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

Regulating orbital interaction to construct quasi-covalent bond networks in Pt intermetallic alloys for high-performance fuel cells

The long-standing challenges facing Pt-based alloy catalysts in oxygen reduction reactions (ORRs) are rapid oxidation and loss of transition metal/Pt in proton exchange membrane fuel cells (PEMFCs). In this work, we report a concept of "covalentization" in intermetallic L10-PtMM' (M = Fe, Co, Ni and M' = one of the 4th-period elements (from Ti to Ge)) alloys to enhance their electrochemical stability. Specifically, the formation of a quasi-covalent bond network in L10-PtMM' due to the less occupied antibonding states induced by high d-band positions of M' elements (e.g., Ti, V, Cr) enhances atomic bond order and strength, diminishing Co anodic dissolution via strengthened Pt/Co-M' bonds and reducing Co cathodic corrosion by inhibiting Pt oxidation through an electron buffering effect. The developed L10-PtCoCr/C catalysts show a high mass activity (MA = 1.27 A mgPt-1) and rated power (16.5 W mgPt-1) in PEMFCs at a low total Pt loading of 0.075 mgPt cm-2. The catalysts also exhibit high electrochemical stability with ~3% and 5% loss of MA and rated power after 30,000 accelerated durability testing cycles and projects a lifetime of about 42,000 hours.

Toward Hydrogen Mobility: Challenges and Strategies in Electrocatalyst Durability for Long-Term PEMFC Operation

Proton exchange membrane fuel cells (PEMFCs) are emerging as a key technology in the transition to hydrogen-based energy systems, particularly for heavy-duty vehicles (HDVs) that face operational challenges, such as frequent startup-shutdown cycles and fuel starvation. However, the widespread adoption of PEMFCs has been limited by their durability and long-term performance issues, which are crucial for heavy-duty applications. This Perspective focuses on recent advancements in PEMFC catalysts and supports, with an emphasis on strategies to enhance their durability. We introduce Pt-based intermetallic catalysts, including Pt transition metal (TM) alloys, which offer improved stability and activity through regular atomic arrangements and strengthened metal-support interactions. Hybrid catalysts combining Pt with M-N-C (M = Fe, Co) have shown promise in boosting performance by enhancing the catalytic activity while reducing the platinum content. Moreover, stringent conditions must be met to meet the HDV requirements. Consequently, alternative support materials, such as metal oxides and graphitized carbons, have been introduced to enhance both the corrosion resistance and the electrical conductivity, thereby addressing the limitations of conventional carbon supports. Structural innovations and material advancements are essential for optimizing catalysts and supports to achieve long-term PEMFC performance. This Perspective provides a comprehensive overview of key developments in catalyst and support design, offering insights into current challenges and future directions for achieving durable and cost-effective PEMFCs.

Phase Changes of Multielemental Alloy Nanoparticles at Elevated Temperatures

Multielemental alloy (MEA) nanomaterials, such as medium and high entropy alloys, display promising catalytic performance in a range of chemical reactions due to their multicomponent structural configurations. These complex structural and chemical arrangements can be influenced by several factors, such as mechanical stress, irradiation, and high temperatures, which impact the performance of MEAs in various applications. Here, we investigated the effect of high temperatures on MEA nanoparticles composed of noble and transition metals (quaternary PtPdFeCo) at the atomic scale and found the material undergoes a series of phase transitions between solid solution and intermetallic phases at elevated temperatures ranging from room temperature to 1073 K. In contrast, the binary PtFe nanoalloy displays a one-way solid solution to intermetallic transition at these temperatures. Our findings, rationalized by density functional theory (DFT) studies, demonstrate how the varied migration energies of elements govern the solid solution to intermetallic transition and how differences in the bonding energies of elemental pairs influence the Gibbs free energy change (ΔG), which dictates the intermetallic to solid-solution transition. Overall, this work provides better guidance in the design, development, and usage of nano-MEAs for high-temperature-based applications.

Tuning catalyst-support interactions enable steering of electrochemical CO2 reduction pathways

Tuning of catalyst-support interactions potentially offers a powerful means to control activity. However, rational design of the catalyst support is challenged by a lack of clear property-activity relationships. Here, we uncover how the electronegativity of a support influences reaction pathways in electrochemical CO2 reduction. This was achieved by creating a model system consisting of Cu nanoparticles hosted on a series of carbon supports, each with a different heteroatom dopant of varying electronegativity. Notably, we discovered that dopants with high electronegativity reduce the electron density on Cu and induce a selectivity shift toward multicarbon (C2+) products. With this design principle, we built a composite Cu and F-doped carbon catalyst that achieves a C2+ Faradaic efficiency of 82.5% at 400 mA cm-2, with stable performance for 44 hours. Using simulated flue gas, the catalyst attains a C2+ FE of 27.3%, which is a factor of 5.3 times higher than a reference Cu catalyst.

