N, Fe co-incorporated CoO nanoarray enhanced by magnetic field for efficient water oxidation†

Abstract

CoO, as a typical water oxidation electrocatalyst, has gradually entered the bottleneck stage of performance modulation through composition optimization. Herein, the N, Fe co-bonded CoO was achieved by N plasma, which suggests further potential to be enhanced by a magnetic field during oxygen evolution reaction (OER) electrocatalysis. N atoms are a bridge for bonding Fe and Co centers, which serve as a fast channel for electron transfer. N, Fe co-doping decreases the electron density around Co²⁺ centers, which increases the unpaired electrons for electron acceptors. As a result, the intrinsic OER activities are boosted, which is further beneficial for amplifying the magnetic enhancement effect. The best performance emerges under a parallel magnetic field with 420 mT intensity, which results in a lowered overpotential of 217 mV and a Tafel slope of 25.1 mV dec⁻¹ in alkaline media. The magnetic enhancement comes from the magnetohydrodynamic effect and the escape energy barrier reduction of the paramagnetic triplet state of O₂. The magnetic enhancement effect would be amplified when the catalytic current becomes larger (magnetic current is 8 mA and 22 mA under 500 mA and 1000 mA total current, respectively). This work provides an in-depth insight into the magnetic enhancing mechanism and a highly feasible strategy for coupling heteroatoms with the magnetic field to operate and break through the bottleneck of non-noble electrocatalysis performance.