Nano-ceramic support materials for low temperature fuel cell catalysts

Synergistic reductive catalytic effects of an organic and inorganic hybrid covalent organic framework for hydrogen fuel production

Electrocatalytic hydrogen generation in alkaline medium has become widely used in a variety of sectors. However, the possibility for additional performance improvement is hampered by slow kinetics. Because of this restriction, careful control over processes such as water dissociation, hydroxyl desorption and hydrogen recombination is required. Covalent organic frameworks (COFs) based on porphyrin and polyoxometalates (POMs) show encouraging electrocatalytic performance, offering a viable route for effective and sustainable hydrogen generation. Their specific architectures lead to increased electrocatalytic activity, which makes them excellent choices for developing water electrolysis as a clean energy conversion method in the alkaline medium. In this regard, TTris@ZnPor and Lindqvist POM were coordinated to create a new eco-friendly and highly active covalent organic framework (TP@VL-COF). In order to describe TP@VL-COF, extensive structural and morphological investigations were carried out through FTIR, 1H NMR, elemental analysis, SEM, fluorescence, UV-visible, PXRD, CV, N2-adsorption isotherm, TGA and DSC analyses. In an alkaline medium, the electrocatalytic capability of 20%C/Pt, TTris@ZnPor, Lindqvist POM and TP@VL-COF was explored and compared for the hydrogen evolution reaction (HER). The TP@VL-COF showed the best catalytic efficiency for HER in an alkaline electrolyte, requiring just a 75 mV overpotential to drive 10 mA cm-2 and outperforming 20%C/Pt, TTris@ZnPor, Lindqvist POM and other reported catalysts. The Tafel slope value also indicates faster kinetics for TP@VL-COF (114 mV dec-1) than for 20%C/Pt (182 mV dec-1) TTris@ZnPor (116 mV dec-1) and Lindqvist POM (125 mV dec-1).

Black Tungsten Oxide Nanofiber as a Robust Support for Metal Catalysts: High Catalyst Loading for Electrochemical Oxygen Reduction

Black valve metal oxides with low oxygen vacancies are identified to be promising for various industrial applications, such as in gas sensing, photocatalysis, and rechargeable batteries, owing to their high reducibility and stability, as well as considerable fractions of low-valent metal species and oxygen vacancies in their lattices. Herein, the nanofiber (NF) of black oxygen-deficient tungsten trioxide (WO_{3- x} ) is presented as a versatile and robust support for the direct growth of a platinum catalyst for oxygen reduction reaction (ORR). The nonstoichiometric, poorly crystallized black WO_{3- x} NFs are prepared by electrospinning the W precursor into NFs followed by their low-temperature (650 °C) reductive calcination. The black WO_{3- x} NFs have adequate electrical conductivity owing to their decreased bandgap and amorphous structure. Remarkably, the oxygen-deficient surface (surface O/W = 2.44) facilitates the growth of small Pt nanoparticles, which resist aggregation, as confirmed by structural characterization and computational analysis. The Pt-loaded black WO_{3- x} NFs outperform the Pt-loaded crystalline white WO_{3- x} NFs in both the electrochemical ORR activity and the accelerated durability test. This study can inspire the use of oxygen-deficient metal oxides as supports for other electrocatalysts, and can further increase the versatility of oxygen-deficient metal oxides.

Durable Tungsten Carbide Support for Pt-Based Fuel Cells Cathodes

In an effort to develop durable, corrosion-resistant catalyst support materials for polymer electrolyte fuel cells, modified polymer-assisted deposition method was used to synthesize tungsten carbide (WC, WC_1-x), which was later used as a support material for Pt-based oxygen reduction reaction catalyst, as an alternative for the corrosion-susceptible, carbon supports. The Pt-deposited tungsten carbide's corrosion-resistance, oxygen reduction reaction electrocatalysis, and durability were studied and compared to that of Pt/C. Bulk free carbon was found to be absent from the ceramic matrix which had particle size in the range of 2-25 nm. Tungsten carbide support appears to enhance the oxygen reduction activity on Pt, showing an increase in mass activity (nearly 2-fold at 0.85 V vs RHE) and specific activity (more than 7 times higher), alongside decrease in overpotential, in comparison to Pt/C. A significant increase in durability was also observed with the tungsten carbide-based system.

Co-Zn-MOFs Derived N-Doped Carbon Nanotubes with Crystalline Co Nanoparticles Embedded as Effective Oxygen Electrocatalysts

The oxygen reduction reaction (ORR) is a crucial step in fuel cells and metal-air batteries. It is necessary to expand the range of efficient non-precious ORR electrocatalysts on account of the low abundance and high cost of Pt/C catalysts. Herein, we synthesized crystalline cobalt-embedded N-doped carbon nanotubes (Co@CNTs-T) via facile carbonization of Co/Zn metal-organic frameworks (MOFs) with dicyandiamide at different temperatures (t = 600, 700, 800, 900 °C). Co@CNTs- 800 possessed excellent ORR activities in alkaline electrolytes with a half wave potential of 0.846 V vs. RHE (Reversible Hydrogen Electrode), which was comparable to Pt/C. This three-dimensional network, formed by Co@CNTs-T, facilitated electron migration and ion diffusion during the ORR process. The carbon shell surrounding the Co nanoparticles resulted in Co@CNTs-800 being stable as an electrocatalyst. This work provides a new strategy to design efficient and low-cost oxygen catalysts.

