Anchoring Ni/NiO heterojunction on freestanding carbon nanofibers for efficient electrochemical water oxidation.

The Ni/NiO-NCNFs are synthesized as highly active and stable freestanding OER catalysts by an electrospinning-carbonization-post oxidation strategy. The Ni/NiO ratio could be modulated via regulating the oxidation time, and the as-prepared Ni/NiO-NCNFs-3h could exhibit a promising OER activity in 0.1 M KOH solution, with an ultrasmall overpotential of 153 mV to achieve a current density of 10 mA cm−2. [Display omitted] • The electrospinning-pyrolysis-oxidation strategy is applied to anchor the Ni/NiO heterojunction on freestanding Ni-based catalysts. • The Ni/NiO ratio can be regulated via tuning the post-oxidation duration. • Density function theory calculations prove that the OER activity could be influenced by the Ni/NiO ratio. • The Ni/NiO-NCNFs-3 h sample exhibits a promising OER activity and long-term durability. • The Ni/NiO-NCNFs-3 h requires an ultrasmall overpotential of 153 mV to achieve the current density of 10 mA cm−2 in 0.1 M KOH solution. Rational design of low-cost and efficient electrocatalyst for the anodic oxygen evolution reaction (OER) to replace noble-metal-based catalysts is greatly desired for the large-scale application of water electrocatalysis. And compared with the conventional powdery catalysts, the freestanding electrode architecture is more attractive owing to the enhanced kinetics and stability. In this work, we report an electrospinning-carbonization-post oxidation strategy to develop the freestanding N -doped carbon nanofibers anchored with Ni/NiO nanoparticles (denoted as Ni/NiO-NCNFs) as efficient OER electrocatalyst. In the synthesized Ni/NiO-NCNFs, the conductive ultrathin carbon layer could promote electron transfer and thus improve the electrocatalytic activity. Meanwhile, the ratio between Ni and NiO could be regulated by tuning the oxidation duration, so as to optimize the adsorption energy of intermediates and improve the OER activity. The Ni/NiO-NCNFs prepared with the oxidation time of 3 h exhibit a promising OER activity and long-term operation durability in 0.1 M KOH solution, requiring an overpotential as small as 153 mV to achieve a current density of 10 mA cm−2. Its overpotential is far lower than that of the reported OER catalysts. This work offers an efficient pathway to develop low-cost and highly active freestanding transitional metal-based OER electrocatalyst for potential renewable electrochemical energy conversion. [ABSTRACT FROM AUTHOR]