Construction of 2D graphic carbon nitrides (g‐CNx) with wide visible light adsorption range and high charge separation efficiency concurrently is of great urgent demand and still very challenging for developing highly efficient photocatalysts for hydrogen evolution. To achieve this goal, a two‐step pyrolytic strategy has been applied here to create ultrathin 2D g‐CNx with extended the π‐conjugation. It is experimentally proven that the extension of π‐conjugation in g‐CNx is not only beneficial to narrowing the bandgap, but also improving the charge separation efficiency of the g‐CNx. As an integral result, extraordinary apparent quantum efficiencies (AQEs) of 57.3% and 7.0% at short (380 nm) and long (520 nm) wavelength, respectively, are achieved. The formation process of the extended π‐conjugated structures in the ultrathin 2D g‐CNx has been investigated using XRD, FT‐IR, Raman, XPS, and EPR. Additionally, it has been illustrated that the two‐step pyrolytic strategy is critical for creating ultrathin g‐CNx nanosheets with extended π‐conjugation by control experiments. This work shows a feasible and effective strategy to simultaneously expand the light adsorption range, enhance charge carrier mobility and depress electron‐hole recombination of g‐CNx for high‐efficient photocatalytic hydrogen evolution.

Photocatalytic production of H2O2 from earth-abundant water and oxygen using low-cost metal-free carbon nitrides (CNs) through oxygen reduction is a prospective route toward a greener future. However, the H2O2 productivity is restricted by rapid electron–hole separation and the low oxygen reduction activity of CNs. Herein, we rationally designed a series of CNs with covalently bonded dual-functional ligands acting as electron acceptors and active sites to achieve high photocatalytic H2O2 production and superior stability. The best-performing carbon nitride displays a H2O2 production rate of 7.3 mmol/g h with an apparent quantum efficiency of 20.2% at 420 nm using formic acid as the electron donor. Moreover, the modified CNs show excellent stable H2O2 generation over 110 h without significant decline. Mechanistic studies reveal that H2O2 was produced through a 2e– oxygen reduction reaction route. Photoluminescence, photo-electrochemical, and Kelvin probe force microscopy results together with theoretical calculations have revealed that the excellent photocatalytic performance originates from the dual-functional ligand. It not only acts as an electron acceptor to promote photogenerated charge carrier separation by withdrawing electrons but also works as an active site to accelerate oxygen reduction by lowering the oxygen adsorption and activation energy. Moreover, this facial strategy of grafting ligands provides a universal approach to synthesize photocatalysts with enhanced reactivity under mild conditions by choosing the proper ligands for a specific reaction.

Molecular junctions with similar backbones, tunable chemical structures and controllable length are critical for systematic study of the structure–functionality relationships of their charge transport behavior. Taking advantage of the feasibility...