Advanced Catalytic Materials for Ethanol Oxidation in Direct Ethanol Fuel Cells

Direct ethanol fuel cells (DEFCs) have emerged as promising and advanced power systems that can considerably reduce fossil fuel dependence, and thus have attracted worldwide attention. DEFCs have many apparent merits over the analogous devices fed with hydrogen or methanol. As the key constituents, the catalysts for both cathodes and anodes usually face some problems (such as high cost, low conversion efficiency, and inferior durability) that hinder the commercialization of DEFCs. This review mainly focuses on the most recent advances in nanostructured catalysts for anode materials in DEFCS. First, we summarize the effective strategies used to achieve highly active Pt- and Pd-based catalysts for ethanol electro-oxidation, including composition control, microstructure design, and the optimization of support materials. Second, a few non-precious catalysts based on transition metals (such as Fe, Co, and Ni) are introduced. Finally, we outline the concerns and future development of anode catalysts for DEFCs. This review provides a comprehensive understanding of anode catalysts for ethanol oxidation in DEFCs.

Development of advanced materials for cleaner energy generation through fuel cells

The use of fuel cells in the transportation sector holds promise as a sustainable option for the generation of cleaner energy along with cumulative lesser GHG emissions.

An environmentally friendly one-pot synthesis method by the ultrasound assistance for the decoration of ultrasmall Pd-Ag NPs on graphene as high active anode catalyst towards ethanol oxidation

An environmentally friendly one-pot synthesis approach for the decoration of Pd-Ag nanoparticles with the ultrasmall size on graphene (Pd-Ag/G) by the assistance of ultrasound is proposed in this paper. This method offers exceptional advantages over other approaches such as environmentally friendly synthesis, being low temperature, reductant, surfactant free, simple, fast and one-pot synthesis. In this work, silver formate is added to the graphene suspension at 25 °C. Then, PdCl₂ is added to the suspension under stirring to fabricate Pd-Ag/G. The uniform dispersity of nanoparticles with an average size of about 2-3 nm is well confirmed by transmission electron microscopy micrographs. The resultant catalyst is applied as anode electrocatalyst towards electrooxidation reaction of ethanol. The Pd-Ag/G catalyst displays exceptional catalytic activity and durability towards electro-oxidation of ethanol. According to the obtained results, it be concluded that the combination of Ag and Pd, ultrasmall and uniform distribution of Pd-Ag nanoparticles led to the improvement of electrocatalytic activity of the Pd-Ag/G catalyst.

TePtFe Nanotubes as High-Performing Bifunctional Electrocatalysts for the Oxygen Reduction Reaction and Hydrogen Evolution Reaction

Currently, a multicomponent platinum-based alloy has been applied as a promising electrocatalyst to improve catalysis and lower the usage of the noble metal platinum. Herein, a tellurium nanowire (NW)-derived ternary TePtFe nanotube (NT) electrocatalyst has been prepared by the Kirkendall effect. The TePtFe NT formed consists of small single-crystal nanoparticles and voids with an open-end and hollow structure. The TePtFe NT electrocatalyst presents an impressive catalytic activity and stability for both the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). Its ORR specific activity and mass activity are 8.5 and 2.4 times, respectively, improved relative to those of commercial platinum catalysts. It is also impressive that, for the HER, a very low overpotential of 28.1 mV at 10 mA cm^-2 can be achieved; this is lower than that of platinum (51.8 mV) catalysts in 0.1 m HClO₄ , and the activity is improved, even after 5000 cycles. This work reveals that TePtFe NTs can be employed as nanocatalysts with an impressive catalytic activity and stability for application in fuel cells and hydrogen production.

Strong metal–support interaction improves activity and stability of Pt electrocatalysts on doped metal oxides

Niobium and antimony doped tin oxide loose-tubes decorated with Pt nanoparticles present outstanding mass activity and stability, exceeding those of a reference carbon-based electrocatalyst.

Polyaniline and Perfluorosulfonic Acid Co-Stabilized Metal Catalysts for Oxygen Reduction Reaction

A proton (perfluorosulfonic acid, PFSA) and electron (polyaniline, PANI) conductor polymer costabilized Pt catalyst (Pt-PFSA/C@PANI) is synthesized to improve the long-term stability of polymer electrolyte membrane fuel cells (PEMFCs). The prepared catalyst not only displays comparable oxygen reduction reaction (ORR) activity, but significantly higher electrochemical stability than commercial porous carbon nanosphere supported Pt catalysts (Pt/C). This robust electrochemical property can be due to the result of PFSA and PANI. PANI as protector inhibits carbon nanospheres from corrosion of carbon supports in harsh chemical and electrochemical conditions. Meanwhile, PFSA wrapped Pt NPs (Pt@PFSA) can also anchor Pt NPs on C@PANI to avoid aggregation and detachment of Pt NPs, due to the increased metal-support interaction caused by the strong electrostatic attraction between PANI and PFSA with corresponding positive and negative charges. Significantly, after coating PANI on carbon supports (C@PANI), almost all micropores in the surface of carbon disappear, effectively avoiding the embedding of Pt nanopaticles into micropores. Furthermore, the triple-phase boundary toward ORR catalysis can be facilitated by PFSA as proton conductor (solid electrolyte). These are of benefit to increase utilization of Pt noble metals and ORR activity of our new catalysts.

