Steps towards highly-efficient water splitting and oxygen reduction using nanostructured β-Ni(OH)2

Abstract

β-Ni(OH)₂ nanoplatelets are prepared by a hydrothermal procedure and characterized by scanning and transmission electron microscopy, X-ray diffraction analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. The material is demonstrated to be an efficient electrocatalyst for oxygen reduction, oxygen evolution, and hydrogen evolution reactions in alkaline media. β-Ni(OH)₂ shows an overpotential of 498 mV to reach 10 mA cm⁻² towards oxygen evolution, with a Tafel slope of 149 mV dec⁻¹ (decreasing to 99 mV dec⁻¹ at 75 °C), along with superior stability as evidenced by chronoamperometric measurements. Similarly, a low overpotential of −333 mV to reach 10 mA cm⁻² (decreasing to only −65 mV at 75 °C) toward hydrogen evolution with a Tafel slope of −230 mV dec⁻¹ is observed. Finally, β-Ni(OH)₂ exhibits a noteworthy performance for the ORR, as evidenced by a low Tafel slope of −78 mV dec⁻¹ and a number of exchanged electrons of 4.01 (indicating direct 4e⁻-oxygen reduction), whereas there are only a few previous reports on modest ORR activity of pure Ni(OH)₂.