Chown Amanda L, Farnum Byron H
Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States.
Inorg Chem. 2022 May 30;61(21):8349-8355. doi: 10.1021/acs.inorgchem.2c00943. Epub 2022 May 19.
The synthesis of nanocrystalline, p-type delafossite metal oxides (CuMO) via hydrothermal methods has been explored for a variety of energy conversion and storage applications. However, isolation of the pure phase ternary product is challenging due to the facile growth of unwanted, binary byproducts (CuO, CuO, and MO) which could ultimately influence the optoelectronic properties of the resulting nanocrystals. Here, we report on the optimized hydrothermal synthesis of CuCrO nanocrystals to limit the production of such byproducts. This material possesses a wide band gap and high reported conductivity, making it attractive for applications as the hole transport layer in a variety of heterojunction solar cells. An important aspect of this work is the consideration of Cr as the reductant used to reduce Cu to Cu. This was confirmed by detection and quantification of CrO as a product of hydrothermal synthesis in addition to the fact that CuCrO purity was maximized at a ratio of 4:3 Cr/Cu, consistent with the proposed stoichiometric reaction: 4Cr + 3Cu + 20 OH → 3CuCrO + CrO + 10 HO. Using a 4:3 ratio of Cr/Cu starting materials and allowing the synthesis to proceed for 60 h eliminates the presence of CuO beyond detection by powder X-ray diffraction (pXRD). Furthermore, washing the solid product in 0.5 M NHOH removes CuO and CrO impurities, leaving behind the isolated CuCrO product as confirmed using pXRD and inductively coupled plasma mass spectrometry.
通过水热法合成纳米晶p型铜铁矿金属氧化物（CuMO）已被用于多种能量转换和存储应用的探索。然而，由于不需要的二元副产物（CuO、Cu₂O和MO）容易生长，分离纯相三元产物具有挑战性，这些副产物最终可能会影响所得纳米晶体的光电性能。在此，我们报告了优化的水热合成CuCrO₂纳米晶体以限制此类副产物的产生。这种材料具有宽带隙和高电导率，使其在各种异质结太阳能电池中作为空穴传输层的应用具有吸引力。这项工作的一个重要方面是将Cr视为用于将Cu²⁺还原为Cu⁺的还原剂。除了在4:3的Cr/Cu比例下CuCrO₂纯度最大化这一事实外，水热合成产物Cr₂O₃的检测和定量也证实了这一点，这与提出的化学计量反应一致：4Cr + 3Cu²⁺ + 20OH⁻ → 3CuCrO₂ + Cr₂O₃ + 10H₂O。使用4:3比例的Cr/Cu起始原料并让合成反应进行60小时，通过粉末X射线衍射（pXRD）检测不到CuO的存在。此外，用0.5 M NH₄OH洗涤固体产物可去除CuO和Cr₂O₃杂质，如使用pXRD和电感耦合等离子体质谱所证实的那样，留下分离出的CuCrO₂产物。
