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Iron‐nitrogen‐doped carbon (Fe‐NC) is an ideal candidate to replace Pt‐based oxygen reduction reaction (ORR) electrocatalysts due to its low cost and comparably high intrinsic activity. To further enhance the ORR performance of Fe‐NC electrocatalysts, efforts have been focused on two main methods. One is to enhance the intrinsic activity of FeNx sites through electronic and geometric regulation, and the other is to increase the density of active sites by introducing high‐nitrogen‐containing precursors or co‐doping methods. Herein, we report a strategy to further increase the Fe loading through the introduction of a trace amount of Cu atoms. Significant enhancement of the electrocatalytic ORR property is observed in the as‐prepared Fe and Cu co‐doped electrocatalyst with superior half‐wave potential (E1/2) in both alkaline and acid electrolyte. Experimental and theoretical study reveals that the introduction of a trace amount of Cu atoms is beneficial for the formation of FeN4 sites, owing to the reduced formation energy. This work opens up a wide avenue to further increase the Fe loading in Fe‐NC electrocatalysts through bimetal co‐doping method. [ABSTRACT FROM AUTHOR]

The strain effect on oxygen reduction reaction (ORR) activity and stability of FeNC electrocatalysts has been studied using density functional theory in this work. Based on the reaction free energy results, the rate-determining step (RDS) of ORR on FeNC is *OH → H2O, and the reaction proceeds with the pathway O2 → *OOH → *O → *OH → H2O on the Fe site. Tensile stress is favorable to enhance the ORR activity, and the highest ORR activity is obtained on the 6%-FeNC electrocatalyst. On the other hand, when the whole oxygen reduction process needs synergy between Fe and adjacent C atoms and proceeds with the pathway O2 → *OOH → *TS → *O & #OH → *O → *OH → H2O, the applied stress will decrease the ORR activity of the FeNC electrocatalyst. We further constructed a Cu@FeNC core–shell model to simulate strained FeNC. However, the adsorption energy of ORR intermediates on Cu@FeNC (1.9%-FeNC) is much weaker than on the corresponding 2%-FeNC, mainly due to the coordination between the Cu substrate and Fe atom. In addition, the formation energy and binding energy indicate that neither tensile nor compressive stress is conducive to the stability of the FeNC electrocatalyst. In summary, tensile stress could enhance the ORR activity of FeNC electrocatalysts when ORR occurs on the Fe atom only. What's more, we should pay more attention to the influence of interface interaction if utilizing a M@FeNC model to achieve strained FeNC. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of structure evolution under working condition of MNC electrocatalysts on the OER activity and stability has been studied with the DFT method. • This work conducted a comprehensive evaluation method for MNC electrocatalysts by taking ΔG *OH as the screening criterion for OER activity and ΔE b of electrocatalysts under working conditions as the stability descriptor. • The stability of MNC electrocatalysts under working conditions, including high temperature, dynamic condition, local electric field and strong specific adsorption has been studied in detail. Developing low-cost, high activity and stability oxygen evolution reaction (OER) catalysts is significantly important but still challenging for water electrolyzers. In this work, we calculated the OER activity and stability of Metal-Nitrogen-Carbon (MNC, M = Co, Ru, Rh, Pd, Ir) based electrocatalyst with different structures (MN 4 C 8 , MN 4 C 10 , MN 4 C 12) using density functional theory (DFT) method. These electrocatalysts were divided into three groups based on the value of ΔG *OH , that is ΔG *OH > 1.53 eV (PdN 4 C 8 , PdN 4 C 10 , PdN 4 C 12), ΔG *OH < 1.23 eV (RuN 4 C 8 , RuN 4 C 10 , RuN 4 C 12 , CoN 4 C 8 , CoN 4 C 10) and 1.23 eV < ΔG *OH < 1.53 eV (RhN 4 C 8 , RhN 4 C 10 , RhN 4 C 12 , IrN 4 C 8 , IrN 4 C 10 , IrN 4 C 12 , CoN 4 C 12), and ΔG *OH determine whether the structure evolution will appear. The results proved that MNC (M = Rh, Ir) with 1.23 eV < ΔG *OH < 1.53 eV shows higher OER activity due to moderate binding energy between reaction intermediates and MNC. Furthermore, these catalysts could maintain M N C structure without further oxidation and structural evolution under working conditions (high temperature, dynamic