High-performance oxygen reduction catalysts in both alkaline and acidic fuel cells based on pre-treating carbon material and iron precursor

Recent progress in pyrolyzed carbon materials as electrocatalysts for the oxygen reduction reaction

This review reports some recent advances in pyrolytic carbon as an ORR catalyst and explores its structure–activity relationship.

Sub-50 nm Iron-Nitrogen-Doped Hollow Carbon Sphere-Encapsulated Iron Carbide Nanoparticles as Efficient Oxygen Reduction Catalysts

Sub-50 nm iron-nitrogen-doped hollow carbon sphere-encapsulated iron carbide nanoparticles (Fe3C-Fe,N/C) are synthesized by using a triblock copolymer of poly(styrene-b-2-vinylpyridine-b-ethylene oxide) as a soft template. Their typical features, including a large surface area (879.5 m2 g-1), small hollow size (≈16 nm), and nitrogen-doped mesoporous carbon shell, and encapsulated Fe3C nanoparticles generate a highly active oxygen reduction reaction (ORR) performance. Fe3C-Fe,N/C hollow spheres exhibit an ORR performance comparable to that of commercially available 20 wt% Pt/C in alkaline electrolyte, with a similar half-wave potential, an electron transfer number close to 4, and lower H2O2 yield of less than 5%. It also shows noticeable ORR catalytic activity under acidic conditions, with a high half-wave potential of 0.714 V, which is only 59 mV lower than that of 20 wt% Pt/C. Moreover, Fe3C-Fe,N/C has remarkable long-term durability and tolerance to methanol poisoning, exceeding Pt/C regardless of the electrolyte.

Selective Etching Induced Synthesis of Hollow Rh Nanospheres Electrocatalyst for Alcohol Oxidation Reactions

The hollow noble metal nanostructures have attracted wide attention in catalysis/electrocatalysis. Here a two-step procedure for constructing hollow Rh nanospheres (Rh H-NSs) with clean surface is described. By selectively removing the surfactant and Au core of Au-core@Rh-shell nanostructures (Au@Rh NSs), the surface-cleaned Rh H-NSs are obtained, which contain abundant porous channels and large specific surface area. The as-prepared Rh H-NSs exhibit enhanced inherent activity for the methanol oxidation reaction (MOR) compared to state-of-the-art Pt nanoparticles in alkaline media. Further electrochemical experiments show that Rh H-NSs also have high activity for the electrooxidation of formaldehyde and formate (intermediate species in the course of the MOR) in alkaline media. Unfortunately, Rh H-NSs have low electrocatalytic activity for the ethanol and 1-propanol oxidation reactions in alkaline media. All electrochemical results indicate that the order of electrocatalytic activity of Rh H-NSs for alcohol oxidation reaction is methanol (C1 ) > ethanol (C2 ) > 1-propanol (C3 ). This work highlights the synthesis route of Rh hollow nanostructures, and indicates the promising application of Rh nanostructures in alkaline direct methanol fuel cells.

Bifunctional 3D n-doped porous carbon materials derived from paper towel for oxygen reduction reaction and supercapacitor

Designing and fabricating cheap and active bifunctional materials is crucial for the development of renewable energy technologies. In this article, three-dimensional nitrogen-doped porous carbon materials (NDPC-X, in which X represents the pyrolysis temperature) were fabricated by simultaneous carbonization and activation of polypyrrole-coated paper towel protected by a silica layer followed by acid etching. The material had a high specific surface area (1,123.40 m²/g). The as-obtained NDPC-900 displayed outstanding activity as a catalyst for the oxygen reduction reaction (ORR) as well as an electrode with a high specific capacitance in a supercapacitor in an alkaline medium. The NDPC-900 catalyst for the ORR exhibited a more positive reduction peak potential of -0.068 V (vs. Hg|HgCl₂) than that of Pt/C (-0.121 V), as well as better cycling stability and stronger methanol tolerance. Moreover, the NDPC-900 had a high specific capacitance of 379.50 F/g at a current density of 1 A/g, with a retention rate of 94.5% after 10,000 cycles in 6 mol/L KOH electrolyte when used as an electrode in a supercapacitor. All these results were attributed to the effect of a large surface area, which provided electrochemically active sites. This work introduces an effective way to use biomass-derived materials for the synthesis of promising bifunctional carbon material for electrochemical energy conversion and storage devices.