Electronic Enhancement Engineering by Atomic Fe–N₄ Sites for Highly‐Efficient PEMFCs: Tailored Electric‐Thermal Field on Pt Surface

Abstract

Fortunately, proton exchange membrane fuel cells (PEMFCs) possess the potential of higher energy densities depending on the amount of carried H 2 , which have realized the commercial application in the field of heavy truck and shipping. Oxygen reduction reaction (ORR) is the cathode reaction of PEMFCs. [1][2] Its sluggish kinetics directly hinder the overall efficiency of PEMFCs. Although commercial carbon supported Pt (Pt/C) has been proven to be the most efficient electrocatalysts for ORR, their scarcity, high cost, and poor stability in long-term operations is a huge impediment to the large-scale deployment of PEMFCs. [3] To address these issues, it is urgently needed to reduce the Pt usage simultaneously improving its activity and stability, or ultimately to replace precious metal Ptbased catalysts with non-precious-metal catalysts.An effective strategy to reduce Pt usage is alloying Pt with a second transition metal (M = Fe, Co, Ni, etc.) and further precisely tuning its composition and structure. [4][5][6][7][8][9][10][11][12][13][14] It is reported that structurally ordered intermetallic Pt-M alloys exhibited a significant enhancement on ORR performance. The enhanced performance is attributed to that incorporating M atoms with a smaller atomic radius in the Pt-M alloys provides a compressive strain to Pt atoms on the surface, lowers its d-band center, Lowering noble-metal Pt usage and simultaneously enhancing electrocatalytic oxygen reduction reaction (ORR) activity and stability of Pt-based ORR electrocatalysts is the key to realize the large-scale application of fuel cells. Here, an effective strategy is developed to reduce Pt usage through the strong electron interaction between uniform Pt nanoparticles (≈4.0 nm) and abundant atomically dispersed Fe-N 4 sites modified on an ordered mesoporous carbon (OMC) surface for efficiently enhancing ORR performance. Density functional theory (DFT) calculations show that the strong electron interactions between Pt and Fe-N 4 sites decrease the d-band center of Pt in Pt@Fe-N-OMC-2 by 0.21 eV relative to that of as-prepared Pt@OMC, indicating the weakened O 2 adsorption and accelerated desorption of oxygenated species on Pt sites. In situ Raman spectra demonstrate that the introduction of Fe-N 4 moieties promotes the O-OH dissociation process. Finite element method simulations reveal that the electric and thermal field of the embedded Pt nanoparticle surface is enhanced through modifying Fe-N 4 sites on the OMC surface, accelerating the accumulation of ORR-related species (O 2 , H + , and H 2 O), which is conductive to electrocatalyzing the ORR. This innovative approach not only illustrates the synergistic mechanism between Pt and Fe-N 4 sites, but also simultaneously provides new avenues to design advanced electrocatalysts for fuel cells.

Confinement Engineering of Zinc Single‐Atom Triggered Charge Redistribution on Ruthenium Site for Alkaline Hydrogen Production

“…The spectrum of N 1s fitted in Figure S14 (Supporting Information) showed four peaks at 398.3, 400.5, 401.3, and 404.4 eV, which were attributed to pyridinic N, pyrrolic N, Zn-N x , and graphitic N, respectively. [32][33][34][35] Besides, in comparison with the Raman spectra of Zn-N-C (Figure S15, Supporting Information), the G band of Ru/Zn-N-C showed a clear red shift, also indicating the strong coupling interaction between Ru and Zn-N-C carrier. [36] To further investigate the valence state and local environment of Ru and Zn species, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) were also conducted for Ru/Zn-N-C. From Figure 2d,e, the Ru K-edge of Ru/Zn-N-C presented a similar trend to that of Ru foil, suggesting the metallic state of Ru.…”

Engineering a High-Loading Sub-4 nm Intermetallic Platinum–Cobalt Alloy on Atomically Dispersed Cobalt–Nitrogen–Carbon for Efficient Oxygen Reduction in Fuel Cells

“…Moreover, a negative shift (∼0.15 eV) was observed in the Pt 4f spectra on PtCo–CoNC compared to that of PtCo–NC, demonstrating that there were interactions between PtCo and CoNC Figure b and Figure S13a show that two main peaks at 780.6 and 795.6 eV in the Co 2p spectra of PtCo–CoNC and PtCo–NC belonged to Co 2p 3/2 and Co 2p 1/2 , respectively, and the deconvolution peaks attributed to Co 2+ (781.8 and 796.9 eV), Co 3+ (779.8 and 794.6 eV), and satellite peaks (786.2 and 802.6 eV) . The N 1 s high-resolution spectra of both PtCo–CoNC and PtCo–NC were fitted into four peaks at 398.1, 400.2, 401.1, and 402.3 eV, corresponding to pyridinic N, pyrrolic N, graphitic N, and oxidized N, respectively (Figure c and Figure S13b).…”

“…42 Figure 2b and Figure S13a show that two main peaks at 780.6 and 795.6 eV in the Co 2p spectra of PtCo−CoNC and PtCo−NC belonged to Co 2p 3/2 and Co 2p 1/2 , respectively, and the deconvolution peaks attributed to Co 2+ (781.8 and 796.9 eV), Co 3+ (779.8 and 794.6 eV), and satellite peaks (786.2 and 802.6 eV). 43 The N 1 s high-resolution spectra of both PtCo−CoNC and PtCo−NC were fitted into four peaks at 398.1, 400.2, 401.1, and 402.3 eV, corresponding to pyridinic N, pyrrolic N, graphitic N, and oxidized N, respectively (Figure 2c and Figure S13b). 44 PtCo− CoNC and PtCo−NC showed similar contents of pyrrolic, graphitic, and oxidized N species (Table S3).…”

Urea with trifunctional effects: an assistant for high exposure of single-atom active sites on 2D nanosheets via structural transformation

“…7,8 Specifically, Fe–N–C catalysts with strong interaction between Fe and N species possess excellent O 2 adsorption and O–O bond breaking capacity. 9–12 Although great ORR intrinsic activity has been demonstrated with Fe–N–C catalysts, their catalytic performance remains inferior to that of commercial Pt/C without the rational design of the carbon support to efficiently disperse and expose the Fe–N–C active sites. 13–15…”