Coupling Single-Atom Sites and Ordered Intermetallic PtM Nanoparticles for Efficient Catalysis in Fuel Cells

The design of an efficient catalytic system with low Pt loading and excellent stability for the acidic oxygen reduction reaction is still a challenge for the extensive application of proton-exchange membrane fuel cells. Here, a gas-phase ordered alloying strategy is proposed to construct an effective synergistic catalytic system that blends PtM intermetallic compounds (PtM IMC, M = Fe, Cu, and Ni) and dense isolated transition metal sites (M-N4 ) on nitrogen-doped carbon (NC). This strategy enables Pt nanoparticles and defects on the NC support to timely trap flowing metal salt without partial aggregation, which is attributed to the good diffusivity of gaseous transition metal salts with low boiling points. In particular, the resulting Pt1 Fe1 IMC cooperating with Fe-N4 sites achieves cooperative oxygen reduction with a half-wave potential up to 0.94 V and leads to a high mass activity of 0.51 A  mgPt -1 and only 23.5% decay after 30 k cycles, both of which exceed DOE 2025 targets. This strategy provides a method for reducing Pt loading in fuel cells by integrating Pt-based intermetallics and single transition metal sites to produce an efficient synergistic catalytic system.

Alloying Matters for Ordering: Synthesis of Highly Ordered PtCo Intermetallic Catalysts for Fuel Cells

Porous carbon-supported atomically ordered intermetallic compounds (IMCs) are promising electrocatalysts in boosting oxygen reduction reaction (ORR) for fuel cell applications. However, the formation mechanism of IMC structures under high temperatures is poorly understood, which hampers the synthesis of highly ordered IMC catalysts with promoted ORR performance. Here, we employ high-temperature X-ray diffraction and energy-dispersive spectroscopic elemental mapping techniques to study the formation process of IMCs, by taking PtCo for example, in an industry-relevant impregnation synthesis. We find that high-temperature annealing is crucial in promoting the formation of alloy particles with a stoichiometric Co/Pt ratio, which in turn is the precondition for transforming the disordered alloys to ordered intermetallic structures at a relatively low temperature. Based on the findings, we accordingly synthesize highly ordered L1₀-type PtCo catalysts with a remarkable ORR performance in fuel cells.

Si Doping Enables Activity and Stability Enhancement on Atomically Dispersed Fe-Nx /C Electrocatalysts for Oxygen Reduction in Acid

Fe-N-C represents the most promising non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR) in fuel cells, but often suffers from poor stability in acid due to the dissolution of metal sites and the poor oxidation resistance of carbon substrates. In this work, silicon-doped iron-nitrogen-carbon (Si/Fe-N-C) catalysts were developed by in situ silicon doping and metal-polymer coordination. It was found that Si doping could not only promote the density of Fe-N_x /C active sites but also elevated the content of graphitic carbon through catalytic graphitization. The best-performing Si/Fe-N-C exhibited a half-wave potential of 0.817 V vs. reversible hydrogen electrode in 0.5 m H₂ SO₄ , outperforming that of undoped Fe-N-C and most of the reported Fe-N-C catalysts. It also exhibited significantly enhanced stability at elevated temperature (≥60 °C). This work provides a new way to develop non-precious metal ORR catalysts with improved activity and stability in acidic media.

Phase diagrams guide synthesis of highly ordered intermetallic electrocatalysts: separating alloying and ordering stages

Supported platinum intermetallic compound catalysts have attracted considerable attention owing to their remarkable activities and durability for the oxygen reduction reaction in proton-exchange membrane fuel cells. However, the synthesis of highly ordered intermetallic compound catalysts remains a challenge owing to the limited understanding of their formation mechanism under high-temperature conditions. In this study, we perform in-situ high-temperature X-ray diffraction studies to investigate the structural evolution in the impregnation synthesis of carbon-supported intermetallic catalysts. We identify the phase-transition-temperature (TPT)-dependent evolution process that involve concurrent (for alloys with high TPT) or separate (for alloys with low TPT) alloying/ordering stages. Accordingly, we realize the synthesis of highly ordered intermetallic catalysts by adopting a separate annealing protocol with a high-temperature alloying stage and a low-temperature ordering stage, which display a high mass activity of 0.96 A mgPt-1 at 0.9 V in H2-O2 fuel cells and a remarkable durability.

