Encapsulated NiCo₂S₄‐based straight bamboo‐shaped N‐CNT as efficient and stable oxygen electrocatalysts

Abstract

Developing highly effective and stable non-precious bifunctional oxygen electrocatalysts is crucial and challenging. Herein, we report nano-mediated straight bamboo-shaped nitrogen-doped carbon nanotubes modified with encapsulated NiCo 2 S 4 -based nanoparticles (E-NiCo 2 S 4 /SBS-NCNTs) by electrodeposition and procedural calcination strategy, in which nitrogen-doped carbon nanotubes with straight bamboo shape (SBS-NCNTs) show more average diameter and encapsulated NiCo 2 S 4 -based nanoparticles (E-NiCo 2 S 4 ) are coated by carbon, and what makes us even more excited is that they are evenly dispersed on SBS-NCNTs surface, not just at the tip or inside. When applied for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), E-NiCo 2 S 4 /SBS-NCNTs show excellent catalytic activity, and onset potential (E onset ) in OER and ORR is only 1.52 V and 0.95 V (vs. RHE) in 0.1 M KOH, respectively. More importantly, the hybrids exhibit good methanol tolerance, with almost unchanged for ORR performance after adding 0.5 M methanol, and it has highly stability, the current density dropped by 22% after 7 h of reaction. The interaction of NiCo 2 S 4 with the external carbon layer can greatly enhance the electrocatalytic activity toward the OER and it has a complete 4ereaction process toward the ORR. The excellent electrocatalytic activity is mainly due to synergistic enhancement effect, in which SBS-NCNTs with highly catalytic activity provide good conductivity, expose more active sites and promotes fast mass transfer; Carbon-coated NiCo 2 S 4 -based nanoparticles can improve the local work function of SBS-NCNT through synergistic electronic interaction, promoting O 2 adsorption, ensure rapid electron transport, and enable SBS-NCNT to improve its electrocatalytic activity. Because of the weakness of Ostwald effect and synergistic enhancement, the stability and catalytic activity of NiCo 2 S 4 -based nanoparticles can be greatly improved. All these advantages can synergistically improve the electrocatalytic efficiency and make it become one of the most promising bifunctional oxygen electrocatalysts.