Synergistic effects have been applied to a variety of hybrid electrocatalysts to improve their activity and selectivity. Understanding the synergistic mechanism is crucial for the rational design of these types of catalysts. Here, we synthesize a MnCo2O4/Co–N–C hybrid electrocatalyst for the oxygen reduction reaction (ORR) and systematically investigate the synergy between MnCo2O4 nanoparticles and Co–N–C support. Theoretical simulations reveal that the synergy is closely related to the distance between active sites. For a pair of remote active sites, the ORR proceeds through the known 2e- + 2e- relay catalysis while the direct 4e– ORR occurs on a pair of adjacent active sites. Therefore, the formation of the undesired byproduct (H2O2) is inhibited at the interface region between MnCo2O4 and Co–N–C. This synergistic effect is further verified on an anion-exchange membrane fuel cell. The findings deepen the understanding of synergistic catalysis and will provide guidance for the rational design of hybrid electrocatalysts.
Yuye Li,Dong Liu,Shuyun Meng,Jiayi Zhang,Libo Li,Tianyan You
Ferrocene (Fc) is a common quencher of Ru(bpy)32+ luminescence. However, interactions between Fc and Ru(bpy)32+ can be extremely complicated. In this work, we reported the first use of Fc to regulate the electrochemiluminescence (ECL) of Ru(bpy)32+ by tuning the length of the DNA sequence between Fc and the luminophore of nitrogen-doped graphene quantum dots-Ru(bpy)32+-doped silica nanoparticles (SiO2@Ru-NGQDs). The ECL of SiO2@Ru-NGQDs was depressed when the distance between Ru(bpy)32+ and Fc was less than 8 nm; a stronger ECL was observed when the distance was more than 12 nm. The switching of the ECL of Ru(bpy)32+ by Fc was attributed to the electron transfer mechanism, in which Fc participated in the redox of Ru(bpy)32+ for “signal-off” ECL; this favored electron transfer at the electrode fabricated with an Fc-labeled aptamer (Fc-apt) and SiO2@Ru-NGQDs for “signal-on” ECL depending on the length of the DNA sequence. Here, a dual-signal readout aptasensor for aflatoxin B1 (AFB1) detection was developed via the enhanced ECL of SiO2@Ru-NGQDs by Fc-apt. The redox currents of Fc and the ECL of Ru(bpy)32+ were simultaneously collected as yardsticks, and both decreased with higher concentrations of AFB1. The aptasensor allowed linear ranges of 3 × 10–5 to 1 × 102 ng mL–1 for ECL mode and 1 × 10–3 to 3 × 103 ng mL–1 for electrochemical mode. Our work provides insight into the interactions between Fc and Ru(bpy)32+. The dual-signal readout strategy is a potential platform for the versatile design of aptasensors.
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