Non-Calcined Layer-Pillared Mn _0.5Zn _0.5 Bimetallic–Organic Framework as a Promising Electrocatalyst for Oxygen Evolution Reaction

Abstract

Electrocatalytic generation of oxygen is of great significance for sustainable, clean, and efficient energy production. Multiple electron transfer in oxygen evolution reaction (OER) and its slow kinetics represent a serious hedge for efficient water splitting, requiring the design and development of advanced electrocatalysts with porous structures, high surface areas, abundant electroactive sites, and low overpotentials. These requisites are common for metal–organic frameworks (MOFs) and derived materials that are promising electrocatalysts for OER. The present work reports on the synthesis and full characterization of a heteroleptic 3D MOF, [Zn ₂(μ ₄-odba) ₂(μ-bpdh)] _n · nDMF (Zn-MUM-1), assembled from 4,4′-oxydibenzoic acid and 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (bpdh). Besides, a series of heterometallic MnZn-MUM-1 frameworks (abbreviated as Mn _0.5Zn _0.5-MUM-1, Mn _0.66Zn _0.33-MUM-1, and Mn _0.33Zn _0.66-MUM-1) was also prepared, characterized, and used for the fabrication of working electrodes based on Ni foam (NF), followed by their exploration in OER. These noble-metal-free and robust electrocatalysts are stable and do not require pyrolysis or calcination while exhibiting better electrocatalytic performance than the parent Zn-MUM-1/NF electrode. The experimental results show that the Mn _0.5Zn _0.5-MUM-1/NF electrocatalyst features the best OER activity with a low overpotential (253 mV at 10 mA cm ^–2) and Tafel slope (73 mV dec ^–1) as well as significant stability after 72 h or 6000 cycles. These excellent results are explained by a synergic effect of two different metals present in the Mn–Zn MOF as well as improved charge and ion transfer, conductivity, and stability characteristics. The present study thus widens the application of heterometallic MOFs as prospective and highly efficient electrocatalysts for OER.

Abstract

New bimetallic MOF-based electrocatalysts were assembled, fully characterized, and explored in the oxygen evolution reaction, highlighting the impact of a second metal on the observed electrocatalytic activity.