Atomically Dispersed Mg-N-C Material Supported Highly Crystalline Pt3Mg Nanoalloys for Efficient Oxygen Reduction Reaction

Single-atom or atomically dispersed metal materials have emerged as highly efficient catalysts, but their potential as excellent supports has rarely been reported. In this work, we prepared Mg-N-C materials derived from annealing of a Mg-based metal-organic framework (MOF). By introducing Pt, Mg-N-C not only serves as a platform for anchoring Pt nanoparticles but also facilitates the integration of Mg into the Pt face-centered cubic lattice, resulting in the formation of highly crystalline Pt3Mg nanoalloys via the metal-support interfacial interaction. Synchrotron radiation-based X-ray absorption spectroscopy (XAS) enables us to study the interfacial interaction and the surface electronic structure of this intricate system. The formation of Pt3Mg nanoalloys induces a downshift of the Pt d-band (gaining d-charge), as revealed by the decrease in the Pt L3-edge white-line (WL) area under the curve. This downshift can weaken the binding of oxygen reduction reaction (ORR) intermediates, hence improving the ORR performance.

Imidazolium ionic Liquid-Regulated Sub-5-nm Pt(111) with a stable configuration anchored on hollow carbon nanoshells for efficient oxygen reduction

Here, N-doped hollow carbon sphere (NHCS)-supported (111)-plane-engineered sub-5-nm Pt (Pt-NHCS) catalysts regulated precisely by imidazolium ionic liquids were synthesized successfully and used to catalyze oxygen reduction. The (111)-plane engineered Pt nanocrystals with a diameter of 4.5 ± 0.5 nm were homogeneously deposited on the 3-dimensional spherical nanoshells. The resulting Pt nanocrystals anchored on the carbon skeleton exhibit a stable configuration in both alkaline and acid electrolytes with the help of imidazolium cations and pyrolysis. Among all as-prepared catalysts, the optimized Pt-NHCS shows remarkable long-term durability. Specifically, Pt-NHCS maintains 95.3% of the original current density after 10,000 potential cycles, while Pt/C benchmarks exhibit a retention of 78.5%. Accelerated durability test results indicate that Pt-NHCS exhibits a high efficiency of 96 % in comparison with initial current density, while a value of 86% for Pt/C. Density functional theory calculations demonstrate that reactive Pt(111) planes with well-defined Schottky defects and vacancies adsorb and activate oxygen molecule rapidly while desorbing the reaction intermediates.

Enhancement of Activity and Development of Low Pt Content Electrocatalysts for Oxygen Reduction Reaction in Acid Media

Platinum is a main catalyst for the electroreduction of oxygen, a reaction of primary importance to the technology of low-temperature fuel cells. Due to the high cost of platinum, there is a need to significantly lower its loadings at interfaces. However, then O₂-reduction often proceeds at a less positive potential, and produces higher amounts of undesirable H₂O₂-intermediate. Hybrid supports, which utilize metal oxides (e.g., CeO₂, WO₃, Ta₂O₅, Nb₂O₅, and ZrO₂), stabilize Pt and carbon nanostructures and diminish their corrosion while exhibiting high activity toward the four-electron (most efficient) reduction in oxygen. Porosity of carbon supports facilitates dispersion and stability of Pt nanoparticles. Alternatively, the Pt-based bi- and multi-metallic catalysts, including PtM alloys or M-core/Pt-shell nanostructures, where M stands for certain transition metals (e.g., Au, Co, Cu, Ni, and Fe), can be considered. The catalytic efficiency depends on geometric (decrease in Pt-Pt bond distances) and electronic (increase in d-electron vacancy in Pt) factors, in addition to possible metal-support interactions and interfacial structural changes affecting adsorption and activation of O₂-molecules. Despite the stabilization of carbons, doping with heteroatoms, such as sulfur, nitrogen, phosphorus, and boron results in the formation of catalytically active centers. Thus, the useful catalysts are likely to be multi-component and multi-functional.

Enhanced Performance of Pt Nanoparticles on Ni-N Co-Doped Graphitized Carbon for Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells

Since the reaction rate and cost for cathodic catalyst in polymer electrolyte membrane fuel cells are obstacles for commercialization, the high-performance catalyst for oxygen reduction reaction is necessary. The Ni encapsulated with N-doped graphitic carbon (Ni@NGC) prepared with ethylenediamine and carbon black is employed as an efficient support for the oxygen reduction reaction. Characterizations show that the Ni@NGC has a large surface area and mesoporous structure that is suitable to the support for the Pt catalyst. The catalyst structure is identified and the size of Pt nanoparticles distributed in the narrow range of 2–3 nm. Four different nitrogen species are doped properly into graphitic carbon structure. The Pt/Ni@NGC shows higher performance than the commercial Pt/C catalyst in an acidic electrolyte. The mass activity of the Pt/Ni@NGC in fuel cell tests exhibits over 1.5 times higher than that of commercial Pt/C catalyst. The Pt/Ni@NGC catalyst at low Pt loading exhibits 47% higher maximum power density than the Pt/C catalyst under H2-air atmosphere. These results indicate that the Ni@NGC as a support is significantly beneficial to improving activity.

Single Co Atoms Implanted into N-Doped Hollow Carbon Nanoshells with Non-Planar Co-N4-1-O2 Sites for Efficient Oxygen Electrochemistry

Facile synthesis of cost-effective carbon-supported Co single atoms (Co-SAs) exhibits huge potential applications in energy storage and conversion devices. We here report the implantation of Co-SAs into hollow carbon spheres (Co-SAs-HCS) via a facile wet-chemistry strategy followed by controlled pyrolysis. Electron-rich histidine acted as a Lewis base effectively immobilizing Co²⁺ (Lewis acid) via the electrostatic effect and hydrogen bonds, thus achieving the scalable synthesis of Co-SAs-HCS. We constructed a series of histidine-Co²⁺ structure models to elucidate the formation of histidine-Co²⁺ complexes by analyzing their binding energy. X-ray absorption fine-structure results verify that central Co atoms with four N coordination atoms possess a non-planar Co-N₄ structure. Electrochemical results indicate that the as-prepared Co-SAs-HCS catalyst shows a low potential difference (0.809 V) between the oxygen evolution reaction potential at 10 mA cm^-2 and the oxygen reduction reaction half-wave potential, outperforming the commercial Pt/C catalysts (0.996 V). Moreover, an assembled Zn-air battery based on Co-SAs-HCS exhibits an unexpected long-term durability. We have demonstrated that non-planar Co-N₄-1-O₂ sites are the source for highly efficient adsorption and dissociation of O₂ molecules and then reduction of the free energy of desorption of the intermediates by density functional theory. Our findings provide a new design insight into the exploration of advanced electrocatalysts, which will be applied in the design of green energy devices in the future.

Synthesis of FeCo–N@N-doped carbon oxygen reduction catalysts via microwave-assisted ammoxidation

A core–shell structured FeCo–N@N-doped carbon derived from biomass wastes (sugarcane and palm kernel shell) is facilely prepared by hydrothermal carbonization and NH₃ microwave ammoxidation methods.