Abstract
The performance of transition metal hydroxides, as cocatalysts for CO2 photoreduction, is significantly limited by their inherent weaknesses of poor conductivity and stacked structure. Herein, we report the rational assembly of a series of transition metal hydroxides on graphene to act as a cocatalyst ensemble for efficient CO2 photoreduction. In particular, with the Ru-dye as visible light photosensitizer, hierarchical Ni(OH)2 nanosheet arrays-graphene (Ni(OH)2-GR) composites exhibit superior photoactivity and selectivity, which remarkably surpass other counterparts and most of analogous hybrid photocatalyst system. The origin of such superior performance of Ni(OH)2-GR is attributed to its appropriate synergy on the enhanced adsorption of CO2, increased active sites for CO2 reduction and improved charge carriers separation/transfer. This work is anticipated to spur rationally designing efficient earth-abundant transition metal hydroxides-based cocatalysts on graphene and other two-dimension platforms for artificial reduction of CO2 to solar chemicals and fuels.
Highlights
The performance of transition metal hydroxides, as cocatalysts for CO2 photoreduction, is significantly limited by their inherent weaknesses of poor conductivity and stacked structure
We report the facile synthesis of a series of different transition metal hydroxides, including Ni(OH)[2], Fe(OH)[3], Cu (OH)[2], and Co(OH)[2], onto the 2D platform of GR to act as cocatalysts ensemble for CO2 photoreduction to solar fuels
At the beginning of the growth process, hexamethylenetetramine (HMTA) as a hydrolyzing agent can tardily decompose to liberate OH– ions, and transition metal cations react with OH– ions to form dense transition metal hydroxides nuclei on the surface of GO17,28
Summary
The performance of transition metal hydroxides, as cocatalysts for CO2 photoreduction, is significantly limited by their inherent weaknesses of poor conductivity and stacked structure. With the Ru-dye as visible light photosensitizer, hierarchical Ni(OH)[2] nanosheet arrays-graphene (Ni(OH)2-GR) composites exhibit superior photoactivity and selectivity, which remarkably surpass other counterparts and most of analogous hybrid photocatalyst system The origin of such superior performance of Ni(OH)2-GR is attributed to its appropriate synergy on the enhanced adsorption of CO2, increased active sites for CO2 reduction and improved charge carriers separation/transfer. There is still a long way to achieve efficient and selective photocatalytic CO2 reduction, especially in diluted CO2, which is primarily because of the low CO2 adsorption, high recombination rate of charge carriers in photocatalysts, concealed active sites, and the competing H2 evolution reaction[7,8,9,10,11] To overcome these limitations, rational construction of hybrid photocatalytic systems, in which photosensitizers and cocatalysts operate in a harmonious manner, has arisen as a promising approach[12,13,14,15,16]. It is hoped that this work would provide instructive guideline for rational design of earth-abundant transition metal hydroxidesbased cocatalysts by harnessing the rich surface chemistry of GR and other 2D materials platforms toward efficient and selective solar light driven CO2 reduction to value-added fuels and chemicals in a sustainable way
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