Hydrogenated graphene as support of Pd nanoparticles with improved electrocatalytic activity for ethanol oxidation reaction in alkaline media

Application of Hydrogenated Graphitic Supports in Electrocatalysts: Effects on Carbon Support Surface Chemistry, Nanoparticle Growth, and Electrocatalytic Activity

One of the key technical challenges before the widespread adoption of proton exchange membrane fuel cells (PEMFCs) is increasing the durability of the platinum catalyst layer to meet a target of 8000 operating hours with only a 10% loss of performance. Carbon corrosion, one of the primary mechanisms of degradation in fuel cells, has attracted attention from researchers interested in solving the durability problem. As such, the development of catalyst supports to avoid this issue has been a focus in recent years, with interest in hydrophobic supports such as highly graphitized carbons. In this research, we propose a method to increase the durability of carbon supports by way of exploiting hydrogenated graphene's hydrophobic properties. By performing a Birch reduction on graphene nanoplatelets, we were able to synthesize hydrogenated graphene nanoplatelets which were used as support for hollow porous PtNi nanoparticles. The structure of these nanoparticle-carbon composites was characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy coupled with scanning transmission electron microscopy (STEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). We found that hydrogenation can strongly affect the morphology of nanoparticles formed as well as increase the electrochemical stability of the composites. Accelerated stress tests for 6000 cycles between 1.0 and 1.6 V vs RHE at 25 °C demonstrated that a hydrogenated support for PtNi increased the retained electrochemical surface from 36.8% to 61.9% when compared to the pristine graphene nanoplatelets. Moreover, the retained activity was increased from 26.6% to 53.0% by use of the hydrogenated carbon support. To confirm that hydrogenation enhanced durability, stress tests combined with Raman spectroscopy showed minimal change in the ID/IG ratio of the hydrogenated composite. Finally, identical location transmission electron microscopy (IL-TEM) was used to support the results of the electrochemical stress tests.

Research on the Morphology Reconstruction of Deep Cryogenic Treatment on PtRu/nitrogen-Doped Graphene Composite Carbon Nanofibers

To improve the performance of PtRu/nitrogen-doped graphene composite carbon nanofibers, the composite carbon nanofibers were thermally compensated by deep cryogenic treatment (DCT), which realized the morphology reconstruction of composite carbon nanofibers. The effects of different DCT times were compared: 12 h, 18 h, and 24 h. The morphology reconstruction mechanism was explored by combining the change of inner chain structure and material group. The results showed that the fibers treated for 12 h had better physical and chemical properties, where the diameter is evenly distributed between 500 and 800 nm. Combined with Fourier infrared analysis, the longer the cryogenic time, the more easily the water vapor and nitrogen enter polymerization reaction, causing changes of chain structure and degradation performance. With great performance of carbonization and group transformation, the PtRu/nitrogen-doped graphene composite carbon nanofibers can be used as an efficient direct alcohol fuel cell catalyst and promote its commercialization.

Pd Nanoparticles Coupled to NiMoO4-C Nanorods for Enhanced Electrocatalytic Ethanol Oxidation

The interfacial interaction including chemical bonding or electron transfer and even physisorption in composite electrocatalysts has a considerable effect on electrocatalytic oxidation reaction. Herein, we report a tremendously enhanced catalytic activity and excellent durability for the ethanol electro-oxidation reaction in NiMoO₄-C-supported Pd composites (Pd/NiMoO₄-C) compared to the commercial Pd/C (10%) catalyst. The X-ray powder diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements disclose that the strong electron transfer between NiMoO₄ nanorods and Pd nanoparticles likely induces the formation of more electrochemical active centers and improves the adsorption-desorption capacity of reactants and corresponding intermediates. In addition, the Pd/NiMoO₄-C composite exhibits superior specific activity for ethanol oxidation compared to the Pd/NiMoO₄ catalyst with physically incorporated carbon black, which further reveals that the stronger anchoring effect between Pd and C and higher electrical conductivity in Pd/NiMoO₄-C composites are also conducive to promote the ethanol oxidation reaction. These discoveries provide an effective and simple method for the design of advanced electrocatalysts and provide more insights into optimizing the electronic interaction between the catalyst and support in general.

Surface Engineering of Flower-Like Ionic Liquid-Functionalized Graphene Anchoring Palladium Nanocrystals for a Boosted Ethanol Oxidation Reaction

The development of low-cost and high-performance electrocatalyst-supporting materials is desirable and necessary for the ethanol oxidation reaction (EOR). Here, we report a facile and universal template-free approach for the first time to synthesize three-dimensional (3D) flower-like ionic liquid-functionalized graphene (IL-RGO). Then, the crystalline Pd nanoparticles were anchored on IL-RGO by a simple wet chemical growth method without a surfactant (denoted as Pd/IL-RGO). In particular, the IL is conducive to form a 3D flower-like structure. The optimized Pd/IL-RGO-2 presents a much-promoted electrocatalytic performance toward the EOR compared with commercial Pd/C catalysts, which is mainly derived from the grafted IL on RGO and the unique 3D flower-like structure. In detail, the IL can control, stabilize, and disperse the Pd nanocrystals as well as serving as the solvent and electrolyte in the microenvironment of the EOR, and the 3D flower-like structure endows the Pd/IL-RGO with high surface areas and rich opened channels, thereby kinetically accelerating the charge/mass transfers. Furthermore, density functional theory calculations reveal that the strong electronic interaction between Pd and IL-RGO generates a downshift of d_center for Pd and thereby enhances the durability toward CO-like intermediates and electrocatalytic reaction kinetics.