The direct synthesis of TiN nanoparticles on carbon black (CB) was achieved using an mpg-C(3)N(4)/CB composite as a template. The obtained TiN/CB composites ensured improved contact between TiN and CB, functioning as an efficient cathode catalyst for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs). The preparation procedure developed in this study is applicable for the synthesis of a variety of supported nano-nitride catalysts.

A Li-O(2) battery with TiN nanoparticles supported on Vulcan XC-72, n-TiN/VC, as the cathode catalyst presented an onset potential for the oxygen evolution reaction (OER) at 2.9 V, contrasting with a mixture of micro-sized TiN and VC (m-TiN/VC), and VC, both at ~3.1 V. The discharge-recharge voltage gap of n-TiN/VC was estimated to be 1.05 V, which is 390 and 450 mV smaller than that of m-TiN/VC and VC, respectively, at 50 mA g(carbon)(-1). These indicate that n-TiN/VC can function as both an active ORR catalyst during discharge and an efficient OER catalyst during recharge.

TiN, NbN, TaN, and Ta 3 N 5 nanoparticles synthesized using mesoporous graphitic (mpg)-C 3 N 4 templates were investigated for the oxygen reduction reaction (ORR) as cathode catalysts for polymer electrolyte fuel cells. The temperature-programmed desorption (TPD) of molecularly adsorbed O 2 at 120−170 K from these nanoparticles was examined, and the resulting amount and temperature of desorption were key factors determining the ORR activity. The size-dependent TiN nanoparticles (5−8 and 100 nm) were then examined. With decreasing particle size, the density of molecularly adsorbed O 2 per unit of surface area increased, indicating that a decrease in particle size increases the number of active sites. It is hard to determine the electrochemical active surface area for nonmetal electrocatalysts (such as oxides or nitrides), because of the absence of proton adsorption/ desorption peaks in the voltammograms. In this study, O 2 -TPD for molecularly adsorbed O 2 at low temperature demonstrated that the amount and strength of adsorbed O 2 were key factors determining the ORR activity. The properties of molecularly adsorbed O 2 on cathode catalysts are discussed against the ORR activity.

Nanoparticles meet nanotubes! Direct synthesis of TiN nanoparticles in a three‐dimensional network of few‐walled carbon nanotubes (FWCNTs) was achieved by using mesoporous graphitic carbon nitride (C3N4) as both a hard template and a nitrogen source. The TiN/FWCNT composite showed high performance for the oxygen reduction reaction in acidic media.

No abstract

The addition of redox-active molecules into electrochemical-capacitor electrolytes provides increased specific energy density. Here we illustrate the underlying operational mechanisms and design principles for carbons with hierarchical pore sizes in the micropore (0.6–2 nm) to mesopore (2–3 nm, 5–30 nm) range as electrode materials in redox-enhanced electrochemical capacitors. When using iodide as a model redox additive, we discover that the redox capacity is correlated to the pore volume of the carbon electrodes when void space is included. The fastest rates are typically observed with pore-sizes >1 nm, while slow self-discharge requires pores <1 nm. When used without an ion-selective-membrane separator, the delivered capacity correlated with the quantity of redox species held within the carbon. A commercial microporous carbon, MSC30, with substantial hierarchy in pore size, including small <0.8 nm pores and larger 1.1–3 nm pores, showed the best overall performance, illustrating key design principles.

No abstract

Niobium oxides are shown to exhibit oxygen reduction reaction (ORR) activity with high onset potential (ca. 0.85 V vs. NHE) comparable to that for Pt-based catalysts along with excellent stability under acidic conditions.