A comprehensive understanding of oxygen evolution reaction (OER) is crucial for the development of high-efficient catalysts that can play a vital role in various electrochemical anodic reactions that convert renewable energy into fuels.
The OER involves multiple proton/electron-transfer processes. The O−H bond cleavage involves an endothermic process, the activation of O−H bond associated with the O−O bond formation is a particular challenge, and since protons are much heavier than electrons, it is possible that the rate of the OER is governed by the rate of proton ferrying. Therefore, the effective activation of the O−H bond of water and the acceleration of the interfacial proton transfer rate of the rate-determining step (RDS) of catalyzing water oxidation reaction is important for efficient OER catalysts.
In photosystem II in nature, some of the hydrogen bond networks between amino acid residues and water molecules originate from the center of the oxygen-evolving catalyst, and generate proton removal channels. In many artificial catalytic systems, the functional groups installed as proton donors or acceptors (i.e., proton relays for proton donation for reduction reactions or for proton removal for oxidation) close to the active center of catalysts can kinetically interfere in the rate-determining sequence of catalytic reactions.
To improve catalytic performance, the author introduced nonafluoro-1-butanesulfonate as the anion into the interlayer of Ni-Fe layered hydroxides. Interestingly, the as-prepared FBS-intercalated Ni-Fe hydroxide catalyst on carbon fiber paper substrate exhibited excellent electrocatalytic OER performance with an overpotential of 200 mV at 10 mA cm−2. It also showed an ultralow Tafel slope of 25.8 mV dec−1 in a 1.0 M solution of KOH. Furthermore, it was compared with NiFe layered double hydroxides with respect to the results of pH-dependent kinetics, the deuterium kinetic isotope effects (KIEs), and electrochemical probe analysis, indicating that the nucleophilic OH− attack on the oxidized electrophilic species on the surface of both NiFe-FBS and NiFe-LDH played an important role in enhancing the reaction rate. Moreover, the proton inventory, as well as the atom proton transfer (APT) behavior of NiFe-FBS, demonstrated that the sulfonate groups of FBS served as proton relays, accelerating the proton transfer in the RDS. Thus, the results of this study provide a strategy for enhancing OER catalytic activity via the introduction of organic groups (anions) into the interlayers of Ni-Fe layered hydroxides to accelerate proton transfer.
See the article:
WL Li, FS Li, YL Zhao, C Liu, YZ Li, H Yang, K Fan, PL Zhang, Y Shan, LC Sun. Promotion of the Oxygen Evolution Catalytic Performance of Ni−Fe Layered Hydroxides via the Introduction of a Proton Transfer Mediator Anion. Sci. China Chem., 2021, DOI: 10.1007/s11426-021-1178-y