Nanopore-rich NiFe LDH targets the formation of the high-valent nickel for enhanced oxygen evolution reaction

Nickel-iron layered double hydroxides (NiFe LDHs) represent a promising candidate for oxygen evolution reaction (OER), however, are still confronted with insufficient activity, due to the slow kinetics of electrooxidation of Ni²⁺ cations for the high-valent active sites. Herein, nanopore-rich NiFe LDH (PR-NiFe LDH) nanosheets were proposed for enhancing the OER activity together with stability. In the designed catalyst, the confined nanopores create abundant unsaturated Ni sites at edges, and decrease the migration distance of protons down to the scale of their mean free path, thus promoting the formation of high-valent Ni^3+/4+ active sites. The unique configuration further improves the OER stability by releasing the lattice stress and accelerating the neutralization of the local acidity during the phase transformation. Thus, the optimized PR-NiFe LDH catalysts exhibit an ultralow overpotential of 278 mV at 10 mA∙cm⁻² and a small Tafel slope of 75 mV∙dec⁻¹, which are competitive among the advanced LDHs based catalysts. Moreover, the RP-NiFe LDH catalyst was implemented in anion exchange membrane (AEM) water electrolyzer devices and operated steadily at a high catalytic current of 2 A over 80 h. These results demonstrated that PR-NiFe LDH could be a viable candidate for the practical electrolyzer. This concept also provides valuable insights into the design of other catalysts for OER and beyond.