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Heteroatom-doped carbon matrices have been attracting significant attention due to their superior electrochemical stability, light weight and low cost. Hence, in this study, various types of heteroatom, including single dopants of N, B and P and multiple dopants of B-N and P-N with a carbon matrix were synthesized by an innovative method named the solution plasma process. The heteroatom was doped into the carbon matrix during the discharge process by continuous dissociation and recombination of precursors. The chemical bonding structure, ORR activity and electrochemical performance were compared in detail for each single dopant and multiple dopants. According to the Raman spectra, the carbon structures were deformed by the doped heteroatoms in the carbon matrix. In comparison with N-doped structures (NCNS), the ORR potential of PN-doped structures (PNCNS) was positively shifted from -0.27 V to -0.24 V. It was observed that doping with N decreased the bonding between P and C in the matrix. The multiple doping induced additional active sites for ORR which further enhanced ORR activity and stability. Therefore, PNCNS is a promising metal-free catalyst for ORR at the cathode in a fuel cell.

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.

N-doped carbon synthesized by a room temperature plasma process demonstrated the synergic effect of amino-N and graphitic-N towards advanced ORR activity.

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As bifunctional oxygen evolution/reduction electrocatalysts, transition-metal-based single-atom-doped nitrogen–carbon (NC) matrices are promising successors of the corresponding noble-metal-based catalysts, offering the advantages of ultrahigh atom utilization efficiency and surface active energy. However, the fabrication of such matrices (e.g., well-dispersed single-atom-doped M-N4/NCs) often requires numerous steps and tedious processes. Herein, ultrasonic plasma engineering allows direct carbonization in a precursor solution containing metal phthalocyanine and aniline. When combining with the dispersion effect of ultrasonic waves, we successfully fabricated uniform single-atom M-N4 (M = Fe, Co) carbon catalysts with a production rate as high as 10 mg min−1. The Co-N4/NC presented a bifunctional potential drop of ΔE = 0.79 V, outperforming the benchmark Pt/C-Ru/C catalyst (ΔE = 0.88 V) at the same catalyst loading. Theoretical calculations revealed that Co-N4 was the major active site with superior O2 adsorption–desorption mechanisms. In a practical Zn–air battery test, the air electrode coated with Co-N4/NC exhibited a specific capacity (762.8 mAh g−1) and power density (101.62 mW cm−2), exceeding those of Pt/C-Ru/C (700.8 mAh g−1 and 89.16 mW cm−2, respectively) at the same catalyst loading. Moreover, for Co-N4/NC, the potential difference increased from 1.16 to 1.47 V after 100 charge–discharge cycles. The proposed innovative and scalable strategy was concluded to be well suited for the fabrication of single-atom-doped carbons as promising bifunctional oxygen evolution/reduction electrocatalysts for metal–air batteries.

High-electrocatalytic-activity noble nanoparticles (NPs) supported on carbon nanoballs (CNBs) were synthesized using an innovative plasma-in-liquid method, which is known as solution plasma processing (SPP). This technique uses a one-step method for the synthesis of NPs on carbon materials. CNBs are formed using benzene as a carbon precursor while gold (Au) or platinum (Pt) nanoparticles are generated instantaneously via sputtering from metal electrodes. The synthesized NP/CNBs were annealed at 850 °C in order to increase the conductivity of the material. The results of structural characterizations reveal that the Au and Pt NPs are smaller than 10 nm and have a uniform size distribution, and these NPs are successfully loaded onto highly mesoporous CNBs that have an average pore diameter between 13 and 16 nm. In the results from cyclic voltammetry measurements, the Au/CNBs and Pt/CNBs show clear peaks corresponding to the oxidation and reduction features in the catalytic reactions. Apart from noble nanoparticles, SPP can also be used to synthesize various kinds of NPs including bimetallic NPs loaded on spherical carbon supports by changing the working electrodes. The proposed mechanism for the synthesis is discussed in detail. This method shows potential to be a candidate for the next-generation synthesis of NP/carbon in the future.

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