Recent development of electrodes construction for HER in electrocatalytic water splitting.

Production of hydrogen (H2) fuel by using hydrogen evolution reaction (HER) through electrocatalysis of water splitting is inexpensive, has optimal performance, and has remarkable stability. The other key factor for innovation of good electrocatalysts with excellent stability and high efficiency is significant and still challenging from past decades for practical applications of HER. Hydrogen generation arises on the HER electrode due to the release of bubbles, proton diffusion, and the transfer of electrons. These considerations should be mindful of the construction and development of the electrode. This review offers a synopsis of recent advancements in various electrodes used for electrocatalysts as a base, such as nickel foam, titanium foil, copper foam, carbon foam, and others, also discusses their HER catalytic activity, with a priority on the release of bubbles, diffusion of ions, the structure of the electrode, and the formulation and preparation process. In conclusion, we provide an overview of ideas to further improve and address the significant issues in the manufacture of HER electrodes.

Metastable gallium hydride mediates propane dehydrogenation on H2 co-feeding.

In heterogeneous catalysis, the catalytic dehydrogenation reactions of hydrocarbons often exhibit a negative pressure dependence on hydrogen due to the competitive chemisorption of hydrocarbons and hydrogen. However, some catalysts show a positive pressure dependence for propane dehydrogenation, an important reaction for propylene production. Here we show that the positive activity dependence on H2 partial pressure of gallium oxide-based catalysts arises from metastable hydride mediation. Through in situ spectroscopic, kinetic and computational analyses, we demonstrate that under reaction conditions with H2 co-feeding, the dissociative adsorption of H2 on a partially reduced gallium oxide surface produces H atoms chemically bonded to coordinatively unsaturated Ga atoms. These metastable gallium hydride species promote C-H bond activation while inhibiting deep dehydrogenation. We found that the surface coverage of gallium hydride determines the catalytic performance. Accordingly, benefiting from proper H2 co-feeding, the alumina-supported, trace additive-modified gallium oxide catalyst GaOx-Ir-K/Al2O3 exhibited high activity and selectivity at high propane concentrations.

Enhancement of charge separation and hole utilization in a Ni2P2O7-Nd-BiVO4 photoanode for efficient photoelectrochemical water oxidation.

It is necessary for photoelectrochemical (PEC) water splitting to reduce the electron-hole recombination rate and enhance the water oxidation reaction kinetics. Here, we prepared Ni2P2O7-Nd-BiVO4 composite photoanodes by coupling Ni2P2O7 co-catalysts to neodymium (Nd)-doped BiVO4 surfaces through photo-assisted electrodeposition. The Ni2P2O7-Nd-BiVO4 photoanode exhibits a high photocurrent density of 3.6 mA cm-2 at 1.23 V vs reversible hydrogen electrode (RHE), which is three times higher than that of the bare BiVO4 (1.2 mA cm-2). Detailed characterizations demonstrate that Nd doping reduces the band gap, significantly increases the carrier density and effectively reduces the charge transfer resistance. More importantly, the Ni2P2O7 co-catalyst has multiple roles. Specifically, it can act as a hole extraction layer to accelerate hole migration and inhibit hole-electron recombination. At the same time, it significantly improves the water oxidation reaction kinetics. In addition, it also provides more water oxidation active sites. This work provides ideas for the design and study of efficient BiVO4-based photoanodes.

Effect of the pore structure of an active alumina catalyst on isobutene production by dehydration of isobutanol.

An alumina catalyst was prepared by mixing and pinching with pseudo-boehmite, and the catalyst was reamed with polyethylene glycol. The catalysts prepared were characterized by means of XRD, mercury injection and NH3-TPD, and the dehydration properties of the catalysts prepared with different amounts of reamer were evaluated in a 10 mL fixed bed reactor with 5% water as a raw material. The results showed that the addition of reamer did not affect the crystal structure and the amount of acid of the catalyst. With the increase of the amount of reamer, the pore volume of the catalyst increased continuously, the number of large pores increased, the conversion rate of isobutanol increased, and the selectivity of isobutene remained basically unchanged. When the amount of reamer is 30%, the isobutanol conversion rate is the best. The isobutanol conversion rate and the isobutene selectivity were 97% and 93% respectively under the conditions of 330 °C, 0.1 MPa and 12 h-1 air velocity of the body liquid.