MnO₂-Templated CuBDC Metal Organic Framework: A Noble-Metal-Free Stable and Efficient pH-Universal Electrocatalyst for Oxygen Reduction Reaction

The development of noble-metal-free, efficient, cost-effective, and stable pH-universal electrocatalysts for the oxygen reduction reaction (ORR) is essential for enabling the widespread adoption of ORR-based fuel cells and batteries in practical applications. Herein, we report the design and fabrication of a MnO2-supported Cu-Metal Organic Framework (Cu-MOF) as a cost-effective, efficient, stable, and above all a pH-universal ORR electrocatalyst. Specifically, a simple and scalable synthetic approach for the templated synthesis of CuBDC MOF networks over presynthesized MnO2 nanosheets for the fabrication of CuBDC/MnO2 composite is presented. The so-crafted CuBDC/MnO2 composite well-characterized for its chemical, morphological, and electrochemical characteristics is demonstrated to be a pH-universal ORR electrocatalyst exhibiting excellent stability and electrocatalytic performance that is at par with that reported recently for the state-of-the-art noble metal-based ORR catalysts. The CuBDC/MnO2 composite exhibits a mass transfer limited four-electron pathway ORR at a potential of just 0.74 V versus the reversible hydrogen electrode (RHE), with an overpotential (ηORR) of 0.45 V under alkaline conditions. The as-fabricated electrocatalyst delivers a specific activity (current per unit area) of −4.58 ± 0.01 mA/cm2 and the mass activity (current per unit mass) of 8641.50 ± 0.01 mA/mgcat. Our detailed physicochemical and electrochemical investigations clearly establish that the unique synergism among the metal-oxide and MOF components in the CuBDC/MnO2 composite endows it with unique features that result in the abundant availability and redox accessibility of Cu-redox sites and easy mass transportation of oxygen across an electronically and ionically good conducting [CuBDC/MnO2]/electrolyte interface. The work presented herein signifies a significant advancement toward the development of cost-effective and sustainable ORR electrocatalysts, potentially paving the way for their widespread adoption in clean and affordable electrochemical technologies for storage and conversion of energy.