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[Display omitted] • Hydroxyaldehydes with variable –OH positions are end-capped into vinylene COF skeleton. • Different substituted groups of aldehydes are end-capped into vinylene COF skeleton. • End-capping groups tune the band gap, hydrophilicity and morphology of pristine COF. • The introduction of - p OH greatly improves the photocatalytic H 2 evolution activity. • The end-capping strategy efficiently reduced the energy barrier for the H* formation. Since the first example was prepared via Knoevenagel condensation in 2016, vinylene-linked covalent organic frameworks (COFs) have attracted increasing interest owing to the high in-plane π-conjugation and robust stability. However, such COFs can only produce few amounts of hydrogen under visible-light irradiation due to the wide band gap and low hydrophilicity. Herein, we developed a facile end-capping strategy to manipulate the band gap, hydrophilicity and morphology of vinylene-linked COF (g-C 18 N 3 -COF). The COFs end-capped with variable positions of hydroxyl groups showed 4.5 times improvement in visible-light-driven hydrogen evolution activity compared to pristine COF. Both experimental and computational studies reveal that optimizing the contents and positions of hydroxyl groups narrowed the band gap and improved the hydrophilicity of pristine COF. The end-capping strategy efficiently reduced the charge recombination and energy barrier for the formation of H intermediate species (H*) explaining the improved hydrogen evolution properties. [ABSTRACT FROM AUTHOR]

• 3D porous BN microbeads are assembled by 2D BN nanosheets by solvent-free strategy. • Porous BN microbeads with defects result in narrowed band gaps and OB 3 structure. • Porous BN as a semiconductor enhances light absorption and electron delocalization. • The change of BN from a photocatalytic inert to highly active material comes true. Due to large band gap and low charge delocalization, hexagonal boron nitride (h-BN) is usually used as catalytic support rather than catalyst, particularly photocatalyst for hydrogen evolution. Herein, three-dimensional porous BN microbeads assembled by 2D BN nanosheets with enriched defects and high specific surface area have been synthesized by solvent-free strategy, leading to multiply narrow band gaps and radical-contained OB 3 structure. Mott-Schottky test indicates that the as-fabricated porous BN is a n-type semiconductor. The narrowed band gaps together with radicals enhance the light absorption and electron delocalization which is further confirmed by Density Functional Theory (DFT) calculation, resulting in the change of BN from a photocatalytic inert to highly active material. This work not only provides a stable and effective BN-based photocatalyst but also benefits to design and develop more highly efficient two-dimensional photocatalysts for hydrogen evolution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ir nanodots-decorated Ni 3 Fe nanoparticles/rGO are prepared as electrocatalysts. • Decent performances for OER, HER, and overall water splitting are achieved. • XPS result reveals the interfacial interaction between Ir and Ni 3 Fe species. • DFT calculations support the observed enhancement. Developing low-cost and high-performance electrocatalysts for water splitting is crucial for advancing the hydrogen production. However, the large-scale practical application is highly dependent on the use of precious catalysts (such as IrO 2 and Pt/C). Herein, a composite of Ir nanodots (7.7 wt%) decorated Ni 3 Fe alloy on reduced graphene oxide (Ir/Ni 3 Fe/rGO) is prepared via an impregnation-reduction method as a bifunctional electrocatalyst for overall water splitting. The low-content decoration enables the composite to exhibit attractive electrocatlytic performances: requiring overpotentials of 254 and 36 mV at a current density of 10 mA cm−2 for the oxygen and hydrogen evolution reactions (OER and HER) in 1.0 M KOH solution, respectively, which surpass those of Ni 3 Fe/rGO (280 and 264 mV) and Ir/rGO (340 and 150 mV). In addition, the electrocatalyst-assembled Ir/Ni 3 Fe/rGO||Ir/Ni 3 Fe/rGO electrolyzer affords a decent cell voltage of 1.570 V at a current density of 10 mA cm−2 for overall water splitting, which outperforms those of Ni 3 Fe/rGO||Ni 3 Fe/rGO (1.730 V), Ir/rGO||Ir/rGO (1.790 V), and commercial IrO 2 ||Pt/C (1.574 V). Furthermore, X-ray photoelectron spectroscopy (XPS) result reveals the strong interfacial interaction between Ir and Ni 3 Fe species, density functional theory (DFT) calculations reveal that Ir species favor water dissociation and optimize the H* adsorption energy for HER, and reduce OOH* energy for OER; all of which give rise to the observed enhancement. The results can provide an effective strategy for designing and preparing low-cost and promising electrocatalysts for water splitting. [ABSTRACT FROM AUTHOR]