Fabrication of a Co(OH)₂/ZnCr LDH “p–n” Heterojunction Photocatalyst with Enhanced Separation of Charge Carriers for Efficient Visible-Light-Driven H₂ and O₂ Evolution

Abstract

Photocatalytic generation of H and O by water splitting remains a great challenge for clean and sustainable energy. Taking into the consideration promising heterojunction photocatalysts, analogous energy issues have been mitigated to a meaningful extent. Herein, we have architectured a highly efficient bifunctional heterojunction material, i.e., p-type Co(OH) platelets with an n-type ZnCr layered double hydroxide (LDH) by an ultrasonication method. Primarily, the Mott-Schottky measurements confirmed the n- and p-type semiconductive properties of LDH and CH material, respectively, with the construction of a p-n heterojunction. The high resolution transmission electron microscopy results suggest that surface modification of ZnCr LDH by Co(OH) hexagonal platelets could form a fabulous p-n interfacial region that significantly decreases the energy barrier for O and H production by effectively separating and transporting photoinduced charge carriers, leading to enhanced photoreactivity. A deep investigation into the mechanism shows that a 30 wt % Co(OH)-modified ZnCr LDH sample liberates maximum H and O production in 2 h, i.e., 1115 and 560 μmol, with apparent conversion efficiencies of H and O evolution of 13.12% and 6.25%, respectively. Remarkable photocatalytic activity with energetic charge pair transfer capability was illustrated by electrochemical impedance spectroscopy, linear sweep voltammetry, and photoluminescence spectra. The present study clearly suggests that low-cost Co(OH) platelets are the most crucial semiconductors to provide a new p-n heterojunction photocatalyst for photocatalytic H and O production on the platform of ZnCr LDH.

Lithium aluminum‐layered double hydroxide chlorides (LDH): Formation enthalpies and energetics for lithium ion capture

“…[2][3][4][5] The LDH-type materials have been developed as photocatalysts for water splitting, CO 2 reduction, and pollutant degradation. [6][7][8][9][10][11] The intercalation of different metals such as Co and Zn in the layered structure appears to facilitate the distribution of cations and stability.…”

Topotactic Transformation of Solvated MgCr-LDH Nanosheets to Highly Efficient Porous MgO/MgCr2O4 Nanocomposite for Photocatalytic H2 Evolution

“…63,64 In Figure 6a, the morphology of MgCr-LDH composed with hexagonal nanoplatelets is shown, which are a typical characteristic of delaminated LDH material and well supported with the corresponding XRD results. 64,65 For further evidence of the formation of hexagonal sheetlike nanoplatelets of MgCr-LDH, the TEM image and SAED pattern of MgCr-LDH was taken into account and the TEM micrograph clearly shows the formation of hexagonal sheetlike nanoplatelets ( Figure S2). As shown in Figure 6b Growth Mechanism.…”

“…The arc in the EIS spectra is ascribed to the contribution of charge transfer resistance (R ct ) and the constant phase element. 65 The inclined line corresponds to the ion diffusion process in the electrolyte in accordance with the Warburg impedance (Z W ). 65 The reduced diameter of the arc radius represents the faster transportation and separation efficiency of the charge carrier, while the enlarged diameter of the arc radius represents the highest resistivity with faster recombination of electron−hole pairs.…”

“…65 The inclined line corresponds to the ion diffusion process in the electrolyte in accordance with the Warburg impedance (Z W ). 65 The reduced diameter of the arc radius represents the faster transportation and separation efficiency of the charge carrier, while the enlarged diameter of the arc radius represents the highest resistivity with faster recombination of electron−hole pairs. These Nyquist plots clearly indicate the reduced diameter of the arc radius of MgO/ MgCr 2 O 4 (MgCr3:1) than other as prepared electrodes, which reveals the faster interfacial charge transportation and separation efficiency of MgO/MgCr 2 O 4 (MgCr3:1).…”

Construction of Nonmetallic p‐n Heterojunction With Face‐to‐Face Structure for Drastically Enhanced Photocatalytic Performance

“…The plenty researches demonstrate that the construction of semiconductor‐semiconductor heterojunction is usually considered as one of the most effective strategy, which can both increases separation efficiency of photo‐generated electron‐hole pairs and widens light absorption range in the solar spectrum, finally improving the H 2 production performance of photocatalysts. Semiconductor‐semiconductor heterojunction systems usually include p‐p, n‐n and p‐n heterojunction, in which fabricating p‐n heterojunction may be the most effective method because it can effectively promote the separation efficiency of photo‐generated charge carriers by forming the built‐in electric field on the interfaces of two semiconductors, leading to the significantly enhanced photocatalytic H 2 production performance ,.…”