Multifunctional MnO₂-pd catalysts and a practical evaluation strategy for unitized regenerative fuel cells

Developing robust, multifunctional electrocatalysts is critical for advancing unitized regenerative fuel cells (URFCs) that couple water electrolysis and fuel-cell operation within a single device. We report a nanostructured palladium-manganese dioxide/carbon nanotube (Pd/MnO₂-CNTs) composite in which hollow MnO₂ nanoflowers are uniformly anchored to CNTs, forming a conductive, high-surface area framework that promotes homogeneous Pd dispersion. Comprehensive structural and surface analyses (SEM, TEM, XRD, XPS, and Raman) indicate strong interfacial interactions among Pd, MnO₂, and CNTs, generating abundant defect sites and mixed-oxide bonding that correlate with enhanced catalytic activity and stability. The composite exhibits multifunctional electrocatalysis toward the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). When integrated into membrane-electrode assemblies, an optimized Pd/MnO₂-CNTs: IrO₂ (1: 9) electrode delivers a roundtrip efficiency of 51.4 ± 0.7 % at 50 mA cm^-2 under ambient conditions, together with durable cycling performance. Beyond materials design, we propose a practical protocol for evaluating URFCs under realistic operating constraints, linking electrode composition, interfacial structure, and device-level metrics. This study establishes a scalable route to multifunctional Pd/MnO₂-CNTs catalysts and provides an experimentally grounded framework for benchmarking URFC performance.