Photocatalytic CO₂ Reduction Using Ni₂P Nanosheets

Abstract

Artificial photosynthesis is an ideal method for solar-to-chemical energy conversion, wherein solar energy is stored in the form of chemical bonds of solar fuels. In particular, the photocatalytic reduction of CO2 has attracted considerable attention due to its dual benefits of fossil fuel production and CO2 pollution reduction. However, CO2 is a comparatively stable molecule and its photoreduction is thermodynamically and kinetically challenging. Thus, the photocatalytic efficiency of CO2 reduction is far below the level of industrial applications. Therefore, development of low-cost cocatalysts is crucial for significantly decreasing the activation energy of CO2 to achieving efficient photocatalytic CO2 reduction. Herein, we have reported the use of a Ni2P material that can serve as a robust cocatalyst by cooperating with a photosensitizer for the photoconversion of CO2. An effective strategy for engineering Ni2P in an ultrathin layered structure has been proposed to improve the CO2 adsorption capability and decrease the CO2 activation energy, resulting in efficient CO2 reduction. A series of physicochemical characterizations including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM) were used to demonstrate the successful preparation of ultrathin Ni2P nanosheets. The XRD and XPS results confirm the successful synthesis of Ni2P from Ni(OH)2 by a low temperature phosphidation process. According to the TEM images, the prepared Ni2P nanosheets exhibit a 2D and near-transparent sheet-like structure, suggesting their ultrathin thickness. The AFM images further demonstrated this result and also showed that the height of the Ni2P nanosheets is ca 1.5 nm. The photoluminescence (PL) spectroscopy results revealed that the Ni2P material could efficiently promote the separation of the photogenerated electrons and holes in [Ru(bpy)3]Cl2·6H2O. More importantly, the Ni2P nanosheets could more efficiently promote the charge transfer and charge separation rate of [Ru(bpy)3]Cl2·6H2O compared with the Ni2P particles. In addition, the electrochemical experiments revealed that the Ni2P nanosheets, with their high active surface area and charge conductivity, can provide more active centers for CO2 conversion and accelerate the interfacial reaction dynamics. These results strongly suggest that the Ni2P nanosheets are a promising material for photocatalytic CO2 reduction, and can achieve a CO generation rate of 64.8 μmol·h −1 , which is 4.4 times higher than that of the Ni2P particles. In addition, the XRD and XPS measurements of the used Ni2P nanosheets after the six cycles of the photocatalytic CO2 reduction reaction demonstrated their high stability. Overall, this study offers a new function for the 2D transition-metal phosphide catalysts in photocatalytic CO2 reduction.

Cobalt Phosphide Cocatalysts Coated with Porous N‐doped Carbon Layers for Photocatalytic CO2 Reduction

“…After being coated with NC layer, CoP@NC hybrid shows much‐enhanced activity and selectivity for CO 2 reduction reaction, affording a CO evolution rate of 54 μmol h −1 and a CO selectivity of 66 %. The CO 2 ‐to‐CO conversion performance of the core‐shell CoP@NC cocatalyst is comparable to those of reported works in similar Ru sensitized systems (Table S1) [14,19,37,38,43,61–70] . Compared to CoP@NC, both CoP@NC 4‐1 and CoP@NC 1‐1 display inferior CO 2 reduction activity and selectivity, suggesting that thickness of the coated NC layer affects the catalytic performance.…”

2D/2D FeNi-LDH/g-C₃N₄ Hybrid Photocatalyst for Enhanced CO₂ Photoreduction

“…After loading FeNi-LDH, the peak intensity is obviously reduced. Particularly, the peak intensity of CN/LDH4 is the weakest, indicating its best charge transfer efficiency 57 . In other word, the introduction of FeNi-LDH could suppress the recombination of photogenerated charges.…”

Review of Z-Scheme Heterojunctions for Photocatalytic Energy Conversion

“…Light absorption, charge separation/transfer and surface chemical reactions determine the overall efficiency of photocatalytic systems [253][254][255][256][257][258][259][260][261][262][263][264][265][266][267][268][269][270] , and the surface redox reactions can be optimized by cocatalyst loading and other surface modification approach [271][272][273][274][275][276][277][278][279][280][281] .…”

“…In photocatalytic reactions, cocatalysts are not the light-harvesting components. Instead, cocatalysts plays the following key roles in photocatalytic process [271][272][273] : 1Reducing the activation energy or overpotential for the surface reactions; (2) Boosting the separation and migration of photoinduced hole-electron pairs in Z-scheme systems; (3) Enhancing the directional redox reactions efficiency and selectivity; (4) Maintaining the stability and lowering the possibility of photocorrosion of semiconductors by timely extracting the photogenerated charge; (5) Suppressing the side and back reactions. Besides, cocatalysts acting as alternative reaction sites can retard the photocorrosion of semiconductor resulted from the charge accumulation and thus improve the photostability.…”

“…Besides, cocatalysts acting as alternative reaction sites can retard the photocorrosion of semiconductor resulted from the charge accumulation and thus improve the photostability. Therefore, loading cocatalysts on the semiconductor is common in the photocatalysis field 219,[271][272][273][274][275][276][277][278][279][280][281][282][283][284] .…”