Modulating Mn³⁺/Mn⁴⁺ Redox Couples in Pd/OMS-2 through Pd–O–Mn Interfacial Chemical Bonds for Boosting Electrocatalytic Oxygen Reduction and Methanol Oxidation

Optimizing the electronic configuration presents a promising approach to enhance intrinsic activity and minimize noble metal use in direct methanol fuel cells (DMFCs). Metal–support interactions, commonly employed to induce interfacial charge redistribution, play a crucial role in this optimization. This study successfully synthesized a Pd/O-OMS-2 electrocatalyst characterized by Pd–O–Mn interfacial chemical bonds and Mn3+/Mn4+ redox couples, serving as a stable bifunctional catalyst for both the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). Unlike the mixed Pd–O/Mn bonds in Pd/O/Mn-OMS-2, the Pd–O–Mn bonds in Pd/O-OMS-2 not only enhance metal–support interactions and promote uniform dispersion of Pd nanoparticles but also facilitate electron transfer and the conversion between Mn3+ and Mn4+. These structural and compositional advantages endow the Pd/O-OMS-2 catalyst with superior ORR and MOR performance. The catalyst achieves a higher half-wave potential (E1/2) of 0.901 V, a mass activity of 0.937 A mgPd–1, and enhanced methanol permeability, outperforming Pd/O/Mn-OMS-2, Pd/OMS-2 and commercial Pd/C catalysts. Moreover, in an alkaline electrolyte, the Pd/O-OMS-2 catalyst follows a typical four-electron reaction pathway for ORR (O2 to H2O) and promotes faster reaction kinetics and charge transfer rates. In terms of durability, the Pd/O-OMS-2 catalyst exhibits minimal E1/2 decay (8 mV) and retains its structural integrity even after 10,000 cyclic voltammetry (CV) cycles. Additionally, it demonstrates the highest mass activity and stability during the MOR process. The exceptional ORR/MOR performance can be attributed to the synergistic effect of strong metal–support interactions, high Pd nanoparticle dispersion, and increased Mn3+ active species. The construction of interfacial chemical bonds offers a prospective strategy to optimize electronic configurations and develop advanced bifunctional electrocatalysts for ORR and MOR.