Sulfate Oxyanion Steered d-Orbital Electronic State of Nickel-Iron Nanoalloy for Boosting Electrocatalytic...

Oxyanion groups recently offer an innovative avenue for improving the sluggish kinetics of electrochemical reactions benefitting from their particular polyanion configurations and large electronegativity. Nevertheless, the exact structure design and deep regulating mechanism of oxyanion species remain poorly understood. Herein, a fresh architecture of the sulfate oxyanion coordinated nickel-iron nanoalloy on nitrogen and sulfur co-doped carbon nanotube (SO₄ ^2--NiFe/NSCT) is newly proposed to study the activity increment effect and mechanism. The SO₄ ^2--NiFe/NSCT displays hierarchical nanostructure with robust-wrinkled surface and highly efficient active sites. Importantly, the SO₄ ^2- group, as a significant manipulation factor, is first evidenced to promote the oxygen reduction reaction (ORR) activity for NiFe nanoalloy under the reductive condition, showcasing outstanding bifunctional properties toward ORR and oxygen evolution reaction (OER), as well as the exceptional performance in non-aqueous Li-O₂ battery. Both experimental and theoretical results elucidate that, as an electron bridge, the introduction of SO₄ ^2- downshifts the d-band center of SO₄ ^2--NiFe/NSCT and gives the electron transfer passageway between the H atom in OH* intermediate and the O atom in SO₄ ^2- group, greatly optimizing the metal-intermediate interaction with weaker bond energy. This work provides a deep insight into the activity enhancement mechanism by the sulfate oxyanion.