Assessing nickel oxide electrocatalysts incorporating diamines and having improved oxygen evolution activity using operando UV/visible and X-ray absorption spectroscopy.

The electrolysis of water using renewable energy is a promising approach to developing a sustainable hydrogen-based economy. To improve the efficiency of this process, it will be necessary to develop highly active electrocatalysts that promote the oxygen evolution reaction (OER). In the present study, the OER activity of a nickel oxide electrocatalyst was dramatically improved following the addition of a diamine to the electrolyte solution during electrodeposition. Operando UV/vis absorption spectroscopy was used to assess a number of nickel catalysts containing various diamines and other organic compounds. The data indicate that Ni(II) complexes were formed with the diamines during electrodeposition. Consequently, the catalytic activity of these materials was enhanced based on increased concentrations of active reaction sites for the OER process. Ni K-edge X-ray absorption spectra showed that these catalysts were composed of γ-NiOOH with a Ni3.6+ valence state. The coordination of the diamine molecules to the γ-NiOOH produced structural distortion that contributed to improved OER activity. This structural distortion is likely the most important factor in enhancing the OER activity of inorganic-organic composite catalysts.

Iron Oxyhydroxide Hierarchical Micro/Nanostructured Film as Catalyst for Electrochemical Oxygen Evolution Reaction.

A key requirement in developing oxygen evolution reaction (OER) electrocatalysts is increasing their surface area. Herein, we report the design of a hierarchical micro/nanostructured catalyst. Based on polystyrene colloidal template electrodeposition, an ordered microcup array surrounded by nanoflakes was fabricated. The effect of the deposition time on the formation of the catalyst and the corresponding OER performance of the catalyst were investigated using scanning electron microscopy, in situ X-ray absorption fine structure (XAFS) spectroscopy, and electrochemical analysis. The in situ XAFS measurements indicate that the structure of the hierarchical structured catalyst is similar to that of γ-FeOOH. The electrochemical analysis indicates that the hierarchical catalyst has a large surface area and a low charge transfer resistance, which lead to its excellent catalytic performance for the OER. Our study provides new insights in designing high-performance OER catalysts. Moreover, the synthesized hierarchical micro/nanostructured catalyst could be used as a platform for further studies on low-cost iron-based electrocatalysts.