Promotion of atomic ordering in Pt-based intermetallic compounds (IMCs) is a proven strategy to enhance catalytic activity and durability, for the cathode catalysts in proton exchange membrane fuel cells (PEMFCs). However, achieving higher atomic ordering typically requires elevated temperature annealing, which induces nanoparticles (NPs) sintering and surface area loss, resulting in a challenge for catalyst design. Here, we demonstrate that Zn incorporation in L10-PtCo IMCs promotes the ordering, endowing the enhanced stability and activity. Machine learning interatomic potential (MLIP) simulations reveal that Zn lowers vacancy formation energies and modifies atomic migration, thereby accelerating ordering during annealing. These results are validated experimentally by X-ray-based analyses. Electrochemical measurements show that L10-Zn-PtCo/ZnNC achieves a mass activity (MA) of 1.76 A mgPt -1 at 0.9 VRHE, outperforming Pt/C (0.24 A mgPt -1). In single-cell tests, it delivers 438 mA cm-2 at 0.7 V, surpassing Pt/C (293 mA cm-2). After 30 000 cycles, it retains 89.7% initial current density, compared with only 54.6% retention for Pt/C. By integrating ML-guided design with experimental validation, this work establishes a rational strategy to engineer atomically ordered Pt-based IMCs under practical conditions, advancing the development of efficient electrocatalysts.

Titanium dioxide (TiO2) is widely used as an inorganic UV filter because its wide bandgap (similar to 3.2 eV) enables strong UVB blocking; however, this same electronic structure intrinsically limits spectral coverage and promotes photocatalytic generation of reactive oxygen species (ROS). Here, we present a dual-engineered inorganic photoprotective material that simultaneously expands UV-to-high energy visible (HEV) light attenuation and suppresses photo-induced ROS generation by integrating abundant nitrogen (N) doping with a metal-phenolic network (MPN) coating. Ammonia-assisted thermal treatment introduces abundant nitrogen-related defect states into TiO2, extending sub-bandgap absorption into the UVA and HEV regions and promoting carrier recombination rather than photocatalytic charge transfer. Subsequent MPN coating further broadens optical attenuation via ligand-to-metal charge transfer (LMCT) and scavenges residual ROS through catechol and galloyl moieties. Consequently, SiO2/N-TiO2/MPN achieves broad-spectrum optical attenuation (99% UVB, 94% UVA, and 79% HEV), yielding approximately twofold and threefold enhancements in SPF and UVAPF compared to pristine SiO2/TiO2. The cooperative defect-engineered core and redox-active shell sustain suppression of apparent hydroxyl radical generation for 6 h under simulated solar irradiation, while in vitro cell viability assays indicate reduced irradiation-induced cytotoxicity under controlled conditions. This strategy establishes a core-shell paradigm for photochemically suppressed, broad-spectrum inorganic UV filters.

Pt-based intermetallic nanocatalysts are gaining increasing attention as durable and active oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs). The ordered atomic configuration of these catalysts strengthens interactions between Pt and alloying metals, tunes the electronic structure, and provides better stability under acidic operating conditions of PEMFCs. This review summarizes the thermodynamic and kinetic principles of nanoscale Pt alloy disorder-to-order transitions and provides a basis for rational synthesis. Advances in composition design, ranging from binary systems to ternary and high-entropy intermetallics (HEIs), are discussed, along with structural and interfacial strategies that enable nanoparticle (NP) size control and high metal loading. Morphology-controlled Pt-based intermetallic catalysts exposing specific facets and having characteristic dimensions are also highlighted. Finally, representative studies employing X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS) are highlighted to illustrate key characterization approaches used to probe intermetallic nanocatalysts. These insights will help in developing Pt-based intermetallic catalysts with both high activity and durability for practical PEMFC applications.