Effect of core/shell structured TiO2@C nanowire support on the Pt catalytic performance for methanol electrooxidation

Core/shell structured carbon-coated titania nanowires combine the advantages of structure and material, improving the electrocatalytic performance of Pt-based catalysts.

Kinetic Role of Carbon in Solid-State Synthesis of Zirconium Diboride using Nanolaminates: Nanocalorimetry Experiments and First-Principles Calculations

Reactive nanolaminates afford a promising route for the low-temperature synthesis of zirconium diboride, an ultrahigh-temperature ceramic with metallic properties. Although the addition of carbon is known to facilitate sintering of ZrB2, its effect on the kinetics of the formation reaction has not been elucidated. We have employed a combined approach of nanocalorimetry and first-principles theoretical studies to investigate the kinetic role of carbon in the synthesis of ZrB2 using B4C/Zr reactive nanolaminates. Structural characterization of the laminates by XRD and TEM reveal that the reaction proceeds via interdiffusion of the B4C and Zr layers, which produces an amorphous Zr3B4C alloy. This amorphous alloy then crystallizes to form a supersaturated ZrB2(C) compound. A kinetic analysis shows that carbon lowers the energy barriers for both interdiffusion and crystallization by more than 20%. Energetic calculations based on first-principles modeling suggest that the reduction of the diffusion barrier may be attributed to the stronger bonding between Zr and C as compared to the bonding between Zr and B.

Highly efficient and durable TiN nanofiber electrocatalyst supports

To date, carbon-based materials including various carbon nanostructured materials have been extensively used as an electrocatalyst support for proton exchange membrane fuel cell (PEMFC) applications due to their practical nature. However, carbon dissolution or corrosion caused by high electrode potential in the presence of O2 and/or water has been identified as one of the main failure modes for the device operation. Here, we report the first TiN nanofiber (TNF)-based nonwoven structured materials to be constructed via electrospinning and subsequent two-step thermal treatment processes as a support for the PEMFC catalyst. Pt catalyst nanoparticles (NPs) deposited on the TNFs (Pt/TNFs) were electrochemically characterized with respect to oxygen reduction reaction (ORR) activity and durability in an acidic medium. From the electrochemical tests, the TNF-supported Pt catalyst was better and more stable in terms of its catalytic performance compared to a commercially available carbon-supported Pt catalyst. For example, the initial oxygen reduction performance was comparable for both cases, while the Pt/TNF showed much higher durability from an accelerated degradation test (ADT) configuration. It is understood that the improved catalytic roles of TNFs on the supported Pt NPs for ORR are due to the high electrical conductivity arising from the extended connectivity, high inertness to the electrochemical environment and strong catalyst-support interactions.

Platinized Graphene/ceramics Nano-sandwiched Architectures and Electrodes with Outstanding Performance for PEM Fuel Cells

For the first time a novel oxygen reduction catalyst with a 3D platinized graphene/nano-ceramic sandwiched architecture is successfully prepared by an unusual method. Herein the specific gravity of graphene nanosheets (GNS) is tailored by platinizing graphene in advance to shorten the difference in the specific gravity between carbon and SiC materials, and then nano-SiC is well intercalated into GNS interlayers. This nano-architecture with highly dispersed Pt nanoparticles exhibits a very high oxygen reduction reaction (ORR) activity and polymer electrolyte membrane (PEM) fuel cell performance. The mass activity of half cells is 1.6 times of that of the GNS supported Pt, and 2.4 times that of the commercial Pt/C catalyst, respectively. Moreover, after an accelerated stress test our catalyst shows a predominantly electrochemical stability compared with benchmarks. Further fuel cell tests show a maximum power density as high as 747 mW/cm(2) at low Pt loading, which is more than 2 times higher than that of fuel cells with the pristine graphene electrode.

Extremely stable platinum nanoparticles encapsulated in a zirconia nanocage by area-selective atomic layer deposition for the oxygen reduction reaction

Encapsulation of Pt nanoparticles (NPs) in a zirconia nanocage by area-selective atomic layer deposition (ALD) can significantly enhance both the Pt stability and activity. Such encapsulated Pt NPs show 10 times more stability than commercial Pt/C catalysts and an oxygen reduction reaction (ORR) activity 6.4 times greater than that of Pt/C.

Oxygen reduction reaction activity and structural stability of Pt–Au nanoparticles prepared by arc-plasma deposition

Sequential arc-plasma deposited Pt–Au alloy nanoparticles show superior electrochemical structural durability compared with arc-plasma deposited Pt nanoparticles before and after electrochemical potential cycles.