Targeted Regulation of the Electronic States of Nickel Toward the Efficient Electrosynthesis of Benzonitrile and Hydrogen Production.

Highly efficient electro-oxidation of benzylamine to generate value-added chemicals coupled with the hydrogen evolution reaction (HER) is crucial but challenging. Herein, targeted regulation of the electronic states of Ni sites was realized via simple yet precise nitridation engineering. Benefiting from the insertion of N atoms into the Ni lattice, the Ni3N electrode exhibits superior activity, selectivity, and stability for the benzylamine oxidation reaction (BOR). Especially, under the industrially relevant current (∼250 mA), the Ni3N catalyst remains ∼95% selective for benzonitrile production, reaching 1.43 mmol h-1 cm-2. Experimental and theoretical findings reveal that the formation of Ni-N bonds upshifts the Ni d-band center and optimizes the electrophilic properties of Ni sites, which contributes to the adsorption and dehydrogenations process of benzylamine. Furthermore, due to the work function difference between Ni and Ni3N, a strong mutual interaction occurs at the heterogeneous interface for Ni-Ni3N, which endows it with the appropriate H* adsorption energy and thus excellent HER performance. Impressively, the integrated solar-energy-driven BOR coupled with the HER electrolyzer affords 10 mA cm-2 at an ultralow voltage of 1.4 V and exhibits a promising practical application (ηsolar-to-hydrogen = 13.8%). This work offers a new perspective for the bifunctional design of nitrides in the field of electrosynthesis.

BiVO4 Ceramic Photoanode with Enhanced Photoelectrochemical Stability.

Monoclinic bismuth vanadate (BiVO4) is an attractive material with which to fabricate photoanodes due to its suitable band structure and excellent photoelectrochemical (PEC) performance. However, the poor PEC stability originating from its severe photo-corrosion greatly restricts its practical applications. In this paper, pristine and Mo doped BiVO4 ceramics were prepared using the spark plasma sintering (SPS) method, and their photoelectrochemical properties as photoanodes were investigated. The as-prepared 1% Mo doped BiVO4 ceramic (Mo-BVO (C)) photoanode exhibited enhanced PEC stability compared to 1% Mo doped BiVO4 films on fluorine doped Tin Oxide (FTO) coated glass substrates (Mo-BVO). Mo-BVO (C) exhibited a photocurrent density of 0.54 mA/cm2 and remained stable for 10 h at 1.23 V vs. reversible hydrogen electrode (RHE), while the photocurrent density of the Mo-BVO decreased from 0.66 mA/cm2 to 0.11 mA/cm2 at 1.23 V vs. RHE in 4 h. The experimental results indicated that the enhanced PEC stability of the Mo-BVO (C) could be attributed to its higher crystallinity, which could effectively inhibit the dissociation of vanadium in BiVO4 during the PEC process. This work may illustrate a novel ceramic design for the improvement of the stability of BiVO4 photoanodes, and might provide a general strategy for the improvement of the PEC stability of metal oxide photoanodes.

Boron containing metal-organic framework for highly selective photocatalytic production of H2O2 by promoting two-electron O2 reduction.

A zirconium-based metal-organic framework containing boron (UiO-66-B) is prepared, which displays efficient photocatalytic H2O2 production. The H2O2 evolution rate is about 1002 µmol g-1 h-1, much higher than that of most known photocatalysts. Pristine UiO-66 displays a much lower activity (314 µmol g-1 h-1) under the same conditions, suggesting the significant role of boron. Both theoretical calculations and the combined experimental results verify the above conclusion, and the role of boron is ascribed to the following aspects: (1) enhanced O2 adsorption, (2) highly selective proton-coupled two-electron transfer, (3) faster carrier separation and surface charge transfer, and (4) faster generation but slower decomposition rates of H2O2. This work highlights key factors in the two-electron O2 reduction reaction (ORR), presents a deeper understanding of the role of boron in enhancing H2O2 production, and provides a new strategy for designing photocatalysts with excellent H2O2 evolution efficiency.

Surface Fluorination Engineering of NiFe Prussian Blue Analogue Derivatives for Highly Efficient Oxygen Evolution Reaction.

Surface engineering is of importance to reduce the reaction barrier of oxygen evolution reaction (OER). Herein, the NiFe Prussian blue analogue (NiFe-PBA)-F catalyst with a multilevel structure was obtained from NiFe-PBAs via a fluorination strategy, which presents an ultralow OER overpotential of 190 mV at 10 mA cm-2 in alkaline solution, with a small Tafel slope of 57 mV dec-1 and excellent stability. Interestingly, surface fluorination engineering could achieve a controllable removal of ligands of the cyan group, contributing to keep the framework structure of NiFe-PBAs. Particularly, NiFe-PBAs-F undergoes a dramatic reconstruction with the dynamic migration of F ions, which creates more active sites of F-doped NiFeOOH and affords more favorable adsorption of oxygen intermediates. Density functional theory calculations suggest that F doping increases the state density of Ni 3d orbital around the Fermi level, thus improving the conductivity of NiFeOOH. Furthermore, based on our experimental results, the lattice oxygen oxidation mechanism for NiFe-PBAs-F was proposed. Our work not only provides a new pathway to realize the controllable pyrolysis of NiFe-PBAs but also gives more insights into the reconstruction and the mechanism for the OER process.