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• Flake-like K 2 Co 3 (P 2 O 7) 2 ·2H 2 O (KCoPi) was prepared by a hydrothermal method. • The as-prepared KCoPi features a layered structure and zigzag chains of CoO 6. • The KCoPi nanoflakes exhibit remarkable OER activity in alkaline solution. Alkali metal cobalt phosphates show great potential as electrocatalysts for oxygen evolution reaction (OER). Herein, a kind of layered potassium cobalt pyrophosphate dehydrate, i.e., K 2 Co 3 (P 2 O 7) 2 ·2H 2 O, was prepared by a simple hydrothermal method, and was proved to be a novel OER electrocatalyst for the first time. The as-developed K 2 Co 3 (P 2 O 7) 2 ·2H 2 O features a layered structure, large specific surface area, and special zigzag CoO 6 octahedral chains, all of which contribute to the highly efficient OER performance. In specific, it achieves 10 mA cm−2 at an overpotential of only 296 mV and a Tafel slope of 40.2 mV dec−1 in 1.0 M KOH. Thus, this present work has opened a new pathway to develop alkali metal cobalt phosphates towards efficient and stable electrocatalytic oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

• Nanoflakes-assembled 3D flower-like nickel hydroxidenitrate was synthesized. • The flower units of as-prepared NiNH composed of ultrathin porous nanosheets. • The as-prepared NiNH exhibits remarkable OER activity in alkaline solution. This paper reports a nanoflakes-assembled 3D flower-like nickel hydroxidenitrate (NiNH) and its application in water oxidation. It is demonstrated for the first time that the NiNH is an efficient oxygen evolution reaction (OER) electrocatalyst in alkaline solution. Specifically, it can drive a current density of 10 mA cm−2 at a fairly low overpotential of 280 mV and a correspondent small Tafel slope of 39.6 mV dec−1. The impressive OER catalytic activity of the as-prepared NiNH can be ascribed to its favorable 3D hierachical microstructure. The present research not only provide us a prospective and cost-effective electrocatalyst for water splitting but also affords us an inspiration for designing effective transition-metal based electocatalysts through microstructure regulation. [ABSTRACT FROM AUTHOR]