Effects of Alternating Magnetic Fields on the OER of Heterogeneous Core–Shell Structured NiFe₂O₄@(Ni, Fe)S/P

Abstract

Composition optimization, structural design, and introduction of external magnetic fields into the catalytic process can remarkably improve the oxygen evolution reaction (OER) performance of a catalyst. NiFe2O4@(Ni, Fe)S/P materials with a heterogeneous core–shell structure were prepared by the sulfide/phosphorus method based on spinel-structured NiFe2O4 nanomicrospheres. After the sulfide/phosphorus treatment, not only the intrinsic activity of the material and the active surface area were increased but also the charge transfer resistance was reduced due to the internal electric field. The overpotential of NiFe2O4@(Ni, Fe)P at 10 mA cm–2 (iR correction), Tafel slope, and charge transfer resistance were 261 mV, 42 mV dec–1, and 3.163 Ω, respectively. With an alternating magnetic field, the overpotential of NiFe2O4@(Ni, Fe)P at 10 mA cm–2 (without iR correction) declined by 45.5% from 323 mV (0 mT) to 176 mV (4.320 mT). Such enhancement of performance is primarily accounted for the enrichment of the reactive ion OH– on the electrode surface induced by the inductive electric potential derived from the Faraday induction effect of the AMF. This condition increased the electrode potential and thus the charge transfer rate on the one hand and weakened the diffusion of the active substance from the electrolyte to the electrode surface on the other hand. The OER process was dominantly controlled by the charge transfer process under low current conditions. A fast charge transfer rate boosted the OER performance of the catalyst. At high currents, diffusion exerted a significant effect on the OER process and low OH– diffusion rates would lead to a decrease in the OER performance of the catalyst.

Sulfidation of CoCuOx Supported on Nickel Foam to Form a Heterostructure and Oxygen Vacancies for a High-Performance Anion-Exchange Membrane Water Electrolyzer

“…Double-layer capacitance ( C dl ) was obtained from CV curves at different scan rates (20, 40, 60, 80, and 100 mV s –1 ) in the non-faradaic region (−0.045 to 0.045 V vs Ag/AgCl) . The electrochemical surface area (ECSA) was measured according to formula ECSA = C dl / C s , where C s is the capacitance of an atomically smooth planar metal surface at a value of 40 μF cm –2 for nonprecious metal electrocatalysts . The durability tests were performed by a chronopotentiometry method at 100 mA cm –2 or 200 mA cm –2 .…”

“…29 The electrochemical surface area (ECSA) was measured according to formula ECSA = C dl /C s , where C s is the capacitance of an atomically smooth planar metal surface at a value of 40 μF cm −2 for nonprecious metal electrocatalysts. 30 The durability tests were performed by a chronopotentiometry method at 100 mA cm −2 or 200 mA cm −2 .…”

Sodium Tartrate-Assisted Synthesis of High-Purity NiFe2O4 Nano-Microrods Supported by Porous Ketjenblack Carbon for Efficient Alkaline Oxygen Evolution

“…More profoundly, the introduction of cheap and commercially available KB during the synthesis of NiFe 2 O 4 /KB and CoFe 2 O 4 /KB produced catalysts with much higher OER activities compared with the corresponding ferrite counterparts (NiFe 2 O 4 and CoFe 2 O 4 ). The η 10 value of 258 mV (vs RHE) measured for NiFe 2 O 4 /KB is one of the smallest values yet reported for ferrite-based electrocatalysts during OER (Table S1), − ,,,,,,− outperforming NiFe 2 O 4 /carbon cloth (340 mV vs RHE), NiFe 2 O 4 /FeNi 3 foam (262 mV vs RHE), NiFe 2 O 4 /Ti 3 C 2 (266 mV vs RHE), NiFe 2 O 4 /Ni@C (330 mV vs RHE), NiFe 2 O 4 -hollow nanoparticles/CNTs (260 mV vs RHE), and NiFe 2 O 4 /rGO (302 mV vs RHE) . Few ferrite-based composite catalysts have been reported with η 10 values lower than NiFe 2 O 4 /KB, though most have complicated compositions and cumbersome preparation routes, such as phosphided NiFe/NiFe 2 O 4 embedded into porous N-doped carbon nanospheres (P-FeNi/FeNiO/CNS, 220 mV vs RHE) or 3D porous CoFe 2 O 4 /C nanorod arrays supported on Ni foam@polyaniline (Ni foam@NC-CoFe 2 O 4 /C, 240 mV vs RHE) …”

Recent Development of External Magnetic Field Assisted Oxygen Evolution Reaction‐A Mini Review

“…Ref. [31] Copyright(2023), with permission from America Chemical Society They believe that the PÀ N junction induced by the magnetic field can change the electron distribution and Fermi level position in heterojunction, so that *OOH intermediate can be better adsorbed on the catalyst surface, and OER can be completed more efficiently. The overpotential at 50 mA cm À 2 of NiFe-LDH/Co3O4/NF is only 274 mV, and the stability is very good.…”