Engineering intermetallic-metal oxide interface with low platinum loading for efficient methanol electrooxidation

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.

Ultrathin Co-N-C Layer Modified Pt-Co Intermetallic Nanoparticles Leading to a High-Performance Electrocatalyst toward Oxygen Reduction and Methanol Oxidation

The development of low platinum-based alloy electrocatalysts is crucial to accelerate the commercialization of fuel cells, yet remains a synthetic challenge and an incompatibility between activity and stability. Herein, a facile procedure to fabricate a high-performance composite that comprises Pt-Co intermetallic nanoparticles (IMNs) and Co, N co-doped carbon (Co-N-C) electrocatalyst is proposed. It is prepared by direct annealing of homemade carbon black-supported Pt nanoparticles (Pt/KB) covered with a Co-phenanthroline complex. During this process, most of Co atoms in the complex are alloyed with Pt to form ordered Pt-Co IMNs, while some Co atoms are atomically dispersed and doped in the framework of superthin carbon layer derived from phenanthroline, which is coordinated with N to form Co-Nx moieties. Moreover, the Co-N-C film obtained from complex is observed to cover the surface of Pt-Co IMNs, which prevent the dissolution and agglomeration of nanoparticles. The composite catalyst exhibits high activity and stability toward oxygen reduction reactions (ORR) and methanol oxidation reactions (MOR), delivering outstanding mass activities of 1.96 and 2.92 A mgPt -1 for ORR and MOR respectively, owing to the synergistic effect of Pt-Co IMNs and Co-N-C film. This study may provide a promising strategy to improve the electrocatalytic performance of Pt-based catalysts.

Fe-Ni Diatomic Sites Coupled with Pt Clusters to Boost Methanol Electrooxidation via Free Radical Relaying

Pt-based catalysts for direct methanol fuel cells (DMFCs) are still confronted with the challenge of over-oxidation of Pt and poisoning effect of intermediates; therefore, a spatial relay strategy was adopted to overcome these issues. Herein, Pt clusters were creatively fixed on the N-doped carbon matrix with rich Fe-Ni diatoms, which can provide independent reaction sites for methanol oxidation reaction (MOR) and enhance the catalytic activity due to the electronic regulation effect between Pt cluster and atomic-level metal sites. The optimized Pt/FeNi-NC catalyst shows MOR electrocatalytic activity of 2.816 A mgPt -1 , 2.6 times that of Pt/C (1.115 A mgPt -1 ). Experiments combined with DFT study reveal that Fe-Ni diatoms and Pt clusters take charge of hydroxyl radical (⋅OH) generation and methanol activation, respectively. The free radical relaying of ⋅OH could prevent the over-oxidation of Pt. Meanwhile, ⋅OH from Fe-Ni sites accelerates the elimination of intermediates, thus improving the durability of catalysts.

Molybdenum Carbide/Ni Nanoparticles Embedded into Carbon Nanofibers as an Effective Non-Precious Catalyst for Green Hydrogen Production from Methanol Electrooxidation

Molybdenum carbide co-catalyst and carbon nanofiber matrix are suggested to improve the nickel activity toward methanol electrooxidation process. The proposed electrocatalyst has been synthesized by calcination electrospun nanofiber mats composed of molybdenum chloride, nickel acetate, and poly (vinyl alcohol) under vacuum at elevated temperatures. The fabricated catalyst has been characterized using XRD, SEM, and TEM analysis. The electrochemical measurements demonstrated that the fabricated composite acquired specific activity for methanol electrooxidation when molybdenum content and calcination temperature were tuned. In terms of the current density, the highest performance is attributed to the nanofibers obtained from electrospun solution having 5% molybdenum precursor compared to nickel acetate as a current density of 107 mA/cm² was generated. The process operating parameters have been optimized and expressed mathematically using the Taguchi robust design method. Experimental design has been employed in investigating the key operating parameters of methanol electrooxidation reaction to obtain the highest oxidation current density peak. The main effective operating parameters of the methanol oxidation reaction are Mo content in the electrocatalyst, methanol concentration, and reaction temperature. Employing Taguchi's robust design helped to capture the optimum conditions yielding the maximum current density. The calculations revealed that the optimum parameters are as follows: Mo content, 5 wt.%; methanol concentration, 2.65 M; and reaction temperature, 50 °C. A mathematical model has been statistically derived to describe the experimental data adequately with an R² value of 0. 979. The optimization process indicated that the maximum current density can be identified statistically at 5% Mo, 2.0 M methanol concentration, and 45 °C operating temperature.

Fabrication of cobaltous telluride and carbon composite as a promising carrier for boosting electro oxidation of ethylene glycol on palladium in alkaline medium

The development of highly active and earth-rich electrocatalysts remains a formidable challenge for the commercialization of fuel cells. Herein, a composite carrier composed of cobaltous telluride (CoTe) and carbon (C) has been designed for the first time to enhance the electrocatalytic performance of palladium (Pd) nanoparticles (NPs) for the electro-oxidation of ethylene glycol (EG). Remarkably, the mass activity for the as-prepared Pd/CoTe-C catalyst during the ethylene glycol oxidation reaction (EGOR) is found to reach up to 3917.3 mA mg^-1, which is 2.2 times higher than that of Pd/Co-C (1785.0 mA mg^-1) and 4.1 times greater than that of commercial Pd/C catalyst (962.4 mA mg^-1), exceeding that obtained for most Pd-based electrocatalysts reported thus far. In particular, the Pd/CoTe-C catalyst shows better electrochemical stability toward the EGOR than the Pd/Co-C and commercial Pd/C catalysts. Thus, the Pd/CoTe-C electrocatalyst is expected to exhibit broad application prospects in the field of fuel cells.