Atomically Dispersed Single Mn Site-Rich Carbon for PtCo Intermetallic Catalysts with Promoted Performance and Durability for Heavy-Duty Fuel Cells

Abstract

Promoting the activity and durability of the Pt-based catalysts with a reduced platinum group metal (PGM) loading holds significance to the deployment of proton-exchange membrane fuel cells (PEMFCs) in the transportation market. In this work, synergistic catalysts, which integrate ultrafine Pt-based nanoparticles with ORR-active single atom catalysts (SACs), were studied to meet the activity and stability milestones for Pt-based catalysts. The synergistic effect between different SACs and ultrafine Pt nanoparticles were firstly elucidated via DFT calculations. It indicates that MnSA-NC catalyst with high surface area and abundant single atoms sites can improve the activity and stability of Pt catalyst via a strong electronic interaction. Ultrafine Pt and L12 Pt3Co intermetallic nanoparticles were uniformly anchored in the MnSA-NC via a facile strategy. The structures of the Pt@MnSA-NC and Pt3Co@MnSA-NC were comprehensively studied by multiple transmission microscopy and X-ray absorption spectroscopy. It reveals that ultrafine Pt and L12 Pt3Co intermetallic nanoparticles are anchored amongst the atomically dispersed MnNx sites. The Pt@MnSA-NC catalyst achieved a mass activity (MA) of 0.698 A mgPt −1 (@0.9ViR-free) and maintained 86 % of its initial performance after 30,000 cycles of accelerated stress test (AST, 0.6 and 0.95 V), exceeding the DOE target for 2025. By intercalating Co into the Pt nanoparticles, the L12 Pt3Co@MnSA-NC catalyst achieved significantly improved activity, achieving a MA of 0.905 A mgPt −1 and 1.631 A cm−2 (@0.7 V, H2-air fuel cell) at 150 kPaabs with 0.10 mgPt cm−2 in the cathode. The loss in the performance at 0.7 V is only 27.2 %, manifesting its high intrinsic stability. Furthermore, the performance of L12 Pt3Co@MnSA-NC catalyst (20 wt.% Pt) was studied under the heavy-duty vehicle (HDV) conditions with a higher Pt loading (0.20 mgPt cm−2) and higher backpressure (250 kPaabs). Encouragingly, the current densities at 0.67 and 0.7 V are 2.12 and 1.80 A cm−2, respectively. After 30,000 cycles of AST, the loss in MA is only 17.4 %, 87.0 % of performance were retained at 0.67 and 0.7 V. The compelling performance holds a great potential to meet the DOE target set for HDVs (>1.07 A cm−2 at 0.7 V after 250,000 hours equivalent operations). The synergistic effect revealed in this work shed light on the design of highly efficient catalysts for PEMFCs.