Heteroatom-doped carbon matrices have been attracting significant attention due to their superior electrochemical stability, light weight and low cost.

As one of the most promising next-generation safe and green energy storage technologies, aqueous Zn-ion batteries have attracted considerable attention in recent years. However, their working mechanism is still controversial. Also, their performance needs to be further improved to meet the requirement of widespread applications. Herein, we developed a nanoflower-like MnO₂/C composite with two-electron reaction pathway for use as a cathode material in aqueous Zn-ion batteries. Benefiting from the large specific surface area of the nanoflower-like structure, high conductivity of the carbon materials and the low crystallinity of birnessite-type MnO₂, the Zn-ion battery using MnO₂/C as the cathode material could carry out a deep and fast reaction via the Mn⁴⁺/Mn²⁺ two-electron pathway. At 300 mA g⁻¹, the battery could retain a high specific capacity of 279.7 mA h g⁻¹ after 300 cycles. The second electronic reaction process of Mn³⁺/Mn²⁺ could also work at a high current density. A high initial discharge capacity of more than 200 mA h g⁻¹ was achieved at a high current density of 2000 mA g⁻¹. A two-electron working mechanism of the layered-MnO₂ cathode material is proposed. Due to the advantages of high capacity, high rate performance and good stability, the MnO₂/C composite is a promising cathode material for aqueous Zn-ion batteries, which holds potential for applications in electric vehicles and grid energy storage.

We present an alternative way to fabricate a N-doped carbon matrix via a room temperature solution plasma process. The type of C–N bonding states was controlled by choosing the structure of the original precursor and additive. In this research, pyridine and acrylonitrile were employed as the heterocyclic and linear structure precursor respectively. A small amount of anthracene (7 mM) was introduced as an additive to further promote the graphitic structure in the carbon matrix. The effects of the structure of the CN precursor on the chemical bonding states and electrocatalytic activities were investigated. The most pronounced peak was pyridinic-N when pyridine was applied as the precursor, whereas the dominant peak shifted to amino-N when the precursor changed to acrylonitrile. Furthermore, graphitic-N increased 30–40% when anthracene was added to the original precursors. From the results of electrochemical measurements, the current density was proportional to the content of graphitic-N, while a higher percentage of amino-N shifted the ORR onset potential to more positive values. N-doped carbon with the highest graphitic-N content showed the highest electron transfer number of 3.7 and the lowest peroxide yield of 30%. In contrast, N-doped carbon consisting of dominant pyridinic-N resulted in the lowest current density, ORR onset and peak potentials. The results indicated that the presence of graphitic-N encouraged a direct four electron transfer pathway for ORR. Herein, our research showed a room temperature solution method to control the chemical bonding states of nitrogen through designing the original precursors for the first time, as well as reports the synergic effect of amino-N and graphitic-N towards advanced ORR activity.