Magnetic Field Manipulation of Tetrahedral Units in Spinel Oxides for Boosting Water Oxidation

Abstract

the sluggish kinetics of oxygen evolution reaction (OER) for water splitting still hinders the wide application of this technology. Ru-and Ir-based oxides are highly active catalysts for OER, nevertheless, the scarcity and cost of Ru and Ir largely constrains the broad deployment of hydrogen production utilities. [4][5][6] To this end, transition metal oxide (TMO) electrocatalysts have been extensively investigated due to their earth-abundant and outstanding OER performance. [7][8][9][10] It is remarkable that spinel oxides present stunning catalytic performance for OER in alkaline electrolytes, benefitting from the coexistence of tetrahedral (T d ) and octahedral (O h ) transition-metal cation sites in TMOs, whereas such a complex structure with multiple sites also brings a great challenge on precise identification toward active sites for OER. [11][12][13][14] The tailoring of catalytic active sites for spinel oxides is of importance on the design of highly efficient electrocatalysts for OER, but the active sites of spinel oxides for OER are still elusive. [11,[15][16][17][18] For example, it is reported that the high OER activity of ZnCo 2 O 4 relies on the amounts of Co 3+ on the O h sites. [19] However, on the contrary, it also has been found that the Zn 2+ at T d sites is contributed Magnetic field enhanced electrocatalysis has recently emerged as a promising strategy for the development of a viable and sustainable hydrogen economy via water oxidation. Generally, the effects of magnetic field enhanced electrocatalysis are complex including magnetothermal, magnetohydrodynamic and spin selectivity effects. However, the exploration of magnetic field effect on the structure regulation of electrocatalyst is still unclear whereas is also essential for underpinning the mechanism of magnetic enhancement on the electrocatalytic oxygen evolution reaction (OER) process. Here, it is identified that in a mixed NiFe 2 O 4 (NFO), a large magnetic field can force the Ni 2+ cations to migrate from the octahedral (O h ) sites to tetrahedral (T d ) sites. As a result, the magnetized NFO electrocatalyst (NFO-M) shows a two-fold higher current density than that of the pristine NFO in alkaline electrolytes. The OER enhancement of NFO is also observed at 1 T (NFO@1T) under an operando magnetic field. Our first-principles calculations further confirm the mechanism of magnetic field driven structure regulation and resultant OER enhancement. These findings provide a strategy of manipulating tetrahedral units of spinel oxides by a magnetic field on boosting OER performance.

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

“…158 While there has been considerable interest in the magnetic field-driven enhancement of the OER in spinel oxides in recent years, the majority of research has focused on spin dynamics. 159,160 Lyu 161 has presented the first strategy for manipulating the tetrahedral units in NiFe 2 O 4 (NFO) using magnetic fields to improve OER performance. Through their research, they found that the application of a magnetic field can cause Ni 2+ ions to migrate from the octahedral ( O h ) site to the tetrahedral ( T d ) site in mixed NFO spinels (Fig.…”

Recent Advances in External Fields‐Enhanced Electrocatalysis

“…Besides, Kan and co‐workers reported that a strong magnetic field can enable Ni 2+ to migrate from the octahedral (Oh) sites to the preferential tetrahedral (Td) sites in a mixed NiFe 2 O 4 (NFO) catalyst, showing better catalytic performance for OER. [ 87 ]…”

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

“…Xiao Lyu [30] found that the external magnetic field can force the Ni 2 + cation in mixed NiFe 2 O 4 (NFO) to transfer from the octahedral (Oh) site to the tetrahedral (Td) site. Under the alkaline condition, the current density of NFO affected by the applied magnetic field is twice higher than that of the original NFO.…”