Operando identification of a side-on nickel superoxide intermediate and the mechanism of oxygen evolution on nickel oxyhydroxide

Ni-Xides (B, S, and P) for Alkaline OER: Shedding Light on Reconstruction Processes and Interplay with Incidental Fe Impurities as Synergistic Activity Drivers

“…The Raman response in Un-KOH (Figure b) is generally the same as the one in P-KOH except that the signals in P-KOH are stronger and the peaks are sharper in relation to those in Un-KOH even though the initial loading of the catalytic materials was the same and they were subjected to the same electrochemical conditions. This gives a further strong hint that more significant reconstruction happened in P-KOH, thus aligning with the previous discussion . It is well established that NiOOH can exist in two phases, namely, γ-NiOOH and β-NiOOH, which exhibit different Raman responses.…”

“…560 cm –1 . With increasing potential, the Ni 2+ /Ni 3+ oxidation potential or higher, the bands at 480 and 560 cm –1 intensified and became more resolved . These two bands are attributed to Ni–O bending and stretching vibrations in NiOOH and thus their intensification with the potential indicates phase transformation from Ni­(OH) 2 to NiOOH, the actual active form of the OER catalyst, regardless of the starting phase.…”

Decoding Natural Strategy: Oxygen-Evolution Reaction on the Surface of Nickel Oxyhydroxide at Extremely Low Overpotential

“…This experiment demonstrates that even under operation at 1.32 V (90 mV overpotential), the ratio of Ni(III)/Ni(II) increases, and the Ni(III) sites produced after charging are capable of performing OER. The low energy efficiencies of OER are the results of its complicated four electron/proton reaction. − Completing one OER cycle requires four electron/proton transfers, involving multiple intermediates. − Chronoamperometry of a foam (5 × 10 cm 2 ) in 0.10 M KOH reveals currents of 0.18, 0.23, 0.30, and 0.43 mA at overpotentials of 90, 120, 150, and 200 mV, respectively (Figure f). The Tafel plot for the foam, across the 90–200 mV range, exhibits linearity in log ( i ) vs overpotential, with a Tafel slope of 297 mV/decade (Figure g).…”

A copper interface promotes the transformation of nickel hydroxide into high-valent nickel for an efficient oxygen evolution reaction

“…At the open circuit potential (OCP), we could observe two overlapped Raman peaks at 449 cm −1 and 495 cm −1 , which can be assigned to the Ni II -OH and Ni II -O vibration modes of Ni(OH) 2 , respectively. 14,35 As the potential increased to 1.53 V vs. RHE, the Raman peaks at 474 cm −1 and 557 cm −1 , corresponding to the Ni III -O bending and tensile vibration of NiOOH, respectively, started to appear. 36,37 The Raman spectra of Ni(OH) 2 /Cu/NF were similar to those of Ni(OH) 2 /NF, with the Ni II -OH and Ni II -O vibration modes of Ni(OH) 2 appearing at the OCP (Fig.…”