直接化学气相沉积法制备二维钴铁氧体用于高效析氧反应

Two-dimensional cobalt ferrite through direct chemical vapor deposition for efficient oxygen evolution reaction

二维(2D)过渡金属氧化物(TMO)的地球丰度高,并且具有独特的物理化学性质和较好的催化性能,是新能源工业领域中非常有应用前景的电催化剂.然而,由于合成高质量和可控厚度的2D TMO具有一定的难度,目前有关2D TMO的微观电化学研究的报道较少.本文采用化学气相沉积法直接合成了2D钴铁氧体(CoFeO),所制得的2D CoFeO呈现结晶性良好的超薄尖晶石结构,其最薄厚度可达到6.8 nm.采用超微电极测试平台考察了碱性条件下2DCoFeO催化析氧反应(OER)的性能.结果表明,2D CoFeO(111)面在10 m Acm^(-2)的电流密度下表现出330 m V的低过电位,在570 m V的过电位下表现出142 m Acm^(-2)的高电流密度.密度泛函理论计算发现2DCoFeO表面上的双金属位点降低了反应能垒.此外,2DCoFeO的超薄厚度使体电阻率降低,同时增加了活性位点的利用率,进而提高了对OER的催化活性,这与在超微电极平台上测得的2D CoFeO厚度-OER活性依赖关系的结果一致.本研究还合成了大面积的2D CoFeO薄膜,其标准三电极体系研究表明2D CoFeO样品仍然表现出较高的催化OER活性和较好的寿命,说明所制备的2D CoFeO具有较好的实际应用潜力.综上,本文采用气相化学沉积法直接合成了超薄2DCoFeO纳米片,其最薄厚度可达6.8 nm,2DCoFeO表现出良好的OER性能,为2DTMOs电催化剂的可控合成开辟了新途径.此外,本文还分析了2DCoFeO电催化OER反应的机理,为二维电催化剂设计提供了新思路.

Two-dimensional(2D) transition metal oxides(TMOs) are promising electrocatalysts for the new energy industry,owing to their earth-abundancy,excellent performance,and unique physicochemical properties.However,microscopic electrochemical study for 2D TMOs is still lacking to provide detailed electrocatalytic mechanisms due to the challenges in synthesizing 2D TMOs with high quality and controlled thickness,which is indispensable for the microscopic studies.In this study,we report the direct synthesis of 2D cobalt ferrite(CoFeO) using a chemical vapor deposition(CVD) method.The as-synthesized 2D CoFeO possesses a well-crystallized spinel structure with an ultrathin thickness of 6.8 nm.Its oxygen evolution reaction(OER) properties under alkaline conditions were accurately assessed using an ultra-microelectrode testing platform.The(111) facet of the 2D CoFeO exhibits a low overpotential of 330 mV at a current density of 10 m A cm~(–2) and a high current density of ~142 m A cm~(–2) at an overpotential of 570 m V.The OER mechanism of the 2D CoFeO was analyzed using density functional theory(DFT) calculations,which reveal the bimetallic sites on the surface reduce the energy barrier and facilitate the reaction.Moreover,we demonstrate the reduced thickness of 2D CoFeO improves the OER activity by lowering the bulk resistance and improving the utilization of active sites,which was confirmed by the thickness-activity dependency(6.8 to 35 nm) tests using the ultra-microelectrode platform.Furthermore,the practical values of the as-prepared 2D CoFeO was demonstrated by synthesizing a large-area continuous film and collecting high OER activity and superb durability from macro-electrochemical experiments.Our study provides new solutions for the controlled synthesis of 2D TMOs electrocatalysts and uncovers the electrocatalytic mechanisms with the ultra-microelectrode platform,which provides new insights for exploring the inherent properties and applications of 2D materials in electrocatalysis.