Graphene Supported Pillared Ni–Co Metal–Organic Framework as an Efficient Electrocatalyst for the Water Oxidation Reaction

Abstract

The oxygen evolution reaction (OER) plays a critical role in the overall efficiency of water electrolysis. To address the ongoing challenge of creating electrocatalysts with high current density, low overpotential, and durable performance, we present a potential electrocatalyst for water oxidation in an alkaline medium in the form of a composite of pillared metal−organic framework (MOF) and graphene (G), designated as Ni 2 Co(bdc) 2 D@G. The bimetallic MOF was synthesized via a solvothermal approach, using nickel and cobalt metal ions that coordinate with 1,4-benzenedicarboxylic acid (bdc) and 1,4diazobicyclo[2.2.2]-octane (DABCO, D) as a pillared ligand. The assynthesized MOF was then combined with graphene to form the composite. Our electrochemical analysis revealed that the Ni 2 Co-(bdc) 2 D@G composite exhibits superior catalytic activity to that of Ni 2 Co(bdc) 2 D, with an overpotential of 350 mV at 10 mA cm −2 and a Tafel slope of 42.7 mV dec −1 , as opposed to 420 mV at 10 mA cm −2 and a Tafel slope of 84.4 mV dec −1 for Ni 2 Co(bdc) 2 D. Furthermore, the MOF@G composite required only 400 mV to achieve a current density of 50 mA cm −2 . This significant improvement in performance is attributed to the synergistic effects between the MOF and graphene, resulting in enhanced current density and reduced overpotential. The high electrocatalytic performance of the composite was attributed to the strong π−π interaction between the MOF and G, as well as the high surface area of the composite. Additionally, during the OER, the composite facilitated the formation of Ni(OH) 2 /NiOOH and Co(OH) 2 / CoOOH species, which further contributed to the overall efficiency of the electrocatalyst.

Prominent development of Ni-based oxygen-evolving electrocatalysts for water splitting

“…18,97,98 Martirez and Carter investigated the doping effects of selected 3d and 4d transition metals on a β-NiOOH catalyst for OER using DFT calculations, suggesting that Co is a promising alternative dopant to Fe; however, with only 0.07 V higher thermodynamic overpotential predicted. 82 Recently, various types of NiCo catalysts for OER have been reported including NiCo oxides, 97,99 spinel NiCo 2 O 4 , 100 NiCo LDH, 101 NiCo MOFs, [102][103][104] NiCo phosphides, 105,106 NiCo sulfides, 107,108 NiCo carbonate hydroxide hydrate, 109 NiCo nitrides, 110 NiCo oxalates, 111 and NiCo alloys. 112 Karmakar and Srivastava reported the preparation of Nisubstituted Co carbonate hydroxide hydrates (NiCo CHHs) for OER catalysis.…”