Rational design of oxide supports for Ir catalysts is a highly promising approach to enhance proton exchange membrane water electrolysis (PEMWE) performance and durability while minimizing Ir usage. Here, we report a curvature-engineered TiO2 support synthesized via a polystyrene (PS) templating method to modulate the Ir nanoparticle dispersion and catalyst-support interaction. By controlling the size of PS spheres, interconnected hollow TiO2 (h-TiO2) structures with tunable curvature can be obtained. The curvature of TiO2 support alters the oxidation state of Ir; higher curvature facilitates electron transfer from Ir to TiO2, increasing the Ir(IV)/Ir(III) ratio and consequently lowering intrinsic activity. In contrast, the electrochemical surface area (ECSA) increased with curvature, enabled by controlled Ir nanoparticle dispersion and connectivity within our unique h-TiO2 structure. By optimizing the trade-off characteristics associated with curvature, we achieved superior mass activity for Ir/h-TiO2 (262 A/gIr at 1.55 VRHE), approximately 2.2 times greater than that of Ir black (119 A/gIr at 1.55 VRHE), as well as improved durability. PEMWE single-cell employing the optimized Ir/h-TiO2 with 0.5 mgIr cm-2 demonstrated comparable performance (1.648 V at 1 A cm-2) to Ir black with 0.7 mgIr cm-2 (1.645 V at 1 A cm-2), indicating its practical applicability with approximately 30 % less Ir usage. This work highlights curvature-tuned support engineering as a viable route to optimize Ir usage.

Water electrolysis technologies in alkaline environments have drawn considerable interest for their potential in low-cost hydrogen production without noble metals. However, it remains challenging to achieve high performance and durability in the alkaline hydrogen evolution reaction (HER) using non-noble metal catalysts because of their intrinsically poor water dissociation kinetic properties. Here, we address this challenge by introducing a cohesive Co and Mo2C heterostructure catalyst strongly confined to N-doped carbon hollow polyhedron (NCHP) supports. Computational analysis and X-ray spectroscopic analysis results reveal that the charge redistribution between metallic Co and Mo2C not only promotes water dissociation on Mo2C sites but also accelerates hydrogen gas evolution kinetics at their interfaces, leading to enhanced HER performance. The Co-Mo2C/NCHP catalyst reduces the HER overpotential by 66% at 10 mA cm-2 compared to the single-active-site catalyst (Co/NCHP). Moreover, the Co-Mo2C/NCHP catalyst demonstrates enhanced durability, exhibiting a 38% lower HER overpotential than commercial Pt/C at 10 mA cm-2 after 1000 cycles. By forming a cohesive structure of Co and Mo2C within the hollow carbon framework, the formation of interfaces is maximized, and physical and chemical degradation is prevented. This study presents key strategies for designing interfaces to overcome the limitations of alkaline HER kinetics and durability.

Wide-bandgap metal-oxide nanoparticles are promising candidates for broad-spectrum sunscreens, yet their application is limited by photocatalytic activity and insufficient high-energy visible (HEV) light absorption. Here, we report a simple, scalable one-pot strategy for the spontaneous formation of a metal-phenolic network (MPN) on zinc oxide (ZnO) nanoparticles (ZnO/MPN NPs), utilizing intrinsic Zn2+ ion release from ZnO to initiate tannic acid (TA) complexation and in situ oxidation. This process forms a nanoscale MPN layer on the ZnO surface, while ZnO-mediated TA oxidation and dimerization (inspired by natural fruit browning) enhance electron delocalization, extending light absorption to the HEV region. The resulting browned MPN-coated ZnO nanoparticles (ZnO/MPN-B NPs) exhibited approximately a threefold enhancement in both sun protection factor (SPF) and UVA protection factor (UVAPF) compared to uncoated ZnO NPs. Additionally, the MPN layer effectively suppresses over 99 % of photogenerated reactive oxygen species (ROS) through its intrinsic ROS scavenging properties, significantly improving photostability. Cell viability assays further demonstrate that the MPN layer mitigates photoinduced cytotoxicity, supporting the safety and biocompatibility of these hybrids. This study suggests ZnO/MPN-B NPs as eco-friendly, high-performance candidates for next-generation sunscreen formulations, offering a scalable, efficient route to address the dual challenges of photoprotection and safety in inorganic sunscreen agents.

