ZIF-8 MOF Encapsulated Co-porphyrin, an Efficient Electrocatalyst for Water Oxidation in a Wide pH Range: Works Better at Neutral pH

Abstract

Water oxidation (WO) is the most important and thermodynamically challenging process associated with water splitting. Several metal porphyrins are reported to perform catalytic WO through the central metal but [5,10,15,20-tetrakis(4-methoxyphenyl)porphyrinato]cobalt(II) (abbreviated as CoTMPP), which is well-known for its ability to perform oxygen reduction reaction (ORR), lacks the capacity to perform WO. Here we have successfully activated CoTMPP towards electrochemical WO by means of its in situ encapsulation inside the cavity of a versatile metal organic framework (MOF), known as zeolitic imidazolate framework-8 (ZIF-8). The composite, thus prepared i. e., CoTMPP@ZIF-8 (abbreviated as CTMZ-8), behaves as a heterogeneous, robust, and efficient electrocatalyst for oxygen evolution reaction (OER) at a wide pH range (from acidic to neutral). Required overpotential (η) of 387.4 mV (neutral pH) and 562.7 mV (pH 2) and high turnover frequency (TOF) of 2.7 s−1 (at neutral pH) make this composite (CTMZ-8) an efficient electrocatalyst for WO. To the best of our knowledge, this is the first report of electrocatalytic WO by CoTMPP.