The design and development of carbon materials with high-efficiency oxygen reduction activity is still a problem. Folic acid (FA) has unique structural characteristics, and it can provide multiple coordination sites for metal ions. Here, folic acid (FA) was used as a metal complex ligand, and Cu-Co-based N-doped porous carbon nanosheets (Cu-CoNCNs) were synthesized by the solvothermal method, the molten salt template-assisted calcination method, and the chemical etching method. The Cu-CoNCNs synthesized by this method have highly efficient oxygen reduction reaction (ORR) activity. In 0.1 mol/L KOH electrolytes, the catalyst exhibits excellent ORR activity and has a fairly high half-wave potential (0.905 V vs reversible hydrogen electrode (RHE)). X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, infrared spectroscopy, and X-ray diffraction (XRD) were used to investigate the reasons why the catalyst has excellent catalytic activity and long-life stability. It was proved that the impressive ORR activity of Cu-CoNCNs comes from Cu doping, which can regulate the surface electronic structure of the catalyst, thereby optimizing the binding ability between the intermediate and adsorbed species and improving the catalytic activity.

Metal nitrogen-carbon catalysts have become a promising alternative to platinum-based catalysts in fuel cells due to their high stability and platinum-like activity. However, the corrosion and deactivation of active sites in the solution still restrict the inherent reaction kinetic rate. For this reason, it is important to stabilize the catalyst through a controllable doping strategy to obtain high activity catalysts for oxygen reduction reactions (ORR). Herein, the pyrolysis strategy is demonstrated in the synthesis of iron-based catalysts co-doped with nitrogen and biomass-derived phosphorus (denoted as N, P-Fe/C), and the pore size of the catalyst is mostly distributed at 1 nm or 50 nm, respectively. The half-wave potential (0.893 V) and the current density (4.05 mA cm−2) at 0.85 V of the catalyst exceed those of the commercial Pt/C. The remarkable ORR performance can be attributed to its distinct hierarchical pore structure, the modulation effect of nitrogen and phosphorus co-doping on the carbon matrix, and the combined effect of the FeNx active sites, which improves the accessibility of reactants and accelerating the absorption/desorption of the reaction intermediate, thereby increasing reaction rates. And N, P-Fe/C has great potential as a promising substitute for platinum-based catalysts.

The introduction of sulfur is beneficial to regulate the electronic structure of M-Nx active site, thus improving oxygen reduction reactions (ORR) catalytic activity. Herein, we adopted a hydrogel method to synthesize ORR catalyst of Co metal atom dispersed on N and S co-doped tremelliform carbon (Co/NSTFC). The as-synthesized catalyst was characterized by TEM, XRD and BET, and results demonstrated that cobalt atoms are highly dispersed on porous N and S co-doped tremelliform carbon, and the specific surface area is as high as 1613 m2 g−1. And XPS analysis confirms the formation Co-Nx coordination bond, while the sulfur atom is successfully doped on the carbon support. The XPS analysis of N 1s and Co 2p prove that the introduction of sulfur atoms can improve the efficiency of electron transferring to graphite nitrogen, and to the vicinity of Co-Nx, thus increasing d-band center of Co metal atoms, consequently improving the oxygen reduction activity. The Co/NSTFC catalyst exhibits high-efficient ORR activity with half-wave potential (E1/2) of 0.882 V in 0.1 M KOH. Furthermore, the measured number of electron transfer is close to 4, and a low yield of hydrogen peroxide and superior stability were confirmed with the Co/NSTFC catalyst. This study provides new insights into the design and synthesis of high the performant ORR catalysts and promoting the development of energy conversion.