MOF-Derived Noble Metal Free Catalysts for Electrochemical Water Splitting

Noble metal free electrocatalysts for water splitting are key to low-cost, sustainable hydrogen production. In this work, we demonstrate that metal-organic frameworks (MOFs) can be controllably converted into catalysts for the oxygen evolution reaction (OER) or the hydrogen evolution reaction (HER). The OER catalyst is composed of FeNi alloy nanoparticles encapsulated in N-doped carbon nanotubes, which is obtained by thermal decomposition of a trimetallic (Zn²⁺, Fe²⁺, and Ni²⁺) zeolitic imidazolate framework (ZIF). It reaches 10 mA cm^-2 at the overpotential of 300 mV with a low Tafel slope of 47.7 mV dec^-1. The HER catalyst consists of Ni nanoparticles coated with a thin layer of N-doped carbon. It is obtained by thermal decomposition of a Ni-MOF in NH₃. It shows low overpotential of only 77 mV at 20 mA cm^-2 with low Tafel slope of 68 mV dec^-1. The above noble metal free OER and HER electrocatalysts are applied in an alkaline electrolyzer driven by a commercial polycrystalline solar cell. It achieves electrolysis efficiency of 64.4% at 65 mA cm^-2 under sun irradiation of 50 mW cm^-2. This practical application shows the promising prospect of low-cost and high-efficiency sustainable hydrogen production from combination of solar cells with high-performance noble metal free electrocatalysts.