Construction of 3D Ni3Se2@NiCo-LDH heterostructured system for efficient electrocatalytic oxygen evolution reaction

We report the controlled synthesis of NiCo layered double hydroxide (LDH) nanoplates using a newly developed high temperature high pressure hydrothermal continuous flow reactor (HCFR), which enables direct growth onto conductive substrates in high yield and, most importantly, better control of the precursor supersaturation and, thus, nanostructure morphology and size. The solution coordination chemistry of metal-ammonia complexes was utilized to synthesize well-defined NiCo LDH nanoplates directly in a single step without topochemical oxidation. The as-grown NiCo LDH nanoplates exhibit a high catalytic activity toward the oxygen evolution reaction (OER). By chemically exfoliating LDH nanoplates to thinner nanosheets, the catalytic activity can be further enhanced to yield an electrocatalytic current density of 10 mA cm(-2) at an overpotential of 367 mV and a Tafel slope of 40 mV dec(-1). Such enhancement could be due to the increased surface area and more exposed active sites. X-ray photoelectron spectroscopy (XPS) suggests the exfoliation also caused some changes in electronic structure. This work presents general strategies to controllably grow nanostructures of LDH and ternary oxide/hydroxides in general and to enhance the electrocatalytic performance of layered nanostructures by exfoliation.

Transition metal nanoparticles (Fe, Co, and Ni) encapsulated in N-doped carbon nanotube hybrids were prepared, and the catalytic activities of three catalysts are compared and discussed. The optimized Co/N-CNT catalyst exhibits superb bifunctional catalytic activity with a Δ E value of 0.78 V. The development of efficient and cheap bifunctional oxygen electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) to be applied in rechargeable metal–air batteries and unitized generative fuel cells (URFCs) operated with alkaline electrolytes is highly crucial and challenging. Here we report high-performance bifunctional electrocatalysts of transition metal nanoparticles encapsulated in nitrogen-doped carbon nanotubes (M/N-CNTs, M = Fe, Co, and Ni). The optimized Co/N-CNT hybrid shows the highest efficient bifunctional catalytic activity and excellent stability towards both the ORR and OER. The oxygen electrode activity parameter Δ E (the criteria for judging the overall catalytic activity of bifunctional electrocatalysts) value for Co/N-CNTs is 0.78 V, which surpasses those of Pt/C and RuO 2 catalysts and most of the non-precious metal based bifunctional electrocatalysts reported in the previous literature studies. Furthermore, excellent long-term catalytic durability holds great promise in fields of renewable energy applications.