Metal‐organic frameworks (MOFs) have attracted increasing attention as a promising electrode material for the oxygen evolution reaction (OER). Comprehending catalytic mechanisms in the OER process is of key relevance for the design of efficient catalysts. In this study, two types of Co based MOF with different organic ligands (ZIF‐67 and CoBDC; BDC=1,4‐benzenedicarboxylate) are synthesized as OER electrocatalysts and their electrochemical behavior is studied in alkaline solution. Physical characterization indicates that ZIF‐67, with tetrahedral Co sites, transforms into α‐Co(OH)2 on electrochemical activation, which provides continuous active sites in the following oxidation, whereas CoBDC, with octahedral sites, evolves into β‐Co(OH)2 through hydrolysis, which is inert for the OER. Electrochemical characterization reveals that Co sites coordinated by nitrogen from imidazole ligands (Co−N coordination) are more inclined to electrochemical activation than Co−O sites. The successive exposure and accumulation of real active sites is responsible for the gradual increase in activity of ZIF‐67 in OER. This work not only indicates that CoMOFs are promising OER electrocatalysts but also provides a reference system to understand how metal coordination in MOFs affects the OER process.
The continuous solid solution NiWO is successfully prepared by using precursor WO with plenty of oxygen defects. The NiWO nanoparticles are characterized by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray absorption spectroscopy. The crystallographic phase of NiWO is stable and characterized by the same feature of the parent lattice WO even with various concentrations of dopant Ni which indicates the existence of oxygen defects. The NiWO nanoparticles could be processed as the appropriate promoter after loading 10 wt % Pt. The Pt/NiWO displays remarkable response for oxygen reduction reaction in alkaline medium compared with the commercial Pt/C. The analysis of the electrochemistry data shows that the existence of abundant oxygen defects in the solid solution NiWO is the key factor for the improved ORR catalyst performance. Ni is effective in the catalysts because of its compatibility with W in the solid solution and its active participation in oxygen reduction reaction.
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