Yu Hongyan, Jiang Kaiming, Kang Sung Gu, Men Yong, Shin Eun Woo
School of Chemical Engineering, University of Ulsan, Daehakro 93, Nam-gu, Ulsan 44610, Korea.
College of Chemistry and Chemical Engineering, Shanghai University of Engineering Science, Shanghai 201620, China.
Nanomaterials (Basel). 2020 Oct 19;10(10):2061. doi: 10.3390/nano10102061.
In this study, we prepared hexagonal and monoclinic phases of LaOCO nanoparticles by different wet preparation methods and investigated their phase-related CO behavior through field-emission scanning microscopy, high-resolution transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, CO-temperature programmed desorption, and linear sweeping voltammetry of CO electrochemical reduction. The monoclinic LaOCO phase was synthesized by a conventional precipitation method via La(OH)CO when the precipitation time was longer than 12 h. In contrast, the hydrothermal method produced only the hexagonal LaOCO phase, irrespective of the hydrothermal reaction time. The La(OH) phase was determined to be the initial phase in both preparation methods. During the precipitation, the La(OH) phase was transformed into La(OH)CO owing to the continuous supply of CO from air whereas the hydrothermal method of a closed system crystallized only the La(OH) phase. Based on the CO-temperature programmed desorption and thermogravimetric analysis, the hexagonal LaOCO nanoparticles (HL-12h) showed a higher surface CO adsorption and thermal stability than those of the monoclinic LaOCO (PL-12h). The crystalline structures of both LaOCO phases predicted by the density functional theory calculation explained the difference in the CO behavior on each phase. Consequently, HL-12h showed a higher current density and a more positive onset potential than PL-12h in CO electrochemical reduction.
在本研究中，我们通过不同的湿法制备方法制备了六方相和单斜相的LaOCO纳米颗粒，并通过场发射扫描显微镜、高分辨率透射电子显微镜、傅里叶变换红外光谱、热重分析、CO程序升温脱附以及CO电化学还原线性扫描伏安法研究了它们与相相关的CO行为。当沉淀时间超过12小时时，通过传统沉淀法经由La(OH)CO合成了单斜相LaOCO。相比之下，水热法仅产生六方相LaOCO，与水热反应时间无关。在两种制备方法中，均确定La(OH)相为初始相。在沉淀过程中，由于空气中CO的持续供应，La(OH)相转变为La(OH)CO，而封闭系统的水热法仅使La(OH)相结晶。基于CO程序升温脱附分析和热重分析，六方相LaOCO纳米颗粒（HL-12h）比单斜相LaOCO（PL-12h）表现出更高的表面CO吸附和热稳定性。密度泛函理论计算预测的两种LaOCO相的晶体结构解释了各相上CO行为的差异。因此，在CO电化学还原中，HL-12h比PL-12h表现出更高的电流密度和更正的起始电位。