Core/Shell-Structured Carbon Support Boosting Fuel Cell Durability

To enhance the lifetime of proton exchange membrane fuel cells, developing highly durable platinum-based cathode catalysts is essential. While two degradation pathways for the cathode catalyst-carbon corrosion and electrocatalyst (platinum nanoparticles) coarsening-have been identified, current approaches to enhance its durability are limited to addressing individual degradation pathways. Herein, the study develops a core/shell-structured carbon support that is designed to afford cathode catalysts capable of simultaneously inhibiting carbon corrosion and electrocatalyst coarsening. The core/shell structure is distinguished by its bifunctional nature: the core is made of highly graphitized carbon tailored to build a robust carbon skeleton, and the shell comprises heteroatom-doped amorphous carbon engineered to prevent electrocatalyst coarsening by chemical/physical anchoring of platinum nanoparticles. Thanks to this elaborate design, the catalyst surpasses the durability targets for carbon supports and electrocatalysts set by the U.S. Department of Energy, as supported by the achieved durability metrics after the square-wave/triangle-wave accelerated stress tests: electrochemical surface area loss at 13%/3%, mass activity loss at 27%/17%, and voltage loss of 29 mV (at 0.8 A cm- 2)/4 mV (at 1.5 A cm- 2).

Nanoconfinement-guided in situ co-deposition of single-atom cascade nanozymes combined with injectable sodium alginate hydrogels for enhanced diabetic wound healing

Treating diabetic wounds remains a major clinical challenge due to high glucose levels, bacterial infection, insufficient oxygen supply, and oxidative stress. Herein, guided by the nanoconfinement effect, single-atom Au/Pt nanoparticles (NPs) are in situ co-deposited in mesoporous metal-organic frameworks (MOF), while synergizing with DNA aptamer (DNA-Apt) with bacterial targeting functionality and an excellent biocompatible sodium alginate hydrogel (Gel), to prepare a multifunctional bimetallic cascade nanozyme combine hydrogels (Au-Pt@ZIF-8/Apt@gel). ZIF-8 degrades in the acidic environment of a wound infection, releasing Zn2+ and Au/Pt nanoparticles, which produce reactive oxygen species (ROS) under the catalysis of glucose to inactivate bacteria. Notably, Au-Pt@ZIF-8 nanozymes depositing Au/Pt nanoparticles exhibit a nanoconfinement effect that enhances the cascade nanozymes activity, which is about 2-3 times higher than that of monoconfined or nonconfined nanozyme. In addition, in vitro bacteriostatic tests show the nanozymes have broad-spectrum antimicrobial effects, with better inhibition of Gram-positive than negative bacteria. In vivo experiments indicate that Au-Pt@ZIF-8/Apt@gel has satisfactory antibacterial efficacy in both normal and diabetic mice, as well as optimal skin wound healing ability and significant reduction of inflammation in infected wounds. Consequently, the proposed system holds great potential for developing integrated nanoplatforms for on-demand treatment of bacterial-infected diabetic wounds.

Pt catalyst protected by graphene nanopockets enables lifetimes of over 200,000 h for heavy-duty fuel cell applications

Proton exchange membrane fuel cells feature considerable scalability advantages over lithium-ion batteries for heavy-duty-vehicle applications. The different driving behaviours and operating conditions of heavy-duty vehicles pose challenging requirements, particularly on fuel cell lifetime and efficiency. Here we report the design of a graphene-nanopocket-protected, pore-confined and electrochemically accessible Pt nanocatalyst supported on Ketjenblack carbon for heavy-duty-vehicle applications. The membrane electrode assembly made from these nanocatalysts delivers an initial mass activity of 0.74 A mgPt-1 and a high rated power density of 1.08 W cm-2, as well as extraordinary long-term durability with an ultrasmall rated power loss of 1.1% after 90,000 aggressive square-wave cycles. The remarkable activity and durability throughout the operation conditions promise an unprecedentedly long fuel cell lifetime of over 200,000 h and high peak efficiency of 71.9%, making it highly attractive for emerging heavy-duty fuel cell applications.

A Universal Solid-Phase Synthetic Strategy for Ultrafine Intermetallic Libraries Confined in Ordered Mesoporous Carbon

Ordered intermetallic nanocatalysts supported on high-surface-area skeletons are of great importance in catalysis and have disclosed notable catalytic activity and stability that are remarkably better than their random alloy counterparts. Ultrafine intermetallic nanocatalysts are synthetically challenging, especially for universal and scaled-up synthesis, because of inevitable sintering and phase separation under high temperatures that promote atomic alloying and ordering. Herein, a universal solid-phase and scaled-up method is reported for synthesizing ultrafine intermetallic nanocatalysts with uniform size distributions and wide compositional spaces confined in ordered mesoporous carbon (OMC) supports, where the strong physical confinement and chemical interaction between metals and sulfur/mesoporous templates remarkably suppress the high-temperature sintering and phase separation even up to 1000 °C. Libraries of intermetallic nanocatalysts are successfully synthesized including 52 combinations of host platinum/palladium/rhodium with 15 guest elements confined in 4 OMC supports. Taking oxygen reduction and hydrogen evolution reactions as examples, the intermetallic PtFe nanocatalysts hold remarkable performance, whose activities reach up to ten times higher than commercial Pt/C and also are comparable to the best electrocatalysts reported recently. This feasible synthetic strategy offers an intermetallic library spanning from binary to senary materials for industrial synthesis and applications.

