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Exploring advanced electrocatalysts for the sluggish oxygen reduction reaction is extremely important for fuel cell commercialization but still remains a great challenge, especially the durability issue that gains increasing attention. Herein, we demonstrate an extremely durable catalyst prototype that combines structurally ordered intermetallic nanoparticles (NPs) with mesoporous carbon. With ZIF-8 derived mesoporous carbon supported Pt3Co intermetallic NPs (Pt3Co/DMC-F) as an example, we illustrate its synthetic details, electrocatalytic performance and durability enhancement mechanism. The Pt3Co/DMC-F catalyst exhibited significant enhancement in activity and durability. More importantly, its extraordinary performance was observed/verified in a H2/air PEM single cell test. The confinement of mesoporous carbon not only efficiently controls the particle size of Pt3Co and hampers their aggregation during thermal annealing and electrochemical reactions, but also significantly suppresses detachment. Beyond offering an advanced electrocatalyst, this study provides a solution to the durability issue of cathodes that has prevented practical application of proton exchange membrane fuel cells.

Highlights All the important single-atom catalysts (SACs) synthetic strategies, such as wet-chemistry method, atomic layer deposition, metal–organic framework-derived method, electrodeposition, high-temperature atom trapping from bulk particles, and vacancies/defects immobilized strategy, have been summarized and discussed in detail.Various metal-based (especially Pt, Pd, Ru, Fe, Co, Ni, Mo, W, V) SACs in electrocatalytic hydrogen evolution reaction (HER) have been systematically reviewed.The current key challenges in SACs for electrochemical HER are pointed out, and some potential strategies/perspectives are proposed., Hydrogen, a renewable and outstanding energy carrier with zero carbon dioxide emission, is regarded as the best alternative to fossil fuels. The most preferred route to large-scale production of hydrogen is by water electrolysis from the intermittent sources (e.g., wind, solar, hydro, and tidal energy). However, the efficiency of water electrolysis is very much dependent on the activity of electrocatalysts. Thus, designing high-effective, stable, and cheap materials for hydrogen evolution reaction (HER) could have a substantial impact on renewable energy technologies. Recently, single-atom catalysts (SACs) have emerged as a new frontier in catalysis science, because SACs have maximum atom-utilization efficiency and excellent catalytic reaction activity. Various synthesis methods and analytical techniques have been adopted to prepare and characterize these SACs. In this review, we discuss recent progress on SACs synthesis, characterization methods, and their catalytic applications. Particularly, we highlight their unique electrochemical characteristics toward HER. Finally, the current key challenges in SACs for HER are pointed out and some potential directions are proposed as well.

Highly active catalyst for the hydrogen oxidation/evolution reactions (HOR and HER) plays an essential role for the water-to-hydrogen reversible conversion. Currently, increasing attention has been concentrated on developing low-cost, high-activity, and long-life catalytic materials, especially for acid media due to the promise of proton exchange membrane (PEM)-based electrolyzers and polymer electrolyte fuel cells. Although non-precious-metal phosphide (NPMP) catalysts have been widely researched, their electrocatalytic activity toward HER is still not satisfactory compared to that of Pt catalysts. Herein, a series of precious-metal phosphides (PMPs) supported on graphene (rGO), including IrP2-rGO, Rh2P-rGO, RuP-rGO, and Pd3P-rGO, are prepared by a simple, facile, eco-friendly, and scalable approach. As an example, the resultant IrP2-rGO displays better HER electrocatalytic performance and longer durability than the benchmark materials of commercial Pt/C under acidic, neutral, and basic electrolytes. To attain a current density of 10 mA cm-2, IrP2-rGO shows overpotentials of 8, 51, and 13 mV in 0.5 M dilute sulfuric acid, 1.0 M phosphate-buffered saline (PBS), and 1.0 M potassium hydroxide solutions, respectively. Additionally, IrP2-rGO also exhibits exceptional HOR performance in the 0.1 M HClO4 medium. Therefore, this work offers a vital addition to the development of a number of PMPs with excellent activity toward HOR and HER.

Preparing Pt–based one-dimensional (1D) ultrafine nanowires with abundant structural defects/grain boundaries and exploring their novel applications have attracted great interest in real-world applications. Here we introduce an environmentally friendly, facile aqueous solution approach to directly prepare a series of sub-3.0 nm PtRu ultrafine wavy nanowires. Characterizations show that the PtRu nanowires are alloy polycrystalline structures with abundant structural defects/grain boundaries. We first introduce the as-synthesized PtRu nanowires into electrochemical biosensors for the detection of DA and find that the Pt7Ru3 nanowires exhibit excellent electrocatalytic activity to DA with fast response, ultralow limit of detection, and excellent selectivity at a potential of 0.3 V in 0.1 M phosphate buffered solution (pH 7.2). This study shows an effective approach to the development of ultrafine PtRu nanowires as electrocatalysts for electrochemical nonenzymatic dopamine biosensors.

Recently, the synthesis of ultrathin nanostructures has attracted increasing interest because of their unique structure and properties. In this work, we report the synthesis of sub-2.0-nm Ru and composition-tunable RuPt nanowire networks using an environmentally friendly aqueous method. The structures were characterized using transmission electron microscopy (TEM), high-resolution TEM, X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) spectroscopy. Moreover, the combined utilization of sodium n-dodecyl sulfate and potassium fluoride was determined to play a key role in the formation of these ultrathin nanostructures. The electrocatalytic properties of the sub-2.0-nm RuPt nanowire networks were investigated for methanol oxidation in an acidic medium. The nanostructures displayed composition-dependent properties, and compared with commercial Ru50Pt50/C, the as-synthesized Ru56Pt44 ultrathin nanowire network exhibited enhanced stability.

The main challenges to the direct methanol fuel cells are the activity and durability of electrocatalysts. To alleviate such issues, a recently proposed strategy introduces an exotic element to form Pt-based alloy nanostructures. This study reports a green route to prepare porous flowerlike Pt72Ru28 nanoalloys assembled with sub-4.0 nm particles. The peak current density and mass activity on these as-synthesized porous flowerlike Pt72Ru28 nanoalloys can be increased to 10.98 mA cm−2 and 1.70 A mg−1 Pt for methanol oxidation in acidic medium. They are respectively 4.19/3.54, 4.27/5.0, and 5.74/1.73 times those on the commercial Pt black, Pt50Ru50 black, and Ru50Pt50/C. These porous flowerlike Pt72Ru28 nanoalloys have a much higher long-term durability than commercial Pt black, Pt50Ru50 black, and Ru50Pt50/C. More significantly, the porous Pt72Ru28 bimetallic nanoalloys have long-term solvent durability after immersion in water for 16 months. The peak current density and mass activity on porous Pt72Ru28 nanoalloys are still 7.76 mA cm−2 and 1.2 A mg−1 Pt. These experimental results show an effective approach to the development of PtRu nanoalloys as electrocatalysts with substantially enhanced activity and durability for direct methanol fuel cells.