Rational Regulation of Crystalline/Amorphous Microprisms-Nanochannels Based on Molecular Sieve (VSB-5) for Electrochemical Overall Water Splitting.

Rational regulation of the composition and structure of electrocatalysts is crucial to the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a new electrocatalyst of nickel phosphate microprism (VSB/NiPO) is developed via a simple solvothermal reaction. The microprism is mainly composed of Versailles-Santa Barbara-5 (VSB-5, molecular sieve) with unique nanochannels, which contribute to accelerating mass transfer and exposing more active sites, thus displaying excellent HER activity. Subsequently, the crystallinity and electronic structure of the framework are modulated by incorporating Fe with the combination of calcination and impregnation. The nanochannels are converted to the amorphous arrangement, and the Ni centers are regulated to the higher valence. The resultant Fe-VSB/NiPO-500 exhibits a low OER overpotential of 227 mV at 50 mA cm-2 . Interestingly, an integrated electrolyzer assembled by VSB/NiPO(-) and Fe-VSB/NiPO-500(+) performs well for overall water splitting, which requires only 1.487 V to achieve 10 mA cm-2 , and remains stable at 100 mA cm-2 over 100 h. This finding opens a new avenue for developing VSB-5 in the field of electrocatalysis.

α-Fe2O3 mediated periodate activation for selective degradation of phenolic compounds via electron transfer pathway under visible irradiation.

Periodate (PI)-photoactivated advanced oxidation process (AOP) has recently received increasing attention for the removal of micropollutants from water. However, periodate is mainly driven by high-energy ultraviolet light (UV) in most cases, and few studies have extended it to the visible range. Herein, we proposed a new PI visible light activation system employing α-Fe2O3 as catalyst. It is completely different from traditional PI-AOP based on hydroxyl radicals (•OH) and iodine radical (•IO3). The vis-α-Fe2O3/PI system can selectively degrade the phenolic compounds via non-radical pathway under the visible range. Notably, the designed system not only shows a well pH tolerance and environmental stability, but also exhibits a strong substrate-dependent reactivity. Both quenching experiments and electron paramagnetic resonance (EPR) experiments demonstrate that photogenerated holes are the main active species in this system. Moreover, a series of photoelectrochemical experiments reveal that PI can effectively inhibit the carrier recombination on the α-Fe2O3 surface, thereby improving the utilization of photogenerated charges and increasing the number of photogenerated holes, which effectively reacts with 4-CP through electron transfer way. In a word, this work proposes a cost-effective, green and mild mean to activate PI, and provides a facile way to solve the fatal shortcomings (i.e., inappropriate band edge position, rapid charge recombination and short hole diffusion length) of traditional iron oxide semiconductor photocatalysts.

Hierarchical Cu2O/NiFeCo layered double hydroxide nanoarrays on copper foam obtained by a self-sacrificial templated route for a highly efficient oxygen evolution reaction.

The design of highly active, economical and highly stable electrocatalysts for the oxygen evolution reaction (OER) is very important for realizing sustainable energy conversion. Herein, a Cu2O/NiFeCo layered double hydroxide electrode on a copper foam (CF) with a nanoarray structure (Cu2O/NiFeCo LDH/CF) is fabricated by using Cu(OH)2 on CF (Cu(OH)2/CF) as a self-sacrificial template. The prepared Cu2O/NiFeCo LDH/CF has a unique hierarchical nanostructure, high electrochemical active area and excellent integration of Cu2O and NiFeCo LDH, resulting in low overpotentials of 228 mV and 269 mV for current densities of 10 and 100 mA cm-2 in 1 M KOH, respectively, as well as an ultrasmall Tafel slope of 40 mV dec-1. In highly alkaline 6 M KOH, a overpotential of only 213 mV can deliver a current density of 100 mA cm-2. Moreover, the assembled water hydrolysis device operates stably for 50 h without a significant change in the potential in the strong alkaline solution. This high-efficiency OER performance and long-term stability make Cu2O/NiFeCo LDH/CF promising for practical applications.

Ultrahigh electrocatalytic activity with trace amounts of platinum loadings on free-standing mesoporous titanium nitride nanotube arrays for hydrogen evolution reactions.

Minimizing Pt loadings on electrocatalysts for hydrogen evolution reactions (HERs) is essential for their commercial applications. Herein, free-standing mesoporous titanium nitride nanotube arrays (TiN NTAs) were fabricated to serve as a substrate for Pt loadings in trace amounts. TiN NTAs were prepared by thermal treatment of anodic TiO2 NTAs at 750 °C for 3 h in a NH3 atmosphere. The uniform TiN NTAs showed an inner diameter of ∼80 nm and a length of ∼7 µm, with many mesoporous holes ranging from 5 to 10 nm in diameter on the nanotube walls. Pt species dissolved from the Pt counter electrode in electrochemical cycling were redeposited on the mesoporous TiN NTAs to produce Pt-TiN NTAs with an ultra-low Pt loading of 8.3 µg cm-2. Pt-TiN NTAs exhibited 15-fold higher mass activity towards HER than the benchmark 20 wt% Pt/C in acidic media, with an overpotential of 71 mV vs. RHE at a current density of 10 mA cm-2, a Tafel slope value of 46.4 mV dec-1 and excellent stability. The performance of Pt-TiN NTAs is also much better than that of Pt species deposited on non-mesoporous nanotube arrays due to the shortcuts originating from the mesoporous holes on the nanotube walls for electron and mass transfer.