Coordination-in-pipe engineering of Pt-based intermetallic compounds with nanometer to angstrom precision

The simultaneous regulation of particle size, surface coordinated environment and composition for Pt-based intermetallic compound (Pt-IMC) nanoparticles to manipulate their reactivity for energy storage is of great importance. Herein, we report a general synthetic method for Pt-IMCs using SBA-15 for coordination-in-pipe engineering. The particle size can be regulated to 3-9 nm by carrying out the coordination in pipes with different diameters and the coordination number of the interface metal atoms can be adjusted by altering the N source. Moreover, this strategy can also be expanded to the synthesis of Pt-IMCs with the majority of fourth period transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn). The Pt3Co IMC using 1,10-phenanthroline as the nitrogen source (Pt3Co@CN) shows the highest catalytic performance in the methanol oxidation reaction (MOR; 2.19 A mgPt -1) among the investigated nitrogen sources. The high chemical states of surface Pt and Co, affected by the nitrogen coordination number at the angstrom scale, facilitate electron accumulation on active sites, reduce the activation energy of the rate-determining step and enhance the catalytic performance of Pt-IMCs in the MOR.

The steric hindrance effect of Co porphyrins promoting two-electron oxygen reduction reaction selectivity

A new Co 5,10,15,20-tetrakis(2',6'-dipivaloyloxyphenyl)porphyrin (1) with eight ester groups in all ortho and ortho' positions of phenyl groups was designed, which displayed significantly improved 2e oxygen reduction reaction (ORR) selectivity compared with a 5,10,15,20-tetrakis(para-dipivaloyloxyphenyl) porphyrin (2) without large steric groups. This work is significant to reveal the steric hindrance effect of metal porphyrins on electrocatalytic ORR selectivity.

In Situ Construction of a Porous Nanotrap: A Pathway for Catalyst Performance Optimization

Supported noble metal catalysts have a high catalytic activity and selectivity. However, fast surface reconstruction and sintering of noble metal particles during a high-temperature reaction process pose a major challenge to the stability of the catalysts. In this study, sinter-resistant supported noble metal catalysts were prepared by constructing an oxide nanotrap. Pt/Al2O3 was used as a research paradigm. Dopamine was applied as a structure-directing agent and pore-forming agent to form a porous CeO2 overlay on the surface of Pt/Al2O3 and encapsulate Pt nanoparticles. Due to the confinement of CeO2 and its interaction with Pt, the modified Pt/Al2O3@CeO2 exhibits superior catalytic activity and antisintering stability. This method can be extended to other supported catalyst systems.

Development of supported intermetallic compounds: advancing the Frontiers of heterogeneous catalysis

Intermetallic compound (IMC) catalysts have garnered significant attention due to their unique surface and electronic properties, which can lead to enhanced catalytic performance compared to traditional monometallic catalysts. However, developing IMC materials as high-performance catalysts has been hindered by the inherent complexity of synthesizing nanoparticles with well-defined bulk and surface compositions. Achieving precise control over the composition of supported bimetallic IMC catalysts, especially those with high surface area and stability, has proven challenging. This review provides a comprehensive overview of the recent progress in developing supported IMC catalysts. We first examine the various synthetic approaches that have been explored to prepare supported IMC nanoparticles with phase-pure bulk structures and tailored surface compositions. Key factors influencing the formation kinetics and compositional control of these materials are discussed in detail. Then the strategies for manipulating the surface composition of supported IMCs are delved into. Applications of high-performance supported IMCs in important reactions such as selective hydrogenation, reforming, dehydrogenation, and deoxygenation are comprehensively reviewed, showcasing the unique advantages offered by these materials. Finally, the prevailing research challenges associated with supported IMCs are identified, including the need for a better understanding of the composition-property relationships and the development of scalable synthesis methods. The prospects for the practical implementation of these versatile catalysts in industrial processes are also highlighted, underscoring the importance of continued research in this field.