Small molecule-assisted synthesis of carbon supported platinum intermetallic fuel cell catalysts

Supported ordered intermetallic compounds exhibit superior catalytic performance over their disordered alloy counterparts in diverse reactions. But the synthesis of intermetallic compounds catalysts often requires high-temperature annealing that leads to the sintering of metals into larger crystallites. Herein, we report a small molecule-assisted impregnation approach to realize the general synthesis of a family of intermetallic catalysts, consisting of 18 binary platinum intermetallic compounds supported on carbon blacks. The molecular additives containing heteroatoms (that is, O, N, or S) can be coordinated with platinum in impregnation and thermally converted into heteroatom-doped graphene layers in high-temperature annealing, which significantly suppress alloy sintering and insure the formation of small-sized intermetallic catalysts. The prepared optimal PtCo intermetallics as cathodic oxygen-reduction catalysts exhibit a high mass activity of 1.08 A mg_Pt^-1 at 0.9 V in H₂-O₂ fuel cells and a rated power density of 1.17 W cm^-2 in H₂-air fuel cells.

Magnetic Nanoparticles: Synthesis, Anisotropy, and Applications

Anisotropy is an important and widely present characteristic of materials that provides desired direction-dependent properties. In particular, the introduction of anisotropy into magnetic nanoparticles (MNPs) has become an effective method to obtain new characteristics and functions that are critical for many applications. In this review, we first discuss anisotropy-dependent ferromagnetic properties, ranging from intrinsic magnetocrystalline anisotropy to extrinsic shape and surface anisotropy, and their effects on the magnetic properties. We further summarize the syntheses of monodisperse MNPs with the desired control over the NP dimensions, shapes, compositions, and structures. These controlled syntheses of MNPs allow their magnetism to be finely tuned for many applications. We discuss the potential applications of these MNPs in biomedicine, magnetic recording, magnetotransport, permanent magnets, and catalysis.

Ordered PtFeIr Intermetallic Nanowires Prepared through a Silica-Protection Strategy for the Oxygen Reduction Reaction

Developing efficient and stable Pt-based oxygen reduction reaction (ORR) catalysts is a way to promote the large-scale application of fuel cells. Pt-based alloy nanowires are promising ORR catalysts, but their application is hampered by activity loss caused by structural destruction during long-term cycling. Herein, the preparation of ordered PtFeIr intermetallic nanowire catalysts with an average diameter of 2.6 nm and face-centered tetragonal structure (fct-PtFeIr/C) is reported. A silica-protected strategy prevents the deformation of PtFeIr nanowires during the phase transition at high temperature. The as-prepared fct-PtFeIr/C exhibited superior mass activity for ORR (2.03 A mg_Pt ^-1 ) than disordered PtFeIr nanowires with face-centered cubic structure (1.11 A mg_Pt ^-1 ) and commercial Pt/C (0.21 A mg_Pt ^-1 ). Importantly, the structure and electrochemical performance of fct-PtFeIr/C were maintained after stability tests, showing the advantages of the ordered structure.

Crystal Orientation in Pt-Based Alloys Induced by W(CO)6: Driving Oxygen Electroreduction Catalysis

Integrating crystal orientation as well as structural and compositional advantages into one catalyst might be a promising strategy for high-performance Pt-based catalysts for proton-exchange membrane fuel cells. Herein, by introducing W(CO)₆ as a structure-oriented template, Pt-based alloys with a well-defined crystal orientation along the (111) facet were obtained. The oxygen reduction reaction mass and specific activities of the crystal-facet-tuned alloys reach a new level. Moreover, the outstanding durability stems from the combination of their exposed crystal facets and incorporated W. The density functional theory calculation results reveal that the formation of the preferred (111) alloys can be attributed to the lower free energy of (111) facets and the weaker adsorption of CO released by W(CO)₆. This proposed synthesis strategy of using transition-metal carbonyl compounds as additives to synthesize alloys with strong crystal orientation may open a door to the design of various alloy catalysts with ultrahigh activity.

Multifunctional Metal Phosphides as Superior Host Materials for Advanced Lithium-Sulfur Batteries

For the past few years, a new generation of energy storage systems with large theoretical specific capacity has been urgently needed because of the rapid development of society. Lithium-sulfur (Li-S) batteries are regarded as one of the most promising candidates for novel battery systems, since their resurgence at the end of the 20th century Li-S batteries have attracted ever more attention, attributed to their notably high theoretical energy density of 2600 W h kg^-1 , which is almost five times larger than that of commercial lithium-ion batteries (LIBs). One of the determining factors in Li-S batteries is how to design/prepare the sulfur cathode. For the sulfur host, the major technical challenge is avoiding the shuttling effect that is caused by soluble polysulfides during the reaction. In past decades, though the sulfur cathode has developed greatly, there are still some enormous challenges to be conquered, such as low utilization of S, rapid decay of capacity, and poor cycle life. This article spotlights the recent progress and foremost findings in improving the performance of Li-S batteries by employing multifunctional metal phosphides as host materials. The current state of development of the sulfur electrode of Li-S batteries is summarized by emphasizing the relationship between the essential properties of metal phosphide-based hybrid nanomaterials, the chemical reaction with lithium polysulfides and the latter's influence on electrochemical performance. Finally, trends in the development and practical application of Li-S batteries are also pointed out.

