A Carbon-Support-Free Titanium Oxynitride Catalyst for Proton Exchange Membrane Fuel Cell Cathodes

The Recent Progress of Oxygen Reduction Electrocatalysts Used at Fuel Cell Level

Proton exchange membrane fuel cells (PEMFCs) are gaining significant interest as an attractive substitute for traditional fuel cells, with higher energy density, lower environmental pollution, and better operation efficiency. However, the cathode reaction, i.e., the oxygen reduction reaction (ORR), is widely proved to be inefficient, and therefore an obstacle to the widespread development of PEMFCs. The requirement for affordable highly-efficient ORR catalysts is extremely urgent to be met, especially at fuel cell level. Unfortunately, most previous reports focus on the ORR performance at rotating disk electrodes (RDE) level instead of membrane electrode assembly (MEA) level, making it harder to evaluate ORR catalysts operating under real vehicle conditions. Obviously, it is extremely necessary to develop an in-depth understanding of the structure-activity relationship of highly-efficient ORR catalysts applied at MEA level. In this work, an overview of the latest advances in ORR catalysts is provided with an emphasis on their performance at MEA level, hoping to cover the novel and systemic insights for innovative and efficient ORR catalyst design and applications in PEMFCs.

Thermoplasmonic In Situ Fabrication of Nanohybrid Electrocatalysts over Gas Diffusion Electrodes for Enhanced H2O2 Electrosynthesis

Large-scale development of electrochemical cells is currently hindered by the lack of Earth-abundant electrocatalysts with high catalytic activity, product selectivity, and interfacial mass transfer. Herein, we developed an electrocatalyst fabrication approach which responds to these requirements by irradiating plasmonic titanium nitride (TiN) nanocubes self-assembled on a carbon gas diffusion layer in the presence of polymeric binders. The localized heating produced upon illumination creates unique conditions for the formation of TiN/F-doped carbon hybrids that show up to nearly 20 times the activity of the pristine electrodes. In alkaline conditions, they exhibit enhanced stability, a maximum H2O2 selectivity of 90%, and achieve a H2O2 productivity of 207 mmol gTiN-1 h-1 at 0.2 V vs RHE. A detailed electrochemical investigation with different electrode arrangements demonstrated the key role of nanocomposite formation to achieve high currents. In particular, an increased TiOxNy surface content promoted a higher H2O2 selectivity, and fluorinated nanocarbons imparted good stability to the electrodes due to their superhydrophobic properties.

Enhancement of oxygen reduction reactivity on TiN by tuning the work function via metal doping

Oxide layers on conductive TiN have recently been investigated to catalyse the oxygen reduction reaction (ORR) in acidic media. The ORR reactivity, i.e., activity and selectivity, has been correlated with the surface nitrogen atoms. A new strategy, optimising the work function via the doping of foreign metals, is revealed herein to enhance the reactivity.

A macroporous titanium oxynitride-supported bifunctional oxygen electrocatalyst for zinc–air batteries

A macroporous titanium oxynitride-supported bifunctional oxygen electrocatalyst was fabricated for the development of rechargeable zinc–air batteries.

Phosphor and nitrogen co-doped rutile TiO2 covered on TiN for oxygen reduction reaction in acidic media

Phosphor and nitrogen atoms were co-doped into rutile TiO₂ phase on TiN to produce new active sites for oxygen reduction reaction.

Morphology-Controlled Nitrogen-Containing Polymers as Synthetic Precursors for Electrochemical Oxygen Reduction Fe/N/C Cathode Catalysts

Nitrogen-containing aromatic polymers such as polyimide are known for their high thermal stability. While they have been widely used in industry, their relevance to catalysis is still quite limited. In recent years, nitrogen-containing polymers have been explored as precursors of nitrogen-doped carbonaceous materials, which are particularly attractive as non-precious metal catalysts for oxygen reduction in fuel cells. The high thermal stability of nitrogen-containing polymers contributes to an effective control over the morphology of the resulting carbonaceous catalysts. This review article provides an overview of the recent progress on the research and development of Fe/N/C oxygen reduction catalysts prepared from morphology-controlled nitrogen-containing polymers.

Ti4O7/g-C3N4 Visible Light Photocatalytic Performance on Hypophosphite Oxidation: Effect of Annealing Temperature

The oxidation of hypophosphite to phosphate is the key to recover the phosphorus resource from the hypophosphite wastewater. In the present work, Ti₄O₇/g-C₃N₄ composites were synthesized at two different temperatures (100 and 160°C) and their performance on photocatalytic oxidation of hypophosphite under visible light irradiation and the corresponding mechanism were evaluated. A hydrolysis method using g-C₃N₄ and Ti₄O₇ was applied to synthesize the Ti₄O₇/g-C₃N₄ composites with their hybrid structure and morphology confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectra (XPS). The annealing temperature significantly affected the photocatalytic performance of Ti₄O₇/g-C₃N₄ that the 160-Ti₄O₇/g-C₃N₄ composite (fabricated at 160°C) showed the highest oxidation efficiency of hypophosphite of 81% and the highest photocatalytic oxidation rate of 0.467 h^-1 comparing with the 100-Ti₄O₇/g-C₃N₄ composite (fabricated at 100°C) and pure g-C₃N₄. The enhanced photocatalytic performance of 160-Ti₄O₇/g-C₃N₄ could be ascribed to the effective charge separation and enhanced photoabsorption efficiency. Additionally, electron spin resonance (ESR) results showed that hydroxyl radicals and superoxide anion radicals were mainly responsible to the oxidation of hypophosphite with superoxide anion radicals accounting for a more significant contribution. Moreover, Ti₄O₇/g-C₃N₄ photocatalysts showed the remarkable stability in the repetitive experiments.

Creation of oxygen reduction reaction active sites on titanium oxynitride without increasing the nitrogen doping level

Active sites were created on ORR-active titanium oxynitride by low-temperature annealing without changing the nitrogen doping level to determine their origin.

Zirconium Oxynitride-Catalyzed Oxygen Reduction Reaction at Polymer Electrolyte Fuel Cell Cathodes

Most nonplatinum group metal (non-PGM) catalysts for polymer electrolyte fuel cell cathodes have so far been limited to iron(cobalt)/nitrogen/carbon [Fe(Co)/N/C] composites owing to their high activity in both half-cell and single-cell cathode processes. Group IV and V metal oxides, another class of non-PGM catalysts, are stable in acidic media; however, their activities have been mostly evaluated for half-cells, with no single-cell performances comparable to those of Fe/N/C composites reported to date. Herein, we report successful syntheses of zirconium oxynitride catalysts on multiwalled carbon nanotubes, which show the highest oxygen reduction reaction activity among oxide-based catalysts. The single-cell performance of these catalysts reached 10 mA cm^-2 at 0.9 V, being comparable to that of state-of-the-art Fe/N/C catalysts. This new record opens up a new pathway for reaching the year 2020 target set by the U.S. Department of Energy, that is, 44 mA cm^-2 at 0.9 V.