Hetero-shaped coral-like catalysts through metal-support interaction between nitrogen-doped graphene quantum dots and PtPd alloy for oxygen reduction reaction

Graphene quantum dots reduce oxidation behavior and mechanical damage of epoxy resin irradiated by γ-rays

Epoxy resin is a widely used polymer, but it generates highly reactive free radicals under gamma ray irradiation, which reduces its structural integrity. Compared with traditional carbon nanomaterials such as carbon nanotubes and graphene oxide, graphene quantum dots (GQDs) exhibit excellent radiation resistance due to their zero-dimensional high specific surface area, strong ability to remove free radicals through surface defects, and real-time oxidation monitoring based on fluorescence. This study explores the role of graphene quantum dots in mitigating radiation damage and the microscopic mechanisms behind their protective effects. GQDs were incorporated into EP (1 wt%) to scavenge free radicals and reduce radiation induced spatial heterogeneity. After 1 MGy gamma ray irradiation, GQD/EP showed a relatively thin oxide layer of 180 μm (pure EP was 480 μm, a decrease of 62.5%) and maintained 67% of the initial mechanical strength (pure EP maintained 51%). The glass transition temperature (Tg) increased by 2.2 °C (while that of pure EP decreased by 1.6 °C), which is related to the decrease in free radical content. Micromechanical nanoindentation indicates that the modulus of the outer oxide layer is higher than that of the inner layer, which is due to the densification effect caused by irradiation. Fourier transform infrared spectroscopy analysis showed that the expressions for CC (1605 cm-1) and carbonyl (1725 cm-1) were suppressed in GQD/EP, confirming the surface defect and hydrogen donor scavenging effects of GQDs on free radicals. The key is that GQDs minimize oxidation cascades by neutralizing peroxyl radicals, as demonstrated by fluorescence quenching proportional to radical neutralization. This dual function - structural reinforcement and real-time damage sensing - provides a mechanical framework for designing radiation resistant composite materials. This study deepens our understanding of the radiation resistance mediated by nanomaterials, linking macroscopic properties with atomic scale interactions in polymer matrices.

Pt/Pd Decorate MOFs Derived Co-N-C Materials as High-Performance Catalysts for Oxygen Reduction Reaction

We report here, a strategy to prepare Pt/Pd nanoparticles decorated with Co-N-C materials, where Co-N-C was obtained via pyrolysis of ZIF-67 directly. As-prepared Pt/Pd/Co-N-C catalysts showed excellent ORR performance, offered with a higher limit current density (6.6 mA cm−2) and similar half-wave potential positive (E1/2 = 0.84 V) compared with commercial Pt/C. In addition to an ORR activity, it also exhibits robust durability. The current density of Pt/Pd/Co-N-C decreased by only 9% after adding methanol, and a 10% current density loss was obtained after continuous testing at 36,000 s.

Anchoring Highly Dispersed Pt Electrocatalysts on TiOx with Strong Metal-Support Interactions via an Oxygen Vacancy-Assisted Strategy as Durable Catalysts for the Oxygen Reduction Reaction

Pt electrocatalysts with high activity and durability have still crucial issues for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). In this study, a novel catalyst consisting of Pt nanoparticles (NPs) on TiO_x/C composites (TiO_x-V_o-H/C) with abundant oxygen vacancies (V_o) is proposed, which is abbreviated as PTO-V_o-H/C. The introduction of V_o helps anchor highly dispersed Pt NPs with low loading and strengthen the strong metal-support interaction (SMSI), which benefits to the enhanced ORR catalytic activity. Moreover, the accelerated durability test (ADT) demonstrates the higher retention of ORR activity for PTO-V_o-H/C. Experimental and theoretical analyses reveal that electronic interactions between Pt NPs and TiO_x/C composite support give rise to an electron-rich Pt NPs and strong SMSI effect, which is favorable for the electron transfer and stabilization of Pt NPs. More importantly, the assembled PEMFC with PTO-V_o-H/C shows only 6.9% of decay on maximum power density after 3000 ADT cycles while the performance of Pt/C sharply decreased. This work provides a new insight into the unique vacancy regulation of dispersive Pt on metal oxides for superior ORR performance.

Hyperbranched concave octahedron of PtIrCu nanocrystals with high-index facets for efficiently electrochemical ammonia oxidation reaction

Ammonia oxidation reaction (AOR) via electrocatalysis is one of the most efficient ways of utilizing ammonia (a zero-carbon fuel with high hydrogen content) for renewable energy systems. However, AOR seriously suffers from the slow kinetics, and low durability due to its multi-electron transfer process and the poison of the reaction intermediates (N_ads and NO_ads) to precious metal catalysts. Herein, hyperbranched concave octahedral nanodendrites of PtIrCu (HCOND) with high-index facets of {553}, {331} and {221} were developed for the first time using a solvothermal method. The HCOND possesses PtIr-rich edges and exhibit highly efficient AOR activity and stability in alkaline media, wherein their onset potential is 0.35 V vs.RHE, which is 60 mV and 160 mV lower than that of the PtIrCu nanoparticles (NPs) (0.41 V) and commercial Pt/C (0.51 V), respectively, and its high mass activity of 40.6 A g_PtIr^-1 at the 0.5 V vs.RHE is 10.3 times, 2.34 times higher than that of commercial Pt/C (3.9 A g_Pt^-1) and PtIrCu NPs (17.3 A g_PtIr^-1), respectively. In addition, its peak current density (122.9 A g_PtIr^-1) is only reduced by 17.7% after 2000-cycles accelerated durability test. Meanwhile, the performance of PtIrCu HCOND is also better than that of other previously reported morphologies of Pt based catalysts (eg. nanoparticles, nanocubes, nanofilm, nanoflowers). The improvement is critically ascribed to unique advantages of the specific HCOND structure including PtIr rich surface, high-index faceted nanodendrites, strong lattice strain and electronic effects. These characteristics endow the HCOND with great promise to reduce Pt and Ir loading dramatically in the practical application of direct ammonia fuel cells.