Iron Cobaltite (FeCo2O4) Nanocatalysts for Water-Oxidation: Effects of Annealing Temperature on Catalytic Properties

The development of efficient, stable, and non-precious metal water oxidation catalysts (WOCs) is a matter of importance for sustainable energy research. In this work, iron cobaltite (FeCo2O4) nanoparticles were prepared by the coprecipitation method, and we present the effect of heat treatment (250, 350, 450, 650 and 900 °C) on the catalytic properties. Catalytic activity tests of FeCo2O4 nanocatalysts were performed in the presence of ammonium cerium(IV) nitrate (CAN), and the formation of oxygen was followed using a Clark-type oxygen electrode. The samples were characterized by infrared (IR), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and their surface areas were determined by the Brunauer, Emmett, and Teller (BET) method. Fourier transform infrared (FTIR) data confirm a metal-oxygen bond at the octahedral and tetrahedral sites. XRDs data were characteristic of spinel-like cubic materials. The XPS results confirmed the presence of trivalent and divalent cobalt and iron ions in the samples and showed that the non-heated sample has a greater amount of cobalt on the nanoparticles’ surface than those heated to 900 °C. The surface area decreased from 92.00 m2 g-1 for the material that was unannealed to 2.00 m2 g-1 for the sample annealed at 900 °C. The unannealed nanomaterials showed an oxygen production of 790 mmol s-1 g-1. This was 790 times greater than the oxygen production from nanomaterials heated to 900 °C. Although the surface structure of nanomaterials is unclear, the amount of surface cobalt appears to have implications for catalytic activity. Optimization of superficial cobalt content may be key to improving catalytic activity.

高效、稳定且非贵金属基水氧化催化剂（WOCs）的开发是可持续能源研究领域的重要课题。本研究通过共沉淀法制备了铁酸钴（FeCo₂O₄）纳米颗粒，并考察了热处理温度（250、350、450、650及900 ℃）对其催化性能的影响。以硝酸铈(IV)铵（CAN）为反应介质开展了FeCo₂O₄纳米催化剂的催化活性测试，采用克拉克型氧电极追踪氧气的生成过程。通过红外光谱（IR）、热重分析（TGA）、粉末X射线衍射（XRD）以及X射线光电子能谱（XPS）对样品进行了表征，并采用布鲁瑙尔-埃米特-泰勒（BET）法测定了样品的比表面积。傅里叶变换红外（FTIR）光谱数据证实了八面体与四面体位点处的金属-氧键存在。XRD数据显示其具有尖晶石型立方结构的特征。XPS结果证实了样品中三价、二价钴离子与铁离子的存在，并发现未热处理样品的纳米颗粒表面钴含量高于经900 ℃热处理的样品。未退火样品的比表面积为92.00 m²·g⁻¹，经900 ℃退火处理的样品比表面积降至2.00 m²·g⁻¹。未退火纳米材料的氧气生成速率可达790 mmol·s⁻¹·g⁻¹，是经900 ℃热处理的纳米材料产氧量的790倍。尽管纳米材料的表面结构尚不明确，但表面钴含量似乎对催化活性具有显著影响，优化表面钴含量或许是提升催化活性的关键所在。