Hydrogen generation from the direct splitting of water by photocatalysis is regarded as a promising and renewable solution for the energy crisis The key to realize this reaction is to find an efficient and robust photocatalyst that ideally makes use of the energy from sunlight Recently, due to the attractive properties such as appropriate band structure, ultrahigh specific surface area, and more exposed active sites, two-dimensional (2D) photocatalysts have attracted significant attention for photocatalytic water splitting This Review attempts to summarize recent progress in the fabrication and applications of 2D photocatalysts including graphene-based photocatalysts, 2D oxides, 2D chalcogenides, 2D carbon nitride, and some other emerging 2D materials for water splitting The construction strategies and characterization techniques for 2D/2D photocatalysts are summarized Particular attention has been paid to the role of 2D/2D interfaces in these 2D photocatalysts as the interfaces and heterojunctions a

Role of Interfaces in Two-Dimensional Photocatalyst for Water Splitting

Electrochemically induced spinel-layered phase transition of Mn3O4 in high performance neutral aqueous rechargeable zinc battery

C2N/WS2 van der Waals type-II heterostructure as a promising water splitting photocatalyst

Nitrogen fixation is one of the most essential processes in chemistry Developing more effective nitrogen fixation systems to catalyze the reaction under mild conditions is one of the most attractive but long-standing challenges In this work, by means of first-principles computations, we systematically investigated the catalytic performance of transition metal atom-anchored C2N monolayer electrocatalysts (TMx@C2N, x = 1 or 2; TM = Ti, Mn, Fe, Co, Cu, Mo, Ru, Rh, Pd, Ag, Ir, Pt, or Au) for N2 fixation The natively N edged uniform holes could fix the TM atoms firmly in TM–Nx configurations, which is beneficial for the N2 fixation Among them, Mo2@C2N exhibits the best catalytic performance for the reduction of N2 to NH3 with a maximum free energy change of 041 eV and an energy barrier of 051 eV, indicating that Mo2@C2N is a promising catalyst with high catalytic activity for the reduction of N2 to NH3 We believe that this work could provide a new idea for the design of N2 fixation catalysts and shed light on C2N monolayers as excellent substrates for catalysis

Double-atom catalysts: transition metal dimer-anchored C2N monolayers as N2 fixation electrocatalysts

The overwhelming challenge of depleting fossil fuels and anthropogenic carbon emissions has driven research into alternative clean sources of energy. To achieve the goal of a carbon neutral economy, the harvesting of sunlight by using photocatalysts to split water into hydrogen and oxygen is an expedient approach to fulfill the energy demand in a sustainable way along with reducing the emission of greenhouse gases. Even though the past few decades have witnessed intensive research into inorganic semiconductor photocatalysts, their quantum efficiencies for hydrogen production from visible photons remain too low for the large scale deployment of this technology. Visible light absorption and efficient charge separation are two key necessary conditions for achieving the scalable production of hydrogen from water. Two-dimensional carbon based nanoscale materials such as graphene oxide, reduced graphene oxide, carbon nitride, modified 2D carbon frameworks and their composites have emerged as potential photocatalysts due to their astonishing properties such as superior charge transport, tunable energy levels and bandgaps, visible light absorption, high surface area, easy processability, quantum confinement effects, and high photocatalytic quantum yields. The feasibility of structural and chemical modification to optimize visible light absorption and charge separation makes carbonaceous semiconductors promising candidates to convert solar energy into chemical energy. In the present review, we have summarized the recent advances in 2D carbonaceous photocatalysts with respect to physicochemical and photochemical tuning for solar light mediated hydrogen evolution.

Sunlight-driven water-splitting using two-dimensional carbon based semiconductors

Exploiting earth-abundant and low-cost photocatalysts for high efficiency photocatalytic water splitting is of profound significance. Herein, we report an improved photocatalytic water splitting activity by P and As substitution at the N-site in the C2N monolayer using state-of-the-art hybrid density functional calculations. Our results show that the band gap can be reduced in C2N by increasing the concentrations of P and As substitution, and at the same time the obtained band gap value is higher than the free energy of water splitting except for As with concentrations of x = 0.333. This indicates that these new compositions of P/As substituted C2N monolayers are thermodynamically suitable to drive hydrogen evolution reaction. The calculated effective mass of charge carriers illustrates that charge transfer to the reactive sites would be easier in the substituted system than the pure C2N, and also our results suggest that the recombination rate would be lower in the substituted system, indicating the enha...