Despite their superior catalytic activity for the oxygen reduction reaction (ORR), ordered platinum (Pt)-transition metal nanoparticles suffer from limitations that hinder their use in polymer electrolyte membrane fuel cells (PEMFCs), such as particle growth during the ordering transformation and insufficient durability over extended operation. In this study, a zeolitic imidazolate framework-8 (ZIF-8) is pyrolyzed into zinc and nitrogen-doped carbon (ZnNC). Pt nanoparticles are synthesized on the ZnNC and undergo heat treatment. Through this simple process, ordered PtZn nanoparticles are obtained with an average particle size of approximately 4.5 nm (OPtZn/ZnNC). In a half-cell, the O-PtZn/ZnNC achieves outstanding ORR mass activity (1.21 A mg Pt- 1 at 0.9 V) and durability (35 % loss of mass activity after 30 k cycles), significantly surpassing Pt/C (0.41 A mg Pt- 1 and 61 % loss). As a cathode catalyst of a PEMFC, the O-PtZn/ZnNC outperforms Pt/C in both performance and durability; O-PtZn/ZnNC and Pt/C cells exhibit current densities of 71 and 39 mA cm- 2 , respectively, at a cell voltage of 0.8 V. These values fall to 43 (-39 %) and 11 (-72 %) mA cm- 2 , respectively, after 30 k cycles. Density functional theory calculations illustrate that ZnNC has a strong binding energy with O-PtZn (-8.13 eV) and a small interfacial minimum distance of 2.03 & Aring;, resulting in exceptional retention of electrochemical active surface area retention for O-PtZn/ZnNC (-7%, from 57.9 to 53.8 m2 g Pt-1 , after 30 k cycles).

Reducing iridium (Ir) usage is essential for the commercial viability of proton exchange membrane water electrolysis (PEMWE), where the oxygen evolution reaction (OER) is a major performance and cost bottleneck. Conventional Ir nanoparticles (∼5 nm) suffer from low dispersion and limited surface utilization. Here, we report a catalyst architecture comprising ultrathin Ir nanosheets (Ir NS) supported on spherical TiO2 particles (Ir NS/TiO2). The ∼100 nm TiO2 particles effectively disperses 1-3 μm-wide, sub 2 nm-thick Ir nanosheets, ensuring full surface exposure and continuous electron transport, despite the intrinsically low conductivity of TiO2. The Ir NS/TiO2 catalyst exhibits enhanced OER activity and durability in both half-cell and PEMWE single-cell configurations. At an Ir loading of 0.7 mgIr cm-2, Ir NS/TiO2 achieves 3.6 A cm-2 at 1.8 V, significantly outperforming commercial Ir nanoparticles (Ir NP, 2.6 A cm-2). Long-term operation at 1.0 A cm-2 over 1000 h shows a low voltage decay rate of 0.095 mV h-1, compared to 0.414 mV h-1 for Ir NP. Moreover, Ir NS/TiO2 with an Ir loading amount of 0.5 mgIr cm-2 delivers comparable performance to Ir NP at 1.4 mgIr cm-2. These results present Ir NS/TiO2 as a highly efficient and durable OER catalyst, supporting its potential for cost-effective, scalable green hydrogen production.

Pt-based electrocatalysts are the primary choice for fuel cells due to their superior oxygen reduction reaction (ORR) activity. To enhance ORR performance and durability, extensive studies have investigated transition metal alloying, doping, and shape control to optimize the three key governing factors for ORR: geometry, local chemistry, and strain of their surface and subsurface. However, systematic optimization remains incomplete, as it requires an atomic-scale understanding of these factors and their dynamics over potential cycling, as well as their relationship to ORR activity. Here, we implement neural network-assisted atomic electron tomography to measure the 3D atomic structural dynamics and their effects on the functional degradation of PtNi alloy catalysts. Our results reveal that PtNi catalysts undergo shape changes, surface alloying, and strain relaxation during cycling, which can be effectively mitigated by Ga doping. By combining geometry, local chemistry, and strain analysis, we calculated the changes in ORR activity over thousands of cycles and observed that Ga doping leads to higher initial activity and greater stability. These findings offer a pathway to understanding 3D atomic structural dynamics and their relation to ORR activity during cycling, paving the way for the systematic design of durable, high-efficiency nanocatalysts.

