In Situ 57Fe Mössbauer Spectroscopy Study of the Electrochemical Behavior of an Iron‐Substituted Nickel Hydroxide Electrode

Abstract

The electrochemical cycling of a hydrated, iron‐substituted nickel hydroxide (20 atomic percent of iron substituted for nickel) in a Ni//Cd cell was studied in situ by 57normalFe Mössbauer spectroscopy. The variations of the iron oxidation state (and spin configuration) were followed throughout the discharge and correlated to the changes of the overall distribution of cationic oxidation states, as well as to the structural modifications. The charge starting from an α‐phase leads to a pure γ oxyhydroxide containing NiIII,NiIV,FeIV , and average valence Fefalse〈3.5+false〉 ions. During the discharge, the evolution of the various cationic populations deduced from the Mössbauer data provides evidence of a γ‐type solid solution domain, in which the NiIV ions are reduced to the trivalent state rather than the iron ions, followed by γ + α biphased domain.

Surpassing electrocatalytic limit of earth-abundant Fe4+ embedded in N-doped graphene for (photo)electrocatalytic water oxidation

“…1 V vs. RHE (Fig. 4a, Table S3) reveals two doublets with respective isomer shifts (d) of 0.32 and 0.30 mm/s and quadrupole splittings (D) of 0.47 and 2.33 mm/s, which are consistent with high-spin, Jahn-Teller distorted Fe 3+ species, similar to previous reports in related materials [40][41][42][43]. The larger quadrupole splitting evident in the 57 Fe 3 N@NG catalyst suggests the Fe 3+ sites in this catalyst with more distorted geometries [44].…”

O3–NaxMn1/3Fe2/3O2as a positive electrode material for Na-ion batteries: structural evolutions and redox mechanisms upon Na+(de)intercalation

“…The first one shows an isomer shift of 0.336 -0.321 mm.s -1 (depending on the Na content) and is attributed to HS-Fe 3+ ions in octahedral environment. The second one is characterized by an isomer shift close to 0 mm.s -1 , typical of the Fe 4+ ion in octahedral environment, as also observed in other oxides, in the High Spin 60 or Low Spin 61,62 states. The spin state of tetravalent iron ions in our compounds has not yet been established.…”

One-step preparation of optically transparent Ni-Fe oxide film electrocatalyst for oxygen evolution reaction

“…Although beneficial effects of Fe on the electrochemical OER activity of Ni in alkaline electrolyte have been reported in a number of studies [25,[42][43][44][45], little is known about the structural or chemical characteristics of crystalline Ni-Fe oxide catalysts, neither the amorphous phase. In this work, we used XPS to detect the surface atomic composition and the chemical shifts of Fe and Ni peaks.…”