Uncovering the dynamics of active sites in the working conditions is crucial to realizing increased activity, enhanced stability and reduced cost of oxygen evolution reaction (OER) electrocatalysts in proton exchange membrane electrolytes. Herein, we identify at the atomic level potential-driven dynamic-coupling oxygen on atomically dispersed hetero-nitrogen-configured Ir sites (AD-HN-Ir) in the OER working conditions to successfully provide the atomically dispersed Ir electrocatalyst with ultrahigh electrochemical acidic OER activity. Using in-situ synchrotron radiation infrared and X-ray absorption spectroscopies, we directly observe that one oxygen atom is formed at the Ir active site with an O-hetero-Ir-N4 structure as a more electrophilic active centre in the experiment, which effectively promotes the generation of key *OOH intermediates under working potentials; this process is favourable for the dissociation of H2O over Ir active sites and resistance to over-oxidation and dissolution of the active sites. The optimal AD-HN-Ir electrocatalyst delivers a large mass activity of 2860 A gmetal−1 and a large turnover frequency of 5110 h−1 at a low overpotential of 216 mV (10 mA cm−2), 480–510 times larger than those of the commercial IrO2. More importantly, the AD-HN-Ir electrocatalyst shows no evident deactivation after continuous 100 h OER operation in an acidic medium.
Water‐soluble polypeptides bearing 1‐alkylimidazolium (methyl or n‐butyl) and various counter‐anions (i.e., Cl−, I− or BF4−) are prepared by ring‐opening polymerization of γ‐4‐chloromethylbenzyl‐l‐glutamate‐based N‐carboxyanhydride (3), post‐polymerization of poly(γ‐4‐chloromethylbenzyl‐l‐glutamate) (4), and ion‐exchange reaction. Circular dichroism (CD) analysis reveals that the resulting polypeptides adopt an α‐helical conformation in water with a fractional helicity in the range of 30%–56% at 20 °C and exhibit good conformational stability against temperature variations. The polypeptides exhibit lower critical solution temperature (LCST)‐type or upper critical solution temperature (UCST)‐type transitions in organic solvents or in water. The UCST‐type transition temperature (Tpt) in water is independent on the molecular weight, yet it decreases upon addition of NaCl and increases upon addition of NaI or NaBF4, suggesting a mainly electrostatic interaction mechanism.
Understanding
the nature of the catalytic active center and its
evolving dynamics under operating conditions is critical for the development
of efficient and highly selective catalysts. By combining synchrotron-based operando X-ray absorption and infrared spectroscopies, here
we uncover at an atomic level a hydroxyl was coupled on the dynamically
released coordination-unsaturated Fe-N2 moieties to form
a highly active OH-Fe-N2 structure and then promotes the
adsorption of O2 during the catalytic oxygen reduction
reaction (ORR), which greatly facilitates the fabrication of the key
*OOH intermediate and simplifies the fracture of the O–O bond
to accelerate the multielectron reaction kinetics. The resulting covalent
organic framework-derived Fe single-site catalyst could efficiently
deliver an excellent ORR catalytic activity with an extremely large
kinetic current density (J
k) of 81.3 mA
cm–2 and an extra high turnover frequency of 5804
h–1, 20 times that of the Pt-C catalyst (288 h–1, 7.7 mA cm–2).
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