Revealing Spin Magnetic Effect of Iron-Group Layered Double Hydroxides with Enhanced Oxygen Catalysis

Abstract

The oxygen evolution reaction (OER) is the bottleneck limiting the reaction process of water splitting. The OER process involves the recombination of oxygen from diamagnetic singlet state OH or H 2 O to paramagnetic triplet state O 2 . The spin conservation for oxygenated intermediates must play an important role in the OER. However, the dynamic mechanism of magnetic field-induced spin polarization is still in its infancy. Herein, based on the spin-coupling interaction of iron group elements, three typical iron group layered double hydroxides (LDHs) were constructed to study the relationship among magnetic field, spin polarization, and OER activity. Combining experimental and theoretical studies, we revealed the spin-magnetic effect of iron group LDHs for enhancing the OER process. There is a positive correlation between the saturation magnetization and OER performance of iron group LDHs under different magnetic fields. The NiCoFe-LDHs (NCFL) endows the strongest OER activity (η 10 = 230 mV) and saturation magnetization (M s = 44 emu mg −1 ) compared with that of CoFe-LDHs (CFL, η 10 = 372 mV, M s = 21 emu mg −1 ) and NiFe-LDHs (NFL, η 10 = 246 mV, M s = 29 emu mg −1 ). The density functional theory calculations show that the Fe sites of NCFL endow a stronger spin-coupling interaction with OH, and Raman spectroscopy further proves the promotion for the formation of the O−O bond of NCFL. Applying an external magnetic field, due to the spin magnetic effect of iron group LDHs, the enhancement amplitude of OER activity is also positively correlated with the magnetism of the catalyst. NCFL has the strongest spin magnetic effect about −34.8 mV T −1 compared with NFL (−27.0 mV T −1 ) and CFL (−16.7 mV T −1 ). The overpotential of NCFL is only 206 mV under the condition of 700 mT magnetic field. In conclusion, we demonstrate the mechanism of underlying influence of the spin magnetic effect on the OER performance and provide insights into the relationship between catalysts and oxygenated intermediates. These insights would help to understand and design catalysts at the spintronic level.

Spin-Modulated Oxygen Electrocatalysis

“…Additionally, increasing the remanent magnetism of the catalysts is also an effective method to boost the intrinsic activity without the assistance of magnetic field. Besides above oxides of magnetic element (Fe, Co, Ni), their hydroxides 115 and sulfides 116 the increase of magnetic field (0∼502 mT) (Figure 9H). The physics of magnetic-field enhancement on the OER is that the external magnetic field can align the magnetic domain configuration of multidomain FM catalysts in an orderly direction, as demonstrated by the schematic diagram in Figure 2C.…”

“…Additionally, increasing the remanent magnetism of the catalysts is also an effective method to boost the intrinsic activity without the assistance of magnetic field. Besides above oxides of magnetic element (Fe, Co, Ni), their hydroxides and sulfides also exhibit obvious magnetic enhancement on OER activity (Figure G, H). For example, Ni, Co, Fe based layered double hydroxides (LDHs) (NCFL) have a strong spin magnetic effect about −34.8 mV/T (Figure G) and the OER performance of Ni doped MoSe 2 is gradually improved with the increase of magnetic field (0∼502 mT) (Figure H).…”

“…Copyright 2019 Springer Nature). (G) LSV curves of NCFL (NiCoFe-LDH, 28 atom % Fe), NCFL-0.25 (25 atom % Fe), NCFL-0.2 (20 atom % Fe), and NCL (NiCo-LDH) under 0 and 700 mT (Reproduced from ref . Copyright 2023 American Chemical Society).…”

Recent advances in catalyst design and activity enhancement induced by a magnetic field for electrocatalysis

“…Magnetic Fe-group (Ni, Co, and Fe) transition metal layered double hydroxides (LDHs) are commonly used as catalysts for the OER in alkaline electrolytes, in addition to spinel structure catalysts. 132,133 Lin 134 constructed three typical Fe-group LDHs based on the spin-coupled interactions of Fe-group elements and investigated the relationship between the magnetic field, spin polarization, and OER activity. The iron group transition metals, including Fe 3+ (t 2g 3 e g 2 ), Co 2+ (t 2g 6 e g 1 ), and Ni 2+ (t 2g 6 e g 2 ), have a spin single electron, causing the LDHs to act as a model structure for studying the spin-magnetic effect (Fig.…”

Fe and Mo Co‐Modulated Coral‐like Nickel Pyrophosphate in situ Derived from Nickel‐Foam for Oxygen Evolution

“…However, their high cost and scarcity hinder their wide practical application and have stimulated the development of new low‐cost and durable non‐noble metal materials [8–10] . Among them, non‐noble transition metal‐based catalysts (TMBCs) with high abundance and diversity, inclusive of Ni, Mn, Co, V, Fe and Mo‐based compounds have been considered as promising alternatives in various forms, such as oxides, [11] (oxy)hydroxides, [12–14] phosphides, [15–17] borides, [18] carbides, [19] nitrides, [20] arsenides, [21,22] sulfides, [23–25] and selenides and tellurides [26] . Among all the transition metal‐based materials, nickel‐based electrocatalysts have attracted more attention due to their high abundance and low cost [27–39] …”