The role of surface substitution in the atomic disorder-to-order phase transition in multi-component core-shell structures

Intermetallic phases with atomic ordering are highly active and stable in catalysts. However, understanding the atomistic mechanisms of disorder-to-order phase transition, particularly in multi-component systems, remains challenging. Here, we investigate the atom diffusion and phase transition within Pd@Pt-Co cubic nanoparticles during annealing, using in-situ electron microscopy and ex-situ atomic resolution element analysis. We reveal that initial outward diffusing Pd partially substitutes Pt, forming a (Pt, Pd)-Co ternary system in the surface region, enabling the phase transition at a low temperature of 400 °C, followed by shape-preserved inward propagation of the ordered phase. At higher temperatures, excessive interdiffusion across the interface changes the stoichiometric ratio, diminishing the atomic ordering, leading to obvious change in morphology. Calculations indicate that the Pd-substitute in (Pt, Pd)-Co system leads to a significantly lower phase transition temperature compared to that of Pt-Co alloy and thus a lower activation energy for atomic diffusion. These insights into atomistic behavior are crucial for future design of multi-component systems.

Strong Electronic Metal-Support Interactions Enable the Increased Spin State of Co-N4 Active Sites and Performance for Acidic Oxygen Reduction Reaction

Nonprecious metal catalysts, particularly M-N-C catalysts, are widely recognized as promising contenders for the oxygen reduction reaction (ORR). However, a notable performance gap persists between M-N-C catalysts and Pt-based catalysts under acidic conditions. In this study, hybrid catalysts comprising single Co atoms and ultralow concentrations of Pt3Co intermetallic nanoparticles (NPs) are introduced to enhance ORR performance. Under acidic conditions, these hybrid catalysts demonstrate ORR efficiency with a half-wave potential of 0.895 V, negligible decay even after 80 000 cycles, and a high maximum power density of 1.34 W cm-2 in fuel cells. This performance surpasses those of Co-N-C and Pt/Co-N-C catalysts. Both experimental findings and theoretical computations suggest that the heightened ORR activity stems from an increase in the spin density of Co sites induced by noble metal NPs, facilitating the activation of O-O bonds via side-on overlapping and enabling a transition in the reaction pathway from associative to dissociative processes. This research offers a promising avenue for the systematic design of M-N-C cathodes with an enhanced performance for acidic fuel cells.

Kinetics-Driven Crystal Facet Evolution Mechanism of Atomically Ordered Intermetallic PtFe Nanocubes toward Electrochemical Catalysis

Crystal structure engineering in nanoparticles has been regarded as a vital method in catalyst development and design. Herein, PtFe nanocubes, manufactured with ordered PtFe intermetallic structure and a desired facet of {202}, have been successfully prepared via the combination of selective deposition strategy and spatial barrier effect. In-situ X-ray photoelectron spectroscopy found that the growth of the high-index facet and formation of the nanocube for o-PtFe-202 materials arise from the surface Fe2+ modification stabilized effect and the selective deposition of Cl-, respectively. Moreover, density functional theory calculations and X-ray adsorption spectroscopies further proved that the improved oxygen reduction reaction activity and stability of o-PtFe-202 mainly originate from the synergistic effect of the desired high-index facet, ordered crystal structure, and resulting optimal d-band center of Pt. As expected, the o-PtFe-202 exhibits excellent mass activity (2.48 mA·ugPt-1) and specific activity (7.78 mA·cm-2), with only a 7.3% decrease in mass activity after 30 000 cycles.

Tailoring Zirconia Supported Intermetallic Platinum Alloy via Reactive Metal-Support Interactions for High-Performing Fuel Cells

Developing efficient and anti-corrosive oxygen reduction reaction (ORR) catalysts is of great importance for the applications of proton exchange membrane fuel cells (PEMFCs). Herein, we report a novel approach to prepare metal oxides supported intermetallic Pt alloy nanoparticles (NPs) via the reactive metal-support interaction (RMSI) as ORR catalysts, using Ni-doped cubic ZrO2 (Ni/ZrO2) supported L10-PtNi NPs as a proof of concept. Benefiting from the Ni migration during RMSI, the oxygen vacancy concentrations in the support are increased, leading to an electron enrichment of Pt. The optimal L10-PtNi-Ni/ZrO2-RMSI catalyst achieves remarkably low mass activity (MA) loss (17.8 %) after 400,000 accelerated durability test cycles in a half-cell and exceptional PEMFC performance (MA=0.76 A mgPt -1 at 0.9 V, peak power density=1.52/0.92 W cm-2 in H2-O2/-air, and 18.4 % MA decay after 30,000 cycles), representing the best reported Pt-based ORR catalysts without carbon supports. Density functional theory (DFT) calculations reveal that L10-PtNi-Ni/ZrO2-RMSI requires a lower energetic barrier for ORR than L10-PtNi-Ni/ZrO2 (direct loading), which is ascribed to a decreased Bader charge transfer between Pt and *OH, and the improved stability of L10-PtNi-Ni/ZrO2-RMSI compared to L10-PtNi-C can be contributed to the increased adhesion energy and Ni vacancy formation energy within the PtNi alloy.

