Photocatalytic CO2 Reduction Using Ni2P Nanosheets

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 Ni-2P 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)]Cl-2 center dot 6H(2)O. More importantly, the Ni2P nanosheets could more efficiently promote the charge transfer and charge separation rate of [Ru(bpy)(3)]Cl-2 center dot 6H(2)O 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 mu mol.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.