Co_1–xFe_xO_y Oxygen Evolution Nanocatalysts: On the Way To Resolve (Electro)Chemically Triggered Surface-Bulk Discrepancy

Delving into Fe-content effects on surface reconstruction of Ba0.50Sr0.50Co1−xFexO3−δ for the oxygen evolution reaction

“…This electrochemical stabilization can then lead to a shift of the Co redox process towards higher potentials into OER, resulting in a decrease of the Co redox couples in the pre-OER potential range towards the Fe-content materials as typically observed in Co-Fe-based electrocatalyst series. 17,18,37…”

“…This extensive surface activation process during OER has already been observed in another flame-spray synthesized Co-Fe-based oxide series, but also there only in the higher Fe-content materials with initially stabilized surface Co 2+ -atoms and the ability to oxidize irreversibly, which then led to an improved OER activity and stability. 37…”

“…This extensive surface activation process during OER has already been observed in another ame-spray synthesized Co-Fe-based oxide series, but also there only in the higher Fe-content materials with initially stabilized surface Co 2+ -atoms and the ability to oxidize irreversibly, which then led to an improved OER activity and stability. 37 Aer considering only the last (25th) CV cycle, a closer look at the changes of the CV as a function of the cycling number reveals a visible growth of the Co redox couples in each cycle for all materials excluding BS(Co 0.01 )Fe 0.99 (Fig. S15c and d †).…”

“…This electrochemical stabilization can then lead to a shi of the Co redox process towards higher potentials into OER, resulting in a decrease of the Co redox couples in the pre-OER potential range towards the Fe-content materials as typically observed in Co-Fe-based electrocatalyst series. 17,18,37 The OER potential range of all CV 's (excluding BS(Co 0.01 )Fe 0.99 with minor OER activity) is analyzed with special attention to which of the two CV scanning directions, the positive or the negative going aerwards, presents the higher OER current density: BSCo 0.99 (Fe 0.01 ) presents the higher OER activity during the positive going potential scan, whereas all the other materials (0.10 # x # 0.79) have the higher OER activity during the negative going potential scan aerwards (Fig. 2c and d).…”

Surface oxidation/spin state determines oxygen evolution reaction activity of cobalt-based catalysts in acidic environment

“…The formation of Co III at the CoO surface is irreversible, as confirmed by the peak intensity ratio I(Co III )/I(Co II ) of 1.49 (Supplementary Table 3 ). The Co III species at the surface layer were removed after sputtering with Ar-ions 36 , suggesting that the bulk Co oxidation state is still 2+. The commercial Co 3 O 4 and the FeCo 2 O 4 , produced using FSS (Supplementary Fig.…”