α and β-motifs Interstratified βbc -Nickel Hydroxide for Enhanced OER and UOR Electrocatalysis

Abstract

Nickel hydroxide presents itself in a variety of interesting polymorphic modifications. One such polymorphic form, βbc–nickel hydroxide, is known to be a poorly ordered solid in which α (~15%) and β motifs are interstratified. The α/β interfaces propel the reconstruction of βbc to Ni4+ containing γ-nickel oxyhydroxide, a process kinetically hindered in the case of pristine ordered β-phase. Defect-rich γ-nickel oxyhydroxide with a high ECSA, boosts electronic conductivity and accelerates charge transfer to drive enhanced oxygen evolution reaction (OER) kinetics delivering higher current densities at lower potentials. βbc–phase outperforms β–nickel hydroxide in OER with lower onset potential (βbc = 1.5 VRHE compared to β = 1.55 VRHE), higher current density and lower Tafel slope (βbc = 60 mV dec-1 compared to β = 95 mV dec-1). The βbc polymorph also efficiently catalyzes urea oxidation reaction (UOR) with a sustained Ni3+/Ni4+ active surface delivering an onset potential of 1.35 VRHE and a Tafel slope of 25 mV dec-1.