Improving catalysts for the oxygen reduction reaction (ORR) is crucial for commercialization of proton exchange membrane fuel cells (PEMFCs) due to the sluggish kinetics of ORR at the cathode. Current ORR catalysts face challenges such as high costs associated with precious metals and poor durability. A common approach to improve catalyst activity is to alloy Pt with transition metals, such as cobalt and nickel, to control the d-band center. Instead of the disordered PtM, Pt intermetallic compounds show improved ORR intrinsic activity and enhanced stability. Also, doping carbon supports with heteroatoms such as nitrogen and sulfur is a feasible strategy to enhance the interaction between the metal nanoparticles of the catalyst and its support, which leads to improved performance and stability of the catalysts. In this study, we synthesized high-loading intermetallic PtCo nanoparticles supported on sulfur-doped carbon. High metal loading catalysts have significant advantages for practical PEMFC applications as they accelerate mass transport, leading to a reduction in voltage loss, especially under high current densities. To synthesize high-loading intermetallic PtCo nanoparticles, uniform sulfur doping on commercial carbon support is introduced, since sulfur sites can anchor metal nanoparticles even during a harsh heat treatment process. The sulfur sites not only minimize sintering, but also improve the electrochemical performance. Using this approach, high-loading (52.5 wt%) sub-5 nm PtCo intermetallic compounds with a Pt-rich shell (PtCo@Pt/S-BP) were successfully synthesized. The morphology and characteristics of the PtCo nanoparticles were confirmed through various techniques, including XRD, TEM, ICP-OES, HAADF-STEM, EDS mapping, and XPS analysis. In the half-cell test, PtCo@Pt/S-BP exhibited over 5-fold enhancement in mass activity and 6-fold increase in specific activity compared to commercial Pt/C. Additionally, the performance of PtCo@Pt/S-BP was maintained even after 50,000 cycles due to thermodynamically stable structure of the intermetallic phase and Pt-rich shell. This synthesis strategy provides a promising pathway for practical application of Pt-based catalysts in future PEMFCs.

The sluggish oxygen reduction reaction (ORR) kinetics has inhibited the widespread commercialization of polymer electrolyte membrane fuel cells (PEMFCs). Therefore, there has been a great need for catalysts that promote the ORR. PtCo intermetallic nanoparticles supported on conductive carbon, which have superior activity and durability toward the ORR, have been considered promising catalysts for the cathode in PEMFCs. In general, high-temperature annealing is required to synthesize intermetallic catalysts, which accompanies the sintering of the nanoparticles, leading to a decrease in electrochemical active surface area (ECSA). Therefore, a sophisticated strategy is required to enhance the ordering degree of PtCo intermetallic compound nanoparticles without making the annealing process extreme. Here, we present L10-Zn-PtCo intermetallic nanocatalysts (Zn-PtCo/Zn-NC) in which the Zn incorporation strategy enhances the ordering degree. Computational calculation using machine learning force field (MLFF) elucidates that introducing Zn atoms can promote diffusion kinetics within the crystal structure of PtCo. X-ray diffraction (XRD) patterns and extended X-ray absorption fine structure (EXAFS) quantitatively confirm the enhancement of the ordering degree due to incorporating Zn atoms. In the half-cell configuration, the synthesized Zn-PtCo/Zn-NC catalyst shows an initial mass activity of 1.76 A mgPt -1 at 0.9 VRHE. In addition, it maintains 93.8% of its initial ECSA after the accelerated durability test (ADT). In H2-Air fuel cells, the Zn-PtCo/Zn-NC cathode achieves a high peak power density of 0.64 W cm-2, compared to that of the Pt/C (0.50 W cm-2), even with a low Pt usage of 0.05 mgPt cm-2 at the cathode.