Tailoring the Electronic Band Gap and Band Edge Positions in the C2N Monolayer by P and As Substitution for Photocatalytic Water Splitting

Two-dimensional (2D) semiconductors have shown great promise as efficient photocatalysts for water splitting. Tailoring the band gap and band edge positions are the most crucial steps to further improve the photocatalytic activity of 2D materials. Here, we report an improved photocatalytic water splitting activity in a C2 N monolayer by isoelectronic substitutions at the C-site, based on density functional calculations. Our optical calculations show that the isoelectronic substitutions significantly reduce the band gap of the C2 N monolayer and thus strongly enhance the absorption of visible light, which is consistent with the observed redshift in the optical absorption spectra. Based on the HSE06 functional, the calculated band edge positions of C2-x Six N and C2-x Gex N monolayers are even more favorable than the pristine C2 N monolayer for the overall photocatalytic activity. On the other hand, for the C2-x Snx N monolayer, the conduction band minima is more positive than the oxygen reduction potential and, hence, Sn substitution in C2 N is unfavorable for the water decomposition reaction. In addition, the isoelectronic substitutions improve the separation of e- -h+ pairs, which, in turn, suppress the recombination rate, thereby leading to enhanced photocatalytic activity in this material. Our results imply that Si-, and Ge-substituted C2 N monolayers will be a promising visible-light photocatalysts for water splitting.

Enhanced Photocatalytic Water Splitting in a C2N Monolayer by C‐Site Isoelectronic Substitution

Influence of hydrogen and halogen adsorption on the photocatalytic water splitting activity of C2N monolayer: A first-principles study

Global environmental issues, in addition to limited fossil fuel resources, are being addressed by quests in search of efficient visible-light-driven water splitting catalysts for hydrogen production. The photocatalytic water splitting activities of CdX/C2N (X = S, Se) heterostructures have been investigated here using hybrid density functional theory calculations. The calculated band gaps of CdS/C2N and CdSe/C2N heterostructures are 1.48 and 2.12 eV, respectively. These are ideal band gap values that make possible harvesting of more visible light from the solar spectrum, which will result in high solar to energy conversion efficiencies. Charge density difference analysis shows that the charge redistributions mainly occur in the interface regions and that the charges transfer from the C2N to CdX layers. It is interesting to note that the CdX/C2N heterostructures possess a type-II band alignment, where the relative band alignment of the C2N and CdX monolayers promotes a spatial separation of the electrons (that resides in C2N) and holes (that resides in CdX). Importantly, the band edges of the heterostructures straddle the water redox potential under different pH conditions. This study demonstrates that the CdS/C2N and CdSe/C2N heterostructures are suitable materials to split water (from various sources) in different ranges of pH values.

Two-Dimensional CdX/C2N (X = S, Se) Heterostructures as Potential Photocatalysts for Water Splitting : A DFT Study

The magnetic and electronic properties of trilayer La4Ni3O8, similar to hole-doped cuprates, are investigated by performing full-potential linearized augmented plane wave method-based spin-polarized calculations with LDA and GGA functionals including Hubbard U parameters to account for strong correlation effects. On the basis of these calculations, we found that La4Ni3O8 is a C-type anti-ferromagnetic (C-AFM) Mott insulator in agreement with previous experimental and theoretical observations. Our calculations suggest that the two crystallographically nonequivalent nickel atoms Ni1 and Ni2 are found to be in high-spin state with an average valency of +1.33. Intermediate band-gap states are originated from dz2 electrons of both types of Ni ions after including the strong correlation effects. To understand the role of hole doping on electronic structure, phase stability, and magnetic properties of La4Ni3O8, similar calculations were performed for La4–xSrxNi3O8 as a function of x, using the supercell approach...

M. R. Ashwin Kishore

Papers

Tailoring the Electronic Band Gap and Band Edge Positions in the C2N Monolayer by P and As Substitution for Photocatalytic Water Splitting

Enhanced Photocatalytic Water Splitting in a C2N Monolayer by C‐Site Isoelectronic Substitution

Influence of hydrogen and halogen adsorption on the photocatalytic water splitting activity of C2N monolayer: A first-principles study

Two-Dimensional CdX/C2N (X = S, Se) Heterostructures as Potential Photocatalysts for Water Splitting : A DFT Study

Electronic and Magnetic Structures of Hole Doped Trilayer La4–xSrxNi3O8 from First-Principles Calculations