磷掺杂提升三氧化钨导带用于高效二氧化碳还原

P-doped WO semiconductor with enhanced conduction band on highly efficient photoelectrocatalytic reduction of CO_(2)

光电催化还原二氧化碳是一种环境友好的高效方法,可将过量排放的CO_(2)转化为燃料与化学品,减少温室效应并存储太阳能为化学能.本研究设计制备了新型磷掺杂的WO_(3)催化剂,并将其用于CO_(2)和水转化为碳基化学品.通过X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、顺磁共振(EPR)等证实了新型催化剂的成功制备;通过紫外可见(UV-vis)、线性扫描伏安曲线(LSV)、莫特-肖特基(Mott-Schottky)和电化学交流阻抗谱(EIS)表征了其光电性能.结果表明,随着P掺杂量的增加,其导带位置从WO_(3)的-0.13 V升高到30-P样品的-0.54 V,增强了其对CO_(2)的还原能力;所有样品X-P比纯WO_(3)有更高的活性,其中15-P电极还原CO_(2)的活性最高,其光电池的表观光量子效率为0.4%,与植物的光合作用相当,且导带位置越高越有利于甲酸和乙酸产物的生成,而相对较低的导带更有利于乙醇的生成.同时,氧空位对反应的正影响也通过设计H_(2)O_(2)猝灭实验进行了验证.

Global warming is considered a serious climate problem caused by excessive emissions of carbon dioxide. Studies on catalytic conversion of CO_(2) are significant in terms of reducing CO_(2) concentration in the atmosphere, thus remain popular in the field. The photoelectrocatalytic(PEC) reduction of CO_(2) is an environment-friendly and efficient method to convert excessive CO_(2) into chemicals. With such conversion, the greenhouse effect can be alleviated through the storage and transformation of solar energy into chemical energy.WO3 is an n-type semiconductor with wide band gap and low conduction band position. Therefore, the use of WO3 is rare for photocatalytic water splitting and CO_(2) reduction. Although some techniques are used to improve the ability of WO3 in photocatalytic water splitting, the light quantum efficiency(AQE) is still less than Ti O_(2). In current study, a facile method is explored to enhance the conduction band position of semiconductors, thereby improving the photoelectrocatalytic reduction of CO_(2).To the best of our knowledge, this is the first paper includes novel P-doped WO_(3) catalysts being designed, prepared, and used in the reduction of CO_(2) to carbon-based chemicals in water. X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), scanning electron microscope(SEM), transmission electron microscope(TEM), and electron paramagnetic resonance(EPR) experiments were applied to confirm the formation of new catalysts. The photoelectric properties of new catalysts were characterized by UV-vis, linear sweep voltammetry(LSV), Mott-Schottky, and electrochemical impedance spectroscopy(EIS) experiments.We have developed a new type of hybrid semiconductor(P-doped WO_(3)|) as catalytic materials by introducing the vaporized phosphide(NaH2PO_(2)) onto the surface of WO_(3) substrate under the flow of argon gas in a tube furnace. The PEC cell of P-doped WO_(3)|SCE|BiVO4 was equipped with a trielectrode system and powered by a chemical workstation, in which, p-doped WO3| was used as photocathodes in photoelectrocatalytic reduction of CO_(2). The PEC cell was fulfilled with an electrolyte containing 1 mmol/L photosensitizer Eosin Y and 0.1 mol/L KHCO3, and bubbled with pure CO_(2) in 30 min to saturation, the experiment of CO_(2) reduction in water was carried out with a proper voltage under irradiation of simulated sun light(300 W Xe lamp) to generate methanol, ethanol, acetone, etc.Our results indicates that the conduction band position of p-doped WO3 increases from -0.13 to -0.54 V along with the increase of P-doped quantity, augmenting its ability to reduce CO_(2). It can be seen that p-doped WO3 with oxygen vacancies has higher activity than pure WO3, in which, the highest activity is the catalyst 15-P, approaching to 0.4% AQE equal to natural plant, yielding methanol in a rate of 20.8 μmol/(L h cm2) and acidic acid at a rate of 4.7 μmol/(L h cm2). The influence of oxygen vacancies on the reaction is positive and verified by the quenching experiments of H2O_(2). The more oxidation time, the less oxygen vacancies. The EPR signal of 15-P catalyst treated by 2 h oxidation was reduced to 10%.The catalytic activity of CO_(2) reduction was decreased to 50%.In summary, we designed and prepared a new type of p-doped WO3 hybrid semiconductor material as efficient catalysts for photoelectrocatalytic reduction of CO_(2), resulting carbon-based chemicals. P-doped WO3 improves the conduction band position of the semiconductors, increases oxygen vacancies and defect sites. Therfore, the activity and efficiency of catalytic reduction of CO_(2) can be improved. The low voltage is favoured to ethanol production, and high voltage is favoured to acid production. The experimental results have guiding significance for the development of new hybrid semiconductor materials and their photoelectrocatalytic reduction of CO_(2).