Ease of Electrochemical Arsenate Dissolution from FeAsO₄ Microparticles during Alkaline Oxygen Evolution Reaction

Abstract

Transition metal-based ABO4-type materials have now been paid significant attention due to their excellent electrochemical activity. However, a detailed study to understand the active species and its electro-evolution pathway is not traditionally performed. Herein, FeAsO4, a bimetallic ABO4-type oxide, has been prepared solvothermally. In-depth microscopic and spectroscopic studies showed that the as-synthesized cocoon-like FeAsO4 microparticles consist of several small individual nanocrystals with a mixture of monoclinic and triclinic phases. While depositing FeAsO4 on three-dimensional nickel foam (NF), it can show oxygen evolution reaction (OER) in a moderate operating potential. During the electrochemical activation of the FeAsO4/NF anode through cyclic voltammetric (CV) cycles prior to the OER study, an exponential increment in the current density (j) was observed. An ex situ Raman study with the electrode along with field emission scanning electron microscopy imaging showed that the pronounced OER activity with increasing number of CV cycles is associated with a rigorous morphological and chemical change, which is followed by [AsO4]3– leaching from FeAsO4. A chronoamperometric study and subsequent spectro- and microscopic analyses of the isolated sample from the electrode show an amorphous γ-FeO(OH) formation at the constant potential condition. The in situ formation of FeO(OH)ED (ED indicates electrochemically derived) shows better activity compared to pristine FeAsO4 and independently prepared FeO(OH). Tafel, impedance spectroscopic study, and determination of electrochemical surface area have inferred that the in situ formed FeO(OH)ED shows better electro-kinetics and possesses higher surface active sites compared to its parent FeAsO4. In this study, the electrochemical activity of FeAsO4 has been correlated with its structural integrity and unravels its electro-activation pathway by characterizing the active species for OER.

Extended X-ray Absorption Fine Structure Revealed the Mechanism of Arsenate Removal by the Fe/Mn Oxide-Based Composite under Conditions of Fully Saturated Sorption Sites

“…The complexity of the envelopment peaks reflects the presence of several phases of iron oxides. The prominent satellite peaks at around 719 eV are in additional support of prevalence of pure Fe 3+ oxidation state …”

Evolution of Mn–Bi2O3 from the Mn-doped Bi3O4Br electro(pre)catalyst during the oxygen evolution reaction

“…In recent years, different transition metal-based electrocatalysts have been explored for electrocatalytic OER. 8,19 In this context, group 15 elements (N and P) serve as the most favourable anionic counterpart of the reactive transition metal-based nitride or phosphide materials. However, the counterions are typically redox-silent and do not take part in the electrocatalysis.…”