Ag Reinforcement in Pd–Ag/MnO2 Nanoensembles Boosts the Electrocatalytic Performance in Low-Temperature Direct Ethanol Fuel Cells: Studies on Ethanol Oxidation and Oxygen Reduction Reaction

Abstract The present investigation involves the validation of Pd–Ag catalyst nanoparticles (NPs) supported on MnO2 nanostructures at both ends of a direct ethanol fuel cell (DEFC) operating in an alkaline environment at low temperatures. The studies are based on evaluating electrode kinetics parameters of ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) over tandem (1:1) Pd–Ag catalysts cast on MnO2 through the green sono-chemical technique. The matrix morphology and compositions were determined through electron microscopy, EDX, and XPS, while electrochemical characterizations were conducted using potentio-dynamic polarization techniques and hydrodynamic voltammetry. The Ag reinforcement in Pd causes desirable d-band shifts in Pd52Ag48/MnO2 NPs, accomplishes the conjugate materials with a high electrochemical surface area (197 m2/g), and imparts distinct bifunctional behavior in electrocatalysis through in situ-generated oxo/superoxo species of Ag delivering reduced polarization loss and substantial current density output and acquiring long-term electrochemical stability compared to the usual Pt/C or Pd/C. The hybrid catalyst NPs fall in the size range of 5–7 nm, while the self-designed (2 × 2) tunnel structure of MnO2 enhances the charge-transfer ability within the matrix and ensures smart intervention of MnO2 directly/indirectly in EOR and ORR sequences. Ion-chromatographic analysis during electrolysis of ethanol solution quantifies the massive yields of 570 ppm acetate and 494 ppm carbonate over Pd52Ag48/MnO2, almost 9 times and 4 times compared to that obtained with Pd/C and Pd/MnO2, while ORR witnesses ∼ 30% lower yield of H2O2 with the combinatorial approach with respect to Pd/C. The outstanding mass activity of 1385 mA/mgPd for EOR signifies energy-efficient conversion of the C2 molecule to considerable amounts of ultimate products, and the mass activity of 1143 mA/mgPd for ORR implies reasonable control over the 2e transfer pathway. The Pd52Ag48/MnO2 catalyst is a highly preferred choice of electrode for low-temperature DEFCs, delivering a power density of 58.6 mW/cm2 at 40oC.