Enhancing Surface Strain of Intermetallic Fuel Cell Catalysts by Composition-Induced Phase Transition

The lattice parameter of platinum-based intermetallic compounds (IMCs), which correlates with the intrinsic activity of the oxygen reduction reaction (ORR), can be modulated by crystal phase engineering. However, the controlled preparation of IMCs with unconventional crystal structures remains highly challenging. Here, we demonstrate the synthesis of carbon-supported PtCu-based IMC catalysts with an unconventional L10 structure by a composition-regulated strategy. Experiment and machine learning reveal that the thermodynamically favorable structure changes from L11 to L10 when slight Cu atoms are substituted with Co. Benefiting from crystal-phase-induced strain enhancement, the prepared L10-type PtCu0.8Co0.2 catalyst exhibits much-enhanced mass and specific activities of 1.82 A mgPt-1 and 3.27 mA cmPt-2, which are 1.91 and 1.73 times higher than those of the L11-type PtCu catalyst, respectively. Our work highlights the important role of crystal phase in determining the surface strain of IMCs, and opens a promising avenue for the rational preparation of IMCs with different crystal phases by doping.

Atom-by-atom optimizing the surface termination of Fe-Pt intermetallic catalysts for alkaline hydrogen evolution reaction

Controlling the atomic arrangement of elemental atoms in intermetallic catalysts to govern their surface and subsurface properties is a crucial but challenging endeavor in electrocatalytic reactions. In hydrogen evolution reaction (HER), adjusting the d-band center of the conventional noble-metallic Pt by introducing Fe enables the optimization of catalytic performance. However, a notable gap exists in research on the effective transition from disordered Fe/Pt alloys to highly ordered intermetallic compounds (IMCs) such as FePt3 in the alkaline HER, hampering their broader application. In this study, a series of catalysts FePt3-xH (x = 5, 6, 7, 8 and 9) supported on carbon nanotubes (CNTs) were synthesized via a simple impregnation method, along with a range of heat treatment processes, including annealing in a reductive atmosphere, to regulate the order degree of the arrangement of Fe/Pt atoms within the FePt3 catalyst. By using advanced microscopy and spectroscopy techniques, we systematically explored the impact of the order degree of FePt3 in the HER. The as-prepared FePt3-8H exhibited notable HER catalytic activity with low overpotentials (η = 37 mV in 1.0 mol L-1 KOH) at j = 10 mA cm-2. The surface of the L12 FePt3-8H catalyst was demonstrated to be Pt-rich. The Pt on the surface was not easily oxidized due to the unique Fe/Pt coordination, resulting in significant enhancement of HER performance.

Site-selective sulfur anchoring produces sintering-resistant intermetallic ORR electrocatalysts for membrane electrode assemblies

Intermetallic compounds are emerging as promising oxygen reduction reaction (ORR) catalysts for fuel cells due to their typically higher activity and durability compared to disordered alloys. However, the preparation of intermetallic catalysts often requires high-temperature annealing, which unfortunately leads to adverse sintering of the metal nanoparticles. Herein, we develop a scalable site-selective sulfur anchoring strategy that effectively suppresses alloy sintering, ensuring the formation of efficient intermetallic electrocatalysts with small sizes and high ordering degrees. The alloy-support interactions are precisely modulated by selectively modifying the alloy-support interfaces with oxidized sulfur species, thus simultaneously blocking both the nanoparticle migration and Oswald ripening pathways for sintering. Using this strategy, sub-5 nm PtCo intermetallic electrocatalysts enclosed by two atomic layers of Pt shells have been successfully prepared even at a metal loading higher than 30 wt%. The intermetallic catalysts exhibit excellent ORR performances in both rotating disk electrode and membrane electrode assembly conditions with a mass activity of 1.28 A mgPt-1 at 0.9 V (vs. RHE) and a power density of 1.0 W cm-2 at a current density of 1.5 A cm-2. The improved performances result from the enhanced Pt-Co electronic interactions and compressive surface strain generated by the highly ordering structure, while the atomic Pt shells prevent the dissolution of Co under highly acidic conditions. This work provides new insights to inhibit the sintering of nanoalloys and would promote the scalable synthesis and applications of platinum-based intermetallic catalysts.

