Phase Transformation in the Charge-Discharge Process and the Structural Analysis by Synchrotron XAFS and XRD for Nickel Hydroxide Electrode

Identification of Highly Active Fe Sites in (Ni,Fe)OOH for Electrocatalytic Water Splitting

“…9,32,53−56 Both α-Ni(OH) 2 and γ-NiOOH form layered structures in which sheets of edgesharing [NiO 6 ] octahedra are separated by intercalated water molecules and hydrated ions (Figure 2d). 56 The Ni−O bond lengths 9,32,53−56 differ significantly between 2.05 Å in Ni(II)containing α-Ni(OH) 2 , and 1.88 Å in γ-NiOOH, which is nonstoichiometric (NiOOH 1−x ) and contains a mixture of Ni(III) and Ni(IV) sites. 57 The significant shift of both the preedge peak and the main absorption edge in the Ni K-edge spectra (Figure 2e) shows nearly complete oxidation of Ni sites when the potential is increased from 1.12 to 1.52 V; the features of the oxidized component then approach saturation with further potential increase.…”

High-energy and high-power Zn–Ni flow batteries with semi-solid electrodes

“…As the Ni(OH) 2 equilibrium potential (1.46 V vs. RHE, Fig. S1 †) is higher than the oxygen evolution reaction (OER) potential ($1.23 V vs. RHE), parasitic reactions such as OER 50,51 can contribute more to the charging capacity when AB volume percentages are low, leading to much smaller discharge capacities and coulombic efficiencies. With high AB volume percentages (>4.3 vol%), the ability to disperse more Ni(OH) 2 particles and reduction in OER contributes to the larger charging capacity, leading to greater rechargeability of Zn-Ni semi-solid batteries.…”

“…Also, compared to the ratio of L 3,high (854.8 eV)/L 3,low (852.7 eV) for the LiNi 3+ O 2 58 shown in Fig.5c, the Ni(OH) 2 cathode aer 100% SOC is still quite low, which is further indication of parasitic reactions. Both XRD and XANES results suggest the charge-discharge scenario for Zn-Ni semi-solid battery should be limited by the Ni(OH) 2 capacity (<60% theoretical SOC) to lower the impact of parasitic reactions (OER) 50,51. In summary, a high power density up to 159 mW cm geo.…”

Understanding the Effects of Composition and Structure on the Oxygen Evolution Reaction (OER) Occurring on NiFeOxCatalysts

“…[37][38][39][40][41][42] Both a-Ni(OH) 2 and g-NiOOH form layered structures of edgesharing [NiO 6 ] octahedra separated by intercalated water molecules and hydrated ions ( Figure 3.7d). 44 The Ni-O bond lengths [39][40][41][42][43][44] differ significantly between 2.05 Å in Ni(II)-containing a-Ni(OH) 2 , and 1.88 Å in g-NiOOH which is non-stoichiometric (NiOOH 1Àx ) and contains a mixture of Ni 31 and Ni 41 sites. 43 The significant shift of both the pre-edge peak and the main absorption edge in the Ni K-edge spectra ( Figure 3.9e) shows nearly complete oxidation of Ni sites when the potential is increased from 1.12 to 1.52 V vs. RHE; the features of the oxidized component then approach saturation with further potential increase.…”