Simplified Microwave Assisted Solvothermal One Pot Synthesis of Highly Active Nickel-Iron Layered Double Hydroxide as Oxygen Evolution Reaction Catalyst

Abstract

The increasing demand for solar fuels and hydrogen as most promising energy carrier requires new materials for electro-catalytic splitting of water or the back-transformation of hydrogen into electricity. Especially, the oxygen electrode caused by sluggish kinetics is hampering progress for cheap hydrogen made by electrolysis. Moreover the low abundance and the high costs of current highly active noble metal catalysts require new developments for novel cheap and abundant materials. Therefore we have developed a new two-component catalyst system consisting of Nickel-Iron layered double hydroxide (NiFe-LDH) and Fe-N doped carbon material (Fe-N-C) as non noble bifunctional catalyst for the oxygen electrode in alkaline unitized reversible fuel cells/electrolyzers (URFC). The combination of NiFe-LDH known as most active non-noble catalyst for the oxygen evolution reaction (OER) in alkaline media and Fe-N-C known as highly active catalyst for the oxygen reduction reaction (ORR) resulted in a combined overpotential with their respective advantages. Highly crystalline NiFe-LDH was prepared by a simple and time-saving microwave assisted solvothermal synthesis route. The crystallinity was confirmed by X-ray diffraction (XRD) spectroscopy and Transmission electron microscopy (TEM) verified morphological characteristics. Rotating Ring disk (RRDE) measurement revealed high selectivity for the multi-component catalyst. We further investigated the behaviour in a membrane based reversible electrolyzer using an anion exchange membrane (AEM, Tokuyama A201). Compared to noble catalyst systems such as Iridium and Platinum the membrane electrode assembly (MEA) measurements proved the ability to compete and supported the initial high activities.