Due to its higher electrical conductivity compared with carbon and its outstanding corrosion resistance, titanium nitride (TiN) has recently been studied intensively for applications as an active electrode as well as catalyst support materials in supercapacitors, fuel cells and Li–air batteries. In this work, we studied the electrocatalytic activities of nano- and micro-sized TiN toward the oxygen reduction reaction (ORR) in an alkaline media using a thin film–rotating-disk electrode (RDE) technique, and investigated their performances as active air electrodes on a newly developed Li–air fuel cell with a hybrid electrolyte. The results show that both nano- and micro-sized TiN exhibit electrocatalytic activities toward ORR in alkaline media but with different mechanisms. The ORR catalyzed by micro-sized TiN proceeds via the serial "2e− + 2e−" pathway in a consecutive manner with the reduction of HO2− starting at a higher electrode potential as a discrete step. On the other hand, the ORR catalyzed by nano-sized TiN proceeds via a dual-path, where the two serial "2e−" steps proceed with smaller intervals and manifest an overall mixed appearance by coexistence of the parallel and serial "2e−" steps. The extent to which the two steps are in parallel or consecutive reveals a potential-dependent feature. Furthermore, both nano- and micro-sized TiN particles demonstrate evident electrocatalytic activities toward ORR in the Li–air fuel cell, with the nano-sized TiN showing a much better catalytic activity, which is comparable to that of the nano-sized Mn3O4.
Sulfur-mediated synthesis has been developed to modify the texture, optical and electronic properties, as well as the photocatalytic functions of a carbon nitride semiconductor. The water oxidation reaction has been achieved at a moderate rate with only photocatalysts without the aid of co-factors.
Abstract Alcohol adsorption on MoO3/SiO2 resulted in formation of two types of alkoxide, spectator and participant for selective oxidation, which exist on SiO2 consuming silanol groups through spillover and migration from MoO3 to SiO2 support.
Using highly ordered porous anodic alumina membrane fabricated with the aid of nanoimprinting as a mask, Ta2O5 nanorod array with uniform diameter, length, and distribution is grown in situ on a Ta substrate by through-mask anodization. The Ta2O5 nanorod array is further transformed into Ta3N5 nanorod array without damaging the nanorod structure by nitridation. Solar-driven photoelectrochemical water splitting with a maximum solar energy conversion efficiency of 0.36% is demonstrated with the Ta3N5 nanorod array after modifying the surface with cobalt-phosphate as a co-catalyst. The Ta2O5 and Ta3N5 nanorod arrays have potential applications in catalysis, photonics, UV photodetection and solar energy conversion.
Water splitting to form hydrogen and oxygen using solar energy in the presence of semiconductor photocatalysts has long been studied as a potential means of clean, large-scale fuel production. In general, overall water splitting can be achieved when a photocatalyst is modified with a suitable cocatalyst. It is therefore important to develop both photocatalysts and cocatalysts. In the past five years, there has been significant progress in water splitting photocatalysis, especially in the development of cocatalysts and related physical and materials chemistry. This work describes the state of the art and future challenges in photocatalytic water splitting, with a focus on the recent progress of our own research.
High-quality nano-/microtextured NaTaO3 crystal layers were successfully fabricated on Ta substrates at a relatively low temperature using molten NaNO3 as the starting material. Ta substrates coated with an aqueous NaNO3 solution were heated at 500 °C in an infrared heating furnace, whereupon Ta reacted with NaNO3 (which acted as both the Na source and the flux) to afford a layer of densely packed cubic NaTaO3 crystals that adhered readily onto the substrate. Nitridation of the NaTaO3 crystal layer by heating at 850 °C under an NH3 flow yielded a Ta3N5 crystal layer. The crystals retained their original size and shape but became highly porous after nitridation. TEM observations clearly indicated that the porous cubic crystals consisted of highly crystalline nanoparticles.
Abstract Most CdTe photoanodes and photocathodes show positive and negative photocurrent onset potentials for water oxidation and reduction, respectively, and are thus unable to drive photoelectrochemical (PEC) water splitting without external applied biases. Herein, the activity of a CdTe photoanode having an internal p‐n junction during PEC water oxidation was enhanced by applying a CdCl 2 annealing treatment together with surface modifications. The resulting CdTe photoanode generated photocurrents of 1.8 and 5.4 mA cm −2 at 0.6 and 1.2 V RHE , respectively, with a photoanodic current onset potential of 0.22 V RHE under simulated sunlight (AM 1.5G). The CdCl 2 annealing increased the grain sizes and lowered the density of grain boundaries, allowing more efficient charge separation. Consequently, a two‐electrode tandem PEC cell comprising a CdTe‐based photoanode and photocathode split water without any external bias at a solar‐to‐hydrogen conversion efficiency of 0.51 % at the beginning of the reaction.
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