condition, local electric field and strong specific adsorption), therefore show excellent stability. However, MNC electrocatalyst with ΔG *OH > 1.53 eV or ΔG *OH < 1.23 eV revealed less stability under working conditions, due to their low intrinsic stability or structural evolution under working conditions, respectively. In conclusion, we proposed a comprehensive evaluation method for MNC electrocatalysts by taking ΔG *OH as the screening criterion for OER activity and stability, as well as ΔE b under working condition as descriptor of stability. This is of great significance for the design and screening of ORR, OER and HER electrocatalysts under working conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Design of the prior PA-resistance electrocatalysts through theoretical calculation. • Discovery of different scaling relationship of the adsorption energy difference of O 2 and H x PO(3-x)- 4 on Pt 3 M(1 1 1) alloy surface. • Pt X Cu as the object for the research of internal mechanism of the potentially high PA resistance property. • Higher PA-resistance performance of Pt 2 Cu compared to the commercial PtC in half-cell and full-cell tests. In high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), dissociative H 3 PO 4 in cathode will block the active sites of Pt-based electrocatalyst, which thus failure to catalyze the oxygen reduction reaction (ORR). Therefore, the electrocatalysts for the ORR in HT-PEMFCs with high resistance to H 3 PO 4 poisoning are significantly important. Due to the similar bonding structure between H x PO 4 3-x/O 2 and Pt (Pt-O), the design of catalysts which could selectively reduce the adsorption energy of the H 3 PO 4 is urgently needed. In this work, we screen proper H 3 PO 4 resistance electrocatalysts through theoretical calculation based on the adsorption energy difference between H x PO 4 3-x and O 2 as an evaluation criterion. Then, we prepared a series of Pt x Cu catalysts based on the theoretical calculation results and further studied the structure-performance relationship of phosphoric acid-resistant catalysts through combining physical property characterization and electrochemical tests including half-cell and single-cell. The mass activity of Pt 2 Cu/C is 0.51 A/mg Pt , exceeding the DOE's 2020 target of 0.44 A/mg Pt. After add 0.1 M H 3 PO 4 into the HClO 4 electrolyte, the half-wave potential (E 1/2) of Pt 2 Cu/C is only negatively shifted by 47 mV, much lower than 90 mV of TKK Pt/C. Furthermore, the HT-PEMFC with Pt 2 Cu/C in the cathode shows a peak power density of 383.4 mW/cm2, which surpasses that of TKK Pt/C for 231.0 mW/cm2. Our strategy of screening catalysts based on the adsorption energy difference study and further verified by experimental methods provides a promising strategy for the design of practical electrocatalyst in the cathode of HT-PEMFCs. [ABSTRACT FROM AUTHOR]

Atomically dispersed Fe-N-C catalyst is fabricated by a rational designed dual-MOFs strategy for efficient and low-cost DMFC application. • A dual-MOFs strategy is developed for the fabrication of atomically dispersed Fe-N-C catalyst. • The formation mechanism of the atomically dispersed Fe-N-C catalyst is well investigated. • The as-prepared catalyst demonstrates high ORR activity, excellent methanol tolerance and outstanding stability in acids. • The DMFC assembled with atomically dispersed Fe-N-C catalyst exhibits excellent performance. The rational design of highly efficient, low-cost and methanol-tolerant catalysts toward the oxygen reduction reaction (ORR) is urgently desired for the commercialization of direct methanol fuel cells (DMFCs). Herein, a novel Fe-N-C catalyst (ZIF/MIL-10-900) is derived from a mixture of ZIF-8 and MIL-101(Fe) and atomically dispersed FeN 4 structures are confirmed by Mössbauer spectra and X-ray absorption spectroscopy. Study on the pyrolysis procedure reveals that Fe atoms in FeN 4 are from MIL-101(Fe), while ZIF-8 acts as structural support and nitrogen sources. The as-prepared catalyst demonstrates a comparable ORR activity with the commercial Pt/C possessing a half-wave potential (E 1/2) of 0.78 V in acids, in combination with excellent methanol tolerance and stability. One of the highest peak power density of 83 mW cm−2 in DMFC (3 M CH 3 OH) by adopting ZIF/MIL-10-900 as cathode catalyst is obtained, which is 2.8-fold higher than that of the commercial Pt/C in the same operating condition. [ABSTRACT FROM AUTHOR]