Precursor accumulation on nanocarbons for the synthesis of LaCoO nanoparticles as electrocatalysts for oxygen evolution reaction.

Oxygen evolution reaction (OER) is a key step in energy storage devices. Lanthanum cobaltite (LaCoO) perovskite is an active catalyst for OER in alkaline solutions, and it is expected to be a low-cost alternative to the state-of-the-art catalysts (IrO and RuO) because transition metals are abundant and inexpensive. For efficient catalysis with LaCoO, nanosized LaCoO with a high surface area is desirable for increasing the number of catalytically active sites. In this study, we developed a novel synthetic route for LaCoO nanoparticles by accumulating the precursor molecules over nanocarbons. This precursor accumulation (PA) method for LaCoO nanoparticle synthesis is simple and involves the following steps: (1) a commercially available carbon powder is soaked in a solution of the nitrate salts of lanthanum and cobalt and (2) the sample is dried and calcined in air. The LaCoO nanoparticles prepared by the PA method have a high specific surface area (12 m g), comparable to that of conventional LaCoO nanoparticles. The morphology of the LaCoO nanoparticles is affected by the nanocarbon type, and LaCoO nanoparticles with diameters of less than 100 nm were obtained when carbon black (Ketjen black) was used as the support. Further, the sulfur impurities in nanocarbons significantly influence the formation of the perovskite structure. The prepared LaCoO nanoparticles show excellent OER activity owing to their high surface area and perovskite structure. The Tafel slope of these LaCoO nanoparticles is as low as that of the previously reported active LaCoO catalyst. The results strongly suggest that the PA method provides nanosized LaCoO without requiring the precise control of chemical reactions, harsh conditions, and/or special apparatus, indicating that it is promising for producing active OER catalysts at a large scale.