Experiment methods with calculation method, SEM/ TEM images, XRD patterns, ESR spectra, iR-uncompensated CV, EIS, TOFs at various overpotentials, Raman and XPS spectra after experiment, XAS spectra of Co reference materials with linear correlation curve, and iR-compensated AEMS performance (PDF)■ AUTHOR INFORMATION

Graphical abstract

The oxygen evolution reaction (OER) is crucial for producing sustainable energy carriers. Herein, Ir (5 mol.%) doped inverse-spinel NiFe 2 O 4 (Ir-NFO) nanoparticles deposited on Ni foam (NF) by scalable solution casting are considered a promising OER electrocatalyst for industrial deployments. The Ir-NFO/NF (with minimal lattice distortion by uniform Ir doping) provides an OER overpotential of 251 mV (intrinsically outperforming NFO/NF and benchmarking IrO 2 /NF) and extraordinary robustness over 130 days at 100 mA cm −2 . In situ X-ray absorption spectroscopy reveals oxidation only for Fe on NFO, whereas concurrent generation of higher-valent Ni and Fe occurs on Ir-NFO during OER. Density functional theory calculations further demonstrate that Ir substitutes the sublayer Ni octahedral site and switches the main active reaction center from Fe Oh Fe Td bridge site (FeOFe) on NFO to Ni Oh -Fe Td bridge site (NiOFe active motif ) on Ir-NFO for a co-catalytic OER. This study sheds new light on precious-metal doped Ni-Fe oxides, which may be applicable to other binary/ternary oxide electrocatalysts.

Reactive chlorine-mediated electrochemical water treatment necessitates selective chlorine evolution reaction (ClER) versus parallel oxygen evolution reaction (OER) in mild pH (7–10), with minimal deployments of precious electrocatalysts. This study reports Ni0.33Fe0.67O y /TiO2 heterojunction anode prepared by a straightforward sol–gel coating with thermal decomposition at 425 °C. The ClER current efficiency (CE, 70%) and energy efficiency (2.3 mmol W h–1) were comparable to benchmarking Ir7Ta3O y /TiO2 at 30 mA cm–2 in 50 mM NaCl solutions with near-neutral pH. Correlations of ClER CE of variable Ni x Fe1–x O y /TiO2 (x: 0.33, 0.8–1) with the flat-band potential and p-band center, as experimental descriptors for surface charge density, nominated the outer TiO2 to be the active ClER center. The underlying Ni0.33Fe0.67O y , characterized as biphasic NiFe2O4 and NiO, effectively lowered the O binding energy of TiO2 by electronic interaction across the junction. The OER activity of Ni0.33Fe0.67O y superior to the other Fe-doped Ni oxides suggested that the conductive OER intermediates generated on Ni0.33Fe0.67O y could also facilitate the ClER as an ohmic contact. Stability tests and NH4 + degradation in synthetic and real wastewater confirmed the feasibility of Ni0.33Fe0.67O y /TiO2 heterojunction anode for mediated water treatments in mild pH.

When coated on top of Ir-based dimensionally stable anodes, binary Bi−Ti oxides could enhance the chlorine evolution reaction (ClER) efficiency for chlor-alkali and mediated water treatment. However, the underlying mechanism and the effects of Bi necessitated further clarification. This study prepared Bi x Ti 10-x O y heterojunction layers on an existing Ir 7 Ta 3 O z anode by thermal decomposition (425 °C) of TiOSO 4 and Bi(NO 3 ) 3 under varied Ti:Bi ratios and precursor matrix (inorganic versus organic solvents). Plain material characterizations (scanning electron microscopy and X-ray diffraction) were performed together with voltammetry and potentiostatic electrolysis (in 50 mM NaCl, 50 mM HCOONa, and 0.1 M NaClO 4 ). The top Bi x Ti 10−x O y was nominated as the Cl − binding site with Ir 7 Ta 3 O z as the ohmic contact. Bi 12 TiO 20 and β-Bi 2 O 3 (formed at x > 5) on the outer layer could elevate the reactivity of surface bound hydroxyl radicals and the ClER selectivity. However, relatively loosely packed and thick overlayers (due to glycolate and isopropanol in precursor) aggravated the current and energy efficiency of ClER as well as the anodic stability.