Owing to the four features summarized in this review, i.e., low-cost resource, high-power performance, all-climate adaptability and full-batty recyclability, sodium ion batteries show great promise for large-scale energy storage systems used for the application of renewable energy sources and smart grids.

The sluggish kinetics and four electron oxidation process of the oxygen evolution reaction (OER) limit the widespread application of electrochemical water splitting. Recently, NiFe-layered double hydroxide (NiFe LDH) has shown great potential to boost the OER process. However, limited active sites and poor conductivity severely hinder the further improvement of the OER performance. Herein, oxygen vacancy-rich hierarchical NiFe LDH (v-NiFe LDH) microtubes assembled from two dimensional (2D) nanosheets were synthesized via a template-assisted strategy. The plentiful oxygen vacancies (V_O) could efficiently promote the intrinsic conductivity of the obtained LDH. Meanwhile, featuring hierarchical microtubes and 2D nanosheets, the as-prepared electrocatalyst exhibits abundant catalytically active sites and excellent structural stability. Benefitting from the defect and morphological engineering, the OER activity of v-NiFe LDH has obviously enhanced, with an ultralow overpotential of 195 mV at 10 mA cm⁻² and a low Tafel slope of 47.9 mV dec⁻¹, as well as long-term stability at 10 mA cm⁻². In addition, theoretical calculations further elucidate that the Fe site is the primary active site in v-NiFe LDH and V_O can enhance the conductivity and accelerate the OER kinetic process through decreasing the bandgap of NiFe LDH and reaction energy of the rate-determining step.