High Valence M-Incorporated PdCu Nanoparticles (M = Ir, Rh, Ru) for Water Electrolysis in Alkaline Solution

The high-valence metal catalysts show extraordinary talent in various electrochemical reactions. However, there is no facile method to synthesize high-valence noble metal-based materials. Herein, we synthesized the different high valence noble metal M-incorporated PdCu nanoparticles (M = Ir, Ru, Rh) by the assistant of Fe³⁺ and exhibit excellent performance for water electrolysis. In 0.1 M KOH, the OER and HER mass activities of Ir₁₆-PdCu/C were 50.5 and 16.5 times as much as PdCu/C, and achieved a current density of 10 mA cm^-2 at 1.63 V when worked for overall water splitting. DFT calculation revealed that the incorporating of high valence Ir could optimize the binding energy of the intermediate products, and promote the evolution of oxygen and hydrogen. Ex situ XPS shows that the huge amount of oxidized Ir (V) formed in OER could promote the formation of O-O bonds.

Constructing Co-N-C Catalyst via a Double Crosslinking Hydrogel Strategy for Enhanced Oxygen Reduction Catalysis in Fuel Cells

Exploiting platinum-group-metal (PGM)-free electrocatalysts with remarkable activity and stability toward oxygen reduction reaction (ORR) is of significant importance to the large-scale commercialization of proton exchange membrane fuel cells (PEMFCs). Here, a high-performance and anti-Fenton reaction cobalt-nitrogen-carbon (Co-N-C) catalyst is reported via employing double crosslinking (DC) hydrogel strategy, which consists of the chemical crosslinking between acrylic acid (AA) and acrylamide (AM) copolymerization and metal coordinated crosslinking between Co²⁺ and P(AA-AM) copolymer. The resultant DC hydrogel can benefit the Co²⁺ dispersion via chelated Co-N/O bonds and relieve metal agglomeration during the subsequent pyrolysis, resulting in the atomically dispersed Co-Nx/C active sites. By optimizing the ratio of AA/AM, the optimal P(AA-AM)(5-1)-Co-N catalyst exhibits a high content of nitrogen doping (12.36 at%) and specific surface area (1397 m² g^-1 ), significantly larger than that of the PAA-Co-N catalyst (10.59 at%/746 m² g^-1 ) derived from single crosslinking (SC) hydrogel. The electrochemical measurements reveal that P(AA-AM)(5-1)-Co-N possesses enhanced ORR activity (half-wave potential (E_1/2 ) ≈0.820 V versus the reversible hydrogen electrode (RHE)) and stability (≈4 mV shift in E_1/2 after 5000 potential cycles in 0.5 m H₂ SO₄ at 60 ºC) relative to PAA-Co-N, which is higher than most Co-N-C catalysts reported so far.

Ultimate Corrosion to Pt-Cu Electrocatalysts for Enhancing Methanol Oxidation Activity and Stability in Acidic Media

Alloying platinum (Pt) with transition metals (M), as an established class of electrocatalysts, reduces the use of Pt and improves the electrocatalytic performance. However, the stability of transition metals in nanostructured platinum alloys is a fundamental and practical problem in electrocatalysis, due to leaching of transition metals under acidic operating condition. Here, a corrosion method has been developed for a Pt-Cu electrocatalyst with high activity (6.6 times that of commercial Pt/C) and excellent stability for the methanol oxidation reaction (MOR) under acidic operating conditions. The mechanism of formation has been studied, and possible mesostructured re-formation and atomic re-organization have been proposed. This work offers an effective strategy for the facile synthesis of a highly acid-stable PtM alloying and opens a door to high-performance design for electrocatalysts.

Template-Directed Rapid Synthesis of Pd-Based Ultrathin Porous Intermetallic Nanosheets for Efficient Oxygen Reduction

Atomically ordered intermetallic nanoparticles exhibit improved catalytic activity and durability relative to random alloy counterparts. However, conventional methods with time-consuming and high-temperature syntheses only have rudimentary capability in controlling the structure of intermetallic nanoparticles, hindering advances of intermetallic nanocatalysts. We report a template-directed strategy for rapid synthesis of Pd-based (PdM, M=Pb, Sn and Cd) ultrathin porous intermetallic nanosheets (UPINs) with tunable sizes. This strategy uses preformed seeds, which act as the template to control the deposition of foreign atoms and the subsequent interatomic diffusion. Using the oxygen reduction reaction (ORR) as a model reaction, the as-synthesized Pd₃ Pb UPINs exhibit superior activity, durability, and methanol tolerance. The favored geometrical structure and interatomic interaction between Pd and Pb in Pd₃ Pb UPINs are concluded to account for the enhanced ORR performance.

Three-step method with self-sacrificial Co to prepare a uniform 5 nm-scale Pt catalyst for the oxygen reduction reaction

Simple and rapid preparation method for a highly dispersed and small-sized CoPt catalyst.