Abstract
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.
Highlights
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
In situ X-ray absorption fine structure (XAFS) spectroscopy revealed that one oxygen atom was formed on the Ir active site in the form of an O–hetero–Ir–N4 moiety under a low driving potential, which accelerated the transfer of electrons from the metal sites to neighboring atoms toward faster reaction kinetics
An ultralow-iridium electrocatalyst with atomically dispersed Ir active sites coupled to a hetero-nitrogen-configured 3D carbon substrate was synthesized via a controllable “electric-driven amino-induced” strategy
Summary
X-ray diffraction results (Supplementary Fig. 6) further showed that no Ir nanoparticles were observed for AD–HN–Ir electrocatalyst, indicating a uniform dispersion of Ir active sites throughout the heteronitrogen-configured 3D carbon substrate. The five fitting peaks of 406.3, 401.2, 400.1, 399.7, 398.9, and 398.4 eV in the N 1s XPS spectra (Fig. 2c) can be assigned to N–O, graphitic N, pyrrolic N, Ir–N, Ir–amino–N and pyridinic N, respectively[24,25] This further demonstrates the formation of hetero-nitrogen-configured Ir active sites for AD–HN–Ir electrocatalyst. The L3-edge EXAFS k2χ(k) of the AD–HN–Ir electrocatalyst (Supplementary Fig. 8) shows that the atomically dispersed Ir active sites with Ir–N coordination configuration in the first shell was anchored to a hetero-nitrogen-configured 3D carbon substrate. The morphology structure and OER performance of Ir electrocatalysts at different pyrolysis temperatures were shown in Supplementary Fig. 10, revealing the AD–HN–Ir (800 °C) electrocatalyst with better carbonization degree and a
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