Optimized electrocatalytic performance of PtZn intermetallic nanoparticles for methanol oxidation by designing catalyst support and fine-tuning surface composition

Nitrogen and Sulfur Co-Doped Graphene Composite Aerogel Microspheres Supporting Pt Electrode-Catalyzed Methanol Electro-Oxidation Reaction

Nitrogen and sulfur co-doped graphene composite aerogel microspheres containing pyrolyzed carbon (NS-GAMs@C) are prepared by pressure-spraying the graphene oxide (GO) dispersion with water-soluble phenolic resin and thiourea, followed by freeze shaping, freeze-drying, and high-temperature carbonization. The resulting NS-GAMs@C possesses interconnected porous structures with large surface areas and high doping levels of N/S elements. Furthermore, the platinum nanoparticles (Pt NPs) are grown onto the NS-GAMs@C via a solvothermal reduction reaction to obtain the Pt/NS-GAMs@C microspheres with an average particle size of ∼32.25 μm. The residual carbon species in situ formed by the high-temperature carbonization of phenolic resin can act as intercalation compounds to reduce the self-stacking of graphene sheets, which contributes to an enhanced specific surface area and doping level. The N/S co-doping in NS-GAMs@C improves the interaction between the Pt and carriers, reduces the size of Pt NPs, ensures their even distribution, and increases the proportion of highly active Pt (111) crystal planes. Consequently, the methanol oxidation activity of Pt/NS-GAMs@C is significantly improved compared to undoped materials. Specifically, the optimized Pt/NS-GAMs@C composites demonstrate a remarkable mass activity of 840.11 mA·mg-1 Pt for methanol electrooxidation, which is approximately 2.39, 3.94, 3.41, and 1.75 times higher than that of commercial Pt/C, Pt/rGO (reduced GO), Pt/GAMs without doping, and Pt/NS-GAB@C (bulk aerogel), respectively. Additionally, the Pt/NS-GAMs@C exhibits long-term electrocatalytic stability. This research provides a novel catalyst system based on aerogel microspheres for methanol electrooxidation fuel cells.

Electro-Oxidation Reaction of Methanol over La2-xSrxNi1-y(Mn/Fe/Co)yO4+δ Ruddlesden-Popper Oxides

Solution combustion-synthesized Ruddlesden-Popper oxides La1.4Sr0.6Ni0.9(Mn/Fe/Co)0.1O4+δ were explored for the methanol electro-oxidation reaction. With optimal doping of Sr2+ in the A site and Co2+ in the B site, Ni3+ with t2g6 d x 2 - y 2 1 configuration in La1.4Sr0.6Ni0.9Co0.1O4+δ exhibited a tetragonal distortion with compression in axial bonds and elongation in equatorial bonds. This structural modification fostered an augmented overlap of d z 2 orbitals with axial O 2p orbitals, leading to a heightened density of states at the Fermi level. Consequently, this facilitated not only elevated electrical conductivity but also a noteworthy reduction in the charge transfer resistance. These effects collectively contributed to the exceptional methanol oxidation activity of La1.4Sr0.6Ni0.9Co0.1O4+δ, as evidenced by an impressive current density of 21.4 mA cm-2 and retention of 95% of initial current density even after 10 h of prolonged reaction. The presence of Ni3+ further played a pivotal role in the creation of NiOOH, a crucial intermediate species, facilitated by the presence of surface oxygen vacancies. These factors synergistically enabled efficient methanol oxidation. In summary, our present study not only yields substantial insights but also paves the way for a novel avenue to fine-tune the activity of Ruddlesden-Popper oxides for the successful electro-oxidation of methanol.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

Design of Pt-Sn-Zn Nanomaterials for Successful Methanol Electrooxidation Reaction

This work highlights the potential for the synthesis of new PtSnZn catalysts with enhanced efficiency and durability for methanol oxidation reaction (MOR) in low-temperature fuel cells. In this research, PtZn and PtSnZn nanoparticles deposited on high surface area Vulcan XC-72R Carbon support were created by a microwave-assisted polyol method. The electrochemical performances of synthesized catalysts were analyzed by cyclic voltammetry and by the electrooxidation of adsorbed CO and the chronoamperometric method. The physicochemical properties of obtained catalysts were characterized by transmission electron microscopy (TEM), thermogravimetric (TGA) analysis, energy dispersive spectroscopy (EDS) and by X-ray diffraction (XRD). The obtained findings showed the successful synthesis of platinum-based catalysts. It was established that PtSnZn/C and PtZn/C catalysts have high electrocatalytic performance in methanol oxidation reactions. Catalysts stability tests were obtained by chronoamperometry. Stability tests also confirmed decreased poisoning and indicated improved stability and better tolerance to CO-like intermediate species. According to activity and stability measurements, the PtSnZn/C catalyst possesses the best electrochemical properties for the methanol oxidation reaction. The observed great electrocatalytic activity in the methanol oxidation reaction of synthesized catalysts can be attributed to the beneficial effects of microwave synthesis and the well-balanced addition of alloying metals in PtSnZn/C catalysts.