Simultaneously Geometrical and Electronic Modulation of L10-PtZn by Trace Ge Boosts High-performance Oxygen Reduction Reaction

Developing a highly active, durable, and low-platinum-based electrocatalyst for the cathodic oxygen reduction reaction (ORR) is for breaking the bottleneck of large-scale applications of proton exchange membrane fuel cells (PEMFCs). Herein, ultrafine PtZn intermetallic nanoparticles with low Pt-loading and trace germanium (Ge) involvement confined in the nitrogen-doped porous carbon (Ge-L10-PtZn@N-C) are reported. The Ge-L10-PtZn@N-C exhibit superior ORR activity with a mass activity of 3.04 A mg-1 Pt and specific activity of 4.69 mA cm-2, ≈12.2- and 10.2-times improvement compared to the commercial Pt/C (20%) at 0.90 V in 0.1 m KOH. The cathodic catalyst Ge-L10-PtZn@N-C assembled in the PEMFC shows encouraging peak power densities of 316.5 (at 0.86 V) and 417.2 mW cm-2 (at 0.91 V) in alkaline and acidic fuel-cell, respectively. The combination of experiment and density functional theory calculations (DFT) results robustly reveal that the participation of trace Ge can not only trigger a "growth site locking effect" to effectively inhibit nanoparticle growth, bring miniature nanoparticles, enhance dispersion uniformity, and achieve the exposure of the more electrochemical active site, but also effectively modulates the electronic structure, hence optimizing the adsorption/desorption of the oxygen intermediates.

Highly dispersed ultrafine PtCo alloy nanoparticles on unique composite carbon supports for proton exchange membrane fuel cells

The design of highly efficient and robust platinum-based electrocatalysts is pivotal for proton exchange membrane fuel cells (PEMFC). One of the long-standing issues for PEMFC is the rapid deactivation of the catalyst under working conditions. Here, we report a simple synthesis strategy for ultrafine PtCo alloy nanoparticles loaded on a unique carbon support derived from a zeolitic imidazolate framework-67 (ZIF-67) and Ketjen Black (KB) composite, exhibiting a remarkable catalytic performance toward the oxygen reduction reaction (ORR) and PEMFC. Benefitting from the N-doping and wide pore size distribution of the composite carbon supports, the growth of PtCo nanoparticles can be evenly restricted, leading to a uniform distribution. The Pt-integrated catalyst delivers an outstanding electrochemical performance with a mass activity that is 8.6 times higher than that of the commercial Pt/C catalyst. Impressively, the accelerated durability test (ADT) demonstrates that the hybrid carbon support can significantly enhance the durability. Theoretical simulations highlight the synergistic contribution between the supports and the PtCo nanoparticles. Moreover, hydrogen-oxygen fuel cells assembled with the catalyst exhibited a high power density of 1.83 W cm-2 at 4 A cm-2. These results provide a new opportunity to design advanced catalysts for PEMFC.

Machine-learning-accelerated design of high-performance platinum intermetallic nanoparticle fuel cell catalysts

Carbon supported PtCo intermetallic alloys are known to be one of the most promising candidates as low-platinum oxygen reduction reaction electrocatalysts for proton-exchange-membrane fuel cells. Nevertheless, the intrinsic trade-off between particle size and ordering degree of PtCo makes it challenging to simultaneously achieve a high specific activity and a large active surface area. Here, by machine-learning-accelerated screenings from the immense configuration space, we are able to statistically quantify the impact of chemical ordering on thermodynamic stability. We find that introducing of Cu/Ni into PtCo can provide additional stabilization energy by inducing Co-Cu/Ni disorder, thus facilitating the ordering process and achieveing an improved tradeoff between specific activity and active surface area. Guided by the theoretical prediction, the small sized and highly ordered ternary Pt2CoCu and Pt2CoNi catalysts are experimentally prepared, showing a large electrochemically active surface area of ~90 m2 gPt‒1 and a high specific activity of ~3.5 mA cm‒2.

A Universal Cross-Synthetic Strategy for Sub-10 nm Metal-Based Composites with Excellent Ion Storage Kinetics

The sub-10 nm metal-based nanomaterials (SMNs) show great potential for the electrochemical energy storage field. However, their ion storage capacity and stability suffer from severe agglomeration and interface problems. Herein, a universal strategy is reported to synthesize a wide range of SMNs (e.g., metal, nitride, oxide, and sulfides) embedded in free-standing carbon foam (SMN/FC-F) composite electrodes by crossing the interfacial confinement of NaCl self-assembly with the thermal-mechanical coupling of powder metallurgy. The pressure-enhanced NaCl self-assembly interfacial confinement is greatly beneficial to preventing SMN agglomeration and promoting SMNs embedded in FC-F which originate from the welding of carbon nanosheets. They are confirmed via a series of advanced characterizations including X-ray photoelectron spectroscopy, and spherical aberration-corrected scanning transmission electron microscopy, with theoretical computations. Benefiting from the unique structure, SMNs/FC-F delivers ultrafast and stable ion-storage kinetics. As a proof-of-concept demonstration, the MoS2 /FC-F shows excellent ion storage kinetics and superior long-term cycling performance for ion storage (e.g., Na3 V2 (PO4 )2 O2 F/C//MoS2 /FC-F sodium-ion batteries exhibit a high reversible capacity of 185 mAh g-1 at 0.5 A g-1 with a decay rate of 0.05% per cycle.). This work provides a new opportunity to design and fabricate promising SMN-based free-standing working electrodes for electrochemical energy storage and conversion applications.

Sulfur-Stabilizing Ultrafine High-Entropy Alloy Nanoparticles on MXene for Highly Efficient Ethanol Electrooxidation

High-entropy alloys (HEAs) are significantly promising candidates for heterogeneous catalysis, yet the controllable synthesis of ultrafine HEA nanoparticles (NPs) remains a formidable challenge due to severe thermal sintering during the high-temperature fabrication process. Herein, we report a sulfur-stabilizing strategy to construct ultrafine HEA NPs with an average diameter of 4.02 nm supported on sulfur-modified Ti3C2Tx (S-Ti3C2Tx) MXene, on which the strong interfacial metal-sulfur interactions between HEA NPs and the S-Ti3C2Tx supports significantly increase the interfacial adhesion strength, thus greatly suppressing nanoparticle sintering by retarding both particle migration and metal atom diffusion. The representative quinary PtPdCuNiCo HEA-S-Ti3C2Tx exhibits excellent catalytic performance toward alkaline ethanol oxidation reaction (EOR) with an ultrahigh mass activity of 7.03 A mgPt+Pd-1, which is 4.34 and 5.17 times higher than those of the commercial Pt/C and Pd/C catalysts, respectively. In situ attenuated total reflection-infrared spectroscopy studies reveal that the high intrinsic catalytic activity for the EOR can be ascribed to the synergy of different catalytically active sites of HEA NPs and the well-designed interfacial metal-sulfur interactions.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

Advanced Architectures of Air Electrodes in Zinc-Air Batteries and Hydrogen Fuel Cells

The air electrode is an essential component of air-demanding energy storage/conversion devices, such as zinc-air batteries (ZABs) and hydrogen fuel cells (HFCs), which determines the output power and stability of the devices. Despite atom-level modulation in catalyst design being recently achieved, the air electrodes have received much less attention, causing a stagnation in the development of air-demanding equipment. Herein, the evolution of air electrodes for ZABs and HFCs from the early stages to current requirements is reviewed. In addition, the operation mechanism and the corresponding electrocatalytic mechanisms of ZABs are summarized. In particular, by clarifying the air electrode interfaces of ZABs at different scales, several approaches to improve the air electrode in rechargeable ZABs are reviewed, including innovative electrode structures and bifunctional oxygen catalysts. Afterward, the operating mechanisms of proton-exchange-membrane fuel cells (PEMFCs) and anion-exchange-membrane fuel cells (AEMFCs) are explained. Subsequently, the strategies employed to enhance the efficiency of the membrane electrode assembly (MEA) in PEMFCs and AEMFCs, respectively, are highlighted and discussed in detail. Last, the prospects for air electrodes in ZABs and HFCs are considered by discussing the main challenges. The aim of this review is to facilitate the industrialization of ZABs and HFCs.

Modulating the d-Band Center Enables Ultrafine Pt3 Fe Alloy Nanoparticles for pH-Universal Hydrogen Evolution Reaction

By providing dual active sites to synergistically accelerate H2 O dissociation and H+ reduction, ordered intermetallic alloys usually show extraordinary performance for pH-universal hydrogen evolution reaction (HER). Herein, activated N-doped mesoporous carbon spheres supported intermetallic Pt3 Fe alloys (Pt3 Fe/NMCS-A), as a highly-efficient electrocatalyst for pH-universal HER, are reported. The Pt3 Fe/NMCS-A exhibits low overpotentials (η10 ) of 13, 29, and 48 mV to deliver 10 mA cm-2 in 0.5 m H2 SO4 , 1.0 m KOH, and 1.0 m phosphate buffered solution (PBS), respectively, as well as robust stability to maintain the overall catalytic performances. Theoretical studies reveal that the strong Pt 5d-Fe 3d orbital electronic interactions negatively shift the d-band center (εd ) of Pt 5d orbital, resulting in reduced H* adsorption energy of Pt sites and enhanced acidic HER activity. With Pt and Fe acting as co-adsorption sites for H* and *OH intermediates, respectively, a low energy barrier is required for Pt3 Fe/NMCS-A to dissociate H2 O to afford H* intermediates, which greatly promotes the H* adsorption and H2 formation in alkaline and neutral conditions. The synthetic strategy is further extended to the synthesis of Pt3 Co and Pt3 Ni alloys with excellent HER activity in pH-universal electrolytes, demonstrating the great potential of these Pt-based alloys for practical applications.

Ultrathin Co-N-C Layer Modified Pt-Co Intermetallic Nanoparticles Leading to a High-Performance Electrocatalyst toward Oxygen Reduction and Methanol Oxidation

The development of low platinum-based alloy electrocatalysts is crucial to accelerate the commercialization of fuel cells, yet remains a synthetic challenge and an incompatibility between activity and stability. Herein, a facile procedure to fabricate a high-performance composite that comprises Pt-Co intermetallic nanoparticles (IMNs) and Co, N co-doped carbon (Co-N-C) electrocatalyst is proposed. It is prepared by direct annealing of homemade carbon black-supported Pt nanoparticles (Pt/KB) covered with a Co-phenanthroline complex. During this process, most of Co atoms in the complex are alloyed with Pt to form ordered Pt-Co IMNs, while some Co atoms are atomically dispersed and doped in the framework of superthin carbon layer derived from phenanthroline, which is coordinated with N to form Co-Nx moieties. Moreover, the Co-N-C film obtained from complex is observed to cover the surface of Pt-Co IMNs, which prevent the dissolution and agglomeration of nanoparticles. The composite catalyst exhibits high activity and stability toward oxygen reduction reactions (ORR) and methanol oxidation reactions (MOR), delivering outstanding mass activities of 1.96 and 2.92 A mgPt -1 for ORR and MOR respectively, owing to the synergistic effect of Pt-Co IMNs and Co-N-C film. This study may provide a promising strategy to improve the electrocatalytic performance of Pt-based catalysts.

Recent Advances in Water-Splitting Electrocatalysts Based on Electrodeposition

Green hydrogen is being considered as a next-generation sustainable energy source. It is created electrochemically by water splitting with renewable electricity such as wind, geothermal, solar, and hydropower. The development of electrocatalysts is crucial for the practical production of green hydrogen in order to achieve highly efficient water-splitting systems. Due to its advantages of being environmentally friendly, economically advantageous, and scalable for practical application, electrodeposition is widely used to prepare electrocatalysts. There are still some restrictions on the ability to create highly effective electrocatalysts using electrodeposition owing to the extremely complicated variables required to deposit uniform and large numbers of catalytic active sites. In this review article, we focus on recent advancements in the field of electrodeposition for water splitting, as well as a number of strategies to address current issues. The highly catalytic electrodeposited catalyst systems, including nanostructured layered double hydroxides (LDHs), single-atom catalysts (SACs), high-entropy alloys (HEAs), and core-shell structures, are intensively discussed. Lastly, we offer solutions to current problems and the potential of electrodeposition in upcoming water-splitting electrocatalysts.

Hydroxyl-Binding Energy-Induced Kinetic Gap Narrowing between Acidic and Alkaline Hydrogen Oxidation Reaction on Intermetallic Ru3 Sn7 Catalyst

Developing highly efficient catalysts toward alkaline hydrogen oxidation reaction (HOR) and narrowing the kinetic gap between acidic and alkaline electrolytes are of great importance for the practical application of alkaline exchange membrane fuel cell . Herein, ordered Ru₃ Sn₇ /C intermetallic compound has been developed for the HOR under alkaline and acidic conditions. The authors demonstrate that the ordered intermetallic Ru₃ Sn₇ /C shows much enhanced HOR activity, stability, and CO-tolerance compared with its disordered RuSn solid solution alloy counterpart. More importantly, the authors find that the kinetic gap of HOR between acidic and alkaline media is significantly narrowed in the as-synthesized intermetallic Ru₃ Sn₇ /C catalysts. Combined experiment results and theoretical calculations, the authors understand that promoted hydroxyl-binding energy on Ru₃ Sn₇ /C derived from the intermetallic-induced strong electron interaction is responsible for the accelerated alkaline HOR performance and narrowed kinetic gap.

A General and Scalable Approach to Sulfur-Doped Mono-/Bi-/Trimetallic Nanoparticles Confined in Mesoporous Carbon

Metal nanoparticles confined in porous carbon materials have been widely used in various heterogeneous catalytic processes due to their enhanced activity and stability. However, fabrication of such catalysts in a facile and scalable way remains challenging. Herein, we report a general and scalable thiol-assisted strategy to synthesize sulfur-doped mono-/bi-/trimetallic nanoparticles confined in mesoporous carbon (S-M@MC, M = Pt, Pd, Rh, Co, Zn, etc.), involving only two synthetic steps, i.e., a hydrothermal process and pyrolysis. The strategy is based on coordination chemistry and hydro-phobic interaction that the metal precursors coordinated with the hydrophobic thiol ligands are located at the hydrophobic core of micelles, in situ confined in the hydrothermally prepared mesostructured polymer, and then converted into sulfur-doped metal nanoparticles confined in MC after pyrolysis. It is demonstrated that the S-PtCo@MC exhibits enhanced catalytic activity and improved durability toward acidic hydrogen evolution reaction due to the confinement effect and S-doping.

Advances in Low Pt Loading Membrane Electrode Assembly for Proton Exchange Membrane Fuel Cells

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.