Insights into the Electrocatalytic Oxygen Evolution Reaction and Photocatalytic Methylene Blue Degradation of Mixed Spinel Ni_xCu_1–xFe₂O₄ Nanocomposites Anchored at Sulfur-Doped g-C₃N₄

Abstract

In consideration of energy conversion and/or environmental protection, it is important to develop electrocatalytic and/or photocatalytic active materials for the oxygen evolution reaction (OER) and photodegradation of methylene blue (MB), respectively. To meet these requirements, mixed spinel ferrites such as Ni x Cu1–x Fe2O4 anchored at sulfur-doped graphitic carbon nitride (SCN) nanosheets was developed for the first time via a simple one-pot hydrothermal method for the construction of a novel bifunctional Ni x Cu1–x Fe2O4@SCN nanocomposite. Initially, the crystal structure, optical properties, surface morphology, elemental composition, and surface area of different nanocomposites, such as NiFe2O4, Ni0.8Cu0.2Fe2O4, Ni0.5Cu0.5Fe2O4, Ni0.2Cu0.8Fe2O4, SCN, and Ni0.5Cu0.5Fe2O4@SCN, were studied through XRD, UV-DRS analysis, FT-IR, FE-SEM with EDX, HR-TEM, and BET analysis. Furthermore, when compared to other prepared electrode nanocomposites such as spinel ferrites or different proportion mixed spinel ferrites, the Ni0.5Cu0.5Fe2O4@SCN nanocomposite loaded 316 SSL mesh electrode demonstrated exceptional electrocatalytic oxygen evolution performance with a very low overpotential of 250 mV at 10 mA cm–2 current density and outstanding stability. Subsequently, the photocatalytic activities of the prepared mixed spinel ferrites, Ni x Cu1–x Fe2O4@SCN nanocomposites, were tested through the degradation of MB under visible-light irradiation. Among the prepared photocatalysts, Ni0.5Cu0.5Fe2O4@SCN nanocomposite showed superior photocatalytic MB degradation under visible light, which is firmly due to the equi-proportion blending of Cu+2 substitutions in mixed spinel ferrites at SCN. Accordingly, the Ni0.5Cu0.5Fe2O4@SCN nanocomposite shows excellent photocatalytic degradation (POD) efficiency of 99.1% for MB in 40 min, while other nanocomposites such as NiFe2O4, SCN, and Ni0.5Cu0.5Fe2O4 show 40.2, 42.5, and 91.2% degradation efficiencies, respectively. Thus, the Ni0.5Cu0.5Fe2O4@SCN nanocomposite could be a promising material for electrocatalytic OER and/or photocatalytic degradation of MB under visible-light irradiation.

Photoelectrochemical Water Splitting: A Visible-Light-Driven CoTiO3@g-C3N4-Based Photoanode Interface Follows the Type II Heterojunction Scheme

“…Water oxidation at the photoanode surface is accelerated, and the quick PEC process is supported by the positive frequency phase shift, implying a shorter charge relaxation lifetime. As a result, eq S8 was applied to different photoanodes to calculate the hole relaxation lifetimes ( p ), which are 97, 127, 65, 52, 41, 10, and 32 ms for CTO, g-CN, CTOCN-a, CTOCN-b, CTOCN-c, CTOCN-d, and CTOCN-e, respectively. The fact that CTOCN-d has the least p demonstrates the fast transfer of holes at the interface between the electrode and the electrolyte, which increases the rate of electron–hole pair separation.…”

“…The fact that CTOCN-d has the least p demonstrates the fast transfer of holes at the interface between the electrode and the electrolyte, which increases the rate of electron–hole pair separation. After obtaining p , the corresponding hole diffusion length ( L D ) of the fabricated photoanodes can be determined using eq S9. ,− As a result, CTOCN-d has the shortest hole diffusion length ( L D = 228 μm), which is accompanied by the highest number of holes used for the water oxidation process. These findings support the development of a heterostructure interface between CTO and g-CN nanosheets, increase the separation of photogenerated electron–hole pairs through faster interfacial charge transfer (ICT) activity, and improve the PEC water splitting ability of the CTOCN-d nanohybrid compared to the other catalysts such as CTO and g-CN nanosheets.…”

Oxophilicity Induced Surface Hydroxylation to Promote Oxygen Evolution in Selectively Substituted Spinel-Type Cobalt Oxides

“…Water electrolyzers based on electrochemical and photoelectrochemical reactions are promising next-generation energy storage systems. 1 In electrolyzers, surplus electrical energy is converted to chemical energy by splitting the water into hydrogen and oxygen. Hydrogen is a potential clean energy resource and an alternative to fossil fuels.…”