Deciphering the Role of Substitution in Transition-Metal Phosphorous Trisulfide (100) Surface: A Highly Efficient and...

The rational design and development of earth-abundant, cost-effective, environmentally benign, and highly robust oxygen reduction reaction (ORR) electrocatalysts can circumvent the obstacles associated with the large-scale commercialization of fuel cells. Here, using first-principles-based density functional theory (DFT), we have computationally screened the potential and feasibility of transition-metal phosphorous trisulfides (TMPS₃ ) (100) surfaces as efficient ORR electrocatalyst in acidic fuel cell application. MnPS₃ (100) surface emerges to be the best among TMPS₃ surfaces with optimal O₂ activation resulting in very low overpotential. The study reveals that ORR occurs on the MnPS₃ surface via 4e reduction associative pathway where the kinetically rate-determining step (RDS) is the formation of O*+H₂ O with an activation barrier of 0.66 eV. Additionally, high CO tolerance and easy desorption of H₂ O make MnPS₃ a robust catalyst. Substitution in half of the Mn sites of MnPS₃ (100) surface with Co considerably enhances the ORR activity. Mn_0.5 Co_0.5 PS₃ (100) surface exhibits an ultralow overpotential of 0.39 V vs RHE switching ORR pathway from associative to dissociative. Spontaneous dissociation of H₂ O₂ on Mn_0.5 Co_0.5 PS₃ proves 4e reduction pathway excluding 2e one. Electronic structure analysis reveals that pristine MnPS₃ (100) surface is a narrow band gap semiconductor which upon Co substitution transforms into a conducting metallic surface enhancing ORR activity. Besides, Mn_0.5 Co_0.5 PS₃ (100) surface obtains the apex of the volcano plot due to its optimal position of the d-band center which further justifies the improved ORR activity. With Pt-like onset potential, facile H₂ O desorption ability, and robust dynamic and thermal stability, this CO tolerant Mn_0.5 Co_0.5 PS₃ catalyst can be a potential alternative to Pt with encouraging practical viability.