Embedding Metal in the Interface of a p-n Heterojunction with a Stack Design for Superior Z-Scheme Photocatalytic Hydrogen Evolution

Abstract

The construction of a p-n heterojunction is an efficient strategy to resolve the limited light absorption and serious charge-carrier recombination in semiconductors and enhance the photocatalytic activity. However, the promotion effect is greatly limited by poor interfacial charge transfer efficiency as well as reduced redox ability of charge carriers. In this work, we demonstrate that the embedding of metal Pd into the interface between n-type C3N4 and p-type Cu2O can further enhance the interfacial charge transfer and increase the redox ability of charge carriers through the design of the C3N4-Pd-Cu2O stack nanostructure. The embedded Pd nanocubes in the stack structure not only trap the charge carriers from the semiconductors in promoting the electron-hole separation but also act as a Z-scheme "bridge" in keeping the strong reduction/oxidation ability of the electrons/holes for surface reactions. Furthermore, Pd nanocubes also increase the bonding strength between the two semiconductors. Enabled by this unique design, the hydrogen evolution achieved is dramatically higher than that of its counterpart C3N4-Cu2O structure without Pd embedding. The apparent quantum efficiency (AQE) is 0.9% at 420 nm for the designed C3N4-Pd-Cu2O. This work highlights the rational interfacial design of heterojunctions for enhanced photocatalytic performance.

High‐Performance Photoelectrochemical Water Oxidation with Phosphorus‐Doped and Metal Phosphide Cocatalyst‐Modified g‐C3N4 Formation Through Gas Treatment

“…As shown in the Mott-Schottky plots (Figure 4f), both g-C 3 N 4 and P-g-C 3 N 4 display positive slopes,r evealing that phosphorus doping does not alter the n-type semiconductingn ature of g-C 3 N 4 .H owever,p hosphorus doping results in two orders of magnitude higherc arrier density,f rom 2.83 10 20 cm À3 in g-C 3 N 4 to 1.88 10 22 cm À3 in P-g-C 3 N 4 .B oth these values are in the range reported for g-C 3 N 4 (1.11 10 21 cm À3 ). [44] This significant change in carrierd ensity indicates an alteration of the electronic properties of g-C 3 N 4 owing to phosphorus species, which can chemically bond with carbon and nitrogen atoms and maintain planarc oordination. In addition, the lone electron pair can delocalize to the p-conjugated framework, which can improvee lectronic conductivity and electron diffusion ability.…”

Phosphorus‐doped Isotype g‐C3N4/g‐C3N4: An Efficient Charge Transfer System for Photoelectrochemical Water Oxidation

“…The positive slopes of P‐g‐C 3 N 4 reveal that phosphorus doping does not reverse the n‐type semiconductor feature of g‐C 3 N 4 , as concluded from photocurrent and Voc decay test. The carrier density ( ), an important parameter influencing the PEC behavior of semiconductors, is extracted from Mott‐Schottky plots using the Equation :, …”

“…in which the is the capacitance of space charge layer, is elemental charge, is the dielectric constant of material (5.25 for g‐C 3 N 4 , is the permittivity of the vacuum, is applied potential and is the flat band potential. In Figure d, phosphorus doping leads to increase of carrier density.…”

Surface and Interface Engineering in Ag2S@MoS2 Core–Shell Nanowire Heterojunctions for Enhanced Visible Photocatalytic Hydrogen Production

“…Generally, ultraviolet (UV) light (wavelength ( λ )<420 nm) accounts for a much smaller fraction (≈5 %) of solar spectrum in comparison with those of visible (420< λ <780 nm, ≈43 %) and near‐infrared (NIR) light (780< λ <2500 nm, ≈52 %). Thus, visible or NIR responsive semiconductor heterojunctions with narrow band gaps are more promising to increase the solar energy conversion efficiency . On the other hand, resulted from the different band structures of semiconductors, photogenerated electrons transfer to one semiconductor with a lower conduction band (CB) edge, while holes migrate to another one with a higher valence band (VB) edge, thus realizing the spatial separation of electrons and holes .…”