews that explain the approaches are available. This review summarizes advances in designing nanocatalysts and optimizing the catalyst layer structure to achieve low-Pt loading MEAs. Different strategies and their corresponding effectiveness, e.g., performance in half-cells or MEA, are summarized and compared. Finally, future directions are discussed and proposed, aiming at affordable, highly active, and durable PEMFCs.
The development of excellent activity and durability catalysts for the oxygen reduction reaction (ORR) is essential for the commercialization of proton exchange membrane fuel cells (PEMFCs). Reducing the size of catalyst particles can provide more reaction sites to mitigate the performance degradation caused by reduced platinum loading. However, at the same time, it makes the particles more prone to agglomeration and exfoliation, leading to a rapid reduction in catalyst activity. Here, we present the design of a composite support (TiO2/CNT) with a porous TiO2 film that immobilizes PtCo nanoparticles (NPs) loaded on the support while protecting the carbon nanotubes inside. The particle size of PtCo NPs was only 1.99 nm (determined by transmission electron microscopy), but the nanocatalyst (PtCo/TiO2/CNT) maintained high catalytic performance and stability on account of the strong metal support interaction (SMSI). PtCo/TiO2/CNT exhibited a high mass activity (MA, 0.476 A mgPt-1) and was found to have MA retention rates of 91.7 and 88.8% in durability tests performed at 0.6-1.0 V and 1.0-1.5 V, respectively.
Hydrogen produced using renewable electricity is considered the key to achieving a low-carbon energy economy. However, the large-scale application of electrochemical water splitting for hydrogen evolution currently requires expensive platinum-based catalysts. Therefore, it is important to develop efficient and stable catalysts based on the rich reserves of transition metals as alternatives. In this study, the authors prepare a carbon-nanotube material enriched with atomically dispersed CoN sites having uniquely low coordination numbers via the simple mixing, pyrolysis, and leaching of inexpensive precursors. These atomically dispersed low-coordinate CoN sites provide an overpotential of only 82 mV at 10 mA cm-2 for the hydrogen evolution reaction (HER) under challenging acidic conditions and show excellent durability in accelerated stability tests. Theoretical simulations also confirm that these unique, low-coordinate CoN2 sites have lower energy barriers in catalyzing the HER than Fe/NiN2 sites and commonly reported CoN3 /N4 sites. Therefore, the method provides a new concept for the design of single-atom catalytic sites with low coordination numbers. It also serves to reduce the cost of hydrogen production in the future owing to the high catalytic activity, low cost, and scalable production process.
Carbon-supported Pt-Co (Pt-Co/C) nanoparticles with a high Pt loading are regarded as promising cathode catalysts for practical applications of proton exchange membrane fuel cells (PEMFCs). Unfortunately, with high loading, it is difficult to improve the catalytic durability while maintaining the particle size between 2 and 5 nm to ensure the initial catalytic activity. Thus, it is of great significance to prepare high-loading Pt-Co/C catalysts with enhanced activity and durability. Herein, we proposed an efficient way to prepare high-Pt-loading (>50 wt %) Pt-Co/C catalysts without using any further surfactants. Furthermore, due to the one-step selective acid etching and surface Au modification, the as-prepared catalysts only need to undergo thermal treatment at as low as 150 °C to achieve a surface structure rich of Pt and Au. The average particle size of the as-prepared Au-Pt-Co/C-0.015 is 3.42 nm, and the Pt loading of it is up to 50.2 wt %. The atomic ratio of Pt, Co, and Au is 94:5:1. The mass activity (MA) is nearly 1.9 times that of Pt/C (60 wt %, JM) and the specific activity is also improved. The MA loss after the 30,000-cycle accelerated degradation test (ADT) is only 9.4%. The remarkable durability is mainly due to the surface Au modification, which can restrict the dissolution of Pt and Co. This research provides an effective synthesis strategy to prepare high-loading carbon-supported Pt-based catalysts beneficial to practical PEMFC applications.
Heterogeneous ternary Pt-Ni-Au nanowires (NWs) with randomly distributed Pt-Ni and Pt-Au micro phases were successfully synthesized following an oriented attachment mechanism. The as-prepared NWs exhibit enhanced activity and durability in both a rotating disk electrode (RDE) and single-cell, originating from the one dimensional (1D) heterogeneous structure.
