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Photocatalytic water splitting has emerged as a promising approach for storing solar energy in the form of chemical energy, which can solve the energy crisis and environmental issues. Herein we have explored the potentiality of nitrogen-doped graphene quantum dots for solar-driven hydrogen evolution. The motivation behind applying quantum dots as a photocatalyst is to utilize a major portion of the solar energy spectrum to enhance hydrogen yield. The alignment of frontier molecular orbitals (FMOs) in comparison to the redox potential of water reveals that all the studied quantum dots are eligible for photocatalytic hydrogen evolution. The energy gap between FMOs varies with the size of quantum dots from 3.01 to 2.32 eV, showing absorption of light in the visible range. The Gibbs free energy calculation shows that the formation of intermediate species is energetically unfavorable without exposure to light at pH=7, except for hydrogen adsorption. However, the photogenerated electron and hole drive the steps of oxygen and hydrogen evolution by making those a downhill process. The optical absorption spectra show that all the studied quantum dots absorb visible light. [Display omitted] • Nitrogen-doped graphene quantum dots are explored for extensive production of hydrogen. • HSE06 functional is applied in most of the calculations. • Negative values of Δ G imply that hydrogen evolution is feasible under solar-light irradiation. • Catalytic activity of different sites is investigated. • All the studied quantum dots absorb visible light of solar energy spectrum. [ABSTRACT FROM AUTHOR]

In this paper, we designed a composite photocatalytic system in which cobalt nanoparticles (Co NPs) are attached to nitrogen-doped carbon (N- d -C) and co-bonded to the surface of the noted photocatalyst graphite carbon nitride (g-C 3 N 4), showing an excellent photocatalytic hydrogen production. The bulk g-C 3 N 4 was formed in the first thermal treatment in air using melamine as a precursor. Subsequently, the secondary calcination under N 2 led to the synchronous fabrication of N- d -C/Co NPs and their combination with g-C 3 N 4 to form a novel ternary photocatalyst (g-C 3 N 4 /N- d -C/Co NPs). Co NPs exposed on the surface of the nanomaterials endowed much more reaction sites than g-C 3 N 4 for photocatalytic hydrogen production. Meanwhile, the embedded N- d -C provided an additional transfer approach for photocarriers. The as-prepared composite nanomaterials own a relatively high specific surface area of 97.45 m2 g−1 with an average pore size of 3.83 nm. As a result, compared with pristine g-C 3 N 4 (∼25.35 μmol g−1 h−1), the photocatalytic performance was increased by over 10 times (∼270.05 μmol g−1 h−1). Our work gives a novel approach for highly active g–C 3 N 4 –based photocatalysts in the field of photocatalysis. [Display omitted] • g-C 3 N 4 /N- d -C/Co NPs were prepared by co-calcination with Co-L-his complex. • The bandgap of g-C 3 N 4 /N- d -C/Co NPs were narrowed to ∼2.72 eV. • Hydrogen evolution rate of g-C 3 N 4 /N- d -C/Co NPs is over 10 times that of pristine g-C 3 N 4. • An approach to enhance solar-driven photocatalytic performance of g-C 3 N 4 was provided. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) exploitation represents the next big frontier in photovoltaic technologies. However, the extraordinary optoelectronic properties of these materials also call for alternative utilizations, such as in solar-driven photocatalysis, to better address the big challenges ahead for eco-sustainable human activities. In this contest the recent reports on MHPs structures, especially those stable in aqueous solutions, suggest the exciting possibility for efficient solar-driven perovskite-based hydrogen (H2) production. In this minireview such works are critically analyzed and classified according to their mechanism and working conditions. We focus on lead-free materials, because of the environmental issue represented by lead containing material, especially if exploited in aqueous medium, thus it is important to avoid its presence from the technology take-off. Particular emphasis is dedicated to the materials composition/structure impacting on this catalytic process. The rationalization of the distinctive traits characterizing MHPs-based H2 production could assist the future expansion of the field, supporting the path towards a new class of light-driven catalysts working in aqueous environments.

Vertically aligned p-silicon nanowire (SiNW) arrays have been extensively investigated in recent years as promising photocathodes for solar-driven hydrogen evolution. However, the fabrication of SiNW photocathodes with both high photoelectrocatalytic activity and long-term operational stability using a simple and affordable approach is a challenging task. Herein, we report conformal and continuous deposition of a di-cobalt phosphide (Co2P) layer on lithography-patterned highly ordered SiNW arrays via a cost-effective drop-casting method followed by a low-temperature phosphorization treatment. The as-deposited Co2P layer consists of crystalline nanoparticles and has an intimate contact with SiNWs, forming a well-defined SiNW@Co2P core/shell nanostructure. The conformal and continuous Co2P layer functions as a highly efficient catalyst capable of substantially improving the photoelectrocatalytic activity for the hydrogen evolution reaction (HER) and effectively passivates the SiNWs to protect them from photo-oxidation, thus prolonging the lifetime of the electrode. As aconsequence, the SiNW@Co2P photocathode with an optimized Co2P layer thickness exhibits a high photocurrent density of-21.9 mA·cm−2 at 0 V versus reversible hydrogen electrode and excellent operational stability up to 20 h for solar-driven hydrogen evolution, outperforming many nanostructured silicon photocathodes reported in the literature. The combination of passivation and catalytic functions in a single continuous layer represents a promising strategy for designing high-performance semiconductor photoelectrodes for use insolar-driven water splitting, which may simplify fabrication procedures andpotentially reduce production costs. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) exploitation represents the next big frontier in photovoltaic technologies. However, the extraordinary optoelectronic properties of these materials also call for alternative utilizations, such as in solar-driven photocatalysis, to better address the big challenges ahead for eco-sustainable human activities. In this contest the recent reports on MHPs structures, especially those stable in aqueous solutions, suggest the exciting possibility for efficient solar-driven perovskite-based hydrogen (H2) production. In this minireview such works are critically analyzed and classified according to their mechanism and working conditions. We focus on lead-free materials, because of the environmental issue represented by lead containing material, especially if exploited in aqueous medium, thus it is important to avoid its presence from the technology take-off. Particular emphasis is dedicated to the materials composition/structure impacting on this catalytic process. The rationalization of the distinctive traits characterizing MHPs-based H2 production could assist the future expansion of the field, supporting the path towards a new class of light-driven catalysts working in aqueous environments. [ABSTRACT FROM AUTHOR]