▎ 摘　　要

Dissolved oxygen (DO) is an essential indicator for evaluating water quality, the exquisitely sensitive electrochemical DO sensor could accurately record response which was based on oxygen reduction reaction (ORR) with a sluggish reaction rate. Thus, high-efficient ORR electrocatalysts are urgently needed for broad applications. As a matter of fact, graphene quantum dots (GQDs) have attracted a great deal of attention, several heteroatoms are extensively introduced in GQDs fragments to regulate their inherent chemical and electrical properties by adjusting their electronic structure. However, B-N-C moieties always exist for some BN-codoped carbons due to the intermolecular force that might prohibit its electrocatalytic activity. Therefore, this research design a strategy to solve this problem; despite substantial efforts, this study shows a metal-free B-doped GQD/N-doped carbon nanotubes (BGQD/NCNTs) electrode significantly influences ORR electrocatalytic activity due to the synergistic effect and abundant active sites. Herein, BGQD/NCNTs exhibit an excellent ORR performance with an onset potential of 0.91 V (vs. RHE), exceeding most reported GQDs-introduced electrocatalysts; it also outperformed the commercial electrocatalyst in terms of long-term stability. For seawater DO sensing, BGQD/NCNTs exhibit ultra-high sensitivity of 0.011 mA/cm(2)ppm and further integrate into an online detection platform to accomplish the aim of continuous monitoring via a wireless connection. (C) 2021 Elsevier Ltd. All rights reserved.