In order to cope with the cataclysmic environmental problems, PEMFCs are in the spotlight as a next-generation renewable energy utilization candidate, but the high platinum unit price used in the catalyst layer is still a sticking point. Accordingly, attempts are being made to maximize platinum utilization and improve performance through shape control of the catalyst, but there is a problem in that the structure collapses under extreme PEMFCs driving conditions and the performance deteriorates rapidly, resulting in wistful durability. In this work, Pt-Cu nanosheet with 15~20 nm lateral size and 1 nm thickness was synthesized on carbon support (PtCu NS/C) and further enhanced durability through surface copper substitution using galvanic replacement reaction (G-PtCu NS/C). To clarify the catalyst structure in more detail, acid-leached Pt-Cu nanosheet (A-PtCu NS/C) was synthesized by eluting copper on the surface, and the differences in electronic structure were compared through XAS and XPS. In the half-cell configuration, G-PtCu NS/C demonstrated high performance and excellent durability retention after 30,000 square-wave cycles (SWC) of accelerated stress test (AST). Moreover, G-PtCu NS/C showed marginal shift in CO adsorption peak after AST, indicating the high stability of catalyst structure. In the full-cell test, performance of G-PtCu NS/C after 30,000 SWC AST is consistent to initial performance, while PtCu NS/C showed noticeable power density drop at high current density region. Ex-situ EDS elemental mapping and XRF of membrane-electrode assembly (MEA) after AST confirms that transition metal dissolution on G-PtCu NS/C was imperceptible. Our study suggests new engineering method for shaped controlled catalysts to be applied on PEMFCs.

Herein, we investigated the potential of downsizing Pt nanoparticles to single atom scale as a strategy to improve Pt utilization efficiency in electrocatalysts. We focused on Pt single atom catalysts anchored on high-surface area N-doped carbon [1-3] , which have shown higher oxygen reduction reaction (ORR) activity than Pt nano-catalysts in fuel cell applications. However, the contribution of Pt nanoparticles in achieving these results has been questioned, and the selectivity of Pt SACs for ORR is still controversial. We prepared different types of carbon-supported Pt catalysts and used electrochemical measurements including rotating-ring disk electrode (RRDE) and hydrogen peroxide reduction reaction (HPRR) tests to elucidate the role of Pt SACs in carbon-supported Pt nano-catalysts. Additionally, we proposed a novel ORR mechanism based on in-situ X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations. References [1] Nat. Commun. 2017, 8, 15938 [2] Angew. Chem. 2019, 131, 1175 [3] ACS Catal. 2021, 11, 1, 466 Figure 1

Accelerating the commercialization of polymer electrolyte membrane fuel cells (PEMFCs) requires urgent improvement of a catalyst for oxygen reduction reaction (ORR) that uses expensive precious metals. It is also important to consider the durability of the catalyst, which can affect its performance even after long-term use. In this study, we synthesized a platinum-cobalt (Pt-Co) catalyst with a platinum (Pt) shell and an intermetallic inner core through the acid-leaching post-treatment process. By introducing a transition metal, we greatly improved the ORR activity, while controlling the intermetallic and core-shell structure greatly improved the catalyst's structural stability and durability. We confirmed through X-ray diffraction (XRD) that the Pt-Co compound was aligned in an intermetallic structure, and that the structure was maintained even after the acid leaching post-treatment. In the half-cell test, L1 0 -PtCo@Pt/C, exposed to 0.5 M sulfuric acid solution for 6 hours, exhibited a 3.9-fold increase in mass activity and a 3.3-fold increase in specific activity compared to commercial Pt/C. Additionally, the electrochemical active surface area (ECSA) of L1 0 -PtCo@Pt/C remained stable even after 30,000 cycles, with an insignificant change of 8% or less, while commercial Pt/C decreased by 30% or more. Nevertheless, when acid treatment was applied for longer than this condition, the increase in performance and its retention were significantly reduced. This is due to the fact that with longer acid leaching times, the Pt shell of the catalyst becomes thicker, resulting in a limitation of the alloying effect of the internal intermetallic core. Our study proposes an optimal combination of Pt-Co intermetallic core and Pt shell through precise control of acid leaching post-treatment process. Pt-Co catalysts with well-aligned intermetallic core and the moderate thickness of Pt shell structure can offer a promising solution for improving the performance and durability of PEMFCs, thereby paving the way for their widespread commercialization.

Extensive commercialization of polymer electrolyte membrane fuel cells (PEMFCs) is restricted by high price of Pt which is commonly used to promote the oxygen reduction reaction (ORR). Therefore, reducing the dosage of Pt in the ORR catalysts while maintaining high activity and stability is important key for accelerating PEMFCs’ commercialization. In this study, Zn-introduced PtCo intermetallic nanoparticles supported on Zn-NC substrate (Zn-PtCo/Zn-NC) were synthesized, demonstrating superior activity and durability toward the acidic ORR in half-cell. The Zn-PtCo/Zn-NC catalyst was synthesized via the gas phase reduction method for the deposition of PtCo nanoparticles (NPs) on Zn-NC, and subsequent post-annealing process. During the annealing procedure, diffusion of Zn atoms into PtCo NPs occurred and leaded to enhanced atom-ordering of the intermetallic NPs. In the half-cell configuration, the Zn-PtCo/Zn-NC catalyst showed about 7.3-fold enhancement in the mass activity, compared to that of the commercial Pt/C catalyst. The high activity of the Zn-PtCo/Zn-NC was attributed to the incorporation of Zn atoms and the ordered structure which synergistically enhanced the ligand effects. In addition, the polarization curve of the Zn-PtCo/Zn-NC showed only a negative shift of 9 mV in a half-wave potential after the accelerated durability test (ADT), indicating the excellent stability of the catalyst. The robustness of the Zn-PtCo/Zn-NC was reinforced due to the thermodynamically stable structure of the atom-ordered intermetallic phase. The synthesis strategy presented in this work provides new pathway for developing the electrocatalysts applicable to the energy conversion devices.

In order to overcome the disadvantage of intermittent production of renewable energy, Polymer electrolyte membrane water electrolysis(PEMWE), which is one of the technologies of producing hydrogen by electrolyzing water, is attracting attention. For the commercialization of PEMWE, it is important to reduce usage of iridium(Ir) for oxygen evolution reaction(OER) in the anode electrode. Many studies have been reported to reduce the amount of iridium used by developing a catalyst with higher performance than the iridium nanoparticle catalyst used as a commercial catalyst. As one of the strategies, the introduction of support materials that can increase the active area of the catalyst is drawing attention. While carbon-based supports are mainly used in other applications, in OER environments, carbon is easily corroded due to high voltage and strong acid conditions. Therefore, it is necessary to use a metal oxide support with high corrosion resistance. In particular, titanium oxide(TiO 2 ) is one of the suitable support candidates because it is a stable material in an acidic OER environment. However, catalysts loaded on TiO 2 with nanoparticles cause an electrical contact problem due to the low electrical conductivity of TiO 2 , which causes a degradation in activity. Many studies have reported doping methods to increase the conductivity of TiO 2 , but there are also reports that these methods reduce the durability of support. Thus, a new approach to synthesizing a better structure of catalysts is needed to utilize metal oxide support. Herein, we present an approach to iridium nanosheet (NS) catalysts supported on TiO 2 (Ir NS/TiO 2 ). Ir NSs were synthesized by an facile method by directly annealing a mixture of Ir precursor and alkali salt. Ir NSs were supported on TiO 2 to be utilized as a reaction site and also acts as an electron path to compensate for the low electrical conductivity of TiO 2 . Ir NS/TiO 2 showed superior OER activity and stability under acidic conditions. These results showed that Ir NS/TiO 2 could be utilized to reduce the amount of precious metal catalyst in PEMWE and increase the stability of OER supported catalysts.

In order to improve the electrocatalytic activity and stability of an iridium (Ir) nanoparticle catalyst toward the oxygen evolution reaction (OER) in acidic electrolyte, carbon nanotube and titanium dioxide nanocomposites (CNT@TiO2) are presented as a high-performance support. TiO2 was synthesized on CNTs by using a novel layer-by-layer solution coating method that mimics atomic layer deposition (ALD) but is cost-effective and scalable. In the nanocomposites, CNTs serve as the electron pathways and the surface TiO2 layers protect CNTs from corrosion under the harsh OER conditions. Thus, CNT@TiO2 demonstrates excellent corrosion resistance as well as a high electrical conductivity (1.6 ± 0.2 S cm-1) comparable to that of Vulcan carbon (1.4 S cm-1). The interaction between Ir and TiO2 promotes the formation of Ir(iii) species, thereby enhancing the OER activity and stability of the Ir nanoparticle catalyst. Compared to commercial carbon-supported Ir (Ir/C) and Ir black catalysts, CNT@TiO2-supported Ir exhibits superior OER activity and stability.