Bifunctional Nanostructured Palladium/MoS_x Electrocatalyst for Cathode Hydrogen Evolution Reaction PEM Water Electrolysis and Oxygen Reduction Reaction

Abstract

The creation of effective Pd‐based architectures with numerous electrocatalytic active sites and efficient charge transfer is of key importance for improving the electrocatalytic performance in water electrolyzer and fuel cell applications. On the other hand, MoS2, possessing multiple electrocatalytic active sites, can act both as support and booster to Pd‐based electrocatalytic structures. Herein, MoSx@Pd hybrids were successfully synthesized by using a one‐pot liquid phase solvothermal strategy with stoichiometric excess of Pd. The optimized MoSx@Pd proves to be an excellent bifunctional electrocatalyst for both hydrogen evolution reaction and oxygen reduction reaction (ORR). Optimized MoSx@Pd operates the process for hydrogen evolution at the same potential as Pt/C and achieves a low overpotential of 76 mV at −10 mA cm−2 due to improved reaction kinetics and charge transfer processes between Pd and MoS2. On top of that, MoSx@Pd exhibits excellent performance and stability as cathode electrocatalyst in a polymer electrolyte membrane water electrolyzer. Simultaneously, the bifunctional electrocatalyst shows enhanced electrocatalytic ORR activity and stability by maintaining 93% of its initial activity outperforming commercial Pt/C. Finally, rotating ring disk electrode analysis reveals that ORR proceeds through the energy efficient 4e− pathway, with water being the main product, rendering MoSx@Pd a promising component for fuel cells.

A Comprehensive Review of MoSx for Improved Photo(electro)catalytic Performance

“…So far, papers in the literature have primarily used Raman and X‐ray photoelectron spectroscopy (XPS) to demonstrate the presence of MoS x . Particularly, XPS can detect distinct valence states (+4, +5, +6) of Mo in MoS x and the various bonding interactions of S. [ 73–81 ] Niu et al designed the synthesis of amorphous MoS x displaying high overpotential under both acidic conditions (0.5 mol L −1 H 2 SO 4 , 156 mV) and basic conditions (1.0 mol L −1 KOH, 232 mV). [ 5 ] Figure a exhibits an example of the high‐magnification XPS spectra of Mo 3 d , from which it can be seen that Mo shows three different valence states, namely Mo 6+ (235.6 eV), Mo 5+ (233.3 and 230.1 eV), and Mo 4+ (232.6 and 229.6 eV).…”

“…So far, papers in the literature have primarily used Raman and X-ray photoelectron spectroscopy (XPS) to demonstrate the presence of MoS x . Particularly, XPS can detect distinct valence states (þ4, þ5, þ6) of Mo in MoS x and the various bonding interactions of S. [73][74][75][76][77][78][79][80][81] Niu et al designed the synthesis of amorphous MoS x displaying high overpotential under both acidic conditions (0.5 mol L À1 H 2 SO 4 , 156 mV) and basic conditions (1.0 mol L À1 KOH, 232 mV). [5] on Mo plates by hydrothermal method and showed excellent hydrogen precipitation properties.…”