Applied Thesis

Recently, Professor Hu Yong of Zhejiang A&F University and Associate Professor Wang Haiyan of Zhejiang Normal University published an article entitled "Nature Communications". “Lattice oxygen activation and local electric field enhancement by co-doping Fe and F in CoO nanoneedle arrays for industrial electrocatalytic water oxidation”The research paper proves that the lattice oxygen activation mechanism and the local electric field can be coupled through the anion and cation double doping strategy, so as to achieve industrial-grade OER.

The authors proposed a simple anionic and cationic double doping strategy to prepare rough CoO nanoneedle arrays (Fe, F-CoO NNAs) co-doped with Fe and F. The results of HRTEM, XRD and Raman show that the double doping of Fe and F has little effect on the lattice structure of the material. In order to further characterize the effect of Fe and F double doping on the electronic structure of CoO, the authors used a benchtop X-ray absorption spectrometer (model: RapidXAFS 2M) from Anhui Absorption Spectroscopy Instrument Equipment Co., Ltd. to analyze the local electronic and coordination structure of the material. The absorption edges in the Co K-edge XANES spectrum are located at CoO and _Co2O3between the standards, indicating that the valence range of Co is between +2 and +3. Compared with CoO NNAs, the valence state of Co in Fe, F-CoO NNAs is lower. The FT-EXAFS spectrum shows two peaks at 1.4 and 2.4 Å, corresponding to the Co−O and Co−Co bonds, respectively. There was no significant change in the bond length of Co-O and Co-Co bonds in the undoped and doped samples, indicating that Fe and F doping had little effect on the crystal structure of CoO, and the above results were consistent with the XRD and XPS results.

Subsequently, the OER performance of the catalyst was tested in a 1 M KOH electrolyte. The results showed that Fe and F-CoO NNAs exhibited an extremely low overpotential of 169 mV at a current density of 10 mA cmcm^–2, and an overpotential of 277 mV and an electrochemical stability of 300 h at an industrial-grade current density of 500 mA cmcm^–2, which exceeded most of the reported OER catalysts, in addition, Fe and F-CoO NNAs also have excellent intrinsic activity and rapid reaction kinetics.

Fig.3 OER performance of Fe, F-CoO NNAs, F-CoO NNAs, Fe-CoO NNAs and CoO NNAs catalysts

In order to explore the mechanism of Fe,F double doping and reveal the catalytic mechanism of the catalyst, the authors used a series of chemical probes, in-situ Raman spectroscopy, ^{and 18O}Isotope technology, differential electrochemical mass spectrometry, combined with theoretical simulations, show that the double doping of Fe and F can synergistically regulate the Co 3d center and O2p orbital, enhance the covalentity of metal-oxygen, and induce the LOM mechanism, which is consistent with the experimental results. These results open up a new way for the design of efficient OER electrocatalysts, and also deepen the understanding of the structure-activity relationship and electrocatalytic mechanism of the catalyst. More broadly, this work could provide important implications for other catalytic reactions, as well as for the study of energy storage systems involving oxidation or mass transfer.

Figure 4: Catalytic mechanism study: chemical probes, in-situ Raman spectroscopy, ^18O isotope techniques, differential electrochemical mass spectrometry