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The Role of Fe Species on NiOOH in Oxygen Evolution Reactions

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journal contribution
posted on 18.05.2020, 17:05 by Yecheng Zhou, Núria López
The Pourbaix diagram of Ni electrodes under reaction conditions presents several metastable NiOxHy phases and Fe doping enlarges the stability area of oxyhydroxo species. For the Ni-only phase, water adsorption and intercalation can significantly lower both the surface and interface energies, and even introduce “negative surface energy”. Thus, water can exfoliate layers, leading to Fe ion adsorption on inner layers, as demonstrated by ab initio molecular dynamics. These single atoms have been carefully speciated (i.e., initially prepared as Fe2+ and Fe3+) and proton coupled electron transfer between the H2O–Fe and lattice oxygen ions has been observed in all ab initio molecular dynamics simulations, which is attributed to the Fe incorporation, since no proton coupled electron transfer occurs under free water conditions. Furthermore, 15 possible oxygen evolution reaction mechanisms near Fe ions show that the main active species corresponds to the Ni2+, which is reduced from Ni3+ via H transfer when a Fe2+ iron adsorbs nearby, and the overpotential can be significantly reduced to 0.23 V.