Highly Efficient and Cost-Effective Electrocatalysts Using Nickel-Based Metal-Organic Frameworks for Water Splitting

Abstract

The low-cost nickel compound is one of the most effective electrocatalysts among the transition metals-based electrocatalysts. Therefore, understanding the electroactivity of nickel-based metal-organic frameworks (MOFs) plays a vital role in green energy production via hydrogen and oxygen evolution reactions. The demand for green and efficient energy devices is increasing rapidly and fuels cells could be one of the solutions for such requirements. This work introduces the use of MOF-derived nickel hydroxide and oxide as highly efficient electrocatalysts. The electrocatalysts were synthesized using a hydrothermal method at different growth temperatures (140, 160, and 180 °C). Glutaric acid was used as an organic ligand. The MOF-based nickel hydroxide was converted to nickel oxide via a facile calcination process at 350 °C. The best sample of MOF-derived nickel oxide (160 °C) showed an oxygen evolution overpotential of 394 mV at 10 mA/cm2 with a Tafel slope of 73 mV/dec. The unique structure of MOF-derived nickel hydroxide provides more electroactive sites. The shorter pathway for ion transference reduces the overpotential to 330 mV at 10 mA/cm2 with the lowest Tafel slope of 107 mV/dec. The best MOF-based nickel oxide electrocatalyst for hydrogen evolution reaction required 103 mV to deliver 10 mA/cm2. On the other hand, MOF-based nickel hydroxide needed 189 mV of overpotential to reach 10 mA/cm2. The stability of the prepared electrocatalysts was tested using cyclic linear voltammetry and chronoamperometry. Both measurements showed high electrocatalytic stability of the prepared samples for over 1,000 cycles of linear voltammetry and 24 hrs of chronoamperometry test. Our research provides cost-effective and highly efficient electrocatalysts for green energy production.