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The coupling of two-dimensional (2D) layered materials is an effective way to realize photocatalytic hydrogen production. Herein, using first-principles calculations, the photocatalytic properties of GaN/CNs heterojunctions formed by two different graphite-like carbon nitride materials and GaN monolayer are discussed in detail. The results show that the GaN/C 2 N heterojunction can promote the effective separation of photogenerated electron and hole pairs, which is attributed to its type-II band orientation and high carrier mobility. However, the low overpotential of GaN/C 2 N for photocatalytic hydrogen production limits the photocatalytic performance. On this basis, we adjust the CBM position of the GaN/C 2 N heterojunction by applying an electric field to enhance its hydrogen evolution capability. In addition, the GaN/g-C 3 N 4 is a type-I heterojunction, which is suitable for the field of optoelectronic devices. This work broadens the field of vision for the preparation of highly efficient photocatalysts. [Display omitted] • The establishment of the GaN/C 2 N type-II heterojunctionhas high carrier mobility. • Applying an electric field is effective to adjust the bandgap and redox potential of the GaN/C 2 N heterojunction. • The GaN/g-C 3 N 4 heterojunction has the advantage of being used in optoelectronic devices. • This work broadens the field of vision for the preparation of highly efficient photocatalysts. [ABSTRACT FROM AUTHOR]

Researches on environmentally friendly semiconductor photocatalysts for efficient photocatalytic hydrogen evolution have important practical significance. Here, using first-principles calculations, the CeO 2 (111)/hBN heterojunction was conceived. The influence of the interface effect on the structural, electronic and optical properties of the heterojunction was investigated in detail. The band gap of the heterojunction is smaller than the two individual components and forms a type-II heterojunction, improving the photocatalytic activity. Furthermore, by doping two C atoms, the band gap of heterojunction was further narrowed. Both the oxidation and reduction potential of CeO 2 (111)/hBN heterojunction meet the requirements of water splitting and has certain advantages over other photocatalysts in the ability for photocatalytic hydrogen evolution. The study revealed the possible mechanism of CeO 2 (111) and hBN monolayers compositing to facilitate photocatalysis and hydrogen evolution ability, which may provide a possible reference direction for the practical design of more high-quality semiconductor photocatalysts. [Display omitted] • CeO2(111)/hBN forms type-Ⅱ heterojunction. • CeO2(111)/hBN has good thermodynamic stability and mechanical stability. • CeO2(111)/hBN has certain advantages in photocatalytic hydrogen evolution. [ABSTRACT FROM AUTHOR]

The design and development of low-cost, abundant reserves, high catalytic activity and durability bifunctional electrocatalysts for water splitting are of great significance. Here, simple hydrothermal and hydrogen reduction methods were used to fabricate a uniform distribution of Fe-doped MoO 2 /MoO 3 sheets with abundant oxygen vacancies and heterojunctions on etched nickel foam (ENF). The Fe– MoO 2 /MoO 3 /ENF exhibited a small overpotential of 36 mV at 10 mA cm−2 for hydrogen evolution reaction (HER), an excellent oxygen evolution reaction (OER) overpotential of 310 mV at 100 mA cm−2 and outstanding stabilities of 95 h and 120 h for the HER and OER, respectively. As both cathode and anode catalysts, the heterogeneously structured Fe– MoO 2 /MoO 3 /ENF required a low cell voltage of 1.57 V at 10 mA cm−2. Density functional theory (DFT) calculations show that Fe doping and MoO 2 /MoO 3 heterojunctions can significantly reduce the band gap of the electrode, accelerate electron transport and reduce the potential barrier for water splitting. This work provides a new approach for designing metal ion doping and heterostructure formation that may be adapted to transition metal oxides for water splitting. Image 1 • Improve the adhesion of the materials by etching nickel foam (NF). • Two-step reaction simultaneously achieves iron doping and heterojunctions. • DFT calculations confirm that Fe doping increased the conductivity. • In situ grown heterojunctions greatly reduce the potential barrier. [ABSTRACT FROM AUTHOR]

[Display omitted] • hBN/g-C 3 N 4 with six different defected types are constructed and studied in detail. • Z-scheme vdW heterojunctions can realize stronger redox capacity. • A suitable band gap width can even obtain full visible light response. • Defect-engineered can increase even more than 20 times the charge transfer between layers. 2D/2D hBN/g-C 3 N 4 nanocomposites with good photocatalytic activity have been successfully prepared, and fortunately defected 2D material heterojunction opens up new possibilities for high-efficiency photocatalysts. However, its photocatalytic performance and mechanism in splitting water have not been thoroughly explored. Herein, using the state-of-theart TDHF-HSE06 method, 2D/2D hBN/g-C 3 N 4 nanocomposites with different defected types were discussed in detail, including C atoms doping and natural point vacancies. We demonstrate that the defect-induced Z-scheme vdW heterojunction is a key for excellent photocatalytic performance. Compared to perfect hBN/g-C 3 N 4 , the defected hBN/g-C 3 N 4 heterojunctions have stronger interfacial interaction with more than 20 times of charge transfer. And it even has full visible-light response due to the suitable band gap width. More importantly, the Z-scheme band edge potentials have perfect redox capacity for water splitting at both PH = 0 and 7. The findings not only explain the existing experimental phenomena, but also provide new insights into the design of high-efficiency metal-free photocatalysts. [ABSTRACT FROM AUTHOR]

Bare nonprecious metal oxides are generally considered to have low HER activity, but they have the advantages of abundant resources and low cost. Herein, a facile strategy to construct abundant oxygen vacancies with heterogeneous structures of oxygen-vacancies CoFe 2 O 4 /oxygen-vacancies cobalt oxides/nickel foam (Ov-CoFe 2 O 4 /CoO x /NF) is developed using gas-phase cation exchange. Benefiting from abundant oxygen vacancies, the strong interfacial coupling effects between oxygen-vacancies CoFe 2 O 4 (Ov-CoFe 2 O 4) and oxygen-vacancies cobalt oxides (Ov-CoO x), a nanorod structure and the highly conductive nickel foam support, Ov-CoFe 2 O 4 /CoO x /NF exhibits a low overpotential of 59 mV and achieved a current density of 10 mA cm−2 in a 1 M KOH solution. Ov-CoFe 2 O 4 /CoO x /NF//Ov-CoFe 2 O 4 /CoO x /NF exhibits a low water splitting voltage of 1.51 V at 10 mA cm−2. Density functional theory calculations suggest that oxygen vacancy and interfacial coupling effects can both improve conductivity of electrocatalysts. This study provides a facile design for simultaneous realization of oxygen vacancy modification and heterostructure, which may become a simple strategy to use oxides to improve HER performance. Image 1 • A simple strategy to achieve oxygen vacancy modification and a heterostructure. • Synergistic effect lead to excellent alkaline HER activity. • 3D self-supported binder-free integrated electrode. • An effective strategy to improve oxides HER performance. [ABSTRACT